Microwave radiometer

To improve efficiency of non-invasive monitoring of the internal brain temperature, a small-size single-channel microwave radiothermograph consisting of a miniature radiometer and a radiometric sensor based on a printed antenna was developed. Such solution is necessary to provide physicians with a system of non-invasive monitoring of diagnosis and treatment processes. Mathematical modeling and experimental verification of the technical solutions obtained are described in this paper. A miniature radiothermometer was developed. It is a balance modulation radiometer designed on the basis of the R.H. Dicke’s circuit with two loads. Taking into account the requirements of miniaturization, a radiometric sensor was developed by means of numerical simulation. As a result of calculations, optimum antenna dimensions were determined (the total size: ø30 mm, the size of the foil flane substrate: ø23 mm, dimensions of the emitter slot: 16 mm×2 mm). According to the mathematical modeling, the depth of detection of thermal anomalies was not less than 20 mm for the printed antenna which is practically the same as for the waveguide antenna successfully used at present in brain radiothermometry. The standing wave coefficient was determined for various head regions: frontal, temporal, parietal, occipital and the transient between the occipital and parietal regions. Experimental tests of the radiothermograph on water phantoms and biological objects have been carried out. A very good coincidence between the data of numerical simulation and the physical SWR experiment in a range of 1.04–1.8 was obtained. As a result of the study, it has been found that the radiothermograph with a printed slot antenna enabled measurement of internal brain temperature with an acceptable accuracy (±0.2 °C). This will ensure control of craniocerebral hypothermia in patients with brain stroke and allow doctors to promptly change the hypothermia tactics. Small size of the created unit will make it possible to combine it with medical robotic systems to improve treatment effectiveness.

Introduction The principle of action of microwave radiometers is based on recording microwave radiation from biological objects (BO) whose temperature is above absolute zero. Measurements of the intensity of body radiation can be used to determine its temperature. This method is termed microwave radiometry (MR). MR is a functional diagg nostic method based on passive radiooheat location [1]. In contrast to infrared thermography, MR provides for noninvasive identification of thermal anomalies at depths of several centimeters. MR is currently used to detect breast cancer [2] and melanomas [3], in monitoring the temperature of the brain [4], and in gynecology [5] and other areas. The radiometer includes an antenna applicaa tor (or several antenna applicators) and a highhsensitivity radiometric receiver. The recorded power of the BO defines the brightness temperature (BT), which is linked to the thermodynamic temperature as (1) where T(r) is the thermodynamic temperature of the BO and W(r) is the radiometric weighting function of the antenna. Integration is performed in terms of BO volume, V. W(r) is defined as (2) where P is the electromagnetic power loss density per unit volume due to absorption, P 0 is the total power dissipatt ed, E(r) is the tension of the electric field of the antenna, and σ(r) is electrical conductivity of the BO. Thus, BT is the averaged thermodynamic temperature of the BO with weighting W(r). Methods Microwave radiation in medical radiometers is detected using special antenna applicators − printed types [6610], waveguides [2, 4], and vibrator and frame types [1, 10], as well as intracavity antennas [5]. Waveguide antenn nas are segments of waveguides in contact with the BO. The most widely used are round waveguides, as the sharp angles of rectangular waveguides are traumatic for patients. Waveguide antennas are connected to the input cascade of the radiometer via a coaxial cable, so the outt put is sent to a microwave connector. Matching of the waveguide is done in various ways; the most common uses a "butterfly" slot [5]. Waveguide antennas are simple to design, have small electrical losses, high measurement depth, adequate shielding, and acceptable matching with the body. The size of the waveguide is usually decreased by The physical basis of microwave radiometry and the construction and technical characteristics of different types of antenna applicators used in medical radiometers are discussed. We present results obtained during the devell opment and the potential uses of new types of antenna applicators in different areas of medicine.

Journal of Oceanography, Vol. 58, pp. 137 to 151, 2002 Review Microwave Remote Sensing of Tropical Cyclones from Space Kristina В. Katsaros1*, Paris W. Vachon2, W. Timothy Liu3 and Peter G. Black1 1 NOAA/Atlantic Océanographie and Meteorological Laboratory, 4301 ...

In studies of weather changes and, especially, in enhancing the performance of rainfall prediction, it is important to measure the water vapor distribution in the atmosphere. We estimated atmospheric water vapor profiles for fourteen days, including periods of severe weather conditions, by processing ground-based Global Positioning System (GPS) measurements and compared our results with microwave radiometer (MWR) and radiosonde (RAOB) observations. As a result, we found that the standard deviation (STD) of wet refractivity profiles between GPS with MWR was smaller than the STD between RAOB and MWR refractivities; the average STD was 9.3 mm km−1. In particular, we found that GPS-based wet refractivities detected inversion layers close to those from MWR when the observed GPS satellites were well distributed in the azimuth and elevation angle directions. When the satellite geometry was better, the mean error of GPS wet refractivities with respect to MWR was reduced to 0.4 from 3.2 mm km−1 for altitudes lower than 3 km. In some cases, however, the precision of GPS refractivities are lower than that of RAOB ones relative to MWR results.

ABSTRACT
Currently, there is growing interest among specialists in the use of non-invasive dose-free technologies for diagnosis and monitoring treatment of various diseases. Microwave radiometry enables non-invasive detection of thermal abnormalities in internal tissues of the human body. The current level of development of the method of microwave radiometry makes it possible to non-invasively detect malignant neoplasms at early stages according to characteristics of the person's own radiothermal fields. For a wider implementation of the method, it is necessary to overcome a series of scientific and technical barriers that impede its development. First of all, it is necessary to ensure miniaturization of the equipment used.

An analytical review of the current state of development in the field of medical radiometers has been performed. Miniaturization of equipment is an important area for studies. It was shown that application of the proposed scheme for designing a null balance radiometer with a sliding scheme of reflection compensation with two matched RF loads will enable creation of a miniature highly stable radiometer. The measurement error of this device does not depend on the ambient temperature, intrinsic temperature of the device and impedance of the studied area of the body. The device calibration procedure was considered and noise signal calculations were performed. Results of experimental verification of correctness of choice of the way of designing the miniature radiometer circuit were presented. Introduction of thermal compensation has made it possible to reduce measurement error associated with the device heating to 0.2 °C when intrinsic temperature of the radiometer changed by 20 °C. It was shown that a radiometer operating in the frequency band 3.4–4.2 GHz can be used to detect various diseases and monitor internal temperature of tissues during treatment. With introduction of autonomous power supply and wireless communication with a smartphone, the miniature radiometer can be used as a wearable device to monitor temperature of internal tissues in everyday human life.

Frequency dependence of brightness temperature (TB) in the range 6–21 GHz is studied as a function of surface roughness, vegetation cover and soil moisture using theoretical models. Frequency dependence of TB is plotted from Multi‐channel Scanning Microwave Radiometer (MSMR) TB data of Indian Remote Sensing Satellite (P‐series) IRS‐P4 for different target types such as ocean, desert, forest, agricultural and snow regions.

In the present study, the effectiveness of nowcasting convective activities using a microwave radiometer has
been examined for Kolkata (22.65° N, 88.45° E), a tropical location. It has been found that the standard deviation
of brightness temperature (BT) at 22 GHz and instability indices like Lifting Index (LI), K Index (KI) and Humidity
Index (HI) has shown definite changes before convective events. It is also seen that combination of standard deviation
of BT at 22 GHz and LI can be most effective in predicting convection. A nowcasting algorithm is prepared
using 18 isolated convective events of 2011 and in all cases, a marked variation of these parameters has been seen
an hour before the event. Accordingly, a prediction model is developed and tested on convective events of 2012
and 2013. It is seen that the model gives reasonable success in predicting convective rain about 7075 min in advance
with a prediction efficiency of 80%.

Although data available from various earth observation systems have been routinely used in many resource applications, however there have been gaps, and data needs of applications at different levels of details have not been met. There is a growing demand for availability of data at higher repetivity, at higher spatial resolution, in more and narrower spectral bands etc. Some of the thrust areas of applications particularly in the Indian context are; Management of natural resources to ensure sustainable increase in agricultural production, Study the state of the environment, its monitoring and assessment of the impact of. various development actions on the environment, Updating and generation of large scale topographical maps. Exploration/exploitation of marine and mineral resources and Operational meteorology and studying various land and oceanic processes to understand/predict global climate changes. Each of these thrust area of application has many components, related to basic re...