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Research Paper

Wireless Passive Sensor for Remote pH Monitoring

[+] Author and Article Information
Sharmistha Bhadra, Douglas J. Thomson, Michael S. Freund

Department of Electrical and Computer Engineering, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada

Greg E. Bridges1

Department of Electrical and Computer Engineering, University of Manitoba, Winnipeg, MB, R3T 2N2, Canadabridges@ee.umanitoba.ca

1

Corresponding author.

J. Nanotechnol. Eng. Med 2(1), 011011 (Feb 07, 2011) (4 pages) doi:10.1115/1.4003350 History: Received December 06, 2010; Revised December 11, 2010; Published February 07, 2011; Online February 07, 2011

In this paper we describe a wireless passive pH sensor for high-resolution remote pH monitoring. The sensor is based on a passive LC coil resonator whose resonant frequency is monitored remotely by measuring the change in impedance of an interrogator coil coupled to the sensor coil. The sensor resonator consists of an inductive coil connected in parallel with a voltage dependent capacitor and a pH combination electrode. Change in the electrode potential in response to variations of the pH of the solution changes the capacitance, and therefore the resonant frequency of the sensor. A linear response with a 0.1 pH resolution is achieved over a 4–10 pH dynamic range. The response time of the sensor is demonstrated to be less than 30 s and is limited by the response time of the pH combination electrode. The described sensor technology is suitable for long-term remote pH monitoring in numerous fields such as biomedical sensing, environmental monitoring, industrial and chemical processing, and structural health monitoring.

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Copyright © 2011 by American Society of Mechanical Engineers
Topics: Sensors , Electrodes
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Figures

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Figure 5

Experimental setup with the coupled-coil sensor and combination electrode in a solution

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Figure 6

Impedance analyzer frequency response for different pH solutions

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Figure 7

Resonant frequency of the sensor versus measured pH of the solution

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Figure 8

Response of the pH sensor and a commercial pH-meter over time

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Figure 9

Block diagram of a sensor coil coupled to an interrogator coil

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Figure 4

Potential difference at the sensor pH combination electrode terminal versus measured pH of a prepared solution

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Figure 3

Prototype wireless passive pH sensor

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Figure 2

Equivalent circuit diagram of the wireless passive pH sensor

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Figure 1

Block diagram of the wireless passive pH sensor

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