Radio-frequency plasma transducer for use in harsh environments

We describe a compact transducer used to generate and modulate low-intensity radio-frequency atmospheric pressure plasma (RF-APP) for high temperature gap measurement and generation of air-coupled ultrasound. The new transducer consists of a quarter-wave transmission line where the ground return pat...

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Veröffentlicht in:Review of scientific instruments 2007-10, Vol.78 (10), p.104701-104701-4
Hauptverfasser: May, Andrew, Andarawis, Emad
Format: Artikel
Sprache:eng
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Zusammenfassung:We describe a compact transducer used to generate and modulate low-intensity radio-frequency atmospheric pressure plasma (RF-APP) for high temperature gap measurement and generation of air-coupled ultrasound. The new transducer consists of a quarter-wave transmission line where the ground return path is a coaxial solenoid winding. The RF-APP is initiated at the open end of the transmission line and stabilized by passive negative feedback between the electrical impedance of the plasma and the energy stored in the solenoid. The electrical impedance of the plasma was measured at the lower-voltage source end of the transducer, eliminating the need to measure kilovolt-level voltages near the discharge. We describe the use of a 7 MHz RF-APP prototype as a harsh-environment clearance sensor to demonstrate the suitability of plasma discharges for a common nondestructive inspection application. Clearance measurements of 0 - 5 mm were performed on a rotating calibration target with a measurement precision of 0.1 mm and a 20 kHz sampling rate.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.2794695