Christos D. Nikolopoulos

On the Modeling of ELF Electric Fields for Space Mission Equipment

The majority of the space missions carry measuring instruments that are sensitive to electric fields and require stringent electromagnetic cleanliness. Therefore, the time variations of electric fields produced from spacecraft equipment have to be characterized, measured, and modeled. In this paper, a novel methodology is proposed, employing equivalent dipole modeling to describe the extremely low frequency (ELF) electric field spectral dependence. Each spectral component of the measured field is considered isolated and produced by one electric dipole. An iteration of this process over the whole frequency range yields the complete ELF model of the equipment under test, which consists of one electric dipole per frequency. In order to validate the accuracy of the proposed methodology, various ELF signals in different distances are studied.

An equivalent dipole method with novel measurement positioning for modeling electric emissions in space missions

ABSTRACT Prediction of the electric emissions in space missions is critical due to the sensitivity of their payload. A reliable method to predict such emissions is the accurate electric source identification. In this work, every space component is modeled by a small number of electric dipoles based on the measurement of the magnitude of the electric field at novel set of near-field positions. The location and electric moment are accurately predicted via stochastic algorithms resulting in the correct reconstruction of the source’s electric field both at measurement and extrapolation points.

Electromagnetic Emission Modeling in Case of Shielded Cabling With Respect to the Ground Dielectric Properties

Satellites and spacecraft subsystems in general are vulnerable in terms of electromagnetic interference. Shielded cables, connecting these subsystems as well as the subsystems themselves, are major sources of electromagnetic (EM) emission. The minimization of these emissions is critical in order to achieve EM cleanliness. An accurate model predicting these emissions could offer great insight and enable interference minimization. In this study, a shielded cable model for predicting EM emission via decomposition of contributing phenomena is presented including the ground dielectric properties. The model is built based on a standardized measurement setup and validated for different cases of ground material and cables position.

Early breast cancer detection method based on a simulation study of single-channel passive microwave radiometry imaging

The aim of the present study is to provide a methodology for detecting temperature alterations in human breast, based on single channel microwave radiometer imaging. Radiometer measurements were simulated by modelling the human breast, the temperature distribution, and the antenna characteristics. Moreover, a simulated lesion of variable size and position in the breast was employed to provide for slight temperature changes in the breast. To detect the presence of a lesion, the temperature distribution in the breast was reconstructed. This was accomplished by assuming that temperature distribution is the mixture of distributions with unknown parameters, which were determined by means of the least squares and the singular value decomposition methods. The proposed method was validated in a variety of scenarios by altering the lesion size and location and radiometer position. The method proved capable in identifying temperature alterations caused by lesions, at different locations in the breast.

Auto Reconfigurable Patch Antenna for Biomedical Single Channel Multi - Frequency Microwave Radiometry Applications

A small patch antenna is associated with passive (reactively loaded) elements (varactors) in order to auto adjust the resonant frequency in a single-channel multi-frequency conflguration appropriate for biomedical applications. As a supplementary study of the authors in the fleld of detection of temperature abnormalities in human tissue phantom using microwave radiometry, this paper adds a contribution to frequency readjustment when a shift occur due to the fact that the human body is a complex and stratifled dielectric object. The optimization of the array is performed using a Genetic Algorithm (GA) tool as a method of choice. The adjustment in the measurement frequency is performed by altering the values of the passive elements according to the shift needed.

A Novel Antenna System for Body Temperature Change Detection Appropriate for Multi-Channel Microwave Radiometry

A planar inverted F antenna is combined with passive (reactively loaded) elements in order to implement a multi-frequency conflguration appropriate for biomedical applications in microwave frequencies. A case study of an electronically Reconflgurable PIFA (R-PIFA) is pursued for the detection of temperature abnormalities in human tissue phantom using microwave radiometry, where the performance of the structure is optimized with respect to input impedance matching in multiple frequencies. The optimization of the array is performed using a Genetic Algorithm (GA) tool as a method of choice. Due to its limited physical size, the proposed R-PIFA can also be used as a portable antenna system for deployment in mobile medical applications.

Effect of LVDS link speed and pattern length on spectrum measurements of a Spacewire harness

Link speed and code word length in spacecraft digital systems have a critical effect on equipment design in terms of operation and electromagnetic interference. In this work the behavior of a Low Voltage Differential Signaling / Spacewire link is evaluated through radiated as well as signal spectrum measurements. Various pulse frequencies and pattern lengths were tested and the results indicate that higher pulse frequencies increase the radiated emissions of the system. Radiated emissions are also affected by pattern length, due to the fact that the magnitude and the spacing of the spectral lines vary as the code word length increases.