Separation of Frequency and Amplitude Modulation Contributions Due to External Vibration on a SAW Resonator

Surface SAW resonators (SA WR) are widely used in radio-frequency (RF) communications, frequency-control, and sensing applications. External vibration-induced modulations of a SA WR's RF response can be detrimental in communications and frequency-control as it generates undesired spurious signals and unwanted phase noise. In sensing applications, vibration-induced response can either be a primary measurand or an undesired spurious signal that reduces sensor accuracy and precision. Therefore, characterization of vibration-induced modulations is important to improve device performance in all the applications listed above. This paper presents an in-phase and quadrature signal analysis technique to demodulate a SA WR RF signal exposed to external vibrations and separate the contributions of amplitude modulation (AM) and frequency modulation (FM). A SA WR was mounted in a cantilever configuration and exposed to external mechanical vibrating signals using a vibration generator. The SA WR was excited close to its resonant frequency using a RF synthesizer and its echo response was measured using a vector signal analyzer. The experimental results and findings reported in this paper confirm that the I-Q analysis developed in this work is effective not only to determine the frequency and spectral amplitude of a mechanical vibrating signal on a SA WR, but also to separate the AM and FM contributions. This analysis contributes to the quantification and understanding of induced external vibrations on SA WRs used in contemporary communications, frequency control, and sensing applications.