CN117066083B - A wearable flexible near-infrared transparent ultrasonic transducer and its preparation method - Google Patents
A wearable flexible near-infrared transparent ultrasonic transducer and its preparation methodInfo
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- CN117066083B CN117066083B CN202310910598.7A CN202310910598A CN117066083B CN 117066083 B CN117066083 B CN 117066083B CN 202310910598 A CN202310910598 A CN 202310910598A CN 117066083 B CN117066083 B CN 117066083B
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- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
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Abstract
本发明公开了一种可穿戴柔性近红外透明超声换能器及其制备方法，包括：PDMS柔性基板、多个微型刚性CMUT元件、蛇形银纳米线电极和与外部连接的电极，多个微型刚性CMUT元件并联设置，基于银纳米线电极相互连接组成蛇形互连线路，微型刚性CMUT元件、蛇形银纳米线电极和与外部连接的电极共同封装于PDMS柔性基板中。可穿戴柔性近红外透明超声换能器允许近红外激光束穿透，能有效实现光源与超声换能器的集成。
The present invention discloses a wearable, flexible, near-infrared, transparent ultrasonic transducer and its preparation method. The transducer comprises a PDMS flexible substrate, multiple rigid micro-CMUT elements, serpentine silver nanowire electrodes, and electrodes for external connections. The multiple rigid micro-CMUT elements are arranged in parallel and interconnected via the silver nanowire electrodes to form a serpentine interconnection circuit. The micro-CMUT elements, serpentine silver nanowire electrodes, and electrodes for external connections are encapsulated within the PDMS flexible substrate. The wearable, flexible, near-infrared, transparent ultrasonic transducer allows near-infrared laser beams to penetrate, effectively integrating the light source and ultrasonic transducer.
Description
Technical Field
The invention relates to the technical field of wearable flexible near infrared transparent ultrasonic transducers, in particular to a wearable flexible near infrared transparent ultrasonic transducer and a preparation method thereof.
Background
An ultrasonic transducer is a device for mutually converting ultrasonic signals and electric signals, and is commonly used in the fields of ultrasonic imaging and photoacoustic imaging systems. It serves as a core component of an imaging system, and can be used as an ultrasonic transmitting device and an ultrasonic receiving and transmitting device. Currently, ultrasound transducers widely used in clinic are typically conventional rigid probes, where the mismatch between the rigid surface and the irregular surface of the target tissue can create an irregularly thick coupling layer, resulting in distortion and sensitivity loss, which can limit the application of certain scenarios. For example, it is not closely fitted to curved, complex and dynamic surfaces of the body and industrial samples, and the contact interface with the skin is uncomfortable, failing to meet the clinical needs of continuous detection and diagnosis. To overcome these drawbacks, researchers have attempted to convert rigid ultrasound transducers into flexible and wearable to further expand the range of applications of imaging systems.
The flexible ultrasonic transducer has a thin and compact structure, can be closely attached to the surface with any shape, has the advantage of self-alignment with the complex surface, can also furthest improve the energy of ultrasonic transmission and realizes high-quality detection. Thus, the high sensitivity, continuous real-time dynamic detection performance of flexible wearable devices can play a key role in remotely monitoring vital signs and cardiovascular health.
In recent years, capacitive Micromachined Ultrasonic Transducer (CMUT) arrays based on microelectromechanical systems technology have been attractive in imaging systems. A typical method of designing a flexible CMUT array is to integrate a plurality of miniaturized rigid CMUT cells on a flexible substrate or to manufacture the whole CMUT array based on flexible materials. CMUTs achieve high electromechanical coupling coefficients through integrated circuit fabrication techniques, provide better load matching and greater bandwidth, and exhibit higher sensitivity.
In addition, in order to solve the problem of the position between the light source and the ultrasonic transducer in the photoacoustic imaging system, researchers are trying to create a flexible CMUT array ultrasonic transducer that is transparent to visible/near infrared light to solve the problem of illumination of the sample tissue target. Therefore, a novel wearable flexible near infrared transparent ultrasonic transducer is developed, and near infrared laser beams are allowed to penetrate for photoacoustic/ultrasonic imaging, so that a wider clinical application scene is realized.
Disclosure of Invention
The invention aims to provide a wearable flexible near infrared transparent ultrasonic transducer and a preparation method thereof, aiming at solving the technical problems in the background technology.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
A wearable flexible near infrared transparent ultrasound transducer, comprising:
The MEMS device comprises a Polydimethylsiloxane (PDMS) flexible substrate, a plurality of micro-rigid CMUT elements, a serpentine silver nanowire electrode and an electrode connected with the outside, wherein the micro-rigid CMUT elements are arranged in parallel, the serpentine interconnection line is formed based on the mutual connection of the silver nanowire electrodes, and the micro-rigid CMUT elements, the serpentine silver nanowire electrode and the electrode connected with the outside are packaged in the PDMS flexible substrate together.
In some embodiments, the micro rigid CMUT element comprises an Indium Tin Oxide (ITO) top electrode, a vibrating membrane, a capacitor plate structure with a vacuum cavity, an ITO bottom electrode and a substrate, wherein the top electrode is fixed on the upper surface of the vibrating membrane, the capacitor plate structure with the vacuum cavity is attached to the lower surface of the vibrating membrane, the ITO bottom electrode is attached to the lower portion of the capacitor plate structure with the vacuum cavity, the substrate is attached to the lower portion of the ITO bottom electrode, the vibrating membrane is a silicon nitride vibrating membrane, and the substrate is a silicon crystal substrate.
In some embodiments, the capacitor plate structure with the vacuum cavity comprises a plurality of insulators BCB, wherein two insulators BCB distributed on the side part and an insulator BCB distributed on the bottom part form a sealed vacuum cavity together with a vibrating membrane, and the capacitor plate structure with the vacuum cavity comprises the insulators BCB, the vibrating membrane and the vacuum cavity.
The application also provides a preparation method of the wearable flexible near infrared transparent ultrasonic transducer, which comprises the following steps:
The manufacturing of the snake-shaped silver nanowire electrode comprises the steps of mixing silver nanowires with silver flake ink, and then performing screen printing on the mixed silver nanowire/silver composite ink on a PDMS flexible substrate at room temperature by using a screen printer;
Manufacturing the CMUT rigid element, namely preparing the CMUT by adopting an adhesive wafer bonding process, and adopting styrene-acrylate cyclobutene as an adhesive and a side wall layer of the CMUT.
The manufacturing of the serpentine silver nanowire electrode comprises the steps of mixing silver nanowires with silver flake ink, and then conducting screen printing on a PDMS flexible substrate at room temperature by using a screen printer on the basis of the mixed silver nanowire/silver composite ink, wherein a custom screen with an open area of a serpentine pattern is used as a printing template, and the silver nanowire/silver composite ink is added to the custom screen.
The manufacturing of the CMUT rigid element comprises the steps of adopting an adhesive wafer bonding process to prepare the CMUT, adopting styrene-acrylate cyclobutene as an adhesive and a side wall layer of the CMUT, and comprising the following steps:
Preparing two wafers, namely a silicon wafer I containing silicon nitride and a silicon substrate wafer II, placing the wafers in a mixed solution of hydrogen peroxide and concentrated sulfuric acid for oxidation dissolution, and cleaning metal impurities;
Depositing a silicon nitride layer on the first silicon nitride wafer by using a low-pressure chemical vapor deposition process to construct a low-stress vibrating membrane;
sputtering a 250-260nm transparent conductive material indium tin oxide layer on a second silicon substrate wafer to form an ITO bottom electrode, and then cleaning in a mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water to remove organic pollutants;
spin coating a layer of AP3000 adhesive on a first silicon substrate wafer and a second silicon substrate wafer at 3000-3200rpm for 25-40 seconds, and then soft baking at 140-160 ℃ for 50-70 seconds;
spin coating BCB on a second silicon substrate wafer at 6500-7000rpm for 40-60 seconds, and soft baking at 50-70 ℃ for 90-100 seconds, wherein the BCB layer is exposed to ultraviolet rays and then baked and cured at 40-60 ℃;
spin-drying after rinsing with DS2100 developer to define cavities;
bonding the first silicon nitride wafer and the second silicon substrate wafer by using a wafer bonding machine through an adhesive;
Sputtering a transparent conductive material ITO layer of 200-210nm on a silicon nitride vibrating membrane as a top electrode, and then patterning the top ITO layer by utilizing positive photoresist and wet etching to define the top electrode of the CMUT element;
And simultaneously packaging the serpentine silver nanowire interconnection electrode and the CMUT array in the PDMS flexible substrate to form the flexible near infrared transparent CMUT array.
The wafer bonding machine is used for bonding the silicon nitride wafer I and the silicon substrate wafer II through an adhesive, the wafer bonding machine comprises the steps of separating the wafers through gaskets to ensure a vacuum sealing gap, after loading the wafers, pumping down a chamber to 0.5mTorr, removing the gaskets, allowing the two wafers to contact each other, forming a vacuum sealing cavity, then applying a compression pressure of 0.5MPa on the wafers for 1 hour, and taking out the wafers from the chamber after cooling.
Compared with the prior art, the invention has the following beneficial effects:
(1) The wearable flexible near infrared transparent ultrasonic transducer has a light and thin and soft structure, can adapt to any shape of a contact interface, and can be self-aligned to a target interface so as to meet clinical requirements of continuous detection.
(2) The wearable flexible near infrared transparent ultrasonic transducer allows near infrared laser beams to penetrate, and the integration of a light source and the ultrasonic transducer can be effectively realized.
Drawings
Fig. 1 is a schematic structural diagram of a pen-type laser according to an embodiment.
Fig. 2 is a schematic structural diagram of a wearable flexible near infrared transparent ultrasonic transducer in an embodiment.
Fig. 3 is a schematic structural diagram of a rigid CMUT in an embodiment.
Fig. 4 is a schematic diagram of the working principle of the photoacoustic/ultrasonic bimodal imaging system in the embodiment.
Fig. 5 is a schematic structural view of a photoacoustic/ultrasound bimodal imaging system for detecting a thoracic center vessel.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the technical solutions in the preferred embodiments of the present application will be described in more detail with reference to the accompanying drawings in the preferred embodiments of the present application. In the drawings, the same or similar reference numerals refer to the same or similar components or components having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of the application. The embodiments described below by referring to the drawings are illustrative and intended to explain the present application and should not be construed as limiting the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
Embodiments of the present application will be described in detail below with reference to the accompanying drawings.
In the description of the present application, it should be noted that, unless explicitly stated and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be fixedly connected, or indirectly connected through intermediaries, for example, or may be in communication with each other between two elements or in an interaction relationship between the two elements. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.
In the description of the present application, it should be understood that the terms "upper," "lower," "front," "rear," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship of the drawings, merely to facilitate description of the present application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application.
Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or display that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed or inherent to such process, method, article, or display.
A wearable flexible near infrared transparent ultrasonic transducer and a method for manufacturing the same according to embodiments of the present application will be described in detail below with reference to fig. 1 to 5. It is noted that the following examples are only for explaining the present application and are not to be construed as limiting the present application. In order to better illustrate the wearable flexible near-infrared transparent ultrasonic transducer and the preparation method thereof, the application is applied to a wearable flexible near-infrared transparent photoacoustic/ultrasonic dual-mode imaging system.
Example 1:
As shown in fig. 1-5, the wearable flexible near infrared transparent photoacoustic/ultrasound dual-mode imaging system comprises a pen-type laser 1 and a wearable flexible near infrared transparent ultrasonic transducer 2, wherein the pen-type laser is used for generating a laser light source, and the wearable flexible near infrared transparent ultrasonic transducer is used for transmitting ultrasonic signals or receiving and transmitting photoacoustic signals generated when the pen-type laser irradiates a blood vessel 3.
The pen-shaped laser realizes the free control of the emission of laser through an external trigger, and when the pen-shaped laser is integrated with an ultrasonic transducer and applied to a photoacoustic imaging system, the pen-shaped laser ensures the synchronous proceeding of near infrared light irradiation and photoacoustic signal reception, thereby realizing the continuous, real-time and dynamic detection of deep tissues.
The pen-type laser can activate the laser driver 12 by controlling the trigger 11 connected to the outside, thereby driving the high-efficiency diode array 13 to emit laser beams, so that the process of irradiating deep tissues with near infrared laser can be freely controlled. When a pen-type laser is integrated with an ultrasonic transducer and applied to a photoacoustic imaging system, this is important for synchronization of laser irradiation and photoacoustic signal reception.
The three-dimensional view of the pen-type laser shows a cylindrical structure, the length of the cylinder is 12cm, and the diameter of the bottom surface is 3cm. The body part located in the center of the pen-shaped laser is a high-efficiency laser diode array, and the laser driver and the cylindrical lens are located at the top and bottom of the array respectively. The laser driver, the high-efficiency laser diode array, the cylindrical lens 14, and the diffractive optical element 15 are connected by a substrate. The top of laser driver is connected with the one end of trigger, and the other end of trigger is connected with the afterbody of cylinder shell to realize the free control laser emission through outside shift knob, in order to satisfy the basic condition of optoacoustic imaging. The circular glass 17 forms the head of a cylindrical housing, and the housing 16 is made of aluminum and has a cooling function to limit the increase in heat.
By pressing a trigger connected to the tail of the pen-shaped laser, a laser driver connected to the other end of the trigger can be started, thereby driving the high-efficiency laser diode array connected by the substrate to emit a near infrared laser beam. The quality of the emitted laser beam is poor and the divergence is very pronounced, so that an optical system is required to achieve collimation and reshaping of the laser beam to minimize energy loss and to ensure that the region of interest of the deep tissue is illuminated with the desired laser beam profile. The emitted laser beam is first collimated by a cylindrical lens placed in front of the high efficiency laser diode array to minimize beam divergence and achieve beam shaping. The collimated laser beam is reshaped by a diffractive optical element, homogenized and irradiated in rectangular form through a circular glass at the bottom of the pen-shaped laser to the region of interest.
The portable pen-type laser provided by the application has a compact structure, realizes miniaturization of an illumination system, and is easy to integrate in a photoacoustic imaging system. The near infrared laser beam emitted by the pen-shaped laser has larger penetration depth, which is beneficial to imaging deep tissues.
The wearable flexible near infrared transparent ultrasonic transducer provided by the application allows near infrared laser beams to penetrate for photoacoustic/ultrasonic imaging so as to realize wider clinical application scenes.
The wearable flexible near infrared transparent ultrasonic transducer is formed by a series of micro CMUT rigid elements which are mutually connected through a snake-shaped silver nano circuit and packaged in flexible PDMS. The device has compact structure, allows near infrared light to penetrate, can be comfortably attached to the surface of a target tissue, can transmit and/or receive ultrasonic signals, obtains continuous, real-time and high-quality detection images, and can be applied to ultrasonic imaging and photoacoustic imaging systems.
The wearable flexible near infrared transparent ultrasonic transducer comprises a PDMS flexible substrate 21, a plurality of micro-rigid CMUT elements 22, a snake-shaped silver nanowire electrode 23 and an electrode 24 connected with the outside, wherein the micro-rigid CMUT elements are arranged in parallel, a snake-shaped interconnection line is formed based on the mutual connection of the silver nanowire electrodes, and the rigid CMUT elements, the snake-shaped silver nanowire electrode and the electrode connected with the outside are packaged in the PDMS flexible substrate together.
The miniature rigid CMUT element comprises an ITO top electrode 25, a vibrating membrane 26, a capacitor plate structure with a vacuum cavity, an ITO bottom electrode and a substrate, wherein the top electrode is fixed on the upper surface of the vibrating membrane, the capacitor plate structure with the vacuum cavity is attached to the lower surface of the vibrating membrane, the ITO bottom electrode is attached to the lower part of the capacitor plate structure with the vacuum cavity, the substrate is attached to the lower part of the ITO bottom electrode 29, the vibrating membrane is a silicon nitride vibrating membrane, and the substrate is a silicon crystal substrate 30.
The capacitor plate structure with the vacuum cavity comprises a plurality of insulators BCB, wherein two insulators BCB distributed on the side parts, an insulator BCB distributed on the bottom part and a vibrating membrane form a sealed vacuum cavity 27, and the capacitor plate structure with the vacuum cavity consists of a plurality of insulators BCB28, a vibrating membrane and the vacuum cavity.
When the CMUT is in operation, a dc bias voltage is typically applied to sink the diaphragm into the vacuum chamber, such that the stress of the diaphragm can increase the sensitivity of the transducer. When transmitting or transmitting ultrasonic waves, an alternating current signal is superimposed with an applied direct current bias voltage. The dc voltage brings the top electrode and the bottom electrode closer together, and the ac voltage drives the diaphragm to generate an ultrasonic signal, the driving frequency of which is the transmission frequency of the ultrasonic wave. When receiving ultrasonic signals, only direct current voltage is applied to keep a fixed potential difference, and the incident sound wave can modulate the height of a vacuum cavity gap according to the frequency of the wave so as to change the capacitance of the vibrating membrane, thereby generating output current. The output current is converted into a voltage signal and enhanced by a transimpedance amplifier to effect reception of the signal.
Manufacturing a serpentine silver nanowire electrode, namely mixing silver nanowires with silver flake ink, and then performing screen printing on the mixed silver nanowire/silver composite ink on a PDMS flexible substrate at room temperature by using a screen printer. In this process, a custom screen with serpentine pattern open areas is used as a printing template and silver nanowires/silver composite ink is added to the custom screen. Thus, when the scraper scrapes across the surface of the screen, the silver nanowire/silver composite ink can be left on the PDMS of the flexible substrate through the open area in the screen, thereby forming a serpentine pattern. All the interconnection electrode wires connected with the ultrasonic transducer and the electrode wires connected with the outside are constructed by the screen printing technology.
The manufacturing of the CMUT rigid element adopts an adhesive wafer bonding process to prepare the CMUT, and BCB is a photosensitive polymer which is used as an adhesive and a side wall layer of the CMUT. The CMUT closed vacuum chamber structure is more advantageous and has better performance in controlling the size, shape and membrane material uniformity of the chamber.
First, two wafers, a silicon wafer I containing silicon nitride and a silicon substrate wafer II, are prepared. And (3) placing the wafer in a mixed solution of hydrogen peroxide and concentrated sulfuric acid for oxidation dissolution, and cleaning metal impurities.
A silicon nitride layer is deposited on a silicon nitride wafer one using a low pressure chemical vapor deposition process to build a low stress diaphragm. And removing the silicon nitride on the back surface of the vibrating membrane under the condition that the photoresist protects the front surface of the vibrating membrane by using photoetching and reactive ion etching processes, and stripping the photoresist on the front surface to form the silicon nitride on the vibrating membrane of the CMUT element.
In order to improve the optical transmittance of the silicon substrate, three key manufacturing steps are required to be satisfied, namely (1) grinding and thinning the second silicon substrate wafer to realize the thickness reduction of the silicon substrate and reduce the light absorption. (2) The chemical mechanical polishing process is used to realize the finish of the mirror surface and reduce the scattering of infrared light in the illumination process to the greatest extent. (3) An anti-reflection coating is added to the surface of the silicon substrate to achieve higher optical transmittance.
And sputtering a 250nm transparent conductive material ITO layer on the second silicon substrate wafer to form an ITO bottom electrode. And then cleaning in a mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water to remove any possible organic pollutants, wherein the ammonia and the hydrogen peroxide can clean particles attached to the surface of the silicon wafer and improve the cleanliness of the particles, and the cleanliness of the particles directly influences the bonding effect of the next step.
To ensure proper adhesion of BCB to the ITO bottom electrode, a thin layer of AP3000 adhesive (dow chemical) was first spin coated on a second silicon substrate wafer at 3000rpm for 30 seconds and then soft baked at 150 ℃ for 60 seconds. This step also needs to be performed on the silicon nitride wafer one to improve adhesion in the adhesive bonding step later in the process. Subsequently, BCB was spin coated on silicon substrate wafer two at 6500rpm for 45 seconds and soft baked at 60 ℃ for 90 seconds. The BCB layer is exposed to uv light and then baked at 50 ℃ for 60 seconds. Subsequently, the cavity was defined by spin drying for 2 minutes after 2 minutes of rinsing with DS2100 developer. The thickness of the BCB layer determines the gap distance of the CMUT cell.
And bonding the first silicon nitride wafer and the second silicon substrate wafer together by using a wafer bonding machine through an adhesive. The wafers are first separated by a spacer to ensure a vacuum-tight gap. After loading the wafers, the chamber was pumped down to 0.5mTorr and the gasket removed allowing the two wafers to contact each other while forming a vacuum tight chamber. Then, a compression pressure of 0.5MPa was applied to the wafer for 1 hour, and the wafer was cooled and taken out of the chamber. The process of removing the wafer silicon handle is accelerated by a combination of dry etching and wet etching.
A 200nm transparent conductive material ITO layer was sputtered on a silicon nitride diaphragm as a top electrode, and then the top ITO layer was patterned using a positive photoresist and wet etching to define a top electrode of the CMUT cell. To reduce the resistivity of the top electrode and maintain the transparency of the device, patterning is performed in the form of thin strips by lift-off techniques. Subsequently, the wafer is diced in predefined horizontal and vertical directions using a dicing tool, diced into chip islands with individual CMUT elements, rapidly spin coated with a PDMS flexible layer on the back of the wafer and cured. And finally, packaging the serpentine silver nanowire interconnection electrode and the CMUT array in the PDMS flexible substrate at the same time to form the flexible near infrared transparent CMUT array.
Some key design factors including diameter, material type and vacuum gap height are considered in manufacturing CMUTs, which may affect the performance of CMUTs. CMUT is modeled as a second order system to obtain important parameters such as resonant frequency and pull-in voltage.
The resonant frequency (ω0) is a key parameter that determines the resolution of an image.
T represents the thickness of the diaphragm, a is the radius of the diaphragm, E represents the Young's modulus of the diaphragm material, v is the Poisson's ratio of the diaphragm, ρ m is the density of the medium, ρ is the density of the diaphragm.
Another key parameter is pull-in voltage (V pull in). The pull-in voltage is the point at which the electrostatic and mechanical forces are equal, which results in the top electrode being stuck to the substrate. Therefore, it is very important to operate the CMUT below the pull-in voltage.
G eff represents the effective gap height, and the calculation formula is
G 0 is the original gap height, t m is the film thickness, t i is the insulator thickness, ε r is the relative dielectric constant of the insulator and film material, ε 0 is the dielectric constant of free space, k is the spring constant, and A is the electrode area.
The wearable flexible near infrared transparent ultrasonic transducer has a light and thin and soft structure, can adapt to any shape of a contact interface, and can be self-aligned to a target interface so as to meet clinical requirements of continuous detection. The wearable flexible near infrared transparent ultrasonic transducer allows near infrared laser beams to penetrate, and the integration of a light source and the ultrasonic transducer can be effectively realized.
The embodiment also provides a wearable flexible near-infrared transparent photoacoustic/ultrasonic bimodal imaging method based on the system implementation, which comprises the following steps:
irradiating the chest central blood vessel by using a pen-type laser to emit near infrared laser beams to generate photoacoustic signals;
adjusting parameters of the ultrasonic scanner to switch to a photoacoustic imaging mode;
A wearable flexible near infrared transparent ultrasonic transducer attached to the chest receives the photoacoustic signal;
constructing a light absorption distribution diagram of the hemoglobin by utilizing an image reconstruction algorithm, and quantifying the blood oxygen saturation according to the absorption coefficient of the hemoglobin;
switching the ultrasound scanner to an ultrasound imaging mode;
transmitting pulse ultrasonic waves through a wearable flexible near infrared transparent ultrasonic transducer to detect a chest central blood vessel, and simultaneously receiving echo signals of a reflector;
the method comprises the steps of displaying B-type gray scale mode images of thoracic central blood vessels by using an image reconstruction algorithm, calculating blood pressure of blood flow in the blood vessels based on the B-type gray scale mode images of the thoracic central blood vessels, and detecting flowing blood flow velocity information and spatial distribution through Doppler effect. The pen-shaped laser is driven by a customized laser driver, the driver emits a near infrared laser beam after being triggered by an external trigger (namely a switch button), at this time, the commercial ultrasonic scanner 4 is synchronously adjusted, the transmission function of ultrasonic waves is prevented, the switching to a photoacoustic imaging mode state is allowed, and the process of laser pulse irradiation and echo signal receiving can be synchronously performed. After the laser beam irradiates the chest central blood vessel, the local tissue causes the thermoelastic expansion effect, generates a photoacoustic signal and continuously propagates outwards to the skin surface, the photoacoustic signal is received by a wearable flexible near infrared transparent ultrasonic transducer attached to the chest, a light absorption distribution diagram of hemoglobin is constructed by utilizing an image reconstruction algorithm, and the oxygen saturation of blood is quantified according to the absorption coefficient of the hemoglobin.
In the near infrared spectral range employed by the present system, the change in carboxyhemoglobin and methemoglobin is not considered, and therefore, the absorption of light reflects mainly the total concentration of deoxyhemoglobin (Hb) and oxyhemoglobin (HbO 2).
In some embodiments, the near infrared laser beam has a wavelength of 900-1100 nm. The imaging system uses near infrared wavelengths as the appropriate spectral range. The depth of the biological tissue penetrable by the near infrared laser is as long as a few centimeters, and the hemoglobin has strong absorption advantage compared with other endogenous chromophores in the near infrared wavelength range. The difference in absorption rate between deoxyhemoglobin and oxyhemoglobin is most pronounced in the 900-1100 nm wavelength range. Furthermore, based on the low absorptivity of silicon to near infrared wavelengths, near infrared light can pass through the CMUT array without strong attenuation, so that the generated photoacoustic signal is successfully received by the wearable flexible near infrared transparent ultrasound transducer.
The quantifying the oxygen saturation of blood based on the absorption coefficient of hemoglobin comprises:
The absorption coefficient μ λ can be calculated by formulas (1) and (2) under the condition that the wavelengths λ 1 and λ 2 satisfy the preset condition:
Wherein C Hb and C HbO2 represent the content of deoxyhemoglobin and oxyhemoglobin, respectively, ε λ1 Hb,ελ2 Hb and ε λ1 HbO2,ελ2 HbO2 represent the extinction coefficients of deoxyhemoglobin and oxyhemoglobin at wavelengths lambda 1 and lambda 2, respectively;
Given that the intensity of the photoacoustic signal is proportional to the absorption coefficient of the tissue, the simplified equation blood oxygen saturation SaO 2 can be calculated by equations (3), (4) and (5):
Subsequently, the commercial ultrasonic scanner is restarted to be in an ultrasonic imaging mode, and the chest central blood vessel is detected through the wearable flexible near infrared transparent ultrasonic transducer so as to realize ultrasonic imaging detection. The wearable flexible near infrared transparent ultrasonic transducer is attached to the corresponding skin surface of the chest central blood vessel, the CMUT array continuously transmits short pulse ultrasonic waves at a certain fixed frequency, and all array elements of the phased array element array participate in the transmission of each acoustic wave beam. The CMUT array transmits pulsed ultrasonic waves along the transmission path of each acoustic beam line, and then receives and processes echo signals of each reflector on the acoustic beam path one by one from shallow and deep. And displaying a B-type gray scale mode image of the chest central blood vessel by using an image reconstruction algorithm.
Given that the arterial vessel under test is rotationally symmetrical and has certain characteristics of very small elasticity and viscoelasticity, the blood pressure waveform (pr (t)) can be calculated from the vessel diameter waveform by equation (6):
the blood pressure waveform (pr (t)) can be calculated from the blood vessel diameter waveform by the formula (6):
pr d is the brachial artery diastolic pressure measured by a cuff sphygmomanometer, ar d is the arterial diastolic cross-section;
Alpha is the rigidity coefficient of the blood vessel and can be calculated by the formula (7):
Pr s is the brachial artery systolic pressure measured by a commercial cuff sphygmomanometer, ar s is the arterial systolic cross section;
ar (t) can be calculated by equation (8):
d (t) is a vessel diameter waveform measured by a wearable flexible near infrared transparent ultrasound transducer.
In some embodiments, detecting the flow velocity information and spatial distribution of flowing blood by doppler effect includes:
Detecting flowing blood information through Doppler effect, adopting multiple acoustic beams to perform rapid sampling, performing phase detection, autocorrelation processing and color coding on the obtained Doppler information, marking blood flow directions by different colors, displaying the speed of color brightness, and superposing the color brightness on a B-type gray scale ultrasonic image to obtain the spatial distribution and flow velocity information of blood flow in blood vessels;
The blood flow velocity (v) of the arterial vessel can be calculated by the formula (9) using the doppler principle:
C is the speed of sound, i.e., the propagation speed of ultrasound in soft tissue, f 0 is the transmit frequency, f d is the Doppler shift, i.e., the difference between the receive frequency and the transmit frequency, and θ is the Doppler angle, i.e., the angle between the ultrasound beam and the direction of blood flow motion.
Therefore, the photoacoustic/ultrasonic bimodal imaging system can realize real-time, continuous and dynamic detection of blood oxygen saturation and hemodynamic information of the chest central blood vessel.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (5)
1. A method for preparing a wearable flexible near infrared transparent ultrasonic transducer, the method comprising:
The MEMS flexible substrate comprises a PDMS flexible substrate, a plurality of micro-rigid CMUT elements, a serpentine silver nanowire electrode and an electrode connected with the outside, wherein the micro-rigid CMUT elements are arranged in parallel, the serpentine interconnection line is formed based on the mutual connection of the silver nanowire electrodes, and the micro-rigid CMUT elements, the serpentine silver nanowire electrode and the electrode connected with the outside are packaged in the PDMS flexible substrate together, and the MEMS flexible substrate comprises the following steps:
The manufacturing of the snake-shaped silver nanowire electrode comprises the steps of mixing silver nanowires with silver flake ink, and then performing screen printing on the mixed silver nanowire/silver composite ink on a PDMS flexible substrate at room temperature by using a screen printer;
Preparing a CMUT by adopting an adhesive wafer bonding process, and adopting styrene-acrylic cyclobutene as an adhesive and a side wall layer of the CMUT;
the manufacturing of the CMUT rigid element comprises the steps of adopting an adhesive wafer bonding process to prepare the CMUT, adopting styrene-acrylate cyclobutene as an adhesive and a side wall layer of the CMUT, and comprising the following steps:
Preparing two wafers, namely a silicon wafer I containing silicon nitride and a silicon substrate wafer II, placing the wafers in a mixed solution of hydrogen peroxide and concentrated sulfuric acid for oxidation dissolution, and cleaning metal impurities;
Depositing a silicon nitride layer on the first silicon nitride wafer by using a low-pressure chemical vapor deposition process to construct a low-stress vibrating membrane;
sputtering a 250-260nm transparent conductive material indium tin oxide layer on a second silicon substrate wafer to form an ITO bottom electrode, and then cleaning in a mixed solution of ammonium hydroxide, hydrogen peroxide and deionized water to remove organic pollutants;
spin coating a layer of AP3000 adhesive on a first silicon substrate wafer and a second silicon substrate wafer at 3000-3200rpm for 25-40 seconds, and then soft baking at 140-160 ℃ for 50-70 seconds;
spin coating BCB on a second silicon substrate wafer at 6500-7000rpm for 40-60 seconds, and soft baking at 50-70 ℃ for 90-100 seconds, wherein the BCB layer is exposed to ultraviolet rays and then baked and cured at 40-60 ℃;
spin-drying after rinsing with DS2100 developer to define cavities;
bonding the first silicon nitride wafer and the second silicon substrate wafer by using a wafer bonding machine through an adhesive;
Sputtering a transparent conductive material ITO layer of 200-210nm on a silicon nitride vibrating membrane as a top electrode, and then patterning the top ITO layer by utilizing positive photoresist and wet etching to define the top electrode of the CMUT element;
And simultaneously packaging the serpentine silver nanowire interconnection electrode and the CMUT array in the PDMS flexible substrate to form the flexible near infrared transparent CMUT array.
2. The method for manufacturing the wearable flexible near infrared transparent ultrasonic transducer according to claim 1 is characterized in that the micro rigid CMUT element comprises an ITO top electrode, a vibrating membrane, a capacitor plate structure with a vacuum cavity, an ITO bottom electrode and a substrate, wherein the top electrode is fixed on the upper surface of the vibrating membrane, the capacitor plate structure with the vacuum cavity is attached to the lower surface of the vibrating membrane, the ITO bottom electrode is attached to the lower portion of the capacitor plate structure with the vacuum cavity, the substrate is attached to the lower portion of the ITO bottom electrode, the vibrating membrane is a silicon nitride vibrating membrane, and the substrate is a silicon crystal substrate.
3. The method for manufacturing the wearable flexible near infrared transparent ultrasonic transducer is characterized in that the capacitor plate structure with the vacuum cavity comprises a plurality of insulators BCB, wherein the insulators BCB distributed on the side parts and the insulators BCB distributed on the bottom parts form a sealed vacuum cavity together with a vibrating membrane, and the capacitor plate structure with the vacuum cavity is composed of the insulators BCB, the vibrating membrane and the vacuum cavity.
4. The method for manufacturing the wearable flexible near infrared transparent ultrasonic transducer according to claim 1, wherein the manufacturing of the serpentine silver nanowire electrode comprises the steps of mixing silver nanowires with silver flake ink, and then performing screen printing on the mixed silver nanowire/silver composite ink at room temperature based on a PDMS flexible substrate by using a screen printer, wherein the screen printing is performed by using a custom screen with an open area of the serpentine pattern as a printing template, and adding the silver nanowire/silver composite ink onto the custom screen.
5. The method of manufacturing a wearable flexible near infrared transparent ultrasonic transducer according to claim 4, wherein the bonding of the first silicon nitride wafer and the second silicon substrate wafer by the wafer bonder comprises separating the wafers by a spacer to ensure a vacuum-tight gap, pumping down the chamber to 0.5mTorr after loading the wafers, removing the spacer to allow the wafers to contact each other while forming a vacuum-tight chamber, and then applying a compression pressure of 0.5MPa to the wafers for 1 hour, and taking out the wafers from the chamber after cooling.
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| CN115055357A (en) * | 2022-06-23 | 2022-09-16 | 复旦大学 | A flexible transparent capacitive micromachined ultrasonic transducer and preparation method thereof |
| CN117017280A (en) * | 2023-07-24 | 2023-11-10 | 西南交通大学 | Wearable flexible near-infrared photoacoustic/ultrasonic dual-mode imaging system and method |
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