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In this paper, a novel analysis technique for the performance evaluation of micro-acoustic devices has been
proposed. Whereas traditional techniques typically focus solely on the frequency domain characteristics, we
employ a Joint Time-Frequency Analysis (JTFA), which has been shown to provide a more complete characterisation
of overall device performance and underlying physical phenomena. Although an emphasis is placed
on a Flexural Plate Wave (FPW) device, the analysis technique presented is applicable to a wider range of
micro-acoustic devices including Surface Acoustic Wave (SAW) structures and Thin-Film Bulk Acoustic Wave
Resonators (TFBARs).
SAWdevices, and indeed general filters, are typically described by a frequency domain characteristic, whereby
the entire time domain information is discarded. This type of analysis assumes that the device has reached quasistationary
conditions. By employing JTFA, the device performance can simultaneously be studied as a function
of both time and frequency. This type of analysis is typically useful where spurious acoustic modes are generated
which may influence the overall filter characteristic.
We have investigated the functional properties of various JTFA kernels, including those appearing in the
Wigner-Ville, Choi-Williams and Page distributions. A known deficiency associated with JTFA is the appearance
of a number of spurious cross-terms in the computations. Whereas the cross-terms are relatively simple to
detect for "monochromatic" (single-component) signals, it is not a trivial task to minimise such artifacts for
"polychromatic" (multi-component) signals, which are typical in micro-acoustic devices. We propose novel
methods for reducing the cross-terms interference appearing in JTFA, thereby improving the performance of the
analysis technique.
To investigate the application of the proposed technique, the simulated time domain response of a FPW
device was investigated. The Finite Element Method (FEM) package ANSYS 8.0 was utilised to obtain the
impulse response of the FPW structure under a dynamic transient analysis. A comparison is also made with the
spectral domain Green's function to verify the FEM solution, where excellent agreement is obtained. Based on
the FEM solutions, the insertion loss characteristics is calculated which represents a commonly applied frequency
domain method of analysing micro-acoustic devices. A comparison has been made between the insertion loss
characteristics and the proposed approach, where it is clearly demonstrated that the problem-adapted technique
provides significantly more detailed information.
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