In some applications, a wireless readout is necessary because of the difficulty of fixed connection between sensors and signal processing unit. The current wireless sensor systems based on data modulation are limited by battery duration and special environment. Wireless surface acoustic wave (SAW) sensors could be used for sensing some physical and chemical measurand passively. However, it is necessary to design SAW sensor specifically in different applications. In this paper, a wireless measurement platform based on SAW technology for sensors is studied. According to the coupling of modes (COM) theory, the reflection magnitude and phase of an interdigital transducer (IDT) is a function of a complex termination impedance at its electrical port and thus conventional sensors varying in impedance can be easily upgraded into wireless sensors. A delay-line SAW device with low insertion loss is designed with the help of a COM model. In order to overcoming the drawback, which evaluates sensor information by amplitude measurement of reflected impulses, the reflection phase is measured using a digital quadrature demodulation unit. This novel wireless measurement platform is applied in weigh measuring with capacitive sensor and the performance of wireless system is given.

Date Published: 15 October 2001
PDF: 6 pages
Proc. SPIE 4601, Micromachining and Microfabrication Process Technology and Devices, (15 October 2001); doi: 10.1117/12.444700

Published in SPIE Proceedings Vol. 4601:
Micromachining and Microfabrication Process Technology and Devices
Norman C. Tien; Qing-An Huang, Editor(s)