Flexural Plate-Wave FPW Devices

MEMBRANE USUALLY THIN COMPARED WITH WAVELENGTH 

MANY MODES OF PROPAGATION SOME MODES DISPERSIVE 

An opposite effect occurs if the tension in the thin plate is increased, for example, by establishing a differential gas pressure across it, by applying a force on the plate, or by bending the fi e that surrounds it. The increased tension causes the real part of the phase velocity to rise. 

One finds experimentally that the amplitudes of the displacements associated with a flexural wave of given total power are large relative to those of the other acoustic sensors discussed here. Peak-to-peak normal displacements up to 100 nm have been measured, using laser diffraction, when only a few milliwatts of wave energy were propagating in a plate a few micrometers thick. As a result of 

---

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. 

In a flexural plate wave (FPW) device, an acoustic wave is excited in a thinned membrane. Figure 3.38 (page 112). As with the other acoustic sensors discussed — the TSM, SAW and APM devices — the flexural-plate-wave (FPW) device can sense quantities that cause its phase velocity, Vp, to change. A unique... 

Figure 3.38 Schematic diagram of a flexural-plate wave (FPW) device.

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... 

Microcantilever sensors offer many orders of magnitude better sensitivity compared to other sensors such as quartz crystal microbalances (QCM), flexural plate wave oscillators (FPW), and surface acoustic wave devices (SAW). There are several distinct advantages of the microcantilever sensors compared to the above mentioned and other MEMS sensors ... 

---