1. bookVolume 9 (2009): Issue 6 (December 2009)
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Journal
eISSN
1335-8871
First Published
07 Mar 2008
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6 times per year
Languages
English
access type Open Access

Auto-Tuned Induction Coil Conductivity Sensor for In-Vivo Human Tissue Measurements

Published Online: 23 Dec 2009
Volume & Issue: Volume 9 (2009) - Issue 6 (December 2009)
Page range: 162 - 168
Journal Details
License
Format
Journal
eISSN
1335-8871
First Published
07 Mar 2008
Publication timeframe
6 times per year
Languages
English
Auto-Tuned Induction Coil Conductivity Sensor for In-Vivo Human Tissue Measurements

Auto-tuned induction coil technology, based upon phase-locked loop circuitry (PLL), was developed and shown to be an effective tool for in-vivo measurement of electrical conductivity of human tissues. Because electrical contact is not required, several disadvantages of the electrode method for conductivity determination are avoided, such as electrode polarization and variable conductivity associated with the stratum corneum of the epidermis. Fixed frequency excitation is supplied to a parallel tuned RLC circuit, or "sensor", while bias applied to a varactor diode is automatically adjusted via PLL circuitry to maintain the RLC sensor at resonance. Since resonant impedance of a coil positioned near a conductive object is known to be frequency dependent, such an arrangement permits precise calibration of the sensor against a set of standard Potassium Chloride solutions. In our experiments, a two-layer spiral coil is used with upper and lower spiral arms staggered so as to reduce inter-winding coil capacitance. Preliminary in-vivo testing was done on the forearms of a single male subject as a prelude to more extensive use in a clinical setting. In that instance, electrical conductivity at the proximal volar forearm location was shown to depend on forearm elevation. Clinical studies using our prototype, as well as further consideration of the "elevation effect", are discussed in a companion paper.

Keywords

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