Acoustic plate mode

A number of methods are available for the characterization and examination of SAMs as well as for the observation of the reactions with the immobilized biomolecules. Only some of these methods are mentioned briefly here. These include surface plasmon resonance (SPR) [46], quartz crystal microbalance (QCM) [47,48], ellipsometry [12,49], contact angle measurement [50], infrared spectroscopy (FT-IR) [51,52], Raman spectroscopy [53], scanning tunneling microscopy (STM) [54], atomic force microscopy (AFM) [55,56], sum frequency spectroscopy. X-ray photoelectron spectroscopy (XPS) [57, 58], surface acoustic wave and acoustic plate mode devices, confocal imaging and optical microscopy, low-angle X-ray reflectometry, electrochemical methods [59] and Raster electron microscopy [60]. 

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. 

This happens in Acoustic plate-mode (Apm) oscillators, which have a thickness of only a few microns. The eigenfrequency of the Apm oscillators is given by the interdigitated electrode spacing p and by the plate thickness t. 

Fig. 4.21 Bulk Lamb waves in Acoustic plate-mode (Apm) and Flextural Plate Wave (FPW) oscillators...

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 1.2 Schematic sketches of the four types of acoustic sensors discussed in detail in this book (a) Resonant quartz crystal like that used in electronic communications systems (after Lu [6]) (b) Suiface-acoustic-wave delay line with selective absorptive coating (after Wohltjen and Dessy [3]) (c) Acoustic-plate-mode delay line made from quartz crystal (after Ricco and Martin [7]) (d) Thin-membrane flexural-plate-wave delay line made by microfabrication techniques from a silicon wafer.

Devices based on piezoelectric crystals, which allow transduction between electrical and acoustic energies, have been constructed in a number of conrigurations for sensor applications and materials characterization. This cluqtter examines those devices most commonly utilized for sensing a( licatithickness-shear mode (TSM) resonator, the surface acoustic wave (SAW) device, the acoustic plate mode (APM) device, and the flexural plate wave (FPW) device. Each of these devices, shown schematically in Figure 3.1, uses a unique acoustic mode. 

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.

Figure 3.33 Schematic of an acoustic plate mode (APM) device showing the shear horizontal (SH) displacement of the mode as it propagates between input and output transducers. (Reprinted with permission. See Ref. (54). 1989 Elsevier Publishers.)...

Acoustic plate-mode -Vpd ST-cut quart 97 —9.5 (zeroth —9.3 (zeroth... 

An example of a two-port device is the surface acoustic-wave (SAW) delay line shown in Figure 6.3. Acoustic plate mode (APM) devices utilize a two-port configuration that is conceptually identical to that of the SAW for the flexural plate wave (FPW), there is typically a third connection to its ground plane (see Section 6.2.3). In principle, the ground plane connection is unnecessary, but in practice more stable operation results when this connection is made. Notice that there... 

SH-APM shear-horizontal acoustic plate mode (SH-APM) sorption (sorb) ST-cut quartz... 

D Mcallister Biode, Inc. Cape Elizabeth, ME DoE Developing a simple sensor for use in waste, surface, and groundwater using a shear horizontal acoustic plate mode (SHAPM) sensor, a form of piezoelectric sensor... 

Liquid-Phase Sensors Based on Acoustic Plate Mode Devices... 

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. 

RICCOETAL. Season Using Acoustic Plate Modes... 

Mode Resolution. By using three devices with different substrate thicknesses, transducer periodicities, and numbers of transducer finger pairs, an estimate of the minimum requirements for resolution of adjacent acoustic plate modes was obtained. Modes were essentially unresolvable using Device 1 (158 MHz), which had a 191-/im thick substrate, 32-im transducer periodicity, and 50 finger pairs (R — 1.4 in Equation 2). Device 2, also operating at 158 MHz, had b -152 fim, d - 32 im, and N - 50 (R - 2.2), and resolved modes well. 

Acoustic plate mode device—Canrtaied comparison to quartz crystal microbalance, 197... 

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