Development of a high-sensitivity strain measurement system based on a SH SAW sensor

• Published in: Journal of micromechanics and microengineering Vol. 22; no. 2; pp. 025002 - 10
• Main Authors: Oh, Haekwan, Lee, Keekeun, Eun, Kyoungtae, Choa, Sung-Hoon, Yang, Sang Sik
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.02.2012; Institute of Physics
• Subjects: Applied sciences; Boards; Circuit boards; coupling of modes; Electrodes; Electronics; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Microelectronic fabrication (materials and surfaces technology); Micromechanical devices and systems; Physics; Precision engineering, watch making; Printed circuits; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Sensors; SH waves; split electrode; Strain; Strain measurement; strain sensor; surface acoustic wave; Surface acoustic waves; Acoustic wave device; Resistance strain gauge; High strain; Microsensor; Measurement sensor; Interdigital transducer; Printed circuit board; Surface wave; Elastic wave; Modeling; Strain sensors; High sensitivity; Adhesive joint; Integrated circuit; S wave; Delay line; Adhesive
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/22/2/025002

A strain measurement system based on a shear horizontal surface acoustic wave (SH SAW) was developed. The developed system is composed of a SAW microsensor, a printed circuit board (PCB), an adhesive and a strain gauge. When a compression force is applied to the PCB by the strain gauge, the PCB is bent so that external strain energy can be evenly delivered to the microsensor without any detachment of the sensor from the board. When a stretching force is applied to the PCB under the condition that one side of the PCB is fixed and the other side is modulated, the actual length of the SAW delay line between the two interdigital transducers (IDTs) is increased. The increase in the delay line length causes a change in the time for the propagating SAW to reach the output IDT. If strain energy is applied to the piezoelectric substrate, the substrate density is changed, which then changes the propagation velocity of the SAW. Coupling-of-modes modeling was conducted prior to fabrication to determine the optimal device parameters. Depending on the strain, the frequency difference was linearly modulated. The obtained sensitivity for stretching was 17.3 kHz % for the SH wave mode and split electrode. And the obtained sensitivity for bending was 46.1 kHz % for the SH wave mode and split electrode. The SH wave showed about 15% higher sensitivity than the Rayleigh wave, and the dog-bone PCB showed about 8% higher sensitivity than the rectangular PCB. The obtained sensitivity was about five times higher than that of existing SAW-based strain sensors.