In-Phase and Quadrature Analysis for Amplitude and Frequency Modulations Due to Vibrations on a Surface-Acoustic-Wave Resonator

Surface-acoustic-wave resonators (SAWRs) have found widespread usage in various modern consumer radio frequency (RF) communications electronics, such as cellular phones, wireless devices, GPS devices, frequency control, and sensing applications. External mechanical vibrations modify an SAWR relative dimensions and the substrate's elastic properties, which alter the device's acoustic wave propagation velocity and ultimately cause the SAWR RF response to change. Detecting vibrations are desirable for dynamic strain or vibration sensing applications, whereas external mechanical excitations can result in spurious signals which compromise SAW-based filters and oscillators used in RF communication, frequency control, and sensors targeting measurands such as temperature and pressure. Therefore, understanding and characterizing the SAWR's response to external vibration is relevant for establishing device operation, and assisting in device design and packaging to either mitigate the impact of vibrations for RF communications and frequency control or enhance the SAWR response for sensor applications. This paper presents an in-phase and quadrature demodulation technique (I-Q technique) to detect, quantify, and analyze the effect of externally induced mechanical vibrations on an SAWR. The I-Q technique disclosed reveals that the mechanical vibrations cause both frequency and amplitude modulations of the SAWR RF response, which can be separated by this technique. Furthermore, the procedure also allows the direct measurement of vibration frequencies and vibration magnitude. The technique, measured results, and analysis established here provide a better understanding of the impact of external mechanical vibrations on an SAWR response, which is important in contemporary communications, frequency control, and sensing applications.