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Open AccessFeature PaperArticle

Low-Frequency RFID Signal and Power Transfer Circuitry for Capacitive and Resistive Mixed Sensor Array

1
Department of Information Engineering, University of Brescia, Via Branze 38, 25123 Brescia, Italy
2
INO-CNR (National Institute of Optics—National Research Council), Via Branze 45, 25123 Brescia, Italy
*
Author to whom correspondence should be addressed.
Electronics 2019, 8(6), 675; https://doi.org/10.3390/electronics8060675
Received: 14 May 2019 / Revised: 3 June 2019 / Accepted: 11 June 2019 / Published: 14 June 2019
(This article belongs to the Section Microwave and Wireless Communications)
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Abstract

This paper presents a contactless measurement system for a mixed array of resistive and capacitive sensors exploiting a low-frequency radio-frequency identification (RFID)-based approach. The system is composed of a reader unit which provides power to and exchanges measurement data with a battery-less sensor unit. The sensor unit is based on a transponder operating at 134.2 kHz and a microcontroller. The microcontroller sequentially measures the elements of the sensor array composed of n capacitive and m resistive sensors which share a common terminal. The adopted technique measures the charging time of a resistor–capacitor (RC) circuit, where the resistor or the capacitor can be either the sensing element or a reference component. With the proposed approach, the measured values of the resistive or capacitive elements of the sensor array are first-order independent from the supply voltage level. A prototype has been developed and experimentally tested with resistive elements in the range 400 kΩ–1.2 MΩ and capacitive elements in the range 200 pF–1.2 nF showing measurement resolution values of 1 kΩ and 5 pF, respectively. Operative distances up to 3 cm have been achieved, with readings taken faster than one element of the array per second. View Full-Text
Keywords: low-frequency RFID; capacitive and resistive sensors; contactless interrogation; power transfer low-frequency RFID; capacitive and resistive sensors; contactless interrogation; power transfer
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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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MDPI and ACS Style

Demori, M.; Baù, M.; Dalola, S.; Ferrari, M.; Ferrari, V. Low-Frequency RFID Signal and Power Transfer Circuitry for Capacitive and Resistive Mixed Sensor Array. Electronics 2019, 8, 675.

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