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Sensors 2014, 14(11), 20245-20261; doi:10.3390/s141120245

Micro-Fabricated DC Comparison Calorimeter for RF Power Measurement

1
Department of Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA
2
Bird Technologies, Solon, OH 44139, USA
*
Author to whom correspondence should be addressed.
Received: 15 July 2014 / Revised: 9 October 2014 / Accepted: 9 October 2014 / Published: 27 October 2014
(This article belongs to the Special Issue On-Chip Sensors)
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Abstract

Diode detection and bolometric detection have been widely used to measure radio frequency (RF) power. However, flow calorimeters, in particular micro-fabricated flow calorimeters, have been mostly unexplored as power meters. This paper presents the design, micro-fabrication and characterization of a flow calorimeter. This novel device is capable of measuring power from 100 \(\mu\)W to 200 mW. It has a 50-Ohm load that is heated by the RF source, and the heat is transferred to fluid in a microchannel. The temperature change in the fluid is measured by a thermistor that is connected in one leg of a Wheatstone bridge. The output voltage change of the bridge corresponds to the RF power applied to the load. The microfabricated device measures 25.4 mm \(\times\) 50.8 mm, excluding the power supplies, microcontroller and fluid pump. Experiments demonstrate that the micro-fabricated sensor has a sensitivity up to 22 \(\times\) \(10^{-3}\) V/W. The typical resolution of this micro-calorimeter is on the order of 50 \(\mu\)W, and the best resolution is around 10 \(\mu\)W. The effective efficiency is 99.9\% from 0–1 GHz and more than 97.5\% at frequencies up to 4 GHz. The measured reflection coefficient of the 50-Ohm load and coplanar wave guide is less than \(-25\) dB from 0–2 GHz and less than \(-16\) dB at 2–4 GHz. View Full-Text
Keywords: RF power sensor; micro-calorimeter; microfluidics; temperature sensor;DC comparison RF power sensor; micro-calorimeter; microfluidics; temperature sensor;DC comparison
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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

Neji, B.; Xu, J.; Titus, A.H.; Meltzer, J. Micro-Fabricated DC Comparison Calorimeter for RF Power Measurement. Sensors 2014, 14, 20245-20261.

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