Packaging and antenna design for wireless SAW temperature sensors in metallic environments

We have developed a radio frequency (RF) transponder based on a surface acoustic wave (SAW) device specifically optimized for wireless temperature measurement of rotating shafts. The SAW sensing element is a reflective delay line type with 3 reflectors. The main foci of the paper are on a new compact packaging, and on antenna simulations for 2.4 GHz radio signal transmission to the interrogator. The novel metallic packaging has been designed for smallest possible outer dimensions of 10.0 × 3.1 × 2.0 mm³. In order to streamline the housing for insertion in a borehole, the electrical feedthroughs have been oriented in the longitudinal axis, contrary to the standard vertical axis approach. Antenna simulations were performed to find an optimized design tuned to the metallic surrounding. A slot antenna type was identified as best joint solution for the objectives radiation pattern and antenna gain.