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A Novel Real-Time Capacitance Estimation Methodology for Battery-Less Wireless Sensor Systems

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4 Author(s)
Hwa Soo Kim ; Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN, USA ; Shyam Sivaramakrishnan ; A. Serdar Sezen ; Rajesh Rajamani

This paper presents a novel method to read a passive capacitive sensor in telemetry by using inductive coupling. While classical inductive coupling approaches measure sensor capacitance by identifying the resonant frequency of the sensor with a sweep of radio frequency (RF) signals, the proposed method estimates the capacitance change in real-time by algebraically manipulating two measurements (the magnitude and the phase of the reflected sensor impedance). Only one RF signal is used in the proposed method instead of a frequency sweep. Analysis is provided to show that some physical parameter errors can deteriorate the capability of the proposed method in accurately measuring sensor capacitance. However, the use of a first order calibration procedure based on error analysis overcomes this shortcoming. Extensive experimental results with the proposed method combined with a first order calibration show that multifrequency and rapid changes in sensor capacitance can be estimated reliably under varying locations and orientations of the interrogator. The battery-less wireless sensors enabled by the developed technology in this paper can be widely used for measurement of fluid pressure, force, acceleration and other capacitance-change based sensor measurements.

Published in:

IEEE Sensors Journal  (Volume:10 ,  Issue: 10 )