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.
Bibliographical noteFunding Information:
Manuscript received January 13, 2010; revised March 07, 2010; accepted March 09, 2010. Date of publication June 10, 2010; date of current version August 04, 2010. This work was supported in part by Korea Research Foundation Grant KRF-2007-357-D00043 and in part by the National Science Foundation under Grant CMMI-0856387. The associate editor coordinating the review of this paper and approving it for publication was Prof. Kiseon Kim.
- Battery-less wireless sensor
- capacitance sensing
- inductive coupling
- mutual inductance