Highly sensitive wireless temperature sensor based on impedance superposition

Abstract

This invention discloses a high-sensitivity wireless temperature sensor based on impedance superposition, belonging to the field of sensor design technology. The sensor includes a piezoelectric substrate, and a temperature-sensitive busbar, connecting wires, interdigitated electrodes, and an acoustic structure disposed on the surface of the piezoelectric substrate. The temperature-sensitive busbar is a composite temperature-sensitive structure composed of a temperature-sensitive dielectric layer and four metal films. The connecting wires are disposed in the outermost region of the acoustic structure, and a series structure of a thermistor and a varistor is set near the endpoint of the acoustic structure to stabilize the impedance of the connecting wires. The acoustic structure integrates a sound-absorbing structure to maximize sound wave reflection efficiency. The temperature-sensitive busbar forms a parallel impedance superposition with the acoustic structure through the connecting wires, superimposing the impedance change of the temperature-sensitive busbars onto the sensor's own response. This invention significantly improves temperature sensitivity without changing the piezoelectric substrate or increasing the sensor area, while maintaining the stability of the connecting wire impedance, and is suitable for resonant and delay-line wireless temperature sensors.

Description

Technical Field

[0001] This invention relates to the field of sensor design technology, and more specifically to a high-sensitivity wireless temperature sensor based on impedance superposition. Background Technology

[0002] Currently, wired temperature measurement is the most common method used in aerospace and civilian fields, with thermocouple and fiber optic temperature measurement being typical examples. Thermocouple temperature measurement requires signal transmission via metal wires, resulting in high wiring complexity and susceptibility to electromagnetic interference. While fiber optic temperature measurement offers advantages in interference resistance, the cost of laying and maintaining fiber optic links is high, and link breakage is common in high-temperature and vibration environments. These inherent drawbacks limit the widespread application of both methods in complex scenarios.

[0003] Surface acoustic wave (SAW) wireless temperature measurement effectively overcomes the shortcomings of traditional wired temperature measurement due to its excellent temperature sensitivity and strong environmental adaptability. Its sensitivity is primarily dependent on the intrinsic parameters of the piezoelectric crystal, specifically:

[0004] First, for resonant SAW wireless temperature sensors, the frequency of the reflected signal is directly proportional to the propagation speed of surface acoustic waves on the piezoelectric substrate. Once the piezoelectric crystal material is selected, the rate of change of the propagation speed of surface acoustic waves caused by temperature fluctuations is fixed, resulting in the temperature sensitivity of the sensor becoming a fixed value that cannot be adjusted.

[0005] Secondly, for delayed linear SAW wireless temperature sensors, the frequency and phase resolution of their signal readout systems have physical limits. When application scenarios demand higher temperature sensitivity, traditional solutions can only improve sensitivity by selecting a piezoelectric crystal with a higher temperature coefficient. However, this approach has two major problems: a. The acoustic characteristics of the newly selected piezoelectric crystal need to be re-evaluated across the entire temperature range, resulting in high engineering complexity; b. Due to the limited variety of existing piezoelectric crystal materials, it is difficult to guarantee the existence of crystal materials with both high temperature coefficient and high acoustic stability suitable for specific application scenarios.

[0006] Although SAW wireless temperature sensor sensitivity enhancement solutions have been reported, they all have obvious drawbacks:

[0007] (1) Substrate replacement scheme: Patent CN102928111A uses three different types of piezoelectric substrates (128°YX-LiNbO3, JCL quartz, and LST quartz) to change the sensitivity coefficient. By selecting different piezoelectric substrates, three different sensitivities are achieved, thereby obtaining the temperature value through the frequency difference of different substrates. However, it has problems with process compatibility and large-scale production. The cutting accuracy requirements, polishing roughness standards, and thin film deposition parameters of different substrates vary greatly, requiring frequent switching of production line processes, which increases production energy consumption and manufacturing costs, and limits its versatility.

[0008] (2) Additional Thin Film Solution: In 2017, Li Jing et al., in their paper "Parylene-Enhanced SAW Sensor and Its Temperature Response", directly coated the sensor surface with Parylene film. The temperature sensitivity of the Parylene-enhanced SAW sensor was 2.855 kHz / ℃, which was 0.807 kHz / ℃ higher than that of the unenhanced SAW sensor. However, the additional thin film may indirectly affect the propagation of surface acoustic waves, causing random fluctuations in the impedance of the connecting wires, which can disrupt the stability of the sensor output signal and fail to meet the requirements of high-precision temperature measurement scenarios.

[0009] (3) Differential frequency superposition scheme: In 2019, Dong Wenxiu proposed using a dual resonance mode differential frequency and anisotropic dual delay line method to achieve sensitivity enhancement in the article "Aluminum nitride surface acoustic wave device and its application in temperature sensing". However, this requires extremely high structural accuracy and the number of reflector electrodes needs to reach 700 pairs, which greatly increases the complexity of the process and the cost of manufacturing surface acoustic wave devices.

[0010] In summary, the existing methods cannot simultaneously achieve the technical goals of "no change to the piezoelectric substrate, no increase in sensor area, guaranteed impedance stability, significantly improved sensitivity, and low process complexity." There is an urgent need for a novel SAW wireless temperature sensor enhancement design to address the shortcomings of existing solutions, such as poor versatility, unstable impedance, and high engineering complexity. Summary of the Invention

[0011] To address the problems existing in the background technology and overcome the limitations of piezoelectric substrates on the temperature sensitivity of existing resonant and delayed linear surface acoustic wave (SAW) temperature sensors, this invention significantly amplifies the impact of temperature changes on the reflected signal by depositing a multilayered metal thin film and a temperature-sensitive dielectric layer in the temperature-sensitive busbar region. Furthermore, the stability of the connection line impedance is ensured by incorporating a series structure of a thermistor and a varistor in the connection line. Combining these two measures, sensitivity improvement can be achieved without replacing the piezoelectric substrate or increasing the sensor area. The specific design scheme of this invention is as follows:

[0012] A highly sensitive wireless temperature sensor based on impedance superposition includes a piezoelectric substrate that provides a propagation path for surface acoustic waves, and a component disposed on the surface of the piezoelectric substrate:

[0013] The temperature-sensitive busbar is a composite temperature-sensitive structure consisting of a temperature-sensitive dielectric layer and four metal films. The temperature-sensitive dielectric layer is strictly controlled to be inside the temperature-sensitive busbar area and does not exceed the boundary of the temperature-sensitive busbar area.

[0014] The acoustic structure forms a parallel impedance superposition structure with the temperature-sensitive busbar through connecting lines;

[0015] The connecting line is located in the outermost area of ​​the acoustic structure to connect the temperature-sensitive busbar to the acoustic structure to form a parallel structure. A series structure of nickel-chromium alloy thermistor and zinc oxide varistor is set near the end of the parallel structure to stabilize the impedance of the connecting line.

[0016] Interdigitated electrodes are electrically connected to the temperature-sensitive busbar to convert impedance changes caused by temperature variations into surface acoustic wave signals.

[0017] When the temperature changes, the impedance of the temperature-sensitive busbar changes linearly with the temperature. Through the connecting wire, it forms a parallel impedance with the acoustic structure, and the impedance change of the temperature-sensitive busbar is superimposed on the response of the sensor itself, thereby increasing the temperature sensitivity.

[0018] Preferably, the temperature-sensitive dielectric layer is made of a dielectric material whose dielectric constant changes linearly with temperature, including one or more of barium titanate, PZT piezoelectric ceramic, and polyimide. The coverage area of ​​the temperature-sensitive dielectric layer is controlled within the temperature-sensitive busbar region to avoid interfering with the propagation path of surface acoustic waves and the piezoelectric effect of the piezoelectric substrate, ensuring that only the impedance of the temperature-sensitive busbar changes with temperature while the acoustic wave propagation path remains stable.

[0019] Preferably, the four metal films are arranged sequentially from the piezoelectric substrate upwards as follows: titanium-zirconium composite metal film, copper-nickel gradient alloy film, palladium-silver composite metal film, and silver-tantalum composite metal film. The adjacent metal film layers are respectively filled with a temperature-sensitive dielectric layer material to form a gradient dielectric filling system, wherein:

[0020] Barium titanate is filled between the titanium-zirconium composite metal film and the copper-nickel gradient alloy film to provide high dielectric constant temperature-sensitive properties.

[0021] PZT piezoelectric ceramic is filled between the copper-nickel gradient alloy film and the palladium-silver composite metal film to provide medium-high dielectric constant temperature-sensitive properties.

[0022] Polyimide is filled between the palladium-silver composite metal film and the silver-tantalum composite metal film to provide low dielectric constant temperature-sensitive properties;

[0023] By using a gradient configuration of multiple temperature-sensitive dielectric layers, the linearity of a single material is prevented from abruptly changing when the temperature crosses the phase transition point, thereby enhancing the linearity and stability of the overall impedance under temperature variations.

[0024] Preferably, the positioning and impedance stabilization mechanism of the connecting line includes:

[0025] The connecting lines are positioned in the outermost area of ​​the acoustic structure to avoid direct interference from surface acoustic waves on the impedance of the connecting lines.

[0026] A series structure of a nickel-chromium alloy thermistor and a zinc oxide varistor is set at the end of the parallel structure near the acoustic structure. When the temperature rises and the impedance of the connecting line increases, the resistance of the nickel-chromium alloy thermistor increases synchronously, and the voltage division ratio of the zinc oxide varistor automatically decreases, so that the total impedance of the parallel structure returns to the preset threshold.

[0027] When the temperature decreases, causing the impedance of the connecting wires to decrease, the resistance of the thermistor decreases accordingly, and the voltage division ratio of the varistor increases, thus achieving impedance compensation.

[0028] Preferably, the structural parameters of the interdigital electrode are: 25 pairs of fingers, 3μm width of the finger strip, 3μm spacing, 430MHz excitation / reception frequency of surface acoustic waves, and the interdigital electrode is electrically connected to the temperature-sensitive busbar to convert the impedance change caused by temperature into the amplitude and phase change of the surface acoustic wave signal.

[0029] Preferably, the number of fingers in the acoustic structure is increased to 20 pairs to improve reflection efficiency; an integrated sound-absorbing structure is provided, which is a wedge-shaped groove array with a groove depth that gradually changes from 5 μm to 20 μm to accommodate sound wave absorption at different frequencies; the grooves are filled with a polyimide-silicon carbide nanocomposite film, wherein silicon carbide nanoparticles account for 15% of the volume, the film thickness is 2 μm, and the sound absorption rate is ≥95%.

[0030] Preferably, the piezoelectric substrate is made of 128° Y-cut lithium niobate material with dimensions of 5mm×5mm×0.5mm. The propagation speed of surface acoustic waves on the substrate is 3400m / s, and the temperature coefficient is 38ppm / ℃. As a supporting substrate for the sensor, it provides a stable acoustic wave propagation path, so that the propagation characteristics of surface acoustic waves on the substrate are not affected by the temperature-sensitive busbar structure.

[0031] Preferably, the impedance of the temperature-sensitive busbar consists of an inductive portion and a capacitive portion, with the inductance of the inductive portion being Z. l The capacitance of the capacitive part is Z. c Z l Determined by the connecting line, and controlled by the geometric parameters of the connecting line; Z c Determined by the composite structure of the temperature-sensitive dielectric layer and the four-layer metal film, it changes linearly with temperature.

[0032] Preferably, the sensor is a delay linear sensor with an acoustic structure of a reflective grating, a temperature-sensitive busbar connected in parallel with the reflective grating, and impedance changes directly modulating the phase characteristics of the reflected wave.

[0033] Preferably, the sensor is a resonant sensor, and its acoustic structure is a resonant cavity. The temperature-sensitive busbar is connected in parallel with the resonant cavity, which affects the resonant frequency response.

[0034] The beneficial effects achieved by this invention are as follows:

[0035] This invention constructs a composite temperature-sensitive structure consisting of a temperature-sensitive dielectric layer and four metal films in the temperature-sensitive busbar region of a sensor, achieving a linear response of the busbar impedance to temperature changes. In the composite structure, adjacent metal film layers are filled with three different temperature-sensitive dielectric materials with varying dielectric constants: barium titanate, PZT piezoelectric ceramic, and polyimide, forming a gradient dielectric filling system. This gradient configuration effectively avoids the abrupt linearity change that occurs when a single temperature-sensitive material crosses the phase transition point, ensuring that the capacitance of the temperature-sensitive busbar maintains good linear response characteristics across the entire temperature range. Simultaneously, the coverage area of ​​the temperature-sensitive dielectric layer is strictly controlled within the temperature-sensitive busbar region, not exceeding its boundary, avoiding interference with the surface acoustic wave propagation path and the piezoelectric effect of the piezoelectric substrate. This ensures that only the temperature-sensitive busbar impedance remains stable with temperature changes, providing a fundamental guarantee for high-precision temperature measurement by the sensor.

[0036] Secondly, this invention places the connecting line in the outermost region of the acoustic structure, avoiding direct interference from surface acoustic waves on the impedance of the connecting line. A series structure of a nickel-chromium alloy thermistor and a zinc oxide varistor is set near the endpoint of the parallel structure. When the temperature rises, causing the impedance of the connecting line to increase, the resistance of the nickel-chromium alloy thermistor increases synchronously, while the voltage division ratio of the zinc oxide varistor automatically decreases. Their synergistic effect causes the total impedance of the parallel structure to return to a preset threshold. Impedance compensation relies entirely on the inherent characteristics of the components, achieving rapid response without external power supply. This ensures that the impedance change of the temperature-sensitive busbar can be accurately and stably superimposed in parallel with the impedance change of the sensor's own temperature-sensitive structure, guaranteeing the stability of the sensor's output signal.

[0037] Third, this invention features an enhanced acoustic structure design to improve reflectivity. By increasing the number of finger strips to a specific logarithm and integrating the sound-absorbing structure, the sound wave reflection efficiency is maximized while reducing interference from sound waves to the connecting lines. The sound-absorbing structure employs a wedge-shaped groove array design with gradually varying groove depths to accommodate sound wave absorption at different frequencies, overcoming the limitation of a single groove depth only accommodating specific frequencies. The polyimide-silicon carbide nanocomposite membrane filled within the grooves contains silicon carbide nanoparticles with excellent chemical inertness, resisting corrosive gases and significantly improving the long-term stability and service life of the sound-absorbing structure. Simultaneously, the physical barrier formed by the wedge-shaped groove array reduces contact between moisture, corrosive gases, and the composite membrane, further maintaining the stability of the connecting line impedance and ensuring reliable sensor operation in complex environments.

[0038] Fourth, this invention achieves a significant improvement in temperature sensitivity based on the principle of impedance superposition. Without changing the piezoelectric substrate material or increasing the sensor area, the impedance change of the temperature-sensitive busbar is directly added to the original temperature response of the sensor through the parallel impedance superposition of the temperature-sensitive structure and the acoustic structure. The impedance of the temperature-sensitive busbar consists of an inductive part and a capacitive part. The inductive part is determined by the connecting wire and its temperature change rate is negligible. The capacitive part is determined by the composite structure of the temperature-sensitive dielectric layer and four metal films and changes linearly with temperature. The sensor is compatible with both resonant and delayed linear wireless temperature sensors. For delayed linear sensors, impedance changes directly modulate the phase characteristics of the reflected wave; for resonant sensors, impedance changes affect the resonant frequency response. This effectively improves temperature sensitivity while maintaining output stability, overcoming the high engineering complexity and poor process compatibility of traditional solutions that require reselecting a piezoelectric crystal to improve sensitivity. Attached Figure Description

[0039] Figure 1 This is the relationship between the attenuation value of S11 in Example 1 and the capacitance.

[0040] Figure 2 This is an exploded view of the structure of a high-sensitivity wireless temperature sensor.

[0041] Figure 3 This is a structural diagram of a high-sensitivity wireless temperature sensor.

[0042] Figure 4 This is a schematic diagram of a high-sensitivity wireless temperature sensor design.

[0043] Numbering on the map:

[0044] 1. Temperature-sensitive busbar; 11. Temperature-sensitive dielectric layer; 12. Four-layer metal film; 2. Connecting wire; 3. Interdigitated electrode; 4. Acoustic structure; 5. Piezoelectric substrate. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Reference Figures 1-4 The high-sensitivity wireless temperature sensor based on impedance superposition provided by this invention introduces a composite temperature-sensitive structure in the temperature-sensitive busbar region, making the impedance of the temperature-sensitive busbar change linearly with temperature. Furthermore, through optimized connection line layout and enhanced reflection characteristics design, impedance stability is ensured, thereby significantly improving temperature sensitivity without replacing the piezoelectric substrate 5 or increasing the device area.

[0047] The present invention discloses a high-sensitivity wireless temperature sensor based on impedance superposition, comprising a piezoelectric substrate 5 providing a propagation path for surface acoustic waves (SAWs), and a temperature-sensitive busbar 1, connecting lines 2, interdigitated electrodes 3, and an acoustic structure 4 disposed on the surface of the piezoelectric substrate 5. The temperature-sensitive busbar 1 is a composite temperature-sensitive structure composed of a temperature-sensitive dielectric layer 11 and four metal films 12, forming a parallel impedance superposition structure with the acoustic structure 4 via the connecting lines 2. The interdigitated electrodes 3 are electrically connected to the temperature-sensitive busbar 1, realizing the conversion of impedance changes caused by temperature variations into SAW signals. When the temperature changes, the impedance of the temperature-sensitive busbar 1 changes linearly with the temperature. The parallel impedance formed by the connecting lines 2 and the acoustic structure 4 superimposes the impedance change of the temperature-sensitive busbar 1 onto the sensor's own response, thereby increasing temperature sensitivity.

[0048] The temperature-sensitive busbar 1 is a composite temperature-sensitive structure consisting of a temperature-sensitive dielectric layer 11 and four metal films. The temperature-sensitive dielectric layer 11 is made of a dielectric material whose dielectric constant changes linearly with temperature, preferably one or more of barium titanate (BaTiO3), PZT piezoelectric ceramic, or polyimide. The coverage area of ​​the temperature-sensitive dielectric layer 11 is strictly controlled within the temperature-sensitive busbar region and does not extend beyond the boundary of the temperature-sensitive busbar region. This design avoids interference with the surface acoustic wave propagation path and the piezoelectric effect of the piezoelectric substrate 5, ensuring that only the impedance of the temperature-sensitive busbar remains stable as the acoustic wave propagation path changes with temperature.

[0049] The four metal films, arranged sequentially from the piezoelectric substrate 5 upwards, are a titanium-zirconium composite metal film (Ti-Zr), a copper-nickel gradient alloy film (Cu-Ni), a palladium-silver composite metal film (Pd-Ag), and a silver-tantalum composite metal film (Ag-Ta). Thermosensitive dielectric layers 11 are filled between adjacent metal film layers, forming a gradient dielectric filling system. Specifically, barium titanate (BaTiO3) is filled between the titanium-zirconium composite metal film and the copper-nickel gradient alloy film, providing high dielectric constant thermosensitive properties. PZT piezoelectric ceramic (Pb(Zr,Ti)O3) is filled between the copper-nickel gradient alloy film and the palladium-silver composite metal film, providing medium-to-high dielectric constant thermosensitive properties. Polyimide is filled between the palladium-silver composite metal film and the silver-tantalum composite metal film, providing low dielectric constant thermosensitive properties. This gradient configuration of multiple thermosensitive dielectric layers 11 avoids abrupt changes in linearity of a single material when the temperature crosses the phase transition point, thereby enhancing the linearity and stability of the overall impedance under temperature changes.

[0050] The composite structure of the multilayer metal film and the temperature-sensitive dielectric layer 11 forms a temperature-sensitive structure, whose impedance value changes linearly with temperature. The thickness of the four metal film layers can be adjusted according to actual needs. Preferably, the thickness of each metal film layer can be set to the same or different values ​​to optimize the overall temperature response characteristics. The temperature-sensitive dielectric layer 11 forms a dielectric layer between adjacent metal film layers. Through the composite material compensation effect, it ensures that the capacitance of the temperature-sensitive busbar changes linearly with temperature while maintaining good stability.

[0051] Connecting line 2 is positioned on the outermost edge of acoustic structure 4 to connect the temperature-sensitive busbar 1 to acoustic structure 4, forming a parallel structure. Positioning connecting line 2 on the outermost edge of acoustic structure 4 avoids direct interference from surface acoustic waves on the impedance of the connecting line. A series connection of a NiCr thermistor and a ZnO varistor is placed near the endpoints of the parallel structure to stabilize the impedance of the connecting line.

[0052] The working mechanism of this series structure is as follows: When the temperature rises, causing the impedance of the connecting line to increase, the resistance of the NiCr thermistor increases synchronously, while the voltage division ratio of the ZnO varistor automatically decreases, causing the total impedance of the parallel structure to return to a preset threshold. When the temperature decreases, causing the impedance of the connecting line to decrease, the resistance of the thermistor decreases synchronously, and the voltage division ratio of the varistor increases, achieving impedance compensation. The entire process requires no external power supply and relies entirely on the inherent characteristics of the components to achieve a fast response. Through this impedance stabilization mechanism, signal transmission loss can be reduced, ensuring the stability of the connecting line impedance, and enabling the temperature-sensitive impedance change of the temperature-sensitive busbar to be accurately and stably superimposed in parallel with the impedance change of the temperature-sensitive structure of the sensor itself.

[0053] The interdigital electrode 3 is electrically connected to the temperature-sensitive busbar 1 and is used to excite and receive surface acoustic waves (SAWs), converting the impedance change caused by temperature variations into SAW signals. The interdigital electrode 3 can be fabricated using the top metal film of the temperature-sensitive busbar 1. The structural parameters of the interdigital electrode 3 include the number of finger pairs, the finger width, and the spacing. Preferably, the number of finger pairs of the interdigital electrode 3 can be set to a value between several pairs and several dozen pairs, and the finger width and spacing can be set to values ​​in the micrometer range. For example, the number of finger pairs of the interdigital electrode 3 can be set to 25 pairs, the finger width can be set to 3 μm, and the spacing can be set to 3 μm. By setting these parameters, the interdigital electrode 3 can excite and receive SAWs of specific frequencies, such as 430 MHz SAWs. The interdigital electrode 3 converts the impedance change caused by temperature into amplitude and phase changes of the SAW signal, realizing the sensing and transmission of temperature signals.

[0054] Acoustic structure 4 forms a parallel impedance superposition structure with temperature-sensitive busbar 1 via connecting line 2. The reflection characteristic enhancement design of acoustic structure 4 includes increasing the number of finger strips and integrating a sound-absorbing structure. The number of finger strips in acoustic structure 4 can be increased to a value between several pairs and dozens of pairs, for example, to 20 pairs, to improve reflection efficiency.

[0055] Acoustic structure 4 can also integrate a sound-absorbing structure. This sound-absorbing structure can be configured as a wedge-shaped groove array, with the groove depth gradually increasing to accommodate the absorption of sound waves at different frequencies. For example, the groove depth can gradually increase from 5 μm to 20 μm. The wedge-shaped groove array forms a physical barrier, reducing the contact between water vapor, corrosive gases, and the sound-absorbing material, thus improving the long-term stability of the sound-absorbing structure. The grooves can be filled with a polyimide-silicon carbide nanocomposite membrane or other composite materials with high sound absorption rates. The silicon carbide (SiC) nanoparticles in the composite membrane have excellent chemical inertness, resisting corrosive gases such as sulfur (S) and chloride (Cl), increasing the sound absorption lifespan. The volume percentage of the silicon carbide nanoparticles can be adjusted according to actual needs, preferably set to a value between 10% and 20%, such as 15%. The thickness of the composite membrane can be set to a value in the micrometer range, such as 2 μm. The sound absorption rate of the sound-absorbing structure can reach 95% or higher. Through enhanced reflection characteristics design, the sound wave reflection efficiency can be maximized, thereby reducing the interference of sound waves on connecting line 2 and maintaining the impedance stability of the connecting line.

[0056] The piezoelectric substrate 5 serves as the supporting structure for the sensor, providing a propagation path for the surface acoustic wave (SAW). The piezoelectric substrate 5 can be made of lithium niobate (LiNbO3), preferably Y-cut lithium niobate, such as 128° Y-cut lithium niobate. The dimensions of the piezoelectric substrate 5 can be designed according to actual needs, for example, it can be set to 5mm × 5mm × 0.5mm. The propagation speed of the SAW on the substrate can be set to 3400m / s. The temperature coefficient of the piezoelectric substrate 5 is 38ppm / ℃. The piezoelectric substrate 5 provides a stable acoustic wave propagation path, ensuring that the propagation characteristics of the SAW on the substrate are not affected by the temperature-sensitive busbar 1 structure.

[0057] The impedance of the temperature-sensitive busbar 1 consists of an inductive and a capacitive portion. The inductive portion is determined by the connecting wire 2 and controlled by its geometric parameters. Due to the physical characteristics of the metal connecting wire, the temperature change rate of the inductive portion is negligible. The capacitive portion is determined by the composite structure of the temperature-sensitive dielectric layer 11 and the four-layer metal film 12, and changes linearly with temperature. The dielectric constant of the temperature-sensitive dielectric layer 11 changes with temperature, causing the equivalent capacitance of the temperature-sensitive busbar to change with temperature, thus making the impedance of the capacitive portion change linearly with temperature. By rationally designing the material and structural parameters of the temperature-sensitive dielectric layer 11, it is possible to ensure that the capacitive portion maintains good linear response and stability across the entire temperature range.

[0058] The high-sensitivity wireless temperature sensor based on impedance superposition of the present invention can be implemented as a delayed linear sensor or a resonant sensor. For the delayed linear sensor, the acoustic structure 4 is a reflective grating, and the temperature-sensitive busbar 1 is connected in parallel with the reflective grating. Impedance changes directly modulate the phase characteristics of the reflected wave. When the temperature changes, the impedance of the temperature-sensitive busbar 1 changes, affecting the reflection characteristics of the reflective grating through the parallel structure, causing a change in the phase of the reflected wave, thereby achieving temperature signal sensing. The delayed linear sensor measures temperature changes by detecting the phase change of the reflected wave, exhibiting high sensitivity and stability.

[0059] For resonant sensors, the temperature-sensitive busbar 1 is connected in parallel with the resonant cavity, affecting the resonant frequency response. When the temperature changes, the impedance of the temperature-sensitive busbar 1 changes. The acoustic structure 4 is the resonant cavity; the parallel structure affects the resonant characteristics of the cavity, causing a change in the resonant frequency, thereby achieving temperature signal sensing. Resonant sensors measure temperature changes by detecting changes in the resonant frequency, exhibiting high sensitivity and stability. Whether it's a delay-line sensor or a resonant sensor, the impedance superposition mechanism of this invention can superimpose the impedance change of the temperature-sensitive busbar 1 onto the original temperature response of the sensor, significantly improving temperature sensitivity.

[0060] This invention introduces a composite temperature-sensitive structure consisting of a temperature-sensitive dielectric layer 11 and multiple metal films into the temperature-sensitive busbar region, causing the busbar impedance to change linearly with temperature. Simultaneously, by optimizing the reflection characteristics of the acoustic structure 4 and the layout of the connecting lines, the influence of acoustic interference on the connecting line impedance is suppressed, ensuring impedance stability. This design can be adapted to both resonant and delayed-linear wireless temperature sensors, thereby significantly improving temperature sensitivity and maintaining output stability compared to existing sensor responses.

[0061] In practical applications, the high-sensitivity wireless temperature sensor based on impedance superposition of this invention allows for the selection of appropriate materials and structural parameters according to specific temperature measurement ranges, accuracy requirements, and operating environments. For example, the temperature-sensitive dielectric layer 11 can be selected from one or more of barium titanate (BaTiO3), PZT piezoelectric ceramics, or polyimide, depending on the required dielectric constant temperature coefficient, or other dielectric materials with similar properties can be chosen. The specific materials and thicknesses of the four metal films can be optimized based on factors such as conductivity, coefficient of thermal expansion, and process compatibility. The geometric parameters of the connecting wire 2 can be designed based on the required inductance value and impedance stability requirements. The number of finger pairs, finger width, and spacing of the interdigitated electrodes 3 can be optimized based on the required operating frequency and surface acoustic wave excitation efficiency. The number of fingers and the sound-absorbing structure of the acoustic structure 4 can be designed based on the required reflection efficiency and acoustic wave isolation effect. The material and dimensions of the piezoelectric substrate 5 can be selected based on the surface acoustic wave propagation characteristics and device size requirements.

[0062] The design principle of this invention is as follows: Under varying temperature conditions, the temperature-sensitive dielectric layer 11 of the temperature-sensitive busbar interacts with the four-layer metal film 12, resulting in a significant impedance drift. The impedance composition mainly includes an inductive component (…). ) and the receptive part ( Meanwhile, this impedance change is transmitted through connecting line 2, forming a parallel superposition with the temperature-sensitive structure of the sensor itself, thereby amplifying the response amplitude of the output signal.

[0063] During temperature changes, the impedance changes with temperature due to the influence of dielectric constant and thermal expansion. The inductance is mainly determined by connecting line 2, and its change is small and can be ignored. The capacitance is designed with a temperature-sensitive dielectric layer to ensure that it can produce a significant capacitance change with temperature.

[0064] The main components of the sensor of this invention include a temperature-sensitive busbar 1, connecting lines 2, interdigitated electrodes 3, a reflective grating or resonant cavity, and a piezoelectric substrate 5. The temperature-sensitive busbar 1 is composed of a temperature-sensitive dielectric layer 11 and four metal films 12, forming a temperature-sensitive structure. The temperature-sensitive dielectric layer 11 covers the interior of the temperature-sensitive busbar area, preventing interference with the acoustic wave path and the piezoelectric effect of the piezoelectric substrate 5. The connecting lines 2 connect the temperature-sensitive busbar 1 to the reflective grating or resonant cavity, and are positioned in the outermost region of the reflective grating or resonant cavity to prevent acoustic wave interference and ensure impedance stability. Simultaneously, the temperature-sensitive busbar 1 and the reflective grating or resonant cavity are interconnected through a parallel structure, and a series structure adjustment unit is added to reduce signal transmission loss on the connecting lines, ensuring the stability of the connecting line impedance. The interdigitated electrodes 3 are used to excite and receive surface acoustic waves (SAWs), are made from the top platinum film of the temperature-sensitive busbar 1, have 25 pairs of fingers, a finger width of 3 μm, a finger spacing of 3 μm, and an excitation / reception frequency of 430 MHz for SAWs. The reflective grating or resonant cavity section enhances reflection characteristics by incorporating 20 pairs of finger strips and an integrated sound-absorbing structure. The piezoelectric substrate 5 is made of lithium niobate (128° Y-cut) material, with dimensions of 5mm × 5mm × 0.5mm, a sound velocity of 3400m / s, and a temperature coefficient of 38ppm / ℃. It serves as the supporting substrate for the sensor and provides a path for sound wave propagation.

[0065] The temperature-sensitive busbar is constructed with four metal films 12. The first layer is a titanium-zirconium composite metal film, followed by a copper-nickel gradient alloy film, a palladium-silver composite metal film, and a silver-tantalum composite metal film. The thickness of each of the four metal films 12 is controlled to 0.35 μm, with a total metal film thickness of 1.4 μm. Three different temperature-sensitive dielectric layers 11, each with a dielectric constant that changes linearly with temperature, are filled between adjacent metal film layers, forming a gradient dielectric filling system. The high-dielectric-constant material barium titanate is filled between the titanium-zirconium composite metal film and the copper-nickel gradient alloy film; the medium-to-high dielectric-constant material PZT piezoelectric ceramic is filled between the copper-nickel gradient alloy film and the palladium-silver composite metal film; and the low-dielectric-constant material polyimide is filled between the palladium-silver composite metal film and the silver-tantalum composite metal film. This avoids abrupt changes in the linearity of a single material when the temperature crosses the phase transition point. This multilayer design allows for the filling of different dielectric materials between adjacent layers. Through composite material compensation, the linearity and stability of the overall impedance under temperature changes are enhanced, primarily ensuring that the capacitance of the temperature-sensitive busbar changes linearly with temperature. The preferred temperature-sensitive dielectric layer 11 must meet the requirement that the dielectric constant changes linearly with temperature, ensuring consistent response across the entire temperature range.

[0066] Connector 2 connects the temperature-sensitive structure of the temperature-sensitive busbar to the reflective grating of the delay linear sensor or the resonant cavity of the resonant sensor, forming a parallel circuit. Since the impedance of the metal connecting wire increases with temperature due to the change in the coefficient of thermal expansion, signal transmission loss increases, compromising the signal transmission efficiency of the parallel structure and affecting the stability of the connecting wire impedance. To address this issue, this invention adds a series structure of a nickel-chromium alloy thermistor and a zinc oxide varistor near the end of the parallel circuit close to the reflective grating. This reduces signal transmission loss and ensures the stability of the connecting wire impedance.

[0067] The specific working process of the series structure is as follows: When the temperature rises and the impedance of connecting line 2 increases, the resistance of the nickel-chromium alloy thermistor increases synchronously, and the voltage division ratio of the zinc oxide varistor automatically decreases. The two work together to make the total impedance of the parallel structure return to the preset threshold. When the temperature drops and the impedance of connecting line 2 decreases, the resistance of the thermistor decreases synchronously, and the voltage division ratio of the varistor increases, thus achieving impedance compensation. The whole process does not require external power supply and relies entirely on the inherent characteristics of the components, with a response time ≤10ms.

[0068] Therefore, for delay-type sensors, the connecting wires connect the temperature-sensitive busbar and the reflector grid in parallel, and the impedance change directly modulates the phase characteristics of the reflected wave. For resonant sensors, the connecting wires connect the temperature-sensitive busbar and the resonant cavity in parallel, affecting the resonant frequency response. The layout of the connecting wires is strictly controlled to be outside the reflector grid or resonant cavity to avoid impedance fluctuations caused by sound wave scattering.

[0069] 3.2.3 Enhanced reflection characteristics of reflective gratings or resonant cavities

[0070] The existing patent CN104579216A uses a fixed depth (0.1-0.6mm) of sound-absorbing ink coating, which is susceptible to humidity and chemical corrosion over long-term use, leading to a decrease in sound absorption performance. To address this issue, this invention incorporates 20 pairs of finger strips and an integrated polyimide-silicon carbide nanocomposite film acoustic structure in the reflective grating or resonant cavity to maximize sound wave reflection efficiency, thereby reducing sound wave interference with connecting line 2 and maintaining the impedance stability of the connecting line. The sound-absorbing structure is designed as a wedge-shaped groove array, forming a physical barrier. The groove walls are plasma passivated (passivation layer thickness 50nm-100nm) to further reduce the contact between water vapor, corrosive gases, and the composite film, extending its service life. The depth of the wedge-shaped grooves gradually varies from 5μm to 20μm, adapting to different frequencies of sound wave absorption and avoiding the limitation of a single groove depth only adapting to specific frequencies. The groove is filled with a "polyimide-silicon carbide nanocomposite membrane". The silicon carbide nanoparticles have excellent chemical inertness, which can resist corrosive gases such as sulfur and chlorine, and increase the sound absorption life. The volume ratio of silicon carbide nanoparticles in the composite membrane is 15%, the membrane thickness is 2μm, and the sound absorption rate is ≥95%, which can avoid the influence of sound waves on the impedance stability of the connecting line 2.

[0071] Based on the linear network theory of surface acoustic wave reflectors, the signal characteristics of the reflector can be obtained through... Matrix representation, where This is the "signal transmission coefficient" of the reflector (characterizing the transmission efficiency of surface acoustic waves in the reflector). The "inherent reflection coefficient" of the reflector (characterizing the temperature response characteristics of the reflector itself, determined by the intrinsic parameters of the piezoelectric substrate 5). The reflection coefficient is the reflection delay line. (Reference reflector) Matrix model, admittance relationship of external impedance, reflection coefficient of reflection delay line The definition is based on the impedance of the temperature-sensitive busbar 1. As an external load introduced into the port network of the reflector, the impedance is derived. With reflection coefficient The correlation formula is as follows:

[0072]

[0073] In the formula, and The coefficients of the P matrix of the reflector. For external impedance, The reflection coefficient. When and When fixed, The changes were entirely due to The impedance of this structure is determined by the change in the inductive component. Harmony and compatibility The design of the two-part connector is mainly used to ensure... The temperature-sensitive busbar section is designed to maintain stability and is mainly used to ensure that... Some of them change with temperature.

[0074] It is the inherent inductance of connecting wire 2. Temperature fluctuations can lead to The overall change is uncontrollable. The values ​​of this part are mainly determined by the dimensional parameters of connecting line 2, since its physical structure is a metal wire. Based on the theoretical formula for the inductance of an infinitely long straight conductor, for a metal wire whose length is much larger than its cross-sectional size, its equivalent radius of the rectangular cross-section is... ,in, The width of the metal wire. The thickness of the metal wire. When the trace length... With cross-sectional dimensions When comparable, the assumption of an infinitely long wire no longer holds, and it is necessary to introduce... The inductance difference and edge effects of the short conductor are compensated for. Therefore, the inductance formula for connecting wire 2 is as follows:

[0075]

[0076] In the formula, For width, For thickness, This represents the trace length. Calculations show that... The rate of temperature change is negligible.

[0077] It is the inherent capacitance of the temperature-sensitive busbar. The values ​​of some parameters are mainly determined by the parameters of the temperature-sensitive busbar, which can be derived from the definition of capacitance and Gauss's law. The capacitance formula is as follows:

[0078]

[0079] In the formula, The vacuum permittivity, The relative permittivity, For the effective overlapping area, The distance between the electrodes is denoted as .

[0080] Therefore, when When the temperature changes linearly, the impedance of the structure also changes accordingly. This can be seen from the response expressed in formula (1). The response changes and is superimposed on the temperature-sensitive structure of the sensor itself, ultimately improving the sensitivity.

[0081] Through the above design scheme, a temperature-sensitive capacitor structure can be constructed by using a stacked metal film and combining it with a temperature-sensitive dielectric layer 11 without changing the material of the piezoelectric substrate 5 or increasing the sensor area. At the same time, by fixing the equivalent inductance with the help of optimized wiring design, the impedance characteristics of the composite structure change with the temperature, and finally enhances the response change amplitude on the basis of the original temperature response of the sensor.

[0082] Compared to traditional SAW temperature sensors, this invention has the advantages of high sensitivity and stable impedance changes in the connecting lines. The impedance change of the temperature-sensitive busbar is directly added to the sensor response, effectively improving the sensitivity. The design of the reflective grid or resonant cavity and the layout of the connecting lines effectively isolate acoustic interference and ensure the stability of the connecting line impedance.

[0083] Experiments have verified that when the operating frequency band is 430MHz, the reflection coefficient is... The response amplitude can be additionally increased by 6dB, which can significantly improve the sensitivity of the temperature sensor.

[0084] In Example 1, under varying temperature conditions, the temperature-sensitive dielectric layer 11 of the temperature-sensitive busbar 1 interacts with the four-layer metal film 12, causing impedance drift. This impedance change is transmitted through the connecting line 2, forming a parallel superposition with the temperature-sensitive structure of the sensor itself, thereby amplifying the response amplitude of the output signal. Therefore, to improve the sensitivity of the temperature sensor, it is necessary to find a suitable range of inductance and capacitance to achieve a reflection coefficient... The response is the strongest.

[0085] Assuming the operating frequency band is 430MHz, what are the parameters of the P matrix? and The sum is a fixed value. Based on formula (1), when the inductance matching range is 30~60nH and the capacitance matching range is 2.5~3.1pF, the reflection coefficient is... The response is the largest. Since the change in inductance is small and negligible, a fixed inductance value can be used to investigate the effect of capacitance change on the sensitivity of the temperature sensor. According to formula (1), when the external load impedance inductance remains constant at 50nH, the capacitance value changes within the range of 2.5 to 3.1pF. The attenuation value first decreases and then increases. When the capacitance value is around 2.8pF, The attenuation value reaches approximately -6dB, with the most significant attenuation response effect. Specific changes are as follows: Figure 1 As shown.

[0086] The above are merely preferred embodiments of the present invention and are 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 within the protection scope of the present invention.

Claims

1. A high-sensitivity wireless temperature sensor based on impedance superposition, characterized in that, This includes a piezoelectric substrate that provides a propagation path for surface acoustic waves, and a component disposed on the surface of the piezoelectric substrate: The temperature-sensitive busbar is a composite temperature-sensitive structure consisting of a temperature-sensitive dielectric layer and four metal films. The temperature-sensitive dielectric layer is strictly controlled to be inside the temperature-sensitive busbar area and does not exceed the boundary of the temperature-sensitive busbar area. The acoustic structure forms a parallel impedance superposition structure with the temperature-sensitive busbar through connecting lines; The connecting line is located in the outermost area of ​​the acoustic structure to connect the temperature-sensitive busbar to the acoustic structure to form a parallel structure. A series structure of nickel-chromium alloy thermistor and zinc oxide varistor is set near the end of the parallel structure to stabilize the impedance of the connecting line. The interdigitated electrodes are electrically connected to the temperature-sensitive busbar to convert the impedance change caused by temperature change into a surface acoustic wave signal.

2. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The temperature-sensitive dielectric layer is made of a dielectric material whose dielectric constant changes linearly with temperature, including one or more of barium titanate, PZT piezoelectric ceramics, and polyimide. The coverage area of ​​the temperature-sensitive dielectric layer is controlled within the temperature-sensitive busbar region to avoid interfering with the propagation path of surface acoustic waves and the piezoelectric effect of the piezoelectric substrate, ensuring that only the impedance of the temperature-sensitive busbar changes with temperature while the acoustic wave propagation path remains stable.

3. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The four metal films are arranged sequentially from the piezoelectric substrate upwards as follows: titanium-zirconium composite metal film, copper-nickel gradient alloy film, palladium-silver composite metal film, and silver-tantalum composite metal film. Adjacent metal film layers are filled with temperature-sensitive dielectric materials to form a gradient dielectric filling system. Barium titanate is filled between the titanium-zirconium composite metal film and the copper-nickel gradient alloy film to provide high dielectric constant temperature-sensitive properties. PZT piezoelectric ceramic is filled between the copper-nickel gradient alloy film and the palladium-silver composite metal film to provide medium-high dielectric constant temperature-sensitive properties. Polyimide is filled between the palladium-silver composite metal film and the silver-tantalum composite metal film to provide low dielectric constant temperature-sensitive properties; By using a gradient configuration of multiple temperature-sensitive dielectric layers, the linearity of a single material is prevented from abruptly changing when the temperature crosses the phase transition point, thereby enhancing the linearity and stability of the overall impedance under temperature variations.

4. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The location setting and impedance stabilization mechanism of the connecting line include: The connecting lines are positioned in the outermost area of ​​the acoustic structure to avoid direct interference from surface acoustic waves on the impedance of the connecting lines. A series structure of a nickel-chromium alloy thermistor and a zinc oxide varistor is set at the end of the parallel structure near the acoustic structure. When the temperature rises and the impedance of the connecting line increases, the resistance of the nickel-chromium alloy thermistor increases synchronously, and the voltage division ratio of the zinc oxide varistor automatically decreases, so that the total impedance of the parallel structure returns to the preset threshold. When the temperature decreases, causing the impedance of the connecting wires to decrease, the resistance of the thermistor decreases accordingly, and the voltage division ratio of the varistor increases, thus achieving impedance compensation.

5. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The structural parameters of the interdigital electrode are as follows: 25 pairs of fingers, 3μm width of the finger strip, 3μm spacing, 430MHz excitation / reception frequency of surface acoustic waves, and the interdigital electrode is electrically connected to the temperature-sensitive busbar to convert the impedance change caused by temperature into the amplitude and phase change of the surface acoustic wave signal.

6. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The number of fingers in the acoustic structure is increased to 20 pairs to improve reflection efficiency; it integrates a sound-absorbing structure, which is a wedge-shaped groove array with a groove depth that gradually changes from 5μm to 20μm to adapt to the absorption of sound waves of different frequencies; the groove is filled with a polyimide-silicon carbide nanocomposite film, in which silicon carbide nanoparticles account for 15% of the volume, the film thickness is 2μm, and the sound absorption rate is ≥95%.

7. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The piezoelectric substrate is made of 128° Y-cut lithium niobate material with dimensions of 5mm×5mm×0.5mm. The propagation speed of surface acoustic waves on the substrate is 3400m / s, and the temperature coefficient is 38ppm / ℃. As a supporting substrate for the sensor, it provides a stable acoustic wave propagation path, so that the propagation characteristics of surface acoustic waves on the substrate are not affected by the temperature-sensitive busbar structure.

8. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The impedance of the temperature-sensitive busbar consists of an inductive part and a capacitive part, with the inductance of the inductive part being Z. l The capacitance of the capacitive part is Z. c Z l Determined by the connecting line, and controlled by the geometric parameters of the connecting line; Z c Determined by the composite structure of the temperature-sensitive dielectric layer and the four-layer metal film, it changes linearly with temperature.

9. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The sensor is a delay linear sensor with an acoustic structure of a reflective grating. A temperature-sensitive busbar is connected in parallel with the reflective grating, and impedance changes directly modulate the phase characteristics of the reflected wave.

10. The high-sensitivity wireless temperature sensor based on impedance superposition according to claim 1, characterized in that, The sensor is a resonant sensor, and its acoustic structure is a resonant cavity. The temperature-sensitive busbar is connected in parallel with the resonant cavity, which affects the resonant frequency response.

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