Shear-horizontal surface acoustic wave sensor

FIGURE 4.9 Permittivity-conductivity chart to derive electrical properties from SH-SAW responses. Kondoh J. and Shiokawa S Shear Horizontal Surface Acoustic Wave Sensors. Sensors Update. 2001. 6. Copyright Wiley-VCH Verlag GmhH Co. KGaA. Reproduced with permission. 

Josse F., Bender F., and Cernosek R. W., Guided shear horizontal surface acoustic wave sensors for chemical and biochemical detection in liquids, Anal. Chem., 73,5937-5944, 2001. 

Kondoh J. and Shiokawa S., Shear horizontal surface acoustic wave sensors, Sens. Update, 6, 2001. 

Shen C.-Y, Hsu C.-L., Hsu K.-C., and Jeng J.-S., Analysis of shear horizontal surface acoustic wave sensors with the coupling of modes theory, Jpn J. Appl. Phys., 44, 1510-1513, 2005. 

Li Z., Jones Y., Hossenlopp J., Cernosek R., and Josse R, Analysis of liquid-phase chemical detection using guided shear horizontal-surface acoustic wave sensors. Anal. Ghent., 77, 4595-4603, 2005. 

Li Z., Guided shear horizontal surface acoustic wave (SH-wave) chemical sensors for detection of organic contaminants in aqueous environments, PhD Marquette University, 2005. 

An electronic tongue based on dnal shear horizontal surface acoustic wave (SH-SAW) devices was developed to discriminate between the basic tastes of sour, salt, bitter, and sweet [57]. Sixty MHz SH-SAW delay line sensors were fabricated and placed below a miniature PTFE housing containing the test liquid. All the tastes were correctly classified without the need for a selective biological or chemical coating. 

A piezoelectric mass sensor is a device that measures the amount of material adsorbed on its surface by the effect of the adsorbed material on the propagation of acoustic waves. Piezoelectric devices work by converting electrical energy to mechanical energy. There are a number of different piezoelectric mass sensors. Thickness shear mode sensors measure the resonant frequency of a quartz crystal. Surface acoustic wave mode sensors measure the amplitude or time delay. Flexure mode devices measure the resonant frequency of a thin Si3N4 membrane. In shear horizontal acoustic plate mode sensors, the resonant frequency of a quartz crystal is measured. 

Fig. 12.3. Mercury sensor based on surface acoustic waves (SAW) with shear-horizontal acoustic plate mode. This approach was tested in Ref. [8].

Figure 3.1 Schematic sketches of the four types of acoustic sensors, (a) Thickness-Shear Mode (TSM) resonator (b) Surface-Acoustic-Wave (SAW) sensor, (c) Shear-Horizontal Acoustic-Plate-Mode (SH APM) sensor, and (d) Flexural-Plate-Wave (FPW) sensor.

This paper has dealt exclusively with SAW sensors that exploit the mass sensitivity of the device to achieve chemical vapor detection. Schemes to exploit the SAW sensitivity to coating conductance changes (17) or elastic modulus changes should afford new opportunities for imaginative chemical vapor sensor designs. Finally, the field of liquid phase chemical analysis may also yield to surface acoustic wave devices that utilize plate waves and horizontally polarized shear waves to minimize acoustic losses in the liquid (18). 

The response of piezoelectric devices propagating shear horizontal acoustic plate modes (SH-APMs) has been modeled and experimentally characterized for variations in surface mass, liquid rheological properties, and solution dielectric coefficient and electrical conductivity. The nature of the SH-APM and its propagation characteristics are outlined and used to describe a range of Interactions at the solid/liquid interface. Sensitivity to sub-monolayer mass changes is demonstrated and a Cu sensor is described. The APM device is compared to the surface acoustic wave device and the quartz crystal microbalance for liquid sensing applications. 

Chemical sensors based on acoustic wave (AW) devices have been studied for a number of sensing applications, the majority of which fall in the category of gas and vapor detection (1-8). Recently, the use of these sensors in liquid environments has been explored (9-13). AW sensors utilize various types of acoustic waves, including the surface acoustic wave (SAW), the shear-horizontal acoustic plate mode (SH-APM) (10-13), and the Lamb wave (also a plate mode) (3.14). Even though most studies of these piezoelectric sensors have centered on SAW devices (1.2.4-8), differences in the propagation characteristics of the various acoustic modes make some better suited than others for a given sensing application. 

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