Surface Acoustic Wave Temperature Research Articles

Wireless Temperature Measurement for Curved Surfaces Based on AlN Surface Acoustic Wave Resonators.

In this paper, we propose a novel method for temperature measurement using surface acoustic wave (SAW) temperature sensors on curved or irregular surfaces. We integrate SAW resonators onto flexible printed circuit boards (FPCBs) to ensure better conformity of the temperature sensor with the surface of the object under test. Compared to traditional rigid PCBs, FPCBs offer greater dynamic flexibility, lighter weight, and thinner thickness, which make them an ideal choice for making SAW devices working for temperature measurements under curved surfaces. We design a temperature sensor array consisting of three devices with different operating frequencies to measure the temperature at multiple points on the surface of the object. To distinguish between different target points in the sensor array, each sensor operates at a different frequency, and the operating frequency bands do not overlap. This differentiation is achieved using Frequency Division Multiple Access (FDMA) technology. Experimental results indicate that the frequency temperature coefficients of these sensors are -30.248 ppm/°C, -30.195 ppm/°C, and -30.115 ppm/°C, respectively. In addition, the sensor array enables wireless communication via antenna and transceiver circuits. This innovation heralds enhanced adaptability and applicability for SAW temperature sensor applications.

Rational Design of a Surface Acoustic Wave Device for Wearable Body Temperature Monitoring.

Continuous monitoring of vital signs based on advanced sensing technologies has attracted extensive attention due to the ravages of COVID-19. A maintenance-free and low-cost passive wireless sensing system based on surface acoustic wave (SAW) device can be used to continuously monitor temperature. However, the current SAW-based passive sensing system is mostly designed at a low frequency around 433 MHz, which leads to the relatively large size of SAW devices and antenna, hindering their application in wearable devices. In this paper, SAW devices with a resonant frequency distributed in the 870 MHz to 960 MHz range are rationally designed and fabricated. Based on the finite-element method (FEM) and coupling-of-modes (COM) model, the device parameters, including interdigital transducer (IDT) pairs, aperture size, and reflector pairs, are systematically optimized, and the theoretical and experimental results show high consistency. Finally, SAW temperature sensors with a quality factor greater than 2200 are obtained for real-time temperature monitoring ranging from 20 to 50 °C. Benefitting from the higher operating frequency, the size of the sensing system can be reduced for human body temperature monitoring, showing its potential to be used as a wearable monitoring device in the future.

Design and Characterization of Surface Acoustic Wave-Based Wireless and Passive Temperature Sensing System.

The surface acoustic wave (SAW) temperature sensor has received significant attention due to its wirelessly powered, battery-free, and chipless capabilities. This paper proposes a wireless sensing system comprising a one-port SAW resonator, helix antenna, and transceiver circuit. The SAW resonator used in this system is based on aluminum nitride (AlN) thin film, which exhibits high velocity and excellent piezoelectric properties. Simulations and experiments were conducted to investigate the performance of the designed SAW resonator. A helix antenna was also designed using finite element simulation to facilitate signal transmission between the SAW temperature sensor and the transceiver. An impedance-matching network was introduced between the helix antenna and the SAW resonator to optimize signal transmission. When the wireless SAW temperature sensor was placed within a certain distance of the mother antenna, the reflection peak of the SAW resonator was observed in the spectrum of the return signal. The frequency of the echo signal increased almost linearly as the temperature increased during the temperature tests. The fitted temperature coefficient of frequency (TCF) was -31.34 ppm/°C, indicating that the wireless temperature sensing system has high-temperature sensitivity.

High-Resolution and High-Precision Demodulation Method for Surface Acoustic Wave Temperature Sensor Based on PRONY Algorithm

High-Resolution and High-Precision Demodulation Method for Surface Acoustic Wave Temperature Sensor Based on PRONY Algorithm

Research and experiment the wireless passive surface acoustic wave technology for conductor temperature monitoring of high voltage equipment

This paper presents the research and design of a passive thermal monitoring system using wireless temperature sensors based on the principle of surface acoustic wave (SAW). The monitoring system is employed on components that need to be monitored for heat generation, including switch contacts, busbars, and cable connections at switchgears or ring main units (RMUs). The basic impulse insulation level (BIL), or voltage spike tolerance, of the wireless SAW temperature sensor utilised in this study, means that it is not necessary to power it with sensors that meet the high criteria for equipment installed in closed cabinets or medium voltage cabinets. The research team’s activities in this study included software development, data transmission design and manufacture, and sensor selection. The system functions steadily, with a temperature error of no more than 2oC, according to the test findings under laboratory settings.

Development of Temperature Sensor Based on AlN/ScAlN SAW Resonators

Temperature monitoring in extreme environments presents new challenges for MEMS sensors. Since aluminum nitride (AlN)/scandium aluminum nitride (ScAlN)-based surface acoustic wave (SAW) devices have a high Q-value, good temperature drift characteristics, and the ability to be compatible with CMOS, they have become some of the preferred devices for wireless passive temperature measurement. This paper presents the development of AlN/ScAlN SAW-based temperature sensors. Three methods were used to characterize the temperature characteristics of a thin-film SAW resonator, including direct measurement by GSG probe station, and indirect measurement by oscillation circuit and antenna. The temperature characteristics of the three methods in the range of 30–100 °C were studied. The experimental results show that the sensitivities obtained with the three schemes were −28.9 ppm/K, −33.6 ppm/K, and −29.3 ppm/K. The temperature sensor using the direct measurement method had the best linearity, with a value of 0.0019%, and highest accuracy at ±0.70 °C. Although there were differences in performance, the characteristics of the three SAW temperature sensors make them suitable for sensing in various complex environments.

Temperature, pressure, and humidity SAW sensor based on coplanar integrated LGS

This paper presents a surface acoustic wave (SAW) sensor based on coplanar integrated Langasite (LGS) that is fabricated using wet etching, high-temperature bonding, and ion beam etching (IBE) processes. The miniaturized multiparameter temperature‒pressure-humidity (TPH) sensor used the MXene@MoS2@Go (MMG) composite to widen the humidity detection range and improve the humidity sensitivity, including a fast response time (3.18 s) and recovery time (0.94 s). The TPH sensor was shown to operate steadily between 25–700 °C, 0–700 kPa, and 10–98% RH. Coupling issues among multiple parameters in complex environments were addressed by decoupling the Δf-temperature coupling factor to improve the accuracy. Therefore, this work can be applied to simultaneous measurements of several environmental parameters in challenging conditions.

Surface acoustic wave temperature sensor based on Pt/AlN/4 H-SiC structure for high-temperature environments

Surface acoustic wave temperature sensor based on Pt/AlN/4 H-SiC structure for high-temperature environments

Influence of electrode apodization weighted structure on the performance of SAW temperature sensors

In order to improve the comprehensive performance of the surface acoustic wave (SAW) temperature sensors and reduce clutter interference, the optimized Chebyshev window function, Blackman window function and Hamming window function are used to carry out the apodization weighting design for interdigital transducer (IDT) and reflective grating respectively. The influence of electrode apodization weighted structure on the performance of SAW temperature sensors is systematically studied through experiments. The results show that the apodization weighted design of IDT and reflective gate can effectively improve the resonance peak intensity and reduce the side lobe interference; the IDT and the reflection grating are designed with apodization weighting at the same time, compared with the single reflection grating weighting, the volatility of the side lobe of the Chebyshev window function and the Hamming window function increases, the volatility of the side lobe of the Blackman window function decreases; after electrode apodization optimization, the resonance frequency, Q value of the SAW sensor and the sensitivity to temperature increases; using a hamming window optimized electrode structure, the peak value of S11 is −36.73 dB and the Q value is 15 030. In order to ensure the signal processing ability and comprehensive performance of the sensor, an optimized Hamming window should be used for the electrode design of the SAW sensors.

Real-Time Monitoring of Tire Condition with Fast Detection Passive and Wireless TPMS

<div class="section abstract"><div class="htmlview paragraph">Accurate tire pressure monitoring system (TPMS) is of great practical importance and the reliability and safety of its power supply module has great concern. The piezoelectric-based surface acoustic wave (SAW) sensor is considered to have great potential in this field because of its passive, wireless and small size advantages. This paper presents the application of passive and wireless SAW sensors for real-time tire condition monitoring. The pressure sensitive structure is optimized and a three-resonator structure is also designed sensing temperature and pressure. Furthermore, a fast detection system is developed to realize high-speed signal acquisition. At last, experiments are executed and the SAW temperature and pressure sensor property is measured. The results show that the designed SAW sensor can realize real-time monitoring of tire condition; the temperature measurement range can reach -40~120°C with an accuracy of ±1°C; the pressure measurement range can reach 0~2MPa with an accuracy of 0.2MPa. This paper indicates the wireless and passive SAW temperature and pressure sensor system has the potential for application in real-time monitoring of tire condition.</div></div>

UV light driven high-performance room temperature surface acoustic wave NH3 gas sensor using sulfur-doped g-C3N4 quantum dots

UV light driven high-performance room temperature surface acoustic wave NH3 gas sensor using sulfur-doped g-C3N4 quantum dots

Single-crystalline AlN/sapphire and composite electrode based ultra-high temperature surface acoustic wave devices

Single crystalline AlN material is very attractive for the development of high temperature electronic devices owing to its high temperature resistance. However, at ultrahigh temperatures, AlN film still will be oxidized and metal electrodes used for the devices will aggregate and vaporize. The deterioration of the material and metal electrodes eventually fails the AlN-based devices. Here, we report a single crystalline AlN film-based ultrahigh temperature surface acoustic wave (SAW) device. By using a thin alumina (Al2O3) protection layer on surface, oxidation of the AlN piezoelectric film was effectively inhibited at high temperatures. A composite electrode based on multilayer structure of Pt-Rh and Al2O3 was designed and fabricated, with the Al2O3 layer as the diffusion barrier layers to suppressed inter-diffusion, agglomeration and vaporization of the metals. The results showed that the developed AlN SAW devices can withstand high temperatures, and work well at temperatures up to 1400 °C.

High thermal stability of ultra-high temperature surface acoustic wave devices with multilayer composite electrodes

The main challenge to maintain high-temperature performance of surface acoustic wave (SAW) devices is to improve the high-temperature resistance of the interdigital transducers (IDT). This work reports on the development of the Pt-Rh alloy-based multilayered composite IDTs for high-temperature applications. Composite electrode-based wire-type resistors with different structures were prepared by magnetron sputtering, and their resistances and surface morphologies at temperatures up to 1600 °C were investigated. The proposed composite electrode has a structure of ZrO2 /Pt-Rh (10%) /Al2O3 /Pt-Rh (10%) /Al2O3 with a 40 nm ZrO2 protective layer at the top of the electrode. It has a 300 nm thickness Pt-Rh (10%) film, a 10 nm Al2O3 layer in the middle of Pt-Rh (10%) layer, and a 20 nm Al2O3 layer between the electrode and the substrate. The results showed that the composite electrodes could withstand a maximum operating temperature up to 1600℃ in air. The electrodes maintained excellent stability even after five cyclic thermal treatments at temperatures up to 1200 ℃ for one hour, and good stability after two cyclic thermal treatments up to 1400 ℃ for 1 h. The SAW devices based on AlN single-crystal piezoelectric film using the composite electrodes showed good stability at 1200 ℃ for 1 h.

4.74-GHz Harmonically Operated SAW Temperature and Strain Sensors

This paper presents the development of surface acoustic wave (SAW) temperature and strain sensors that can operate at high frequencies up to 4.74 GHz. The third harmonic response of the SAW device was utilized to enable operation at higher frequencies, which helped overcome the limitations of the contact photolithography process used in fabrication. Specifically, a design of an orthogonal frequency coding (OFC) SAW device provided by Pegasense LLC and originally designed for use with lithium niobate YZ was implemented on lithium niobate YX 128 cut, which increased the device’s operating frequency from 4.3 GHz to 4.74 GHz. The SAW device demonstrated wireless temperature sensing capabilities with a standard deviation of 0.044C after signal processing using a thousand averages and a matched filter. Additionally, initial measurements of a strain sensor at 4.74 GHz showed good correlation with commercial strain sensor measurements, with a standard deviation of 2.278μstrains using 1000 averages and a frequency sensitivity of -1.260lstrains approximately. The potential of SAW technology to impact super high frequencies (SHF) and its practical application in wireless temperature and strain sensing will be highlighted.

Minimally diffracting quartz for ultra-low temperature surface acoustic wave resonators

We simulate and experimentally demonstrate the existence of an orientation of quartz, which minimizes diffraction losses in surface acoustic wave (SAW) resonators at ultra-low temperatures. The orientation is optimized for applications to quantum technologies, which benefit from high mechanical quality factors, strong electromechanical coupling, and narrow acoustic apertures. We fabricate narrow aperture SAW resonators on this substrate and measure internal quality factors greater than 100 000 at mK temperatures.

High-Performance SAW Low Temperature Sensors with Double Electrode Transducers Based on 128° YX LiNbO3.

Low temperature measurement is crucial in deep space exploration. Surface acoustic wave (SAW) sensors can measure temperature wirelessly, making them ideal in extreme situations when wired sensors are not applicable. In this study, 128° YX LiNbO3 was first introduced into low temperature measurements for its little creep or hysteresis in cryogenic environments and affordable price. The finite element method was utilized to raise the design efficiency and optimize the performance of SAW sensors by comparing the performance with different interdigital transducer (IDT) structure parameters, including the height of electrodes, pairs of IDTs, reflecting grid logarithm and acoustic aperture. Once the parameters were changed, a novel design of high-performance SAW temperature sensors based on 128° YX LiNbO3 with double electrode transducers was obtained, of which the Q value could reach up to 5757.18, 4.2-times higher than originally reported. Low temperature tests were conducted, and the frequency responsiveness of SAW sensors was almost linear from -100 °C to 150 °C, which is in good agreement with the simulation results. All results demonstrate that double electrode transducers are considerably efficient for performance enhancement, especially for high-Q SAW sensors, and indicate that LiNbO3 substrate can be a potential high-performance substitute for cryogenic temperature measurements.

High-temperature Pt–Al2O3 composite nano-thick interdigital electrodes for surface acoustic wave sensors

High-temperature stability of ultra-thin film electrodes is vital for surface acoustic wave (SAW) devices in harsh environments. This paper proposed the Pt–Al2O3 composite Nano-thick interdigital electrodes (IDEs) for langasite-based high-temperature SAW sensors. The sandwich structure of the IDEs was composed of Pt layers and Al2O3 armors. The armor consisting of barrier and coating layers was introduced to reduce the agglomeration, oxidation, and interdiffusion of IDEs at high temperatures. Capacitive bonding pads were proposed to transmit radiofrequency signals through the closed armor. The composite IDEs (226 nm thickness) had good structural stability and impurities concentration less than 1% at 1000 °C (3 h, air condition). Improved quality factors of 8805, and matched electrical impedance of 51 Ω and −16° were achieved through the electroacoustic optimized IDEs. Finally, multiple SAW temperature sensors using the composite IDEs presented fitting errors less than 1% and hysteresis errors below 4% in 80–1000 °C exceeded 9 h, which was 150 °C higher than existing ones. The proposed composite IDEs enable SAW devices to be applicated in 80–1000 °C.

Fabrication of grooved LGS resonators based high temperature SAW sensors and analysis with FEM simulation

Langasite (LGS) based surface acoustic wave (SAW) sensors are widely used in high temperature circumstances due to their advantages of being passive and wireless. In this research, the platinum electrodes are deposited into the grooves of the LGS instead of on the surface to further improve the acoustic properties and prolong the lifetime of the resonators at high temperature. Proper MEMS fabrication techniques are proposed to fabricate such structures. The result of every step is evaluated, and the corresponding process parameters are optimized. With the optimal processes, two types of resonators with different Euler angles of (0∘, 22∘, 30∘) and (0∘, 22∘, 90∘) are fabricated on the LGS substrate. Furthermore, the process-influenced structure parameters such as metal ratio and sidewall angle are well investigated via a weak form nonlinear finite element method simulation model. The temperature dependence of the resonance frequency is measured, and the recorded thermal behaviors match well with the prediction of the simulation. In addition, the further endurance test shows that the devices could work at 1000 ∘C for 12 h. This research proves the validity of the grooved resonator structure and the prominent role of the simulation model in further optimizing the LGS-based SAW devices design.

Novel Surface Acoustic Wave Temperature-Strain Sensor Based on LiNbO3 for Structural Health Monitoring.

In this paper, we present the design of an integrated temperature and strain dual-parameter sensor based on surface acoustic waves (SAWs). First, the COMSOL Multiphysics simulation software is used to determine separate frequencies for multiple sensors to avoid interference from their frequency offsets caused by external physical quantity changes. The sensor consists of two parts, a temperature-sensitive unit and strain-sensitive unit, with frequencies of 94.97 MHz and 90.05 MHz, respectively. We use standard photolithography and ion beam etching technology to fabricate the SAW temperature–strain dual-parameter sensor. The sensing performance is tested in the ranges 0–250 °C and 0–700 μԑ. The temperature sensor monitors the ambient temperature in real time, and the strain sensor detects both strain and temperature. By testing the response of the strain sensor at different temperatures, the strain and temperature are decoupled through the polynomial fitting of the intercept and slope. The relationship between the strain and the frequency of the strain-sensitive unit is linear, the linear correlation is 0.98842, and the sensitivity is 100 Hz/μԑ at room temperature in the range of 0–700 μԑ. The relationship between the temperature and the frequency of the temperature-sensitive unit is linear, the linearity of the fitting curve is 0.99716, and the sensitivity is 7.62 kHz/°C in the range of 25–250 °C. This sensor has potential for use in closed environments such as natural gas or oil pipelines.

A surface acoustic wave hydrogen sensor with tin doped indium oxide layers for intermediate temperatures

High temperature surface acoustic wave (SAW) gas sensors with conducting sensing layers require tuning of the sheet conductivity for optimal response. Conducting metal oxides are attractive sensing materials for their tunable electronic properties and high thermal stability, amongst others. Here, we have investigated the application of indium oxide (IO) and indium tin oxide (ITO) films on langasite (LGS)-based SAW reflective delay line sensor devices for monitoring hydrogen at 350 °C. Specifically, we modeled the effect of the IO and ITO sensing layer thickness on the wave velocity, attenuation, and effective electromechanical coefficient. This was followed by an experimental demonstration of tuning of the ITO film sheet conductivity by controlling the dopant concentration and yielding an improvement in the sensor sensitivity. The current study provides a pathway towards the development of conductivity-based sensing layers for high temperature SAW gas sensors with improved sensitivity.