Wireless 4.74 GHz Harmonically Operated SAW Temperature Sensor

Over the years, SAW devices have been providing solutions to many sensors needs such as measurement of temperature, strain, and magnetic field. SAW sensors are passive (battery-less), small, lightweight, low cost, sensitive, can be operated wirelessly, and capable of including multiple identification coding schemes. With the everyday advances of different technologies, there is increasing use of the electromagnetic spectrum, and many emerging applications need to use higher frequencies. SAW sensors have been commonly developed to work on different frequencies up to 3 GHz; however, SAW sensor operation at higher frequencies had been demonstrated to be a challenge due to minimum size fabrication limitations and higher propagation losses in the sensor response. This paper presents the development of a wireless SAW temperature sensor at 4.74 GHz. Harmonic operation of the SAW device is used to demonstrate the capability of the SAW technology to impact higher frequencies. Near range, wireless temperature measurements using 3rd harmonic 4.74 GHz SAW temperature sensors have been achieved. SAW device response predictions will be given using the coupling of modes (COM) model and compared with device measurements. Antenna design and device embodiment with SAW device matched to the antenna impedance will be presented. Interrogation of the 4.74 GHz temperature sensor and preliminary measurements of temperature using an SDR transceiver system will be given. This work aims to bring the inherent benefits of SAW technology to 4.74 GHz providing sensor solutions to actual and future applications.