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.

Driver Behavior Classification System Analysis Using Machine Learning Methods

“…These signals are used to detect the major distraction factor, which is driver fatigue [32,33]. Physiological data can now be acquired using nano sensors embedded in human bodies [34,35].…”

Micro-Fabricated RTD Based Sensor for Breathing Analysis and Monitoring

“…The size of thermistors is quite small and they are relatively cheap, which facilitates their application as reference instruments in many studies. Thermocouples, on the other hand, use the Seebeck effect as a principle to explain the relation between voltage and temperature [24,25]. When two different conductors are connected, the electromotive force that occurs is proportional to the temperature of the free ends and the temperature of the junction between them.…”