Wireless passive SAW sensors using single-electrode-type IDT structures as programmable reflectors

• Published in: Sensors and actuators. A. Physical. Vol. 122; no. 2; pp. 203 - 208
• Main Authors: Fu, Qiuyun, Stab, Helmut, Fischer, Wolf-Joachim
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2005
• Subjects: Actuators; Deposition; Devices; Film thickness; Passive; Programmable reflector; Reflection coefficient; Reflectors; Sensors; Single-electrode-type IDT; Surface acoustic waves; Wireless passive SAW sensors; Single-electrode-type IDT; Passive; Programmable reflector; Wireless passive SAW sensors
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2005.05.006

Sensor information can be read out wirelessly by an antenna if the surface acoustic wave (SAW) delay line is connected to an external classical sensor. This is a passive device also called impedance-loaded SAW sensor. In the last decade, many researchers have made great efforts researching such devices, in which the double-electrode-type interdigital transducer (IDT) has been used as programmable reflector because its short-circuit reflection coefficient is very small. In this paper, the single-electrode-type IDT structure is proposed to be used as programmable reflector. The metallic periodic structure deposited on 128°YX LiNbO 3 shows an extraordinary characteristic: for a certain ratio of the film thickness to the periodicity, the reflection of the short-circuited single-electrode-type IDT almost disappears. This characteristic enables great amplitude modulation when the impedance-loaded SAW sensor employs the single-electrode-type IDT as programmable reflector. The fundamental operating frequency of SAW devices using the single-electrode-type IDT structure is twice that of SAW devices using the double-electrode-type IDT structure with the same critical dimension. This means higher operating frequencies for such devices can be reached with the achievable linewidth in current manufacturing technologies.