Kenjiro Okaguchi

Magnetic Sensor Based on Surface Acoustic Wave Resonators

In this paper, we describe a new type of magnetic surface acoustic wave (SAW) sensor that consists of interdigital transducers made of a magnetostrictive material, Ni, on a quartz substrate. This sensor can be used as an element of a resonator-type wireless SAW sensor system because it has a high Q. Moreover, it has the merits of being fabricated easily using the existing process for SAW devices because its structure is the same as that of general SAW resonators. When an external magnetic field of about 100 mT was applied perpendicularly to the direction of SAW propagation, the frequency change obtained was 200 ppm. In addition, the developed sensor was applied in a passive and wireless open/close sensing system and the reading distance obtained was 3 m.

SAW magnetic sensors composed of various Ni electrode structures on quartz

A shear horizontal type of surface acoustic wave (SAW) magnetic sensor composed of a Ni electrode of magnetrostrictive metal and an ST-cut 90°X quartz (propagation direction: perpendicular to X-axis) substrate was fabricated. In order to obtain a higher magnetic sensitivity, one-port SAW resonators composed of 3 kinds of Ni electrodes structures on the quartz, such as (a) grooved Ni electrodes, (b) additional overlaid Ni films on grooved Ni electrodes, and (c) Ni electrodes on the quartz, were fabricated. Their sensitivities were almost same, but the SAW resonator composed of (c) structure had highest Q. Using this SAW resonator, a passive, battery-less, and wireless communication system was realized.