Surface Acoustic Wave Strain Sensor Research Articles

Electromechanical sensitivity of ZnO thin films at high-pressure regime for SAW strain sensor applications

This paper employs Density Functional Theory (DFT) to investigate the influence of high hydrostatic pressure on the piezo-elastic properties of ZnO with a specific focus on its repercussions for Surface Acoustic Wave (SAW) devices. Our findings reveal a significant enhancement in the piezoelectric coefficient d33 under high-pressure conditions, particularly reaching 13.09 pC/N at 8 GPa compared to the unpressurized state. This noteworthy improvement directly contributes to an overall enhancement in the electromechanical coupling coefficients (K2), emphasizing for the first time the potential of high-pressure conditions to positively influence the performance of ZnO/Al2O3 SAW devices. To confirm that, we utilized the Finite Element Method (FEM) to analyze the performance of a Surface Acoustic Wave (SAW) device based on ZnO for both propagating modes, namely Rayleigh and Sezawa, under elevated pressure conditions. We observed an improvement in the electromechanical coupling factor (K2) for the Rayleigh and the Sezawa modes, with enhancements of approximately 23% and 52%, respectively, under an applied pressure of 8 GPa compared to 0 GPa. Furthermore, we found that the Sezawa mode exhibits eight times greater sensitivity to pressure variations compared to the Rayleigh mode. These findings provide designers with a better understanding of the electromechanical responsivity and sensitivity of the ZnO-SAW devices to high level of applied pressure.

Flexible Langasite-Based Surface Acoustic Wave Strain Sensor for High-Temperature Operation

Flexible Langasite-Based Surface Acoustic Wave Strain Sensor for High-Temperature Operation

Modulating the Performance of the SAW Strain Sensor Based on Dual-Port Resonator Using FEM Simulation.

Surface acoustic wave (SAW) strain sensors fabricated on piezoelectric substrates have attracted considerable attention due to their attractive features such as passive wireless sensing ability, simple signal processing, high sensitivity, compact size and robustness. To meet the needs of various functioning situations, it is desirable to identify the factors that affect the performance of the SAW devices. In this work, we perform a simulation study on Rayleigh surface acoustic wave (RSAW) based on a stacked Al/LiNbO3 system. A SAW strain sensor with a dual-port resonator was modeled using multiphysics finite element model (FEM) method. While FEM has been widely used for numerical calculations of SAW devices, most of the simulation works mainly focus on SAW modes, SAW propagation characteristics and electromechanical coupling coefficients. Herein, we propose a systematic scheme via analyzing the structural parameters of SAW resonators. Evolution of RSAW eigenfrequency, insertion loss (IL), quality factor (Q) and strain transfer rate with different structural parameters are elaborated by FEM simulations. Compared with the reported experimental results, the relative errors of RSAW eigenfrequency and IL are about 3% and 16.3%, respectively, and the absolute errors are 5.8 MHz and 1.63 dB (the corresponding Vout/Vin is only 6.6%). After structural optimization, the obtained resonator Q increases by 15%, IL decreases by 34.6% and the strain transfer rate increases by 2.4%. This work provides a systematic and reliable solution for the structural optimization of dual-port SAW resonators.

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.

Test and Analysis of SAW High Temperature Strain Sensor Based on Langasite

In this study, we fabricate a surface acoustic wave strain sensor based on langasite. By constructing a temperature-strain composite testing platform, we examine this sensor for the strains of 0 to 500 <inline-formula> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> at temperatures ranging from 18 to <inline-formula> <tex-math notation="LaTeX">$700~^{\circ }\text{C}$ </tex-math></inline-formula>. The value obtained from the tests for the strain sensitivity of the sensor is 20.09 Hz/<inline-formula> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> at 700 &#x00B0;C, and the maximum relative error and hysteresis error are 3.35&#x0025; and 6.98&#x0025;, respectively. Moreover, the sensor exhibits a stable response at high temperatures. Considering the sensitivity of the temperature and strain of the sensor at high temperatures, a temperature - strain decoupling method is proposed. The strain values obtained after the calculation agreed well with the reference strain values, and the maximum error was between &#x2212;4.2&#x0025; and 5.425&#x0025;. Therefore, the proposed temperature - strain decoupling method could help eliminate the influence of temperature on the strain measurements of this sensor.

Surface Acoustic Wave Strain Sensor With Ultra-Thin Langasite

Langasite (LGS) surface acoustic wave (SAW) sensor is considered as an ideal wireless passive sensing technology application in complex environments. However, existing LGS-based SAW strain sensor has low strain range and its sensing accuracy is affected by temperature greatly as well as strain, which can not meet the application requirements. By exploiting ultra-thin substrate and a custom calibration algorithm, this paper proposes an ultra-thin 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> LGS SAW with (0°, 138.5°, 72°) Euler angle to extend strain range to 1200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500^{\circ }\text{C}$ </tex-math></inline-formula> , which is twice higher than the state-of-the-art. The ultra-thin SAW sensor has lower temperature coefficient and hysteresis loop effect, compared with thick LGS SAW. Aiming to improve sensing accuracy, the mechanism of temperature effects on strain sensitivity is investigated in different temperature stages, including thermal expansion mismatch effect and high-temperature glue strain transfer ratio effect. The mechanism can explain strain sensitivity curve under various temperature nicely. Based on the mechanism, a new calibration method is also developed to eliminate temperature effects. The testing results show that this calibration method can improve the measured strain accuracy effectively.

High temperature effects on surface acoustic wave strain sensor

Surface acoustic wave sensors (SAW), as a wireless passive sensor, are susceptible to temperature disturbance for high-temperature strain measurements, which results in poor accuracy and repeatability of the strain sensing. This paper investigates temperature effects on SAW strain sensors. Results show that high temperature not just induces frequency drift, but also reduces strain transfer ratio due to glue softening. The resonant frequencies of the langasite (LGS) SAW sensor have a linear relationship with strain for fixed temperatures, while the strain sensitivity is greatly affected by temperature. The results also show that the difference of measured strain sensitivities between the two resonant frequencies for one device is much less affected by temperature because they suffer the same strain transfer ratio and temperature characteristics, but different strain responses. A method to eliminate temperature effects has been proposed and accurate high-temperature strain measurements with SAW sensor were conducted to extend strain range up to 380 με with high repeatability under 500 °C.

High-Precision Demodulation Method for Surface Acoustic Wave Strain Sensor Based on Hybrid Changing Area Niche Genetic Algorithm

The echo signal energy of surface acoustic wave (SAW) strain sensor is weak, resulting in low demodulation accuracy. In order to improve the measurement result, a SAW sensor demodulation method by combining hybrid changing area niche genetic algorithm and MUSIC algorithm was proposed. The proposed method was based on the MUSIC algorithm to construct the power spectrum function of SAW echo signal. A hybrid changing area niche genetic algorithm (CANGA) and particle swarm optimization (PSO) algorithm was developed to improve the spectrum peak search accuracy and reduce the amount calculations of MUSIC algorithm. The power spectrum function of the MUSIC algorithm was used as the fitness function of the hybrid algorithm. The echo frequency was estimated by the variable value corresponding to the optimal solution. The proposed hybrid PSO-CANGA has the characteristics of strong global search ability and fast convergence speed to improve the performance of MUSIC algorithm. The numerical comparisons were performed. The results showed that the hybrid PSO-CANGA gives fastest convergence and the highest estimation accuracy compared to original PSO and NGA. In addition, compared with traditional spectrum estimation algorithms, the proposed algorithm had a minimum estimation error with standard deviation of 0.27KHz. The proposed demodulation method was used to SAW strain system. The nonlinearity of the strain measurement was improved, with a nonlinearity of 0.55%. Simulation and experiment results verified the effectiveness of the proposed algorithm for the demodulation of the SAW strain sensor system. It helps to improve the accuracy of SAW strain measurement.

Strain Measurements With Langasite SAW Resonators at High Temperature

The strain sensitivities of the langasite surface acoustic wave resonators are strongly dependent on the temperature, which causes measurement strain to shift greatly at high temperature. To cancel the effect of temperature, a surface acoustic wave strain sensor which consisted of three langasite surface acoustic wave resonators was presented in this work. The surface acoustic wave resonators are configured to ensure that the propagation directions of the surface acoustic wave in the three surface acoustic wave resonators are parallel, perpendicular and at an orientation of 30° to the applied strain. The strain sensitivities of the three surface acoustic wave resonators from room temperature to 250 °C were investigated. Functional relationships of the resonance frequency shifts of the three surface acoustic wave resonators due to both the temperature and applied strain were established. It was deduced that the strain was linearly represented by the resonance frequency shifts of the three surface acoustic wave resonators. Experimental results demonstrated that the langasite surface acoustic wave strain sensor was well worked within the temperature range from room temperature to 250 °C. The average values of the calculated strains were in agreement with the practical applied strains. There was a little fluctuation between the calculated and preset strains. The measurement error was about 1%. The maximal standard deviation was about 18.5 με.

Development of a wireless and passive temperature-compensated SAW strain sensor

A temperature-compensated surface acoustic wave (SAW) device was developed to build a wireless and passive strain sensor. Y-cut 35° X quartz with perfect temperature stability was employed as the piezoelectric substrate of the sensing device patterned by one-port resonator. Optimization by coupling of modes (COM) model towards sensing chip was conducted to determine the optimal design parameters, which offers lager Q-value. The prepared sensing device by standard photolithographic technique operating at 434MHz was characterized wirelessly. High strain sensitivity, excellent temperature stability, and high resolution were achieved in the wireless measurements.

Highly Sensitive Surface Acoustic Wave Flexible Strain Sensor

This letter presents a highly sensitive flexible strain sensor based on surface acoustic wave (SAW) working principle. The SAW strain sensor employs the piezoelectric single crystal PMN-PT thick film, which significantly improves the sensitivity of the strain sensor to 1243.49 Hz/ $\mu \varepsilon $ . Meanwhile, the flexible strain sensor fabricated by the chemical and mechanical polishing process can realize a wide strain measurement range from −1000 to $+ 1000\,\,\mu \varepsilon $ . The repeatability of the device is also evaluated under the strain of 0 and $900~\mu \varepsilon $ . The testing results demonstrate that this developed sensor is an excellent candidate for small stain measurement.

Flexible dual-mode surface acoustic wave strain sensor based on crystalline LiNbO3 thin film

This work presents the development of flexible dual-mode surface acoustic wave (SAW) sensor based on single crystalline thin film lithium niobate (TF-LN). Numerical modeling is conducted to investigate the SAW propagation and the effects on strain sensitivity. The dependence of strain sensitivity on angles between the applied strain and SAW propagation direction is analyzed numerically and experimentally, showing that the maximum strain sensitivity is at 45° rather than longitudinal direction. 128° Y-cut TF-LN (~50 µm), obtained by micromachining technique, is utilized as the piezoelectric substrate to fabricate the SAW strain sensors with dual-mode, namely Rayleigh mode and thickness shear mode. The sensor has excellent flexibility and demonstrates remarkable capability for an ultra-wide range strain measurement up to ±3000 . Temperature effects on resonant frequency and strain sensitivity are investigated in the range of 25 °C–100 °C, and similar temperature characteristics are observed for the dual modes. A method of beat frequency between the dual modes is introduced which is able to eliminate the temperature effect on strain sensing, an on-chip temperature influence removing capability. All the results clearly show that this sensor exhibits great potential for applications in flexible electronics and microsystems.

Flexible surface acoustic wave strain sensor based on single crystalline LiNbO3 thin film

A flexible surface acoustic wave (SAW) strain sensor in the frequency range of 162–325 MHz was developed based on a single crystalline LiNbO3 thin film with dual resonance modes, namely, the Rayleigh mode and the thickness shear mode (TSM). This SAW sensor could handle a wide strain range up to ±3500 με owing to its excellent flexibility, which is nearly six times the detecting range of bulk piezoelectric substrate based SAW strain sensors. The sensor exhibited a high sensitivity of 193 Hz/με with a maximum hysteresis less than 1.5%. The temperature coefficients of frequency, for Rayleigh and TSM modes, were −85 and −59 ppm/°C, respectively. No visible deterioration was observed after cyclic bending for hundreds of times, showing its desirable stability and reliability. By utilizing the dual modes, the strain sensor with a self-temperature calibrated capability can be achieved. The results demonstrate that the sensor is an excellent candidate for strain sensing.

Highly sensitive surface acoustic wave strain sensor for the measurement of tire deformation

We developed a surface acoustic wave (SAW) strain sensor system with high sensitivity for real-time monitoring tire deformation. The SAW sensor utilizes a shear horizontal wave and split interdigital transducer (IDT). After the SAW sensor was attached to the tire specimen, the characteristics of the SAW sensor were investigated using tensile and three-point bending tests, respectively. When external deformation is applied to the SAW sensor, the strain of the piezoelectric substrate changes the distance between the two IDTs and alters the velocity of the propagating SAW, resulting in a change in the center frequency of the SAW sensor. Based on the degree of changes in the center frequency, we can evaluate the extent of the tire deformation. The center frequency linearly decreases by 20 kHz as the tire is strained to 20%. As the tire specimen with SAW sensor was bent upto 2 mm, the center frequency linearly decreased by 25 kHz. The sensitivity and linearity of the SAW strain sensor were measured to be 2.5 kHz/% and 0.97. These results indicate that the developed SAW sensor has excellent sensitivity for external deformation and it is capable of measuring tire deformation.

Wireless SAW Strain Sensor Using Orthogonal Frequency Coding

Wireless sensors offer a unique solution for many applications where wired designs may not be feasible. This paper presents the design and experimental results of a passive, wireless surface acoustic wave (SAW) strain sensor using orthogonal frequency coding (OFC) for the device identification. The sensor operates at a frequency of 915 MHz with a bandwidth of 68 MHz. A vector network analyzer is used to interrogate the sensor from a range of 60 cm (2 ft), with further range possible by increased transmitter output power or averaging. The sensor is bonded directly to a steel cantilever test structure and could be attached directly to other structures. An external connection site facilitates an antenna, with bond wires joining the connection site to the SAW die. A 3-D printed package protects the sensor while allowing the antenna to be mounted externally from the sensor package. Experimental results show that the wireless SAW strain sensor performs comparably to a wired, commercial strain gage. In addition, the strain sensitivity is extracted for this SAW OFC strain sensor embodiment which describes the frequency shift with the applied strain (-1.80 ppm/με).

Development of flexible ZnO thin film surface acoustic wave strain sensors on ultrathin glass substrates

Flexible surface acoustic wave (SAW) strain sensors made on ZnO/ultrathin glass (100 μm) substrates have been developed. The sensitivity of the SAW strain sensors under different strain angles and annealing temperatures, as well as the mechanical stability, are investigated. It was shown that the thickness of ZnO has a strong effect on the sensitivity of the strain sensors, and thicker ZnO makes sensors with better performance. Thermal annealing at a temperature up to 200 °C also improves the sensitivity of the strain sensor significantly. The temperature coefficient of frequency remains unchanged under different strains, showing good thermal stability. A cyclic bending test with the strain varied between zero and 2000 με exhibits good mechanical stability and reliability of SAW strain sensors. All the results demonstrate the great potential of flexible SAW strain sensors for flexible electronic applications.

Strain Transfer Analysis of Integrated Surface Acoustic Wave Sensors

This paper presents a strain transfer investigation for Surface Acoustic Wave (SAW) strain sensors. For evaluation, a SAW strain sensor is assembled with a pretested bond material for potentially high strain transfer on a test holder. The setup is stressed with an axially homogeneous strain up to 500 ppm. The strain transfer ratio is computed from the applied load, the reference measurements with foil strain gauge, and the measured SAW strain sensor signal. The strain transfer performance of the bond material is also investigated with respect to the temperature dependency in the range between 22 °C and 85 °C. At these elevated temperatures an average strain transfer ratio of 0.606 ± 0.7% was measured. Mechanical load cycling tests up to 1000 cycles are used for the evaluation of the elastic fatigue of the bond material. The effects of mechanical load cycling and aging of the bond layer are analyzed with the SAW strain sensor response. After 1000 mechanical load cycles, the transferred strain into the SAW strain sensor is 0.582 ± 0.153%. Finally, the experimental results are compared with the results of a 3D FEM simulation which are deviating by less than 10%.

레일리파 기반의 고감도 변형률 센서에 관한 연구

Piezoresistive-type, capacitive-type, and optical-type sensors have mainly been used for measuring a strain. However, in building a sensor network for remote monitoring using these conventional sensors there are disadvantages such as the complexity of a measuring system including wireless communication circuitry and high cost. In this paper, we demonstrates a highly-sensitive surface acoustic wave (SAW) strain sensor which is advantageous to harsh environments and wireless network. We designed and fabricated the SAW strain sensor. The SAW strain sensor attached on a specimen was tested with a tensile tester. The strain on the sensor surface was measured with a commercial strain gauge and compared with that obtained from strain analysis. The central frequency shift of the SAW sensor was measured with a network analyzer. The sensitivity of the SAW strain sensor is 134 Hz/με which is high compared to previous results.

Experimental Study of Highly Sensitive Sensor Using a Surface Acoustic Wave Resonator for Wireless Strain Detection

We developed a highly sensitive strain sensor employing a surface acoustic wave (SAW) resonator for a wireless sensing system. The aim of this study is to monitor the distribution of the strain in the earth crust or giant infrastructures, such as bridges, skyscrapers and power plants, for disaster prevention. A SAW strain sensor was fabricated using LiNbO3 and a quartz substrate, and applied in a tensile test by attaching the steel specimen based on Japanese Industrial Standards (JIS Z2441-1). The results confirmed that the developed sensor could detect a strain of 10-6 order with linearity.

Experimental Study of Highly Sensitive Sensor Using a Surface Acoustic Wave Resonator for Wireless Strain Detection

We developed a highly sensitive strain sensor employing a surface acoustic wave (SAW) resonator for a wireless sensing system. The aim of this study is to monitor the distribution of the strain in the earth crust or giant infrastructures, such as bridges, skyscrapers and power plants, for disaster prevention. A SAW strain sensor was fabricated using LiNbO3 and a quartz substrate, and applied in a tensile test by attaching the steel specimen based on Japanese Industrial Standards (JIS Z2441-1). The results confirmed that the developed sensor could detect a strain of 10-6 order with linearity.