Line Surface Acoustic Wave Research Articles

SH-BAW devices with abnormal mass-loading effect for chemical sensing

Surface acoustic wave (SAW) devices are promising for chemical and biological sensing applications. This work studies the basic operating principles and the physical behaviors of the “Rayleigh”-SAW and the “Shear Horizontal (SH-)” bulk acoustic wave (BAW), particularly in relation to the chemisorption process. A complete 3D delay line SAW model is developed and performed by the finite element analysis, and a methodology was introduced for characterizing the transmission characteristics (S21) of these devices. Notably, our investigation unveils an intriguing phenomenon in the behavior of SH-BAW in response to loading mass. We observed an anomalous shift in the central frequency, which increases as the chemical adsorbate concentration rises. Leveraging these insights, we designed and constructed a SAW-based gas sensor, and the vinyl-terminated polydimethylsiloxane was synthesized for the detection of chloroform, a challenging pollutant to identify. Through a comparative study, we illustrate distinct responses of Rayleigh-SAW and SH-BAW devices to accumulated loading mass and gaseous contaminants. These experimental results validate and corroborate our simulations. This work demonstrates a unique mass-loading effect exhibited by SH-BAW devices, which differs from the existing theories. These findings offer the opportunity to refine and enhance models for accurately describing the functionality of delay line SAW sensors, thereby contributing to improved sensor reliability.

Maximum measurement range and accuracy of SAW reflective delay line sensors.

In a surface acoustic wave (SAW) wireless sensor with a reflective delay line structure, three reflectors are often used to eliminate 2π ambiguity of phase measurement. The maximum range of the measured parameter and the maximum accuracy have recently been attracting much research attention. In this paper, an analytical formula for all the factors influencing the measurement range and accuracy of the delay line SAW sensor are deduced for the first time. The factors include: the sensor sensitivity, the topology of the delay line, the available wireless bandwidth and the allowed maximum phase measuring error of the reading system, which is easier to retrieve and more fully describes the possible noises than SNR. Additionally, many designers believe that increasing the reflector could improve accuracy continuously or realize multi-resolution measurement. However, they ignore some certain criteria that the reflector location must satisfy. The reachable maximum accuracy by every increase of a reflector is also presented. A SAW temperature sensor system using 128° YX-LiNbO3 is designed to verify the above theoretical analysis.

A ZnO nanorod-based SAW oscillator system for ultraviolet detection

A high-precision ultraviolet (UV) detector combining ZnO nanostructure and a dual delay line surfaceacoustic wave (SAW) oscillator system is presented. The UV detector is made of ZnO nanorods ona 128°YX-LiNbO3-based two-port SAW oscillator. The ZnO nanorod synthesized by chemical solutionmethod is used as a UV sensing material. The center frequency of the SAW device is at145 MHz. A dual delay line SAW oscillator system was constructed to eliminate externalenvironmental fluctuations. Under illumination of a UV source consisting of an Xe lampand a monochromator, frequency shifts of the UV detector were measured. A maximumfrequency shift of over 40 kHz was observed under 365 nm illumination for several on–offcycles, indicating the ZnO nanorod-based detector was sensitive to UV light and with goodrepeatability. Moreover, frequency shifts reached a value of 19 kHz after 365 nm was turnedon for 10 s, which implies a real-time high-sensitivity UV sensor was successfullyfabricated. Results show a ZnO nanostructure-based SAW oscillator system is apromising candidate for a real-time, fast-response, high-precision UV detector.

Ultraviolet detector based on a surface acoustic wave oscillator system with ZnO‐nanostructure sensing material

Recently, ultraviolet (UV) detectors based on surface acoustic wave (SAW) devices utilizing the acoustoelectric effect have been demonstrated. However, most of presented cases were based on semiconductor sensing films. Sensors with nanostructure sensing material not only possess high sensitivity but also accelerate response and recovery time due to their high surface‐to‐volume ratio and fast charge diffusion rate. In this paper, ZnO‐nanostructure and a dual delay line SAW oscillator system are combined to develop a high precision UV detector. The UV detector is made of ZnO nanorod on a 128oYX‐LiNbO3 based SAW device. The operating frequency is around 145MHz. The system is illuminated by a UV source consists of a Xe lamp and a monochromator, resulting in frequency shifts. The frequency shifts related to different light wavelengths and power are measured and discussed. Results show the ZnO‐nanostructure based SAW oscillator is a promising candidate for a real‐time and high precision UV detector.