Limitations of Fourier Transform Analysis in the Wireless SAW Sensor Systems

Surface acoustic wave resonators (SAWR) attract engineers' attention by their wireless and battery-less features and have been used for measuring temperature, pressure, and torque in laboratories, industries, and even harsh environments. This work presents a theoretical study of SAWR sensors' measuring process by using FFT analysis and evaluates the theoretical formula with experimental results. Also, it gives a survey of measurement unit blocks. The frequency response of the SAWR response signal is studied by considering an ADC and a processor calculating FFT. In addition, the paper could be assisted to find out the functionality of SAWR sensor and choose the better frequency of the local oscillator used in the radio frequency (RF) system to avoid low accuracy and high cost. Compared to former works that IF frequency was chosen experimentally, new formulae are presented for upper and lower bounds of theoretical IF frequency region.