Resonant phase shift technique for the measurement of small changes in grounded capacitors

Abstract

A simple technique has been developed for the high resolution measurement of small changes in capacitors which have one grounded electrode. The capacitor is arranged to be the tuning element in a series resonant LC tank circuit that is driven by a transistor emitter follower. Signal information is provided by observing the phase shift in the transistor collector current that results from any small change in the capacitor value. Implementation is simple, readily analyzable, provides good diagnostics, is easily multiplexed into arrays, and has potential applications in a number of areas including high resolution proximity sensing, capacitive topography, atomic force microscopy, and capacitor microphones.

Novel undercoupled radio-frequency (RF) resonant sensor for gaseous ethanol and interferents detection

“…The concept of resonant sensor is has been illustrated in [2], and patented in [3,4], with [3] specifying the interrogation method of frequency-sweeping and [4] indicating the use of reflection amplitude and phase of the resonant sensor response to achieve passive sensing capabilities against ambient chemicals or analytes (e.g., volatile organic compounds, VOCs). Other resonant sensor designs were reported in [5,6], which also use resonant sensor configurations for active sensing applications.…”

A Comparison of Frequency Pullability in Oscillators Using a Single AT-Cut Quartz Crystal and Those Using Two Single AT- Cut Crystals Connected in Parallel with a Series Load Capacitance or Series Load Inductance

“…In the case of capacitively pulled dual-crystal unit the equation is To compare the amount of pullability exhibited by a given crystal unit, the oscillator frequency was measured by the Heterodyne method, where df = f 1 – f 2 [ 7 - 8 ]. This is the reason why the results are shown in the frequency range 0-20 kHz ( Fig.…”

Greatly Improved Small Inductance Measurement Using Quartz Crystal Parasitic Capacitance Compensation

“…They are based on the application of a series or parallel resonance LC circuit as elements of either a bridge circuit or a two-port (four-terminal) “T”-type network. The joint error of the inductance measurement results are similar as when using ac bridge method (depending on the quality of the elements) [ 3 ].…”