A hydrogel-based wireless sensor using micromachined variable inductors with folded flex-circuit structures for biomedical applications

TitleA hydrogel-based wireless sensor using micromachined variable inductors with folded flex-circuit structures for biomedical applications
Publication TypeConference Paper
Year of Publication2008
AuthorsSridhar, V., and K. Takahata
Conference NameMicro Electro Mechanical Systems, 2008. MEMS 2008. IEEE 21st International Conference on
Pagination70 -73
Date Publishedjan.
Keywordsbiomedical applications, biomedical electronics, biomedical equipment, biomedical measurement, bioMEMS, coplanar dual spiral coil, copper-clad polyimide film, folded flex-circuit structures, hydrogel wound dressing, hydrogel-based wireless sensor, inductive wireless sensor, inductors, microfabrication, micromachined variable inductors, micromachining, passive resonant device, poly(vinyl alcohol)-poly(acrylic acid) hydrogel, polymer gels, size 5 mm to 10 mm, size 50 mum, wireless frequency measurement, wireless monitoring, wireless sensor networks, wounds
Abstract

This paper reports a flexible, inductive wireless sensor that can be combined with a variety of hydrogel materials for biomedical applications. The variable inductor is formed by folding coplanar dual spiral coil with 5-10 mm size that are microfabricated using 50-mum-thick copper-clad polyimide film so that when folded, the two coils are aligned to each other and the mutual inductance depends on the gap between the aligned coils. A hydrogel element is sandwiched by the folded substrate to modulate the gap, or inductance of the device as it swells/deswells depending on the target parameter. The response of a variable inductor to the displacement of the coils is measured to be 0.40 nH/mum. A sensitivity of 113 ppm/mum in wireless frequency measurement is obtained using the passive resonant device that combines the variable inductor with a fixed capacitor. The resonant devices are coupled with a commercial hydrogel wound dressing as well as pH-sensitive poly(vinyl alcohol)-poly(acrylic acid) hydrogel. Wireless monitoring of the swelling of the wound dressing is experimentally demonstrated.

URLhttp://dx.doi.org/10.1109/MEMSYS.2008.4443595
DOI10.1109/MEMSYS.2008.4443595

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