Wireless passive surface acoustic wave temperature, humidity and pressure sensor and preparation method thereof

Abstract

The invention provides a wireless passive surface acoustic wave temperature, humidity and pressure sensor and a preparation method thereof, and belongs to the field of surveying and mapping devices. The interdigital transducer is arranged in the middle of the three areas; each pair of reflecting gratings is arranged on the two sides of the interdigital transducer; the resonant frequency of the resonant acoustic wave sensors is adjusted by adjusting the interdigital period of each interdigital transducer and the period of the reflecting grating, and the three resonant acoustic wave sensors are made to detect the surface temperature, the surface humidity and the surface pressure respectively; and the coating is coated on the surface of the area for detecting the surface humidity. Different structural designs are selected based on the surface acoustic wave principle, the resonant frequency of the resonant sensor is adjusted by changing the interdigital period of the interdigital transducer and the period of the reflecting grating, and multi-parameter detection of temperature, humidity and pressure is achieved on the same substrate.

Description

Technical Field

[0001] The invention relates to the technical field of surveying and mapping devices, and in particular to a wireless passive surface acoustic wave temperature, humidity and pressure sensor and a preparation method thereof. Background Art

[0002] With the development of science and technology, especially the advancement of technologies such as the Internet of Things (IoT), artificial intelligence (AI) and big data, smart devices have been widely used in various fields. The temperature, humidity, pressure and other tests of smart devices require greater flexibility and convenience. Traditional wired active sensors such as piezoelectric sensors, photoelectric sensors, and thermoelectric sensors cannot meet this requirement. Currently, there are three main types of wireless passive sensors that are developing rapidly: wireless passive based on LTCC technology, wireless passive surface acoustic wave (SAW) sensors, and microwave resonant ring passive wireless sensors. Among them, wireless passive surface acoustic wave (SAW) sensors have outstanding performance in consistency, repeatability, temperature stability and radiation resistance, and are suitable for applications that require high information sensitivity accuracy and real-time information detection.

[0003] However, current wireless passive sensors are only suitable for detecting a single signal. For example, Chinese patent CN118424374A discloses an integrated wireless passive thin-film intelligent sensing system and its preparation method and application. It uses a resonant type combined with a delay type to simultaneously measure temperature and pressure, which is difficult to prepare and has high cost. Summary of the invention

[0004] In view of this, the present invention proposes a wireless passive surface acoustic wave temperature, humidity and pressure sensor and a preparation method thereof, which are used to solve the problem that the current wireless passive sensor is only applicable to the detection of a single signal.

[0005] The technical solution of the present invention is implemented as follows: the present invention provides a wireless passive surface acoustic wave temperature, humidity and pressure sensor, including a piezoelectric substrate, whose upper surface is provided with three areas; three interdigital transducers, which are respectively arranged in the middle of the three areas; six groups of reflection gratings, two groups of reflection gratings in a pair, and each pair of reflection gratings is arranged on both sides of a corresponding interdigital transducer; a coating, which is made of humidity-sensitive material; wherein the interdigital transducers in each area and the two groups of reflection gratings on both sides thereof constitute a resonant acoustic wave sensor, and the resonant frequency of the resonant acoustic wave sensor is adjusted by adjusting the interdigital period of each interdigital transducer and the period of the reflection grating, and the three resonant acoustic wave sensors are respectively used to detect surface temperature, surface humidity and surface pressure; the coating is coated on the upper surface of the piezoelectric substrate, the coating is located in the area where the surface humidity is detected, and the coating covers the interdigital transducers and the bars of the reflection grating.

[0006] On the basis of the above technical solution, preferably, the interdigital period is adjusted by controlling the interdigital width of the interdigital transducer and the spacing between adjacent interdigits, and the interdigital period λ=2×(b+c), wherein b is the interdigital width and c is the spacing between adjacent interdigits.

[0007] More preferably, the interdigital transducer is a mean interdigital structure, and b=c.

[0008] More preferably, the IDT b and c of the IDT located in the temperature detection area are smallest, the IDT b and c of the IDT located in the humidity detection area are centered, and the IDT b and c of the IDT located in the pressure detection area are largest.

[0009] More preferably, the period of the reflection grating satisfies p=λ×n / 2, wherein n is a positive integer.

[0010] Further preferably, the reflective grating includes several pairs of grating bars, the reflective grating period in the area for detecting temperature is the smallest and the number of grating bar pairs is the least, the reflective grating period in the area for detecting humidity is centered and the number of grating bar pairs is centered, and the reflective grating period in the area for detecting pressure is the largest and the number of grating bar pairs is the largest.

[0011] On the basis of the above technical solution, preferably, the reflective grid is an open grid, a short grid or a positive and negative grid.

[0012] In the second aspect, the present invention also provides a method for preparing a wireless passive surface acoustic wave temperature, humidity and pressure sensor, which is used to prepare the above-mentioned wireless passive surface acoustic wave temperature, humidity and pressure sensor, including the following steps: step one, preparing a piezoelectric substrate and preparing a humidity sensitive material; step two, using ultraviolet photolithography technology to directly form a pattern of interdigital electrodes on the piezoelectric substrate, and realizing the patterning of the interdigital electrodes through magnetron sputtering technology and stripping processing technology, and forming an interdigital transducer and a reflection grating on the piezoelectric substrate; step three, using a syringe or a micropipette to drop the humidity sensitive material onto the surface of the area used to detect the surface humidity and drying it to form a coating.

[0013] In the third aspect, the present invention also provides a measuring device, including the above-mentioned wireless passive surface acoustic wave temperature, humidity and pressure sensor, and also including a controller, a DDS signal generator, a PLL module, a mixer, an analog-to-digital converter and a radio frequency antenna; a transmitting link and a receiving link are respectively connected between the controller and the wireless passive surface acoustic wave temperature, humidity and pressure sensor, and the controller, DDS signal generator, PLL module and wireless passive surface acoustic wave temperature, humidity and pressure sensor are connected in sequence in the transmitting link, and the wireless passive surface acoustic wave temperature, humidity and pressure sensor, the mixer and the analog-to-digital converter and the controller are connected in sequence in the receiving link, so that the transmitting link and the receiving link form a loop; the radio frequency antenna is connected to the wireless passive surface acoustic wave temperature, humidity and pressure sensor, and the radio frequency antenna sends and receives signals.

[0014] In a fourth aspect, the present invention also provides a method for using a measuring device, which uses the above-mentioned measuring device and includes the following steps: step 1, a controller configures a DDS signal generator to generate an adjustable signal component, sends it to a PLL module for phase locking and frequency multiplication, and generates an intermittent sinusoidal excitation signal, amplifies the power of the signal after filtering, and inputs it into a wireless passive surface acoustic wave temperature, humidity and pressure sensor; step 2, switching the transmitting link and the receiving link is achieved by switching high and low levels, and sending and receiving signals through a radio frequency antenna; step 3, receiving the echo signal generated by the wireless passive surface acoustic wave temperature, humidity and pressure sensor after the excitation resonance by electromagnetic coupling, filtering it after low-noise amplification, and then converting and filtering the signal through a mixer, and sending it to an analog-to-digital converter, using the controller to collect the resonant echo signal and calculate the resonant frequency of the echo signal.

[0015] The wireless passive surface acoustic wave temperature, humidity and pressure sensor and the preparation method thereof of the present invention have the following beneficial effects compared with the prior art:

[0016] (1) The present invention selects different structural designs based on the surface acoustic wave principle, adjusts the resonant frequency of the resonant sensor by changing the interdigital period of the interdigital transducer and the period of the reflection grating, and realizes multi-parameter detection of temperature, humidity and pressure on the same substrate.

[0017] (2) The processing technology of each sensor sensitive unit of the present invention can be obtained only through the processing of the electrode structure and the coating of the moisture sensitive material, and the process is simple.

[0018] (3) The detection device of the present invention realizes multi-parameter testing by integrating three different single-port resonators with antennas, and connects the sensor to the transceiver or reader unit through a wireless circuit to obtain test information in real time. It does not require an external power supply and is suitable for some occasions where wiring is difficult or movement is required. It is small in size, light in weight, and easy to integrate into various devices. It has high sensitivity to the measurement of temperature, humidity, and pressure, and can achieve high-precision measurement. It can be used in harsh environments such as high temperature, humidity, and chemical corrosion. Due to its passive characteristics, the sensor basically does not require maintenance and can maintain good performance for a long time, reducing costs. Traditional wireless passive sensor devices have shortcomings such as a single structure and a short transmission distance, which limit their ability to move and test multiple parameters in different locations. Wireless passive surface acoustic wave (SAW) sensor devices have outstanding performance in consistency, repeatability, temperature stability, and radiation resistance, and are suitable for applications that require high information sensitivity and real-time information detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A stereogram of the wireless passive surface acoustic wave temperature, humidity and pressure sensor of the present invention;

[0021] Figure 2 is a top view of the interdigital transducer of the present invention;

[0022] Figure 3 is a top view of the temperature sensor of the present invention;

[0023] Figure 4 is a top view of the humidity sensor of the present invention;

[0024] Figure 5 is a top view of the pressure sensor of the present invention;

[0025] Figure 6 The figure is a flow chart of the method for using the measuring device of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] like Figure 1 As shown, a wireless passive surface acoustic wave temperature, humidity and pressure sensor of the present invention comprises a piezoelectric substrate 1, an interdigital transducer 2, a reflection grating 3 and a coating 4.

[0028] Among them, three areas 101 are arranged on the upper surface of the piezoelectric substrate 1. The piezoelectric substrate 1 is made of lithium niobate (LiNbO3, LN), which can also be replaced by piezoelectric materials such as lithium tantalate and quartz. The working principle of the surface acoustic wave multi-physical quantity-temperature / humidity / pressure sensor device is that the change of the external environment temperature / humidity / pressure causes the physical properties of the piezoelectric material of the piezoelectric substrate 1 to change, thereby affecting the propagation rate of the surface acoustic wave in the piezoelectric substrate 1 or the change of the device structure, which is finally reflected as the change of the resonant frequency of the surface acoustic wave sensor to test its change.

[0029] The three IDTs 2 are respectively arranged in the middle of the three regions 101. The interdigital bars of the IDT 2 and the bars of the reflective grating 3 are both metal bars, which are sputtered on the piezoelectric substrate 1 by magnetron sputtering technology.

[0030] The six groups of reflection gratings 3 are divided into two groups and one pair, and each pair of reflection gratings 3 is arranged on both sides of the corresponding interdigital transducer 2, and its function is to reflect sound waves. Each reflection grating 3 has a plurality of bars arranged in parallel. The existence of the reflection grating 3 will make the acoustic impedance discontinuous, and then reflect the surface acoustic wave, thereby forming a standing wave; each individual reflection grating 3 will reflect the incoming sound wave and interfere with each other.

[0031] The coating 4 is made of humidity sensitive material. Humidity sensitive functional material is a kind of functional material with the property of adsorbing water molecules. Its physical and chemical properties, such as resistance, capacitance, length, volume and color, will respond to the ambient humidity. The humidity sensitive material adopts a mixed solution of nanodiamond (ND) and chitosan (CS).

[0032] In this embodiment, the interdigital transducers 2 in each area 101 and the two groups of reflection gratings 3 on both sides thereof constitute a resonant acoustic wave sensor 10. This single-port structure sensor is often used to make a wireless passive surface acoustic wave sensor. The resonant frequency of the resonant acoustic wave sensor 10 is adjusted by adjusting the interdigital period of each interdigital transducer 2 and the period of the reflection grating 3, and the three resonant acoustic wave sensors 10 detect the surface temperature, surface humidity and surface pressure respectively; the coating 4 is coated on the surface of the area 101 for detecting the surface humidity on the piezoelectric substrate 1, and the coating 4 covers the interdigital transducers 2 and the bars of the reflection grating 3. The structural size of the interdigital transducer 2 determines the frequency of the sensor, and the relationship is f=v / λ. Among them, v is the propagation speed of the surface acoustic wave (SAW) on the piezoelectric substrate, λ is the interdigital period of the interdigital transducer 2 (IDT), and f is the resonant frequency of the sensor. When IDT excites sound waves, it is a series of wave sources. The sound waves generated by each pair of interdigital excitations are superimposed on each other. According to the principle of wave interference, when the interdigital period λ is an integer multiple of the surface acoustic wave wavelength, the surface acoustic wave amplitude excited by IDT reaches the maximum. When the frequency of the transmitted signal is equal to the IDT center frequency, the SAW emitted by IDT reaches the strongest. Therefore, this paper designs three resonant sensors with different structures on the same piezoelectric substrate 1 by adjusting the interdigital period of the interdigital transducer 2 and the period of the reflection grating. The resonant frequencies are different. The transmitted signals of different frequencies pass through the same circuit and are reflected as different frequencies of the received signals under the influence of temperature, humidity and pressure.

[0033] exist Figure 2In a preferred embodiment shown, according to the aforementioned principle, on the same piezoelectric substrate 1, when the propagation speed of the surface acoustic wave on the piezoelectric substrate 1 is the same, in order to make the resonant frequency f of the sensor different, it is only necessary to make the interdigital period λ different. In the structure of the interdigital transducer 2, the number of the interdigital fingers is n, the length is a, the width is b, the spacing between adjacent interdigital fingers is c, the wavelength is λ, and the acoustic aperture represents the overlapping length of adjacent metal electrodes and is set to w. Therefore, the interdigital period λ can be adjusted by controlling the interdigital width b and the spacing c between adjacent interdigital fingers in the interdigital transducer 2, that is, the interdigital period λ=2×(b+c).

[0034] exist Figure 2 In a preferred embodiment shown, in order to facilitate detection and calculation, the interdigital transducer 2 generally adopts a mean interdigital structure, that is, the interdigital width b is the same as the spacing c between adjacent interdigits.

[0035] exist Figure 3 or Figure 4 or Figure 5 In a preferred embodiment shown, b and c of the IDT 2 located in the area 101 for detecting temperature are the smallest, b and c of the IDT 2 located in the area 101 for detecting humidity are centered, and b and c of the IDT 2 located in the area 101 for detecting pressure are the largest.

[0036] For example, in the temperature sensor sensitive unit, b1 is 3μm, λ1 is 12μm, and n1 is 18 pairs; in the humidity sensor sensitive unit, b2 is 4μm, λ2 is 16μm, and n1 is 24 pairs; in the pressure sensor sensitive unit, b3 is 5μm, λ3 is 20μm, n3 is 30 pairs, w is 1000μm, and a is 1400μm. According to the detection requirements, b1, b2, and b3 take different parameters to make the resonant frequency of each sensor different.

[0037] exist Figure 2 In a preferred embodiment shown, it is known from the Bragg reflection theory that when the metal fingers are arranged and distributed according to a specific period, the reflected surface acoustic waves can be in the same phase, the amplitudes can be superimposed, and the reflectivity of the device can be enhanced. Therefore, in order to maximize the reflectivity, or even achieve total reflection, the design of the SAW sensor reflection grating 3 structure needs to meet the following conditions: p = λ × n / 2, where p refers to the period of the reflection grating 3 and n is a positive integer. The SAW resonator needs the sound wave reflected by the reflection grating 3 to meet the Bragg condition, while the incident wave and the reflected wave need to meet the standing wave resonance condition, so the distance d between the incident wave and the reflected wave g Should meet: g =(n-1)×λ / 2, where n is a positive integer, thereby ensuring the effective operation of the device.

[0038] exist Figure 3 or Figure 4 or Figure 5 In a preferred embodiment shown, the reflection grating 3 located in the area 101 for detecting temperature has the smallest period and the least number of grating bar pairs, the reflection grating 3 located in the area 101 for detecting humidity has a central period and the central number of grating bar pairs, and the reflection grating 3 located in the area 101 for detecting pressure has the largest period and the largest number of grating bar pairs.

[0039] For example, in the temperature sensor sensitive unit, the reflective grating 3 has 18 pairs of bars, d g1 =12μm; in the humidity sensor sensitive unit, the reflective grating 3 has 24 pairs of bars, d g2 =16μm; in the pressure sensor sensitive unit, the number of bars of the reflective grating 3 is 30 pairs, d g3 =20μm.

[0040] exist Figure 1 In a preferred embodiment shown, the reflective grid 3 is an open grid, a short-circuit grid or a positive-negative grid. An open grid means that each finger is independent and has no electrical connection; a short-circuit grid means that each finger is connected to a bus bar and there is an electrical connection between the fingers; a positive-negative grid is a combination of an open grid and a short-circuit grid. The reflective grid 3 in this embodiment can be arbitrarily selected and replaced.

[0041] like Figure 1 As shown, a method for preparing a wireless passive surface acoustic wave temperature, humidity and pressure sensor of the present invention is used to prepare a wireless passive surface acoustic wave temperature, humidity and pressure sensor of any of the above embodiments, comprising the following steps:

[0042] Step 1: Prepare the piezoelectric substrate for cleaning. Select 4-inch lithium niobate with a thickness of 500 μm as the substrate material to make a piezoelectric substrate 1, and use a standard RCA cleaning process to remove surface impurities. At the same time, prepare the humidity sensitive material. The humidity sensitive material uses a mixed solution of nanodiamond (ND) and chitosan (CS). Use an electronic balance to weigh 300 mg of CS powder and 600 mg of ND powder respectively. Use a measuring cylinder to measure 10 ml of deionized water, put it in a clean beaker, stir evenly and ultrasonically disperse for 1 hour.

[0043] Step 2: Use ultraviolet photolithography to directly form the pattern of interdigital electrodes on the piezoelectric substrate 1. First, magnetron sputtering is used to sputter the interdigital electrodes on the piezoelectric substrate 1 according to the pattern of the interdigital electrodes. Adhesion layer and Metal layer: the aluminum of the metal layer can be replaced by gold, copper and other metals, and the chromium of the adhesion layer can be replaced by titanium and other metals. Then, the interdigital electrodes are patterned by a lift-off process, thereby forming an interdigital transducer 2 and a reflective grating 3 on the piezoelectric substrate 1.

[0044] Step 3: Use a syringe or a micropipette to drop the humidity sensitive material onto the surface of the area 101 for detecting surface humidity, and dry it on a heating table at 100° C. to form a coating 4 .

[0045] like Figure 1 As shown, a measuring device of the present invention includes a wireless passive surface acoustic wave temperature, humidity and pressure sensor of any of the above embodiments, and also includes a controller, a DDS signal generator, a PLL module, a mixer, an analog-to-digital converter and a radio frequency antenna;

[0046] Among them, the controller is the main control chip, and its function is to control the opening and closing of each component connected to it and the reception and processing of detection data. A transmitting link and a receiving link are respectively connected between the controller and the wireless passive surface acoustic wave temperature, humidity and pressure sensor. In the transmitting link, the controller, DDS signal generator, PLL module and wireless passive surface acoustic wave temperature, humidity and pressure sensor are connected in sequence, and in the receiving link, the wireless passive surface acoustic wave temperature, humidity and pressure sensor, mixer, analog-to-digital converter and controller are connected in sequence, so that the transmitting link and the receiving link form a loop.

[0047] The radio frequency antenna is connected to the external port of the wireless passive surface acoustic wave temperature, humidity and pressure sensor, and the radio frequency antenna sends and receives signals.

[0048] like Figure 6 As shown, a method for using a measuring device of the present invention uses a measuring device of the above embodiment to realize a wireless non-contact measuring method. The principle is to use the resonant frequency strength of the sensor to calculate the measured signal of the measured area. When the transmitted sweep signal is the same as the resonant frequency of the answering antenna, the resonant frequency generated by the sensor being excited is the strongest. Specifically, the following steps are included:

[0049] Step 1: The controller is configured with a DDS signal generator to generate an adjustable signal component, which is sent to the PLL module for phase locking and frequency multiplication. The modulation switch generates an intermittent sinusoidal excitation signal by periodically opening and closing, amplifies the power of the signal, and then passes the filtered signal through a first-level power amplifier. The power of the signal after filtering is amplified and input into the wireless passive surface acoustic wave temperature, humidity and pressure sensor.

[0050] Step 2: The controller controls the on and off of the switch, thereby realizing the selection of the transmitting link and the receiving link by switching the high and low levels. The single-pole double-throw transmit-receive isolation switch is turned to the upper transmitting link to connect, and to the lower receiving link to connect. The signal is sent and received through the RF antenna.

[0051] Step 3: Receive the echo signal generated by the wireless passive surface acoustic wave temperature, humidity and pressure sensor after the excitation resonance by electromagnetic coupling, amplify the received sensor signal by using a low noise amplifier, filter the amplified signal, remove the useless signal components, and then convert and filter the signal by a mixer, and send it to the analog-to-digital converter. Use the analog-to-digital converter (ADC) inside the controller to collect the resonant echo signal and solve the resonant frequency of the echo signal to realize the functions of measuring temperature, humidity and pressure.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A wireless passive surface acoustic wave temperature, humidity and pressure sensor, characterized in that: include: A piezoelectric substrate (1) having three regions (101) arranged on its upper surface; Three interdigital transducers (2) are respectively arranged in the middle of the three areas (101); Six groups of reflection gratings (3), two groups of the reflection gratings (3) forming a pair, and each pair of the reflection gratings (3) being arranged on both sides of a corresponding interdigital transducer (2); The coating (4) is made of a moisture sensitive material; The interdigital transducers (2) in each of the regions (101) and the two groups of reflection gratings (3) on both sides thereof constitute a resonant acoustic wave sensor (10); the resonant frequency of the resonant acoustic wave sensor (10) is adjusted by adjusting the interdigital period of each of the interdigital transducers (2) and the period of the reflection grating (3); and the three resonant acoustic wave sensors (10) are used to detect surface temperature, surface humidity and surface pressure respectively; The coating (4) is coated on the upper surface of the piezoelectric substrate (1), the coating (4) is located in the area (101) for detecting surface humidity, and the coating (4) covers the fingers of the interdigital transducer (2) and the bars of the reflection grating (3).

2. The wireless passive surface acoustic wave temperature, humidity and pressure sensor according to claim 1, characterized in that: The interdigital period is adjusted by controlling the interdigital width of the interdigital transducer (2) and the spacing between adjacent interdigits, wherein the interdigital period λ=2×(b+c), wherein b is the interdigital width and c is the spacing between adjacent interdigits.

3. The wireless passive surface acoustic wave temperature, humidity and pressure sensor according to claim 2, characterized in that: The interdigital transducer (2) is a mean interdigital structure, and b=c.

4. The wireless passive surface acoustic wave temperature, humidity and pressure sensor according to claim 2, characterized in that: The b and c of the interdigital transducer (2) located in the area (101) for detecting temperature are the smallest, the b and c of the interdigital transducer (2) located in the area (101) for detecting humidity are in the middle, and the b and c of the interdigital transducer (2) located in the area (101) for detecting pressure are the largest.

5. The wireless passive surface acoustic wave temperature, humidity and pressure sensor according to claim 2, characterized in that: The period of the reflection grating (3) satisfies p=λ×n / 2, where n is a positive integer.

6. The wireless passive surface acoustic wave temperature, humidity and pressure sensor according to claim 2, characterized in that: The reflection grating (3) comprises a plurality of pairs of grating bars. The reflection grating (3) located in the area (101) for detecting temperature has the smallest period and the least number of grating bar pairs. The reflection grating (3) located in the area (101) for detecting humidity has a central period and the central number of grating bar pairs. The reflection grating (3) located in the area (101) for detecting pressure has the largest period and the largest number of grating bar pairs.

7. The wireless passive surface acoustic wave temperature, humidity and pressure sensor according to claim 1, characterized in that: The reflective grid (3) is an open grid, a short grid or a positive or negative grid.

8. A method for preparing a wireless passive surface acoustic wave temperature, humidity and pressure sensor, characterized in that: The method for preparing a wireless passive surface acoustic wave temperature, humidity and pressure sensor according to any one of claims 1 to 7 comprises the following steps: Step 1, preparing the piezoelectric substrate (1) and preparing a humidity sensitive material; Step 2: using ultraviolet lithography technology to directly form a pattern of interdigital electrodes on the piezoelectric substrate (1), using magnetron sputtering technology and lift-off processing technology to achieve patterning of the interdigital electrodes, and forming an interdigital transducer (2) and a reflective grating (3) on the piezoelectric substrate (1); Step three: use a syringe or a micropipette to drop the humidity sensitive material onto the surface of the area (101) for detecting surface humidity and dry it to form a coating (4).

9. A measuring device, characterized in that: A wireless passive surface acoustic wave temperature, humidity and pressure sensor comprising any one of claims 1 to 7, further comprising a controller, a DDS signal generator, a PLL module, a mixer, an analog-to-digital converter and a radio frequency antenna; A transmitting link and a receiving link are respectively connected between the controller and the wireless passive surface acoustic wave temperature, humidity and pressure sensor, wherein the controller, the DDS signal generator, the PLL module and the wireless passive surface acoustic wave temperature, humidity and pressure sensor are connected in sequence in the transmitting link, and the wireless passive surface acoustic wave temperature, humidity and pressure sensor, the mixer, the analog-to-digital converter and the controller are connected in sequence in the receiving link, so that the transmitting link and the receiving link form a loop; The radio frequency antenna is connected to the wireless passive surface acoustic wave temperature, humidity and pressure sensor, and the radio frequency antenna sends and receives signals.

10. A method for using a measuring device, characterized in that: The method of preparing a measuring device according to claim 9 comprises the following steps: Step 1, the controller is configured with a DDS signal generator to generate an adjustable signal component, which is sent to the PLL module for phase locking and frequency multiplication to generate an intermittent sinusoidal excitation signal, and the power of the signal is amplified after filtering and input into a wireless passive surface acoustic wave temperature, humidity and pressure sensor; Step 2, switching the transmitting link and the receiving link is realized by switching the high and low levels, and sending and receiving signals through the radio frequency antenna; Step three, receiving the echo signal generated by the wireless passive surface acoustic wave temperature, humidity and pressure sensor after the excited resonance through electromagnetic coupling, filtering it after low-noise amplification, and then converting and filtering the signal through the mixer, sending it to the analog-to-digital converter, and using the controller to collect the resonant echo signal and calculate the resonant frequency of the echo signal.

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