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Sensors 2017, 17(6), 1264; doi:10.3390/s17061264

Analysis and Validation of Contactless Time-Gated Interrogation Technique for Quartz Resonator Sensors

1
Department of Information Engineering, University of Brescia, Via Branze 38, Brescia 25123, Italy
2
INO-CNR (National Research Council), Via Branze 45, Brescia 25123, Italy
*
Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Received: 7 April 2017 / Revised: 18 May 2017 / Accepted: 25 May 2017 / Published: 2 June 2017
(This article belongs to the Special Issue State-of-the-Art Sensors Technologies in Italy 2016)
View Full-Text   |   Download PDF [3662 KB, uploaded 8 June 2017]   |  

Abstract

A technique for contactless electromagnetic interrogation of AT-cut quartz piezoelectric resonator sensors is proposed based on a primary coil electromagnetically air-coupled to a secondary coil connected to the electrodes of the resonator. The interrogation technique periodically switches between interleaved excitation and detection phases. During the excitation phase, the resonator is set into vibration by a driving voltage applied to the primary coil, whereas in the detection phase, the excitation signal is turned off and the transient decaying response of the resonator is sensed without contact by measuring the voltage induced back across the primary coil. This approach ensures that the readout frequency of the sensor signal is to a first order approximation independent of the interrogation distance between the primary and secondary coils. A detailed theoretical analysis of the interrogation principle based on a lumped-element equivalent circuit is presented. The analysis has been experimentally validated on a 4.432 MHz AT-cut quartz crystal resonator, demonstrating the accurate readout of the series resonant frequency and quality factor over an interrogation distance of up to 2 cm. As an application, the technique has been applied to the measurement of liquid microdroplets deposited on a 4.8 MHz AT-cut quartz crystal. More generally, the proposed technique can be exploited for the measurement of any physical or chemical quantities affecting the resonant response of quartz resonator sensors. View Full-Text
Keywords: quartz crystal resonator; quartz crystal microbalance; contactless electromagnetic interrogation; resonant sensor; liquid solution microdroplet measurement quartz crystal resonator; quartz crystal microbalance; contactless electromagnetic interrogation; resonant sensor; liquid solution microdroplet measurement
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Baù, M.; Ferrari, M.; Ferrari, V. Analysis and Validation of Contactless Time-Gated Interrogation Technique for Quartz Resonator Sensors. Sensors 2017, 17, 1264.

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