Frequency Readjustment of Excitation Signals for Resonant Surface Acoustic Wave Sensors in the 2.45 GHz ISM Band

In this publication an essential step is described to use a six-port based instantaneous frequency measurement (IFM) system for determining applied force on a resonant surface acoustic wave (SAW) sensor in the worldwide approved 2.45 GHz industrial, scientific and medical (ISM) band. Due to the comparably high frequency for such sensors, side spurs may arise in the frequency response close to the main resonance because of non-linearities in the materials and the manufacturing process of these sensors. In order to keep the measurement error low and the signal to noise ratio (SNR) high, the readjustment of the excitation frequency of the sensor is proposed. Measurements were performed that show a significant difference between readjusted and constant excitation frequency. This improvement thus makes the system far more tolerant for sensors with unexpected side spurs.