Abstract
Impedance measurement is a promising avenue for noninvasive glucosemonitoring. Specifically,resonance-basedimpedancemeasurements exhibit good correlation with glucose levels at excitations from tens of MHztoover 100 MHz. Additionally, plethysmographic impedance measurements are needed to separate arterial blood signals, which contain strongerglucose information, frominterstitialfluidsignals. Weanticipate that plethysmographic measurements across a range of frequencies— spectroscopic plethysmography—at excitations from tens to over 100 MHz could enable resonance-based monitoring with higher selectivity for arterial glucose than previous work. Afour-point impedance measurement circuit is designed, and its ability to measure constant and periodically time-varying impedance is demonstrated. This circuit presents high impedance to the device-undertest (DUT), which fails in the target range of tens to over 100 MHz due to the detrimental effects of parasitic capacitance. An active quasi-circulator (AQC) overcomes this challenge by instead presenting a controlled low impedance to the DUT. Thus, an impedance measurement technique utilizing the AQC is proposed. An initial version of the integrated circuit (IC) is fabricated and measured to demonstrate the proposed technique. Incorporating the AQC measurement technique, along with a proposed multirate filtering method which overcomes the challenge of impractically-high-Q filtering in post processing, a culminating version of the IC is presented. This IC is designed for the target application of resonance-based impedance measurements of human tissue at excitations from tens of MHz to over 100 MHz. The IC measures spectroscopic impedance plethysmography up to 255 MHz. In addition to the AQC, the IC features a source-follower DAC, excitation signal generation, and frequency downconversion. Electrical and human test results demonstrate, for the first time, spectroscopic plethysmography for resonance-based measurements, thus laying the groundwork for future studies of blood glucose–impedance correlation and other impedance measurements involving wearable arterial blood monitoring at these frequencies.
Degree
PhD
College and Department
Ira A. Fulton College of Engineering; Electrical and Computer Engineering
Rights
https://lib.byu.edu/about/copyright/
BYU ScholarsArchive Citation
Poff, Sharisse, "An Active Quasi-Circulator IC and Technique for 1-255 MHz Resonance-Based Spectroscopic Impedance Plethysmography" (2025). Theses and Dissertations. 11429.
https://scholarsarchive.byu.edu/etd/11429
Date Submitted
2025-08-01
Document Type
Dissertation
Keywords
active quasi-circulator, bioimpedance, impedance measurement, multirate filtering, heart rate monitoring, impedance plethysmography, spectroscopic plethysmography
Language
english