These sensors could be used in harsh environments.

Two simple position or displacement sensors based on inductance- capacitance resonant circuits have been conceived. These sensors are both powered and interrogated without use of wires and without making contact with other objects. Instead, excitation and interrogation are accomplished by means of a magnetic- field- response recorder — an apparatus previously reported in “Magnetic- Field-Response Measurement-Acquisition System” (LAR- 16908), NASA Tech Briefs, Vol. 30, No. 6 (June 2006), page 28. To recapitulate: The magnetic-field-response recorder generates an alternating magnetic field that excites oscillations in the resonant circuit, measures the magnetic response of the circuit, and determines the resonance frequency from the response.

Figure 1. The Distance Between the Plates of a capacitor in a capacitor-inductorresonant circuit is varied. The distance can be calculated as a known function ofthe measured resonance frequency.

where L is the inductance, ε₀ is the vacuum permittivity, and l and w are the dimensions of the capacitor plates as indicated in Figure 1.

Figure 2. The Length of Overlap of the Plates of a capacitor in a capacitorinductorresonant circuit is varied. As in the case of Figure 1, this length can becalculated as a known function of the measured resonance frequency.

Simple inductance- capacitance circuits of the type used in these sensors are inherently robust; their basic mode of operation does not depend on maintenance of specific environmental conditions. Hence, these sensors can be used under such harsh conditions as cryogenic temperatures, high pressures, and radioactivity.

This work was done by Stanley E. Woodard of Langley Research Center and Bryant D. Taylor of Swales Aerospace. For further information, contact the Langley Innovative Partnerships Office at (757) 864-8881. LAR-16617-1.