Measurement of Acoustic-Wave Device Frequency Response

2 MEASUREMENT OF ACOUSTIC-WAVE DEVICE FREQUENCY RESPONSE 

Measurement of frequency response is important for several reasons. The response of an acoustic-wave device to an external perturbation, for example in a chemical sensing application, can be better understood if the device s frequency response is known in advance. Measurement of the frequency response is also important if the most stable and accurate measurement system is to be designed for a particular device. Finally, the change in the frequency response of a device that results from some significant modification of its surface environment, such as the deposition of a polymer layer or immersion of the surface in a liquid, can 

In general terms, the frequency response of a device is the magnitude and phase of its output signal as a function of the fi quency of a (constant amplitude) input signal. The nature of the output signal varies from one type of device to the next, as discussed in detail in the following. The two related variations on the instrumentation that can be used to measure frequency response are discussed next as well. 

63J REAL-TIME MONITORING OF ACOUSTIC-WAVE DEVICES FOR SENSING AND CHARACTERIZATION APPLICATIONS 

The most complete and unambiguous characterization of the response of an AW device is always obtained from a complete frequency response spectrum, including all four S parameters. In addition, there are cases, particularly for fairly complex interactions between the AW and a surface film, in which the nature of the response might never be understood without this important tool. There are several important reasons, however, not to attempt the measurement of an entire 

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