Total Power Radiometer for Medical Sensor Applications Using Matched and Mismatched Noise Sources

Abstract

This paper presents a simple total power radiometer to noninvasively measure the temperature of the human body. The proposed 3-GHz radiometer consists of an antenna collecting the noise power generated by a target, a low-noise and high-gain receiver amplifying the noise power, and a detector converting the noise power to voltage. A single-pole-triple-throw (SP3T) switch is placed between the antenna and the receiver, while a personal computer is used to control the SP3T switch, collect and process the data such as detector output voltages and physical temperatures of the reference noise sources and the target. The fabricated radiometer shows a good performance agreement with a thermometer in the temperature measurement of water from 25.0 to 43.1 °C. For the accurate prediction of the target temperature, the radiometer is calibrated adaptively to the environment and radiometer variations. For this purpose, two reference noise sources (hot and cold) are proposed using matched and mismatched resistors at room temperature. These resistor-based noise sources offer a reliable performance without complex temperature control systems. Furthermore, they can be easily calibrated in real time by periodically measuring the physical temperatures of the resistors. In addition, the logarithmic detector with wide dynamic range is adopted and logarithmically-fitted based on the measurement results instead of linear approximation, which reduces the error caused by the limited dynamic range of resistor-based noise sources. In order to further increase the accuracy, the performance imbalances between ports in the SP3T switch are also taken into account by employing offsets in the radiometer output voltages.

Design and Implementation of a Novel Interferometric Microwave Radiometer for Human Body Temperature Measurement

“…It can be seen from Table 3 that the temperature resolution of the interferometric microwave radiometer designed in this paper is higher than that of the total power microwave radiometer [ 6 ], the one-dimensional synthetic aperture microwave radiometer [ 25 ], the Ka-band direct detection radiometer [ 26 ], the W-band direct detection radiometer [ 27 ], the Dicke microwave radiometer without constant temperature treatment in reference [ 28 ] and Ka-band AC radiometer [ 29 ]. After designing the thermostat, the temperature resolution of the interferometric microwave radiometer designed in this paper will be further improved.…”

“…This paper innovatively designs the hardware structure of the interferometer microwave radiometer. The water temperature measurement results show that the temperature resolution of the interferometer microwave radiometer designed in this paper is better than that of the total power microwave radiometer [ 6 ], the Dicke microwave radiometer [ 5 , 28 ], the one-dimensional synthetic aperture microwave radiometer [ 25 ], the Ka-band direct detection radiometer [ 26 ], the W-band direct detection radiometer [ 27 ] and Ka-band AC radiometer [ 29 ]. Through the design of correction algorithm, calibration scheme and inversion algorithm, the temperature measurement accuracy of the microwave radiometer will be further improved.…”

“…Then they carried out contact and non-contact temperature measurement experiments on water. In 2017, Park and Jeong [ 6 ] produced a total power microwave radiometer for non-contact measurement of human body temperature. The radiometer and thermometer show good performance consistency in water temperature measurement from 298.15 to 316.25 K. The measurement error of radiometer is 0.90 K between 300.95–298.15 K by linear fitting method, the error reduced to 0.85 K by logarithmic fitting method.…”

“…The calibration of microwave radiometer can characterize the relationship between the output voltage of the radiometer and the brightness temperature received by the antenna [ 10 ]. In 2017, Park and Jeong [ 6 ] calibrated the radiometer with resistances of 22 and 50 Ω. Then, according to the reflection coefficient of the antenna, the insertion loss of the transmission line and the efficiency of the antenna, they deduced the brightness temperature received by antenna.…”

Design of Cavity-Backed Bow-Tie Antenna with Matching Layer for Human Body Application

“…Microwaves have also been used for hyperthermia, where they generate heat inside the human body to destroy malignant tissues, such as cancer [4]. In addition, various microwave medical radiometers have been introduced to non-invasively measure and image internal body temperatures [5,6,7,8,9]. The on-body radiometric sensors can be used for the monitoring of core body temperature and deep brain temperature, and the detection of breast cancer [6,7,8,9,10].…”