ABSTRACT
A sensor is a device for detecting the presence of a physical, chemical, or biological property and, by appropriate transduction, transforming the detected quantity into an electrical signal. Sensors, in general, are of many types, based on sensing mechanisms that may be electrical, optical, acoustic, magnetic, and so on, in nature. Acoustic microsensors may be configured as one- or two-port devices. A one-port device, which is active, contains a feedback loop that converts the device into an oscillator. The response of resonators with a viscoelastic film deposited on one face is important because viscoelastic polymer films are often used as chemically selective layers on thickness-shear mode and other acoustic sensors for gas sensing. The Quartz-crystal microbalance has been the workhorse for many years in applications where mass loading is the basic interaction of interest.
