CN106532277A - Wireless sensor adopting multi-port tag antenna and solar energy collection function - Google Patents

Abstract

A wireless sensor using a multi-port tag antenna and solar energy collection, including a sensor for collecting signals, a control chip for receiving the signals collected by the sensor, a radio frequency identification chip for communicating with the control chip, and a dual port patch antenna, a solar battery for power supply, and a power management unit capable of obtaining energy from radio frequency signals in the surrounding environment for power supply, wherein the first port of the patch antenna is connected to a radio frequency identification chip, and the patch antenna The second port of the chip antenna is connected to the input end of the power management unit, and the output end of the power management unit and the output end of the solar cell are respectively connected to the power input ends of the sensor, the control chip and the radio frequency identification chip. The invention utilizes the multi-port tag antenna and solar energy collection to solve the problems of energy supply and short working distance of the RFID tag sensor. The RFID tag sensor realizes long-distance communication, enhances the sensing accuracy and greatly optimizes the life of the sensor.

Description

Wireless Sensors Using Multiport Tag Antennas and Solar Energy Harvesting

technical field

The invention relates to a wireless sensor. In particular, it relates to a wireless sensor using a multi-port tag antenna and solar energy harvesting.

Background technique

RFID technology is a technology that relies on radio frequency signals for identification and information transmission. It can exchange information in a non-contact manner and achieve identification goals through the transmitted information. The core part of RFID is the tag. RFID integrates many technologies, including antenna technology, integrated circuit technology, electromagnetic field propagation technology, encoding and decoding technology and data information exchange. Radio Frequency Identification (RFID) has become a key element in numerous industrial and commercial processes. Among the currently emerging applications for RFID, the scope extends to secure access, logistics inventory and supply chain management, medical care, smart space allocation, Internet of Things (IOT) and wireless sensor networks (WSN). Due to its low cost and ease of deployment, RFID technology has recently been used in sensor applications. In these RFID tag-based sensors, there are generally two schemes to realize the sensing function. In the first solution, the tag antenna is used to realize the sensor function and data transmission. In this solution, the simplest implementation method is to use the tag antenna as a sensor or integrate a passive sensor as a part of the tag antenna layout. Simplicity and the elimination of the need for batteries and power supplies are advantages of these RFID tag-based sensors, but this comes at the expense of reduced read and write distances. Due to the low accuracy of these sensors, they are often used as threshold sensors.

The second option is to use an independent sensor to collect the readout data, and then communicate with the reader through the RFID tag. This solution can improve the reading and writing distance and the accuracy of sensing, in which the data of the RFID tag is provided by an independent sensor. But it is difficult for us to integrate the sensor inside the RFID chip, because the sensor needs sufficient energy supply and the chip needs to be embeddable. Only a small number of sensors meet these stringent conditions, such as temperature, light and pressure sensors. The energy harvesting unit that powers the sensor and the microprocessor plays an important role in the performance, detection range and lifetime of the RFID tag sensor. The present invention adopts the second sensor scheme, the innovative design of the tag antenna and the arrangement of multi-port and multi-antenna is a promising technology, which provides a new possibility for solving the energy and cost constraints of RFID-based tag sensors .

Contents of the invention

The technical problem to be solved by the present invention is to provide a wireless sensor using a multi-port tag antenna and solar energy collection that can realize long-distance communication, enhance sensing accuracy and greatly improve the life of the sensor.

The technical solution adopted by the present invention is: a wireless sensor adopting multi-port tag antenna and solar energy collection, including a sensor for collecting signals, a control chip for receiving signals collected by the sensor, and a control chip connected to the control chip A radio frequency identification chip for communication, a dual-port patch antenna, a solar cell for power supply, and a power management unit capable of obtaining energy from radio frequency signals in the surrounding environment for power supply, wherein the first of the patch antenna The port is connected to the radio frequency identification chip, the second port of the patch antenna is connected to the input end of the power management unit, and the output end of the power management unit and the output end of the solar cell are respectively connected to the power input of the sensor, the control chip and the radio frequency identification chip end.

The patch antenna includes a metal sheet, a first coil connected to the metal sheet as a first port connected to the radio frequency identification chip, and connected to the metal sheet as a first coil connected to the power management unit Connect the second coil to the second port.

The power management unit includes: an RF-DC rectifier circuit, a charge pump, and a voltage regulator circuit connected in sequence for obtaining energy from radio frequency signals in the surrounding environment, wherein the input terminal of the RF-DC rectifier circuit Connect the second port of the patch antenna, the output of the voltage stabilizing circuit is respectively connected to the power input terminals of the sensor, the control chip and the radio frequency identification chip, and the output terminal of the RF-DC rectifier circuit is also grounded through the first capacitor, The charge pump is also grounded through the second capacitor.

The radio frequency identification chip includes a matching network, a demodulation circuit, a digital baseband circuit and a modulation circuit sequentially connected in series, wherein the input end of the matching network is connected to the first port of the patch antenna, and the modulation The output end of the circuit is connected to the input end of the matching network.

The demodulation circuit includes: an envelope detector, a low-pass filter and a hysteresis comparator connected in series in sequence, the input end of the envelope detector is connected to the first port of the patch antenna, and the hysteresis The output end of the comparator is connected to the input end of the digital baseband circuit.

The wireless sensor using the multi-port tag antenna and solar energy collection of the present invention solves the problems of energy supply and short working distance of the RFID tag sensor by using the multi-port tag antenna and solar energy collection. The RFID tag uses a CMOS process, and the tag antenna is a multi-port patch antenna covered with a solar cell film that collects energy. Compared with other battery-operated RFID sensors, the RFID tag sensor realizes long-distance communication, enhances sensing accuracy and greatly optimizes the life of the sensor. The invention has the following advantages:

1. Compared with the dipole antennas used in other RFID tag sensors, the design of the dual-port antenna significantly reduces the area and cost of the tag. The dual-port patch antenna used in the present invention can not only achieve higher gain, but also has good Unidirectional radiation.

2. The dual energy acquisition mode of solar battery energy supply and tag antenna energy acquisition provides sufficient energy for the entire tag circuit, which not only improves the performance of the tag sensor, greatly increases the working distance of the RFID tag, and expands the RFID The application range of the label sensor prolongs the life of the RFID label sensor.

To sum up, the wireless sensor using the multi-port tag antenna and solar energy collection of the present invention has a good application prospect.

Description of drawings

Fig. 1 is the whole block diagram that the present invention adopts the wireless sensor of multi-port tag antenna and solar energy collection;

Fig. 2 is the structural representation of patch antenna among the present invention;

Fig. 3 is the circuit block diagram of radio frequency identification chip among the present invention;

Fig. 4 is a schematic circuit diagram of the demodulation circuit in the radio frequency identification chip of the present invention.

in the picture

1: RFID chip 2: Control chip

3: Sensor 4: RF-DC rectifier circuit

5: Charge pump 6: Regulator circuit

7: Solar cell 8: Patch antenna

11: Matching network 12: Demodulation circuit

13: Digital baseband circuit 14: Modulation circuit

81: metal sheet 82: first port

83: Second port 83 121: Envelope detector

122: Low-pass filter 123: Hysteresis comparator

detailed description

The wireless sensor adopting the multi-port tag antenna and the solar energy collection of the present invention will be described in detail below in combination with the embodiments and the accompanying drawings.

The wireless sensor adopting multi-port tag antenna and solar energy collection of the present invention,

As shown in Figure 1, the wireless sensor adopting multi-port tag antenna and solar energy collection of the present invention includes a sensor 3 for collecting signals, a control chip 2 for receiving signals collected by the sensor 3, and is also provided with a A radio frequency identification chip 1 for communication with the chip 2, a dual-port patch antenna 8, a solar cell 7 for power supply, and a power management unit capable of obtaining energy from radio frequency signals in the surrounding environment for power supply, wherein the patch The first port 82 of the patch antenna 8 is used for radio frequency communication and connected to the radio frequency identification chip 1, and the second port 83 of the patch antenna 8 is used for receiving radio frequency signals from the reader or the surrounding radio frequency radiation environment, and generating a DC voltage , to supply power for the digital circuit, the second port 83 is connected to the input end of the power management unit, and the output end of the power management unit and the output end of the solar battery 7 are respectively connected to the power input ends of the sensor 3, the control chip 2 and the radio frequency identification chip 1 .

In the present invention, solar cells are used as the main energy source. Solar cells choose solar flexible films to harvest energy to power digital modules and sensors. The solar film and the patch antenna share an area, and the solar film is adhered to the surface of the patch antenna, which enables compact packaging.

In the embodiment of the present invention, the control chip is a 16-bit low-power microprocessor (MCU) MSP430. In the working mode, the power consumption of the processor is 230uA/MHz, and in the standby mode is 0.5 uA/MHz. In order to reduce the number of system hardware interfaces as much as possible, we use a single I ² C bus to realize the communication between the microprocessor, the radio frequency identification chip and the digital sensor. In solar-powered mode, the sensor can use a 14-bit analog-to-digital converter (ADC) for increased bit resolution. The operation of the MCU in the working mode includes querying new data from the sensor and transferring the formatted data to the EPC memory of the RFID chip. The new temperature and humidity data read from the sensor by the MCU are data in the original format, and converting the raw data into Celsius and relative humidity requires the use of sensor-related conversion formulas.

The sensor is a temperature and humidity sensor, which can measure in the range of -40°C to 125°C, the accuracy can reach ±0.25°C, and the humidity measurement range is 0 to 100%.

As shown in Figure 2, the patch antenna 8 includes a metal sheet 81, connected to the metal sheet 81 as the first coil of the first port 82 connected to the radio frequency identification chip 1, and connected to the The metal sheet 81 is connected as the second coil of the second port 83 connected to the power management unit.

The width-to-length ratio of the patch antenna achieves conjugate impedance matching and achieves maximum power transmission at a center frequency of 915MHz. In the present invention, the radio frequency identification chip 1 of the sensor 3 control chip 2 constitutes an integrated circuit, the power management unit forms an integrated circuit, the patch antenna with two ports is connected to the two integrated circuits, and the port 1 is connected to the radio frequency identification chip The port 2 is connected to the power management unit, and both the radio frequency identification chip and the power management unit have complex input impedances. Therefore, the induction coil matching technology can be used to match the patch antenna port, and the size of the induction coil has been optimized by HFSS to achieve the effect of conjugate matching. The second port of the patch antenna is used in the present invention to receive the RF signal from the RFID reader and other RF radiation in the surrounding environment to generate a DC voltage that can be used by the digital module for the sensor, control chip and radio frequency The identification chip provides energy for measuring temperature and humidity and updating the sensing data in the memory of the RFID chip. Through the energy harvesting achieved in this way, the invention can work without relying on batteries, and make the life of the sensor reach the level of traditional passive RFID tags.

As shown in Figure 1, the power management unit includes: an RF-DC rectifier circuit 4, a charge pump 5 and a voltage stabilizing circuit 6 connected in sequence for obtaining energy from radio frequency signals in the surrounding environment, wherein the The input end of the RF-DC rectifier circuit 4 is connected to the second port 83 of the patch antenna 8, and the output of the voltage stabilizing circuit 6 is respectively connected to the power input ends of the sensor 3, the control chip 2 and the radio frequency identification chip 1, so The output end of the RF-DC rectifier circuit 4 is also grounded through the first capacitor C1, and the charge pump 5 is also grounded through the second capacitor C2.

The power management unit is to obtain energy from the RF signal in the surrounding environment. The power management unit includes a rectifier diode operating at 915MHz, that is, an RF-DC rectifier circuit, a charge pump and a voltage regulator circuit, which can convert the radio frequency signal into a DC voltage. . The charge pump is suitable for ultra-low voltage applications, and its oscillation start voltage is as low as 0.35V. Once the oscillation starts, the storage capacitor starts charging. When the capacitor is charged to 2.4V, the internal monitoring circuit adjusts the capacitor to the load. The time period required for the charge pump to charge depends on the input voltage and the value of the storage capacitor.

As shown in Figure 3, the radio frequency identification chip 1 includes a matching network 11, a demodulation circuit 12, a digital baseband circuit 13 and a modulation circuit 14 connected in series, wherein the input end of the matching network 11 is connected to the The first port 82 of the patch antenna 8, the output end of the modulation circuit 14 is connected to the input end of the matching network 11.

As shown in Figure 4, the demodulation circuit 12 includes: an envelope detector 121, a low-pass filter 122 and a hysteresis comparator 123 connected in series in sequence, and the input end of the envelope detector 121 is connected to the The first port 82 of the patch antenna 8 , the output terminal of the hysteresis comparator 123 is connected to the input terminal of the digital baseband circuit 13 .

There is no internal power supply in the radio frequency identification chip 1, and the energy it needs is to use the RF-DC rectifier circuit to convert the radio frequency signal emitted by the reader into a direct current signal. The demodulation circuit is used to demodulate the command received from the reader, and the digital baseband circuit is the core part of the tag, which decodes the command of the reader and responds accordingly according to the EPC-G-2 space interface protocol. A modulation circuit is used to backscatter the tag's response to the reader.

Claims (5)

1. a wireless sensor adopting multi-port tag antenna and solar energy collection, comprising a sensor (3) for collecting signals, a control chip (2) receiving the signal collected by the sensor (3), characterized in that, it is also set There is a radio frequency identification chip (1) communicating with the control chip (2), as well as a two-port patch antenna (8), a solar cell (7) for power supply, and a radio frequency signal that can be obtained from the surrounding environment A power management unit for power supply, wherein the first port (82) of the patch antenna (8) is connected to the radio frequency identification chip (1), and the second port (83) of the patch antenna (8) is connected to a power supply The input end of the management unit, the output end of the power management unit and the output end of the solar cell (7) are respectively connected to the power input ends of the sensor (3), the control chip (2) and the radio frequency identification chip (1). 2. the wireless sensor adopting multi-port tag antenna and solar energy collection according to claim 1, is characterized in that, described patch antenna (8) comprises metal sheet (81), and described metal sheet (81 ) connected as the first coil of the first port (82) connected to the radio frequency identification chip (1), and connected to the metal sheet (81) as the second port connected to the power management unit ( 83) of the second coil. 3. The wireless sensor adopting multi-port tag antenna and solar energy collection according to claim 1, characterized in that, said power management unit includes: sequentially connected for obtaining energy from radio frequency signals in the surrounding environment RF-DC rectifier circuit (4), charge pump (5) and voltage stabilizing circuit (6), wherein, the input end of described RF-DC rectifier circuit (4) is connected the second of described patch antenna (8) Port (83), the output of the voltage stabilizing circuit (6) is respectively connected to the power input terminals of the sensor (3), the control chip (2) and the radio frequency identification chip (1), and the RF-DC rectifier circuit (4) The output terminal is also grounded through the first capacitor (C1), and the charge pump (5) is also grounded through the second capacitor (C2). 4. the wireless sensor adopting multi-port tag antenna and solar energy collection according to claim 1, is characterized in that, described radio frequency identification chip (1) comprises the matching network (11) that serially connects successively, demodulation circuit (12), digital baseband circuit (13) and modulation circuit (14), wherein, the input end of described matching network (11) connects the first port (82) of described patch antenna (8), described modulation The output end of the circuit (14) is connected to the input end of the matching network (11). 5. The wireless sensor adopting multi-port tag antenna and solar energy collection according to claim 4, characterized in that, said demodulation circuit (12) comprises: an envelope detector (121) connected in series successively, A low-pass filter (122) and a hysteresis comparator (123), the input end of the envelope detector (121) is connected to the first port (82) of the patch antenna (8), and the hysteresis comparator ( The output end of 123) is connected to the input end of the digital baseband circuit (13).