Shear Horizontal Mode Surface Acoustic Wave Research Articles

Design and implementation of shear-horizontal mode surface acoustic wave formaldehyde gas sensor

Surface acoustic wave (SAW) sensors have garnered significant attention due to high performance in gas detection. Love wave as the special mode of SAW has greater attractiveness for molecules detection in gas or liquid. To investigate the detection performance of Love wave SAW (Love-SAW) devices towards toxic gases, the influence of interdigitated electrodes on the propagating performance of Rayleigh and shear horizontal (SH) waves along ST-X and ST-90°X quartz substrates was analyzed by finite element method (FEM). The effect of the guiding layer based on different substrates of SAW devices has been discussed by changing the thickness of the zinc oxide (ZnO) layer. The results indicate that the SH wave excited on ST-90°X quartz substrate couples into the Love wave mode through the ZnO guiding layer, and Rayleigh waves in ST-X quartz do not exhibit mode coupling. The Love-SAW sensor covering the ZnO guiding layer (0.5 µm) has shown high mass sensitivity. The vibration distribution of SH wave excited by different thicknesses of electrodes is different, indicating that the mass-loading is one of the reasons for the transformation of SH wave into Love wave. Furthermore, the 50 ppm, 95 ppm and 110 formaldehyde-load leads the short-circuit resonance frequency of the polyetherimide (PEI) covered Love-SAW devices to drop by 100.1 kHz, 200.2 kHz and 300.3 kHz, respectively. The maximum detection sensitivity reached about 2.73 kHz/ppm. This work can provide valuable insights for designing and investigating the SAW formaldehyde gas sensors.

Investigation of spurious mode suppression in 3.8 GHz shear-horizontal mode surface acoustic wave resonators based on LiNbO3/SiO2/Si multilayer structure

LiNbO3(LN)/SiO2/Si multilayer structures have recently attracted much attention due to their superior performance in realizing wideband radio-frequency acoustic filters. However, the spurious modes, which are commonly found in LN-on-insulator (LNOI) resonators, often cause in-band ripples and a deteriorated out-of-band suppression level. Although much research work has been done on the suppression of spurious modes in LNOI resonators operating in the <3 GHz region, little has been reported for >3 GHz devices. This work investigates the spurious mode suppression techniques for a 3.8 GHz shear-horizontal mode 36° YX-LNOI surface acoustic wave (SAW) device based on an LN/SiO2/Si multilayer structure. Specifically, we explore different techniques based on apodized electrodes, dummy electrodes and a double busbar structure. The measured results show that the effect of spurious mode suppression can be improved by combining the benefits of these techniques, which provides a promising solution for designing spurious-free LNOI SAW resonators operating above 3 GHz.

SH-SAW sensor based microfluidic system for the detection of heavy metal compounds in liquid environments

In this work, a guided shear horizontal mode surface acoustic wave (SH-SAW) sensor, fabricated by patterning gold (Au) interdigitated electrodes (IDE) on a 64° YX-LiNbO3 based piezoelectric substrate, was used for the detection of heavy metal compounds. A flow cell, with a reservoir volume of 3μL, which employs inlet and outlet valves for the microfluidic chamber and polydimethylsiloxane (PDMS) based microfluidic channels, was also designed and fabricated using an acrylic material. The frequency based response of the SAW sensor toward varying concentrations of heavy metal compounds such as lead nitrate (PbNO3) and cadmium nitrate (CdNO3) were investigated. As the surface acoustic wave propagates on the substrate, between input and output IDEs, a shift in the resonant frequency of the SAW device was observed due to the change in velocity of the wave caused by the varying concentrations of the test analytes. The results obtained demonstrated the capability of the system to detect picomolar level concentrations. The response of the SAW sensor is analyzed and presented in this paper.

Passive Strain Sensor using SH-SAW Reflective Delay Line

A shear horizontal-mode surface acoustic wave (SH-SAW) has the unique characteristic of complete reflection at a free edge normal to the direction of propagation, making it possible to construct a reflective delay line. A passive SAW strain sensor based on such a reflective delay line is presented. The reflective delay line is constructed on a 36° YX LiTaO 3 substrate. The SH-SAW velocity is shown to provide a reliable measure of the strain of a propagation surface, and incorporation of an oscillator circuit is demonstrated to allow wireless remote monitoring of strain using this sensor.

Functional Passive Sensor System Using Reflective SAW Delay Line

ABSTRACTA new passive and remote SAW sensor system having ID tag function is presented. Surface acoustic wave (SAW) devices have been widely used as a chemical and physical sensor for measuring the environment. SAW devices have been also used as identification tags (ID tags). The majority of the work reported on SAW sensors to date has used Rayleigh mode SAW and are concerning a delay line. The other hand, it has been shown that the sensors utilizing the shear horizontal mode SAW (SH-SAW) can be designed to sense the liquid properties. The SH-SAW has the unique characteristic of complete reflection at a 90 degree edge normal to the direction of the propagation. This characteristic makes it possible to construct a reflective delay line using the edge reflection. The reflective delay line can be used for as passive and remote sensing.In this paper, a passive and remote SAW sensor with a function of identification tags has been designed by using the reflective SH-SAW delay line. The reflective delay line was constructed on the 36 YX LiTaO3 substrate having a 90 degree edge normal to the direction of the SAW propagation. Passive and remote SAW sensor consists of several reflective delay lines having different propagation length. The passive sensor and ID tags were made by the multi-channel delay line. The responses of the sensor and ID tags using the edge reflection of SH-SAW are obtained in time domain. Several experiments were performed to verify the performances of the multi-channel edge reflection sensor. The basic characteristics of the reflective SAW sensor were obtained by measuring the amplitude and phase of reflected wave. The obtained results showed that the reflective SH-SAW sensor was very effective for sensing the physical and chemical properties.Wireless systems are also suggested for the effective operation of the passive SAW sensor. A novel and simple electronic circuit system for accurately measuring the phase characteristics of responses form multi-channel is proposed. In the application, the reflective delay line has been mounted on cantilever to monitor the strain experimentally. The variation of the SH-SAW velocity on the delay line caused by a strain was measured as the passive SAW sensor response. The velocity varied in proportion to the strain applied to the propagation surface. The results showed that the passive sensor was very effective to measure the strain in a wireless mode and it was found that the system is very suitable to health and safety monitoring of building or airplane wing.Finally it will be shown some applications of the wireless sensor with ID tags on the measurement of the conductivity and viscosity of same liquids.

Liquid sensor probe using reflecting SH-SAW delay line

A new liquid sensor probe has been designed by using SH-SAW device. Shear horizontal mode surface acoustic wave (SH-SAW) has a unique characteristic of complete reflection at the free edges of the substrate. The SH-SAW are excited on a 36° YX LiTaO 3 and the right angle edge of the substrate has been used to reflect the SAW. Multi-channel reflecting SAW delay lines were constructed on the substrate. Both the phase and amplitude of the SH-SAW reflected from the edge were measured as a sensor response. Several experiments were performed to verify the edge reflection type SAW sensor in liquid phase. A sensing system configuration is also suggested for the effective operation of the sensor probe. An electronic circuits system for accurately measuring the phase characteristics of the reflected wave and for detecting the output from the multi-channel SAW sensor probe was shown.

Gas Sensor Using Complete Reflection at Free Edge of SH-SAW

A new gas sensor has been designed by using SH-SAW device. Shear horizontal mode surface acoustic wave (SH-SAW) has a unique characteristic of complete reflection at the free edges of the substrate. The SH-SAW are excited on a 36° YX LiTaO 3 and the right angle edge of the substrate has been used to reflect these waves. Both the phase and amplitude of the SH-SAW reflected from the edge were measured as a sensor response. Several experiments were performed to verify the edge reflection type SAW sensor in gas phase.

Enzyme-immobilized SH-SAW biosensor

A shear horizontal mode surface acoustic wave (SH-SAW) device has many attractions for chemical-sensing applications in liquid media. The SH-SAW that propagates on 36° rotated Y-cute, X-propagating LiTaO 3 is affected by a strong acoustoelectric interaction between the piezoelectric potential and electric properties of the adjacent liquid. This paper describes an enzyme-immobilized SH-SAW biosensor in which the detection principle is the acoustoelectric interaction due to the pH change in the enzyme reaction. Two kinds of enzymes, urease and cholinesterase, are immobilized on the sensor surface and highly sensitive detection of the enzyme reaction is obtained experimentally. The urease-immobilized SH-SAW biosensor is implemented in a liquid-flow system. By using the cholinesterase-immobilized SH-SAW sensor, we have succeeded in detecting an inhibition effect of a pesticide.

New Biosensor Using Shear Horizontal Surface Acoustic Wave Device

This paper describes a new biosensor to detect an enzyme reaction in liquid using surface acoustic wave (SAW) devices fabricated on 36°-rotated Y-cut, X-propagating LiTaO3. The sensing wave on the substrate is a predominantly shear-horizontal-mode SAW (SH-SAW) and is affected by a strong acoustoelectric interaction between the piezoelectric potential and electrical properties of the materials in the adjacent liquid. As an example of an electrical property, pH change associated with an enzyme reaction leads to measurable perturbation in the wave-propagation characteristic. Taking advantage of this phenomenon we realized a SAW biosensor which consists of an immobilized urease membrane on the surface. Also, highly sensitive detection for the urea solution was obtained in our preliminary experiments.