title: Micro-fabricated DC comparison calorimeter for RF power measurement.
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 μW 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 × 50.8 mm, excluding the power supplies, microcontroller and fluid pump. Experiments demonstrate that the micro-fabricated sensor has a sensitivity up to 22 × 10⁻³ V/W. The typical resolution of this micro-calorimeter is on the order of 50 μW, and the best resolution is around 10 μW. 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.
authors.affiliation: Department of Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA. bilelnej@buffalo.edu.
authors.forename: Bilel
authors.initials: B
authors.lastname: Neji
authors.affiliation: Department of Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA. jingxu@buffalo.edu.
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA. ahtitus@buffalo.edu.
authors.forename: Albert H
authors.initials: AH
authors.lastname: Titus
authors.affiliation: Bird Technologies, Solon, OH 44139, USA. JMeltzer@bird-technologies.com.
authors.forename: Joel
authors.initials: J
authors.lastname: Meltzer