CN102708400B - A kind of RFID label tag, rfid system and magnetic field detection method with magnetically sensitive device - Google Patents

Abstract

The invention provides an RFID tag with a magnetic sensitive device, an RFID system and a magnetic field detection method. The magnetic sensitive device is connected to the two pins and forms a parallel structure with the antenna of the RFID tag. The magnetic sensitive device and the chip of the RFID tag There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the connected circuit, and the connected circuit, the logic circuit and the voltage-resistance conversion device are part of the chip: when the logic circuit is disconnected, the magnetic sensitive device does not In parallel with the antenna, it is placed under a certain magnetic field strength at this time, and the first resonant frequency and signal strength of the antenna remain unchanged; when the logic circuit is connected, the magnetic sensitive device is connected in parallel with the antenna, and it is placed in a certain magnetic field at this time Intensity, the antenna works at the second resonant frequency; the RFID tag receives the instructions sent by the RFID reader to control the on and off of the logic circuit, so as to detect the change of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna . It can detect magnetic field changes at low cost.

Description

RFID tag with magnetic sensitive device, RFID system and magnetic field detection method

technical field

The invention relates to the technical field of RFID (Radio Frequency Identification, radio frequency identification), in particular to an RFID tag with a magnetic sensitive device, an RFID system and a magnetic field detection method.

Background technique

In recent years, RFID systems have become increasingly common. RFID systems are mainly used for the identification of people and objects. Generally, the system includes at least one RFID reader, which can transmit and receive radio frequency signals from one or more RFID tags within a set range. The RFID tag is usually encapsulated and can be attached to an object, and it includes a microchip that communicates with the antenna. The microchip is generally an integrated circuit that stores and processes information, modulates and demodulates radio frequency signals, and performs other specialized functions. An RFID tag's antenna is used to receive and transmit radio frequency signals, and is usually adapted to a specific frequency.

In some installations, RFID systems with magnetically sensitive devices have been used to monitor when the magnetic field in the product's environment exceeds acceptable field strengths. Typically these devices require a continuous power source for the sensing device to detect changes in the magnetic field, but this adds to the cost of the device. In addition, some devices require the sensing device to be connected with a comparator circuit to detect the degree of deviation from the reference voltage, which greatly increases the cost of the device. In summary, there is a need for improved RFID systems that can detect magnetic field changes without the use of a continuous energy source or with a low-cost additional circuit.

Contents of the invention

Embodiments of the present invention provide an RFID tag with a magnetic sensitive device, an RFID system, and a magnetic field detection method to detect changes in the magnetic field at relatively low cost.

On the one hand, the embodiment of the present invention provides an RFID tag with a magnetic sensitive device, and there are two pins on the chip of the RFID tag; the magnetic sensitive device is connected to these two pins, and is connected to the RFID The antenna of the tag forms a parallel structure, and changes in the strength of the external magnetic field will cause changes in the voltage or current at both ends of the magnetic sensitive device. There is a logic circuit for controlling on-off and a The voltage-resistance conversion device, the connected circuit, the logic circuit and the voltage-resistance conversion device are part of the chip, and the voltage-resistance conversion device is used to convert the change of voltage or current across the magnetic sensitive device into a change of resistance, The on-off of the logic circuit determines whether the magnetic-sensitive device is connected in parallel with the antenna: when the logic circuit is disconnected, the magnetic-sensitive device is not connected in parallel with the antenna. At this time, it is placed under a certain magnetic field strength, and the first resonant frequency and signal strength of the antenna remain unchanged; when the logic circuit is turned on, the magnetic sensitive device is connected in parallel with the antenna, and at this time it is placed under a certain magnetic field strength, at least one of the characteristic frequency and signal strength of the antenna will change, and the antenna works at the second At the resonant frequency: the RFID tag receives instructions sent by the RFID reader to control the on-off of the logic circuit, so as to detect the change of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna.

Optionally, in an embodiment of the present invention, the antenna of the RFID tag is a monopole antenna.

Optionally, in an embodiment of the present invention, the antenna of the RFID tag is a double dipole antenna: the magnetic sensitive device and the voltage-resistance conversion device connected to the magnetic sensitive device form a parallel structure with one of the antennas ; or the magnetic sensitive device and the voltage-resistance conversion device connected to the magnetic sensitive device form a parallel structure with two antennas at the same time.

Optionally, in an embodiment of the present invention, the voltage-resistance conversion device includes: a device for converting a variable voltage into a variable resistance, or a trench type field effect transistor, or an equivalent circuit of a field effect transistor, The magnetic sensitive device includes: a Hall device, a Hall switch integrated device, a Hall linear integrated device, a magnetic sensitive diode, a magnetic sensitive triode, a CMOS magnetic sensitive device, a Wiegand magnetic sensitive device, and a fluxgate sensitive device.

On the other hand, the embodiment of the present invention provides an RFID tag with a magnetic sensitive device. There is a pin on the chip of the RFID tag; one end of the magnetic sensitive device is connected to this pin, and the other end is connected to the pin. On the antenna of the above-mentioned RFID tag, and form a parallel structure with the antenna, the change of the external magnetic field strength will cause the change of the voltage or current at both ends of the magnetic sensitive device, and there is a control on the circuit connecting the magnetic sensitive device and the chip of the RFID tag On-off logic circuit and a voltage-resistance conversion device, the connected circuit, the logic circuit and the voltage-resistance conversion device are part of the chip, and the voltage-resistance conversion device is used to convert the voltage or current between the two terminals of the magnetic sensitive device The change is converted into a change in resistance. The on-off of the logic circuit determines whether the magnetic-sensitive device is connected in parallel with the antenna: when the logic circuit is disconnected, the magnetic-sensitive device is not connected in parallel with the antenna. At this time, it is placed under a certain magnetic field strength. The first resonant frequency and signal strength remain unchanged; when the logic circuit is turned on, the magnetic sensitive device is connected in parallel with the antenna, and at this time it is placed under a certain magnetic field strength, at least one of the characteristic frequency and signal strength of the antenna will change. At this time, the antenna works at the second resonant frequency; the RFID tag receives instructions sent by the RFID reader to control the on-off of the logic circuit, thereby realizing the detection of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna Change.

Optionally, in an embodiment of the present invention, the antenna of the RFID tag is a monopole antenna.

Optionally, in an embodiment of the present invention, the antenna of the RFID tag is a double dipole antenna: the magnetic sensitive device and the voltage-resistance conversion device connected to the magnetic sensitive device form a parallel structure with one of the antennas ; or the magnetic sensitive device and the voltage-resistance conversion device connected to the magnetic sensitive device form a parallel structure with two antennas at the same time.

Optionally, in an embodiment of the present invention, the voltage-resistance conversion device includes: a device for converting a variable voltage into a variable resistance, or a trench type field effect transistor, or an equivalent circuit of a field effect transistor, The magnetic sensitive device includes: a Hall device, a Hall switch integrated device, a Hall linear integrated device, a magnetic sensitive diode, a magnetic sensitive triode, a CMOS magnetic sensitive device, a Wiegand magnetic sensitive device, and a fluxgate sensitive device.

In yet another aspect, the embodiment of the present invention provides an RFID tag with a magnetic sensitive device, the magnetic sensitive device is connected to the antenna of the RFID tag, and forms a parallel structure with the antenna, the change of the external magnetic field strength will cause magnetic There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the line connecting the magnetic-sensing device and the antenna. The connected line, the logic circuit and the voltage- The resistance conversion device is a part of the chip. The voltage-resistance conversion device is used to convert the change of voltage or current across the magnetic sensitive device into a change of resistance. The on-off of the logic circuit determines whether the magnetic sensitive device is connected in parallel with the antenna: when the logic circuit When it is disconnected, the magnetic sensitive device is not connected in parallel with the antenna. At this time, it is placed under a certain magnetic field strength, and the first resonant frequency and signal strength of the antenna remain unchanged; when the logic circuit is connected, the magnetic sensitive device is connected in parallel with the antenna. At this time, when placed under a certain magnetic field strength, at least one of the characteristic frequency and signal strength of the antenna will change, and the antenna works at the second resonance frequency; the RFID tag receives instructions sent by the RFID reader to control the logic The circuit is turned on and off, so as to detect the change of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna.

Optionally, in an embodiment of the present invention, the antenna of the RFID tag is a monopole antenna.

Optionally, in an embodiment of the present invention, the antenna of the RFID tag is a double dipole antenna: the magnetic sensitive device and the voltage-resistance conversion device connected to the magnetic sensitive device form a parallel structure with one of the antennas ; or the magnetic sensitive device and the voltage-resistance conversion device connected to the magnetic sensitive device form a parallel structure with two antennas at the same time.

Optionally, in an embodiment of the present invention, the voltage-resistance conversion device includes: a device for converting a variable voltage into a variable resistance, or a trench type field effect transistor, or an equivalent circuit of a field effect transistor, The magnetic sensitive device includes: a Hall device, a Hall switch integrated device, a Hall linear integrated device, a magnetic sensitive diode, a magnetic sensitive triode, a CMOS magnetic sensitive device, a Wiegand magnetic sensitive device, and a fluxgate sensitive device.

In yet another aspect, an embodiment of the present invention provides an RFID system with a magnetic sensitive device, the RFID system includes an RFID tag and an RFID reader, and the RFID tag includes the above-mentioned RFID tag with a magnetic sensitive device; the RFID reader The controller sends instructions to control the on and off of the logic circuit of the RFID tag, thereby detecting the change of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna.

In yet another aspect, an embodiment of the present invention provides a magnetic field detection method for an RFID system with a magnetic sensitive device. The magnetic field detection method is applied to the above RFID system with a magnetic sensitive device, including: sending instructions through the RFID reader To control the on-off of the logic circuit of the RFID tag; receive the instructions sent by the RFID reader through the RFID tag to control the on-off of the logic circuit: when the logic circuit is disconnected, the magnetic sensitive device is not connected in parallel with the antenna, and it is placed in a certain position at this time Under a certain magnetic field strength, the first resonant frequency and signal strength of the antenna remain unchanged; when the logic circuit is connected, the magnetic sensitive device is connected in parallel with the antenna. At this time, it is placed under a certain magnetic field strength, and the characteristic frequency and signal At least one of the strengths will change while the antenna is working at the second resonant frequency; using the RFID reader to compare the difference between the signal strengths of different frequencies from the antenna to detect the change of the magnetic field.

The above technical solution has the following beneficial effects: because the magnetic sensitive device is connected to the two pins and forms a parallel structure with the antenna of the RFID tag, there is a logic for controlling on-off on the circuit connecting the magnetic sensitive device and the chip of the RFID tag Circuit and a voltage-resistance conversion device, the connected line, the logic circuit and the voltage-resistance conversion device are part of the chip: when the logic circuit is disconnected, the magnetic sensitive device is not connected in parallel with the antenna, and is placed at a certain Under a certain magnetic field strength, the first resonant frequency and signal strength of the antenna remain unchanged; when the logic circuit is connected, the magnetic sensitive device is connected in parallel with the antenna, at this time it is placed under a certain magnetic field strength, and the antenna works at the second resonant frequency Next; the RFID tag receives the instructions sent by the RFID reader to control the on-off of the logic circuit, so as to realize the technical means of detecting the change of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna, so it can be lower Cost to detect the technical effect of magnetic field changes, and use the energy obtained by RFID to solve the power supply problem of magnetic field detection.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the schematic diagram that the magnetosensitive device of the embodiment of the present invention is connected with RFID tag chip;

Fig. 2 is the equivalent circuit diagram of the internal antenna of the RFID tag chip;

3 is a schematic diagram of the connection between the magnetic sensitive device, the logic switch and the voltage-resistance conversion device of the embodiment of the present invention and the equivalent circuit of the internal antenna of the RFID tag chip;

4 is a schematic diagram of the direct connection between the magnetic sensitive device and the RFID tag antenna according to the embodiment of the present invention;

Fig. 5 is a structural explanatory diagram of a magnetic sensitive device according to an embodiment of the present invention;

FIG. 6 is a flowchart of a method for detecting magnetic field strength based on signal strength according to an embodiment of the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

There are at least three situations in which the magnetic sensitive device in the embodiment of the present invention is connected to the chip of the RFID tag:

Two-pin structure:

The present invention is a device, system and technique for detecting changes in magnetic field strength. The system consists of a tag with two pins on the chip. The magnetic sensing device is connected to these two pins, forming a parallel structure with the antenna. Changes in the strength of the external magnetic field will cause changes in the voltage or current across the magnetic sensitive device. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the pin and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance.

The on-off of the logic circuit determines whether the magnetic-sensing device is connected in parallel with the antenna. When the logic circuit is disconnected, the magnetic sensitive device is not connected in parallel with the antenna. At this time, the magnetic sensitive device is placed under a certain magnetic field strength, and the first resonant frequency and signal strength of the antenna remain unchanged. When the logic circuit is turned on, the magnetic sensitive device is connected in parallel with the antenna. At this time, it is placed under a certain magnetic field strength. At least one of the characteristic frequency and signal strength of the antenna will change. At this time, the antenna works at the second resonance frequency. The reader can send instructions to the tag to control the on-off of the logic circuit. When the logic circuit is turned on, it can detect the change of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna.

As an example, the system consists of a tag with only one antenna (monopole antenna). There are two pins on the chip of this tag. The magnetic sensing device is connected to these two pins, forming a parallel structure with the antenna. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the pin and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance.

When the logic circuit is turned on, the magnetic sensitive device is placed under a certain magnetic field strength, at least one of the characteristic frequency and signal strength of the antenna will change, and it works at the second resonance frequency. The reader can send instructions to the tag, and can detect the change of the magnetic field by comparing the difference between the signal strength of different frequencies when the logic circuit is turned on and off. More precisely, the voltage-resistance conversion device may be a device for converting a variable voltage into a variable resistance, a trench field effect transistor or an equivalent circuit of a field effect transistor. Specific examples of magnetic sensitive devices include: Hall devices, Hall switch integrated devices, Hall linear integrated devices, magnetic sensitive diodes, magnetic sensitive transistors, CMOS magnetic sensitive devices, Wiegand magnetic sensitive devices, fluxgate sensitive devices Wait.

As another example, the system includes a tag with two antennas (dual dipole antenna). There are two situations at this point. In the first case, the magnetic sensing device is connected to these two pins, forming a parallel structure with the first antenna. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the pin and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance. At this time, the voltage-resistance conversion device connected to the magnetic sensitive device is also connected in parallel with the first antenna, while the second antenna always communicates normally at the first resonance frequency.

When the logic circuit is turned on and placed under a certain magnetic field strength, at least one of the characteristic frequency and signal strength of the first antenna will change, and it works at the second resonance frequency. The reader is able to send commands to the tag and detect changes in the magnetic field by comparing the difference between the signal strengths of the different frequencies of the first and second antennas when the logic circuit is switched on. Changes in the magnetic field can also be detected by comparing the difference in signal strength at different frequencies when the second antenna's own logic circuit is switched on and off.

In the second case, the magnetic sensitive device is connected to these two pins, forming a parallel structure with the two antennas at the same time. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the pin and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance. At this time, the voltage-resistance conversion device connected to the magnetic sensitive device is also connected in parallel with the two antennas at the same time, which is similar to the case where the tag only has one antenna. When the logic circuit is turned on and placed under a certain magnetic field strength, at least one of the characteristic frequency and signal strength of the antenna will change, and the antenna works at the second resonance frequency. The reader can send instructions to the tag, and can detect the change of the magnetic field by comparing the difference between the signal strength of different frequencies when the logic circuit is turned on and off.

In the first case, the circuit connection is relatively simple, and the resonant frequencies of the two antennas may be different during operation, which will affect the measurement accuracy. In the second case, the circuit connection is more complicated, but the resonant frequency of the two antennas is the same during operation, and the measurement accuracy is higher. More precisely, the voltage-resistance conversion device may be a device for converting a variable voltage into a variable resistance, a trench field effect transistor or an equivalent circuit of a field effect transistor. Specific examples of magnetic sensitive devices include: Hall devices, Hall switch integrated devices, Hall linear integrated devices, magnetic sensitive diodes, magnetic sensitive transistors, CMOS magnetic sensitive devices, Wiegand magnetic sensitive devices, fluxgate sensitive devices Wait.

One pin structure:

The chip of this tag may have only one pin, and this pin is externally connected to one end of the magnetic sensitive device, and the other end of the magnetic sensitive device is directly connected to the antenna. The connection point of the pin inside the chip is similar to that of the two pins, and the purpose of parallel connection with the antenna is still to be achieved in the end. At the same time, there is a logic circuit for controlling on-off on the line connecting the pins to the internal circuit of the chip. In addition, a voltage-resistance conversion device is connected in parallel to the circuit of the antenna, and the voltage-resistance conversion device has lines connected to the two ends of the magnetic sensitive device and the logic circuit.

When the logic circuit is disconnected, the magnetic sensitive device is not connected in parallel with the antenna, and at this time it is placed under a certain magnetic field strength, and the first resonant frequency and signal strength of the antenna remain unchanged. When the logic circuit is turned on, the magnetic sensitive device is connected in parallel with the antenna. At this time, it is placed under a certain magnetic field strength. At least one of the characteristic frequency and signal strength of the antenna will change, and it works at the second resonance frequency. The reader can send instructions to the tag to control the on-off of the logic circuit. When the logic circuit is turned on, it can detect the change of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna.

As an example, the system consists of a tag with only one antenna (monopole antenna). The magnetic sensitive device is connected to this pin, and the other end of the magnetic sensitive device is directly connected to the antenna to form a parallel structure with the antenna. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the pin and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance.

When the logic circuit is turned on and placed under a certain magnetic field strength, at least one of the characteristic frequency and signal strength of the antenna will change, and the antenna works at the second resonance frequency. The reader can send instructions to the tag, and can detect the change of the magnetic field by comparing the difference between the signal strength of different frequencies when the logic circuit is turned on and off. More precisely, the voltage-resistance conversion device may be a device for converting a variable voltage into a variable resistance, a trench field effect transistor or an equivalent circuit of a field effect transistor. Specific examples of magnetic sensitive devices include: Hall devices, Hall switch integrated devices, Hall linear integrated devices, magnetic sensitive diodes, magnetic sensitive transistors, CMOS magnetic sensitive devices, Wiegand magnetic sensitive devices, fluxgate sensitive devices Wait.

As another example, the system includes a tag with two antennas (dual dipole antenna). The magnetic sensitive device is connected to each pin, and the other end of the magnetic sensitive device is directly connected to the antenna, forming a parallel structure with the first antenna. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the pin and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance. At this time, the voltage-resistance conversion device connected to the magnetic sensitive device is also connected in parallel with the first antenna, while the second antenna always communicates normally at the first resonance frequency.

When the logic circuit is turned on and placed under a certain magnetic field strength, the first antenna works at the second resonance frequency, and at least one of its characteristic frequency and signal strength will change. The reader is able to send commands to the tag and detect changes in the magnetic field by comparing the difference between the signal strengths of the different frequencies of the first and second antennas when the logic circuit is switched on. The change of the magnetic field can also be detected by comparing the difference between the signal strengths of different frequencies when the logic circuit of the first antenna itself is turned on and off. More precisely, the voltage-resistance conversion device may be a device for converting a variable voltage into a variable resistance, a trench field effect transistor or an equivalent circuit of a field effect transistor. Specific examples of magnetic sensitive devices include: Hall devices, Hall switch integrated devices, Hall linear integrated devices, magnetic sensitive diodes, magnetic sensitive transistors, CMOS magnetic sensitive devices, Wiegand magnetic sensitive devices, fluxgate sensitive devices Wait.

No lead structure:

When there are no pins on the chip of the RFID tag, the magnetically sensitive device can be directly connected to the antenna. The magnetic sensitive device and the antenna form a parallel structure. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the antenna and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance. In this case, the antenna associated with the magneto-sensitive means cannot communicate at the first resonant frequency apart from the magneto-sensitive means. When placed under a certain magnetic field strength, at least one of the second resonant frequency and the signal strength of the antenna will change. The reader can send commands to the tag device to detect changes in the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna.

As an example, the system consists of a tag with two antennas (dual dipole antenna). The magnetic sensitive device is directly connected to the first antenna. The magnetic sensitive device and the antenna form a parallel structure. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the antenna and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance. However, the second antenna always communicates normally at the first resonant frequency without being connected with the magnetic sensitive device. When placed under a certain magnetic field strength, at least one of the characteristic frequency and signal strength of the first antenna will change, and it works at the second resonance frequency, while the characteristic frequency and signal strength of the second antenna will not change. The reader is able to send commands to the tag and detect changes in the magnetic field by comparing the difference between the signal strengths of the first and second antennas at different frequencies. More precisely, the voltage-resistance conversion device may be a device for converting a variable voltage into a variable resistance, a trench field effect transistor or an equivalent circuit of a field effect transistor. Specific examples of magnetic sensitive devices include: Hall devices, Hall switch integrated devices, Hall linear integrated devices, magnetic sensitive diodes, magnetic sensitive transistors, CMOS magnetic sensitive devices, Wiegand magnetic sensitive devices, fluxgate sensitive devices Wait.

By extension, the antenna chip may or may not have pins, and may have one pin or multiple pins. The number of antennas can be one, two or even multiple. Correspondingly, one or more magnetic sensitive devices can also be connected, and the models of the magnetic sensitive devices can be the same or different. In addition, the voltage-to-resistance conversion device connected thereto can also have many variations. In one embodiment of the device, at least one of the resonant frequency and the signal strength of the antenna associated with the magnetosensitive device changes when placed in a certain magnetic field strength. The reader can send commands to the tag device to detect changes in the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna.

For an embodiment of a magnetically sensitive device, the method of simultaneously comparing values includes comparing the comparison values to a majority signal strength value. These signal strength values belong to different frequencies and are related to the majority of the magnetic field strength, while the strength of the magnetic field can be detected based on the comparison mentioned above.

However, in another aspect, an RFID system includes an RFID tag device and an RFID reader device. This RFID tag device is used to transmit two kinds of signals, namely the signal when the logic circuit is off and the signal when the logic circuit is on, at least one of these two signals will respond to the received request. The RFID reader device is configured to send at least one request to the RFID tag device. The reading device is installed to receive from the tag a comparison between the signal strength value when the logic circuit is on and the signal strength value when the logic circuit is off, and to convert these comparison values into different levels of the magnetic field.

In one example, the antenna of the RFID tag is connected to the magnetic sensitive device, and there is a logic circuit for controlling on-off on this connecting line. The magnetic sensitive device and the antenna form a parallel structure. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the antenna and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance. In the two situations of whether the logic circuit is on or off, the antenna has two different frequencies corresponding thereto, that is, the first resonant frequency and the second resonant frequency. When the logic circuit is connected and the tag device is placed under a certain magnetic field strength, different signal strength values will be generated due to the change of the resonant frequency.

In one example, the RFID tag device includes first and second antennas. Even better, the first antenna is connected to the magnetic sensitive device and the voltage-resistance conversion device. When the tag device is placed under a certain magnetic field strength, the second signal strength value will be generated due to the change of the resonance frequency. Different from the first signal strength value.

In yet another aspect, an embodiment of the present invention provides an RFID system with a magnetic sensitive device, the RFID system includes an RFID tag and an RFID reader, and the RFID tag includes the above-mentioned RFID tag with a magnetic sensitive device; the RFID reader The controller sends instructions to control the on and off of the logic circuit of the RFID tag, thereby detecting the change of the magnetic field by comparing the difference between the signal strengths of different frequencies from the antenna.

In yet another aspect, an embodiment of the present invention provides a magnetic field detection method for an RFID system with a magnetic sensitive device. The magnetic field detection method is applied to the above RFID system with a magnetic sensitive device, including: sending instructions through the RFID reader To control the on-off of the logic circuit of the RFID tag; receive the instructions sent by the RFID reader through the RFID tag to control the on-off of the logic circuit: when the logic circuit is disconnected, the magnetic sensitive device is not connected in parallel with the antenna, and it is placed in a certain position at this time Under a certain magnetic field strength, the first resonant frequency and signal strength of the antenna remain unchanged; when the logic circuit is connected, the magnetic sensitive device is connected in parallel with the antenna. At this time, it is placed under a certain magnetic field strength, and the characteristic frequency and signal At least one of the strengths will change while the antenna is working at the second resonant frequency; using the RFID reader to compare the difference between the signal strengths of different frequencies from the antenna to detect the change of the magnetic field.

As shown in FIG. 1 , it is a schematic diagram of a magnetic sensitive label 10 in which a magnetic sensitive device is connected with an RFID tag chip according to an embodiment of the present invention. As shown in FIG. 1 , the tag device 10 includes a base 15 , an integrated circuit board 13 , two pins 16 , 17 and a double dipole antenna 11 , 12 . There are two pins 16 and 17 on the integrated circuit board 13, and these two pins are connected to the magnetic sensitive device 14 outwardly, and these two pins are connected in parallel with the equivalent circuit of the antenna inside the chip, and on the connected circuit There is a logic circuit that controls on-off. The magnetic sensitive device and the antenna form a parallel structure. There is a logic circuit for controlling on-off and a voltage-resistance conversion device on the circuit connecting the antenna and the chip, and the connected circuit, the logic circuit for controlling on-off and the voltage-resistance conversion device are part of the chip. The function of the voltage-resistance conversion device is to convert the change of voltage or current across the magnetic sensitive device into a change of resistance. Whether the magnetic sensitive device is connected into the chip circuit can be controlled through the on-off of the logic circuit, thereby affecting the frequency of the antenna connected to the radio frequency module. When the logic circuit is off, the tag antenna communicates at the first resonant frequency. When the logic circuit is turned on and placed under a certain magnetic field strength, the antenna works at the second resonance frequency, and at least one of its characteristic frequency and signal strength will change.

In one example, the transmitting antennas 11, 12 are made of one or more different low-resistance materials with high conductivity, such as copper, silver, and aluminum, which are compatible with the above-mentioned magnetic sensitivity. The device is connected to the antennas 11 and 12 through two pins 16 and 17. When the antennas 11 and 12 are placed under a certain magnetic field strength, the magnetic sensitive device will cause the resonance frequency of one or more transmitters to change. The frequency of this change is not the same as the frequency of reception and transmission. For example, when the logic circuit is turned on, the magnetic sensitive device is placed under a certain magnetic field strength, which will cause at least one of the transmitting frequency and the receiving frequency to change.

In another example, the antenna frequency value will initially be set higher than the antenna frequency for a certain magnetic field environment, and then when a certain magnetic field is reached, it will be lowered. In another example, the antenna frequency is initially set lower than the antenna frequency at a certain magnetic field strength, and it is increased when a certain magnetic field strength is reached. Such magnetic sensitive devices that can be used in the present invention include: Hall device, Hall switch integrated device, Hall linear integrated device, magnetic sensitive diode, magnetic sensitive triode, CMOS magnetic sensitive device, Wiegand magnetic sensitive device, magnetic flux door sensor etc.

Depending on the type of magnetic sensing device, the resulting varying magnetic field strength may be a specific magnetic field value or a selective range of magnetic field values. The length of time will inevitably lead to changes in the resonant frequency of the antenna, and the quality of the antenna will also cause different changes. For example, the type of magnetically sensitive device on the antenna can affect how long it takes to change the resonant frequency of the antenna.

As shown in Figure 2, it is an equivalent circuit diagram of the RFID tag antenna. When the tag coil antenna enters the alternating magnetic field generated by the reader, the interaction between the tag antenna and the reader antenna is similar to a transformer. The coils of both are equivalent to the primary and secondary coils of the transformer. The resonant circuit formed by the tag antenna is shown in Figure 2, including the coil inductance (L), parasitic capacitance (Cp) and parallel capacitance (C2) of the tag antenna, and its resonant frequency is In the formula, C is the parallel equivalent capacitance of Cp and C2, and R1 and R2 are the equivalent resistance of the inductance coil and other devices in the circuit. The carrier frequency used for two-way communication between the tag and the reader is f. When the tag antenna coil is required to have a small shape, that is, a small area, and a certain working distance is required, the mutual inductance of the antenna coil between the RFID tag and the reader obviously cannot meet the actual needs, and a high magnetic permeability can be inserted inside the tag antenna coil. The ferrite material is used to increase the mutual inductance, thereby compensating the problem of small cross-section of the coil.

As shown in FIG. 3 , it is a schematic diagram of the connection between the magnetic sensitive device, the on-off logic circuit and the voltage-resistance conversion device of the embodiment of the present invention and the equivalent circuit of the RFID tag antenna. The resonant circuit formed by the tag antenna is shown in the figure, including the coil inductance (L), parasitic capacitance (Cp) and parallel capacitance (C2) of the tag antenna, and its resonant frequency is Formula C is the parallel equivalent capacitance of Cp and C2, and R1 and R2 are the equivalent resistance of the inductance coil and other devices in the circuit. M is a variable resistor representing the magnetic sensitive device, S is a logic circuit for controlling on-off, R3 is an equivalent resistance connected in series with the magnetic sensitive device, and F is a voltage-resistance conversion device. When the logic circuit is disconnected, the magnetic sensitive device is not connected in parallel with the antenna, and at this time it is placed under a certain magnetic field strength, and the first resonant frequency and signal strength of the antenna remain unchanged. When the logic circuit is turned on, the magnetic sensitive device is connected in parallel with the antenna. At this time, it is placed under a certain magnetic field strength. At least one of the characteristic frequency and signal strength of the antenna will change. At this time, the antenna works at the second resonance frequency.

As shown in FIG. 4 , it is a schematic diagram of a magnetic sensitive device directly connected to an RFID tag antenna according to an embodiment of the present invention, that is, a schematic diagram of a passive RFID tag device 40 that can detect changes in a magnetic field. As shown in FIG. 4 , the tag device 40 includes a base 45 , an integrated circuit 43 and a double dipole antenna 41 , 42 . The magnetically sensitive device 44 connected to the antenna 42 will affect the resistance of the antenna 42 . The material used for the magnetic sensitive device 44 can control the frequency of any given point according to the current voltage of any one of the antennas 41,42. As an example, the antennas 41, 42 are mounted so that they resonate at the same frequency. As another example, antennas 41, 42 may be installed to resonate at different frequencies.

In one example, the transmitting antennas 41, 42 are made of one or more different low-resistance materials with high conductivity, such as copper, silver, and aluminum, which are compatible with the above-mentioned magnetic sensitivity. The devices are connected, and when the antennas 41, 42 are placed under a certain magnetic field strength, the magnetically sensitive device will cause a change in the resonant frequency of one or more transmitting ends, resulting in a different frequency. The change in this frequency is not the same as the received and transmitted frequency. For example, placing the magnetic sensitive device under a certain magnetic field strength will cause at least one of the transmitting frequency and the receiving frequency to change.

In another example, the antenna frequency value will initially be set higher than the antenna frequency for a certain magnetic field environment, and then when a certain magnetic field is reached, it will be lowered. In another example, the antenna frequency is initially set lower than the antenna frequency at a certain magnetic field strength, and it is increased when a certain magnetic field strength is reached. Such magnetic sensitive devices that can be used in the present invention include: Hall device, Hall switch integrated device, Hall linear integrated device, magnetic sensitive diode, magnetic sensitive triode, CMOS magnetic sensitive device, Wiegand magnetic sensitive device, magnetic flux door sensor etc.

Depending on the type of magnetic sensing device, the resulting varying magnetic field strength may be a specific magnetic field value or a selective range of magnetic field values. The length of time will inevitably lead to changes in the resonant frequency of the antenna, and the quality of the antenna will also cause different changes. For example, the type of magnetically sensitive device on the antenna can affect how long it takes to change the resonant frequency of the antenna.

As shown in Fig. 5, the Wiegand magnetic sensitive device is a magnetic sensitive device made according to the Wiegand effect. After special processing of permalloy and other ferromagnetic metal alloys, the coercive force of the inner and outer layers of the wire can be significantly different: the coercive force of the outer layer is an order of magnitude larger than that of the inner layer. This metal wire is called Wiegandes, as shown in Figure 5 (1). Due to the large difference in coercivity between the inner and outer layers, Wiegandes has two stable magnetization states: the inner and outer layers are magnetized in the same direction, and the inner and outer layers are magnetized in opposite directions. Using an appropriate external magnetic field, the magnetization state of the inner layer of Wiegandes can be suddenly reversed, from state a to state b, or from state b to a, and this state reversal occurs under the action of an external magnetic field. The effect is called the Wiegand effect. As shown in Figure 5 (2), it is a tactile sensor made of Wiegandes. There is a detection coil on the Wiegandes, and a permanent magnet below it to magnetize the Wiegandes. When the upper key moves downward to contact the lower part, the upper magnet is closer to the Wiegand wire, but the polarity of the magnetic pole is opposite to that of the lower magnet, which reverses the magnetization direction of the inner layer of the wire, and the detection coil outputs a spikes. Wiegandes is generally about several centimeters long, about 0.3mm in diameter, the number of coil turns of the magnetic sensitive element is about 1000-2000 turns, the output pulse voltage is on the order of several volts, and the pulse width is 20μs.

As shown in FIG. 6 , it is a flowchart of a method for detecting magnetic field changes by using a multi-antenna tag device according to the present invention. It should be taken into consideration that the aforementioned devices use a single tag IC to communicate with multiple antennas.

As shown in Figure 6, 50, the RFID reader sends energy and commands to the tag device. 52. The logic circuit is in the disconnected state at the initial time, and the tag device receives energy and instructions through the antenna not connected to the magnetic sensitive device. 54. The tag device converts the electromagnetic wave carrying energy into DC (direct current) voltage, so that the tag can execute the instruction. And this conversion needs to use a charge pump, a rectifier circuit, or connect them to each other, or use other energy conversion devices. 56. The tag device sends a signal to the reader through the antenna not connected with the magnetic sensitive device. 58. The reader measures and records the energy intensity of the received signal. 60. The reader sends an instruction to turn on the logic circuit to the tag device. 62. The tag device sends data through the antenna connected to the magnetic sensitive device. 64. The reader measures the energy strength of the received signal. 66. The reader calculates a comparison value reflecting the signal strength. 68. The reader converts the comparison value into different magnetic field strength values. As an example, the reader will set a time period to receive the signal of the tag, if no signal is received, the reader will record the signal strength as 0.

In this system, the reader uses the signal strength value from the antenna not connected to the magnetic sensitive device as a reference value, and compares it with the signal strength value from the tag antenna connected to the magnetic sensitive device. By receiving signals from transmitters connected to and not connected to the magnetic-sensing device, the reader collects comparison values representing different signal strengths. The RFID reader then converts such a comparison value into the strength of the magnetic field to which the tag is placed. For a specific example, the RFID reader is configured to convert the difference in strength of a received RF signal from an antenna connected or not connected to a magnetic sensing device to a magnetic field value by using stored reference data.

In the best case, use the antenna without the magneto-sensitive device as a reference to filter out variations due to coupling between the tag and the reader. Additionally, as mentioned earlier, a magnetically sensitive device is incorporated into the design so that its impedance changes in a one-to-one relationship with the amount of time the tag is placed in a particular magnetic field. For example, positioning the magnetically sensitive device on only one antenna allows the signal from the RFID tag device to vary over a certain range as a function of the time the antenna is placed in a certain magnetic field. Only function. As above, by using the present invention, under the passive condition of the RFID tag, the RFID reader can detect whether the tag device has been placed under a certain magnetic field and whether the magnetic field is within an acceptable range.

Various RFID tags that do not use two antennas can also use magnetic sensitive devices to sense changes in the magnetic field. The changes in the perceived magnetic field are based on changes in the resonant frequency of the antennas and can also identify changes in the signals received by the antennas.

For example, through the design of the antenna connected to the magnetic sensitive device, the frequency of the antenna can be changed in the ISM (Industrial Scientific Medical, industrial, scientific, medical) frequency band, and the magnetic sensitive device and logic circuit can be connected to the standard label connected antenna.

For example, in a specific example, the tag antenna can be set like this. Before being exposed to a certain magnetic field environment, the resonant frequency of the antenna is 902-928MHZ, but once the tag is exposed to a certain magnetic field environment, due to the influence of the magnetic field, the resonance frequency of the antenna The frequency is reduced to 899.5-927.5MHZ. In the US RFID frequency band (902-928MHZ) is divided into 52 channels. In these 52 channels, the reader can randomly skip the channels that cannot be received. The benefit of this jump is that it can effectively prevent conflicts caused by multiple readers trying to use the same frequency in the same physical space.

For example, in one example, the RFID frequency band (902-928MHZ) is not divided into 52 channels but divided into n channel labels evenly. The antenna of the label is set to work in this frequency band (902-928MHZ). Since the tag antenna is connected to the magnetic sensitive device, as long as the magnetic field exceeds the preset value range, the working frequency of the antenna tag antenna will drop to the frequency range of (899.5-927.5MHZ). Therefore, compared with the original frequency band, channel n is excluded from the frequency range, so the changed frequency band (899.5-927.5MHZ) no longer allows the tag to communicate with channel n.

In a specific example, if the environment where the tag is located exceeds the expected magnetic field range, the reader can only send instructions to the tag through channels 1 to n-1, and the tag can also respond, because the antenna in the tag can only be in the Working in this frequency range, when the reader sends instructions to the tag at the n-channel frequency, the tag antenna's resonance frequency has dropped to 899.5-927.5MHZ due to the change of the tag's magnetic field, and it will no longer reach 928MHZ, so the tag will no longer do it. Responds and transmits the information back to the reader.

An advantageous aspect is that changes in the operating frequency of the antenna due to magnetic fields exceeding a predetermined value are reflected by the disappearance of this communication.

In the model, the reader can send a command between channel n-1 and channel n to the tag to further confirm that the working frequency range of the tag antenna has drifted, because the tag can receive the signal sent through channel n-1 command, and can feed back information to the reader through channel n-1, because the tag cannot receive commands sent through channel n, and cannot feed back information to the reader through channel n, thus determining the tag antenna The operating frequency range has drifted.

The change of the magnetic field causes the working frequency of the tag antenna to drift up and down and the present invention is not limited to dividing the frequency band into n channels equally.

The embodiment of the present invention can detect the change of the magnetic field at a low cost, and utilizes the energy obtained by the RFID to solve the power supply problem of the magnetic field detection.

The implementation of each feature of this system may involve software, and the hardware may also involve a combination of software and hardware. For example, the implementation of many advantages of the system is achieved through programming with a high-level processing and object-oriented programming language and computer It is realized by means of mutual communication with other equipment and machines. Each of these functional programs may be stored in a storage medium such as a read-only memory and read by a computer and processor to implement the above-mentioned functions.

Those skilled in the art can also understand that various illustrative logical blocks (illustrativelogical blocks), units, and steps listed in the embodiments of the present invention can be implemented by electronic hardware, computer software, or a combination of both. To clearly demonstrate the interchangeability of hardware and software, the various illustrative components, units and steps above have generically described their functions. Whether such functions are implemented by hardware or software depends on the specific application and overall system design requirements. Those skilled in the art may use various methods to implement the described functions for each specific application, but such implementation should not be understood as exceeding the protection scope of the embodiments of the present invention.

The various illustrative logic blocks or units described in the embodiments of the present invention can be implemented by general-purpose processors, digital signal processors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to implement or operate the described functions. The general-purpose processor may be a microprocessor, and optionally, the general-purpose processor may also be any conventional processor, controller, microcontroller or state machine. A processor may also be implemented by a combination of computing devices, such as a digital signal processor and a microprocessor, multiple microprocessors, one or more microprocessors combined with a digital signal processor core, or any other similar configuration to accomplish.

The steps of the method or algorithm described in the embodiments of the present invention may be directly embedded in hardware, a software module executed by a processor, or a combination of both. The software modules may be stored in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM or any other storage medium in the art. Exemplarily, the storage medium can be connected to the processor, so that the processor can read information from the storage medium, and can write information to the storage medium. Optionally, the storage medium can also be integrated into the processor. The processor and the storage medium can be set in the ASIC, and the ASIC can be set in the user terminal. Optionally, the processor and the storage medium may also be set in different components in the user terminal.

In one or more exemplary designs, the above functions described in the embodiments of the present invention may be implemented in hardware, software, firmware or any combination of the three. If implemented in software, the functions can be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media and communication media that facilitate transfer of a computer program from one place to another. Storage media may be any available media that can be accessed by a general purpose or special computer. For example, such computer-readable media may include, but are not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other device that can be used to carry or store instructions or data structures and Other medium of program code in a form readable by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. In addition, any connection is properly defined as a computer-readable medium, for example, if the software is transmitted from a web site, server, or other remote source via a coaxial cable, fiber optic computer, twisted pair, digital subscriber line (DSL) Or transmitted by wireless means such as infrared, wireless and microwave are also included in the definition of computer readable media. Disks and discs include compact discs, laser discs, optical discs, DVDs, floppy discs, and Blu-ray discs. Disks usually reproduce data magnetically, while discs usually reproduce data optically with lasers. Combinations of the above can also be contained on a computer readable medium.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (5)

1. the RFID label tag with magnetically sensitive device, is characterized in that, the chip of described RFID label tag has two pins, described magnetically sensitive device and this two pins are connected, and form parallel-connection structure with the antenna of described RFID label tag, the change of external magnetic field intensity can cause the change of magnetically sensitive device both end voltage or electric current, the circuit that described magnetically sensitive device is connected with the chip of RFID label tag has logical circuit and an electric piezo-resistive conversion equipment controlling break-make, the circuit of this connection, this logical circuit and this electric piezo-resistive conversion equipment are parts for chip, electricity piezo-resistive conversion equipment is for converting the change of resistance to by the change of magnetically sensitive device both end voltage or electric current, the break-make of logical circuit determine magnetically sensitive device whether with sky line parallel: when logical circuit disconnects, magnetically sensitive device not with sky line parallel, under being now placed on certain magnetic field intensity, first resonant frequency of antenna and signal intensity remain unchanged, when logical circuit is connected, magnetically sensitive device and sky line parallel, under being now placed on certain magnetic field intensity, the characteristic frequency of antenna and signal intensity at least have one and change, and now Antenna Operation is under the second resonant frequency, described RFID label tag receives instruction that RFID reader sends with the break-make of control logic circuit, thus realizes the change being detected magnetic field by the difference between comparing from the signal intensity of the different frequency of antenna,

Wherein, the antenna of described RFID label tag is monopole antenna or double-doublet antenna;

Wherein, described magnetically sensitive device is Wei Gende magnetosensitive device, described Wei Gende magnetosensitive device is the magnetic-sensitive elements made according to Wei Gende effect, the tinsel adopted in manufacturing process is Wei Gendesi, Wei Gendesi is wound with detecting coil, below Wei Gendesi, is one makes Wei Gendesi permanent magnet magnetized.

2. the RFID label tag as claimed in claim 1 with magnetically sensitive device, it is characterized in that, when the antenna of described RFID label tag is double-doublet antenna, described magnetically sensitive device and the electric piezo-resistive conversion equipment that is connected with this magnetically sensitive device and a wherein antenna form parallel-connection structure; Or described magnetically sensitive device and the electric piezo-resistive conversion equipment be connected with this magnetically sensitive device and two antennas form parallel-connection structure simultaneously.

3. the RFID label tag as claimed in claim 1 with magnetically sensitive device, it is characterized in that, described electric piezo-resistive conversion equipment comprises: a variable voltage converts the equivalent electrical circuit of variable-resistance device or a ditch type field effect transistor or field effect transistor to, and described magnetically sensitive device comprises: hall device, Hall switch integrating device, Hall linear Integrated device, magnetodiode, magnetic sensitive transistor, CMOS magnetosensitive device, Wei Gende magnetosensitive device, fluxgate sensor.

4. the rfid system with magnetically sensitive device, described rfid system comprises RFID label tag and RFID reader, it is characterized in that,

Described RFID label tag comprises the RFID label tag with magnetically sensitive device according to any one of claim 1-3;

Described RFID reader sends instruction to control the break-make of the logical circuit of RFID label tag, thus detects the change in magnetic field by the difference between comparing from the signal intensity of the different frequency of antenna.

5. a magnetic field detection method for the rfid system with magnetically sensitive device, is characterized in that, described magnetic field detection method is applied to the rfid system with magnetically sensitive device described in claim 4, comprising:

Instruction is sent to control the break-make of the logical circuit of RFID label tag by described RFID reader;

The instruction of RFID reader transmission is received with the break-make of control logic circuit: when logical circuit disconnects by RFID label tag, magnetically sensitive device not with sky line parallel, under being now placed on certain magnetic field intensity, the first resonant frequency of antenna and signal intensity remain unchanged; When logical circuit is connected, magnetically sensitive device and sky line parallel, be now placed under certain magnetic field intensity, and the characteristic frequency of antenna and signal intensity at least have one and change, and now Antenna Operation is under the second resonant frequency;

Utilize described RFID reader to compare from the signal intensity of the different frequency of antenna between difference to detect the change in magnetic field.