André Vander Vorst

Microwave properties of metallic nanowires

We report on the microwave properties of arrays of parallel magnetic nanowires constituted of nickel, cobalt, or Ni/Fe alloy embedded in nanoporous track-etched polymer membranes. The experiments consist of transmission measurements carried out on microwave stripline structures using a magnetically loaded membrane as the substrate. Measurements were performed at frequencies ranging from 100 MHz to 40 GHz and under static magnetic fields up to 5.6 kOe applied along the wires axis. Resonance phenomena have been observed in the magnitude of the complex transmission coefficient at frequencies which depend on the nature of the material and applied static magnetic field. Results are consistent with those expected for a ferromagnetic resonance (FMR) experiment and the observed behaviors are analyzed in the framework of the classical FMR theory

Experimental thermographic analysis of thermal effects induced on a human head exposed to 900-MHz fields of mobile phones

This paper summarizes the results of an experimental research of thermal effects induced by electromagnetic exposure to wireless mobile communication equipment. A series of experiments has been performed in order to examine the time evolution of the temperature of some body-part surfaces exposed to electromagnetic radiation emitted by global system for mobile communication mobile phones (900 MHz). Special attention has been paid to the analysis of the human head, as this is the human part mainly exposed in normal conditions of mobile phone use.

Results of a Long-Term Low-Level Microwave Exposure of Rats

This paper summarizes the results of experimental research on biological effects induced by electromagnetic exposure to low-level microwaves. We exposed four-month-old Wistar albino rats during 21 months to two different microwave frequencies and exposure modes, 2 h a day, seven days a week. In order to assess possible biological effects of microwaves, we selected among others the following parameters: leucocytes, erythrocytes, monocytes, neutrophils, lymphocytes, hemoglobin, mean corpuscular hemoglobin concentration, and mortality rate. After three and eight months of exposure, we found a statistically significant difference of about 20% between the 970-MHz continuous wave group and sham-exposed group regarding the monocytes in both considered periods. After 14 and 18 months of exposure, we observed a significant increase in white blood cells and neutrophils of about 15% and 25%, respectively. Lymphocytes fell down after 18 months of exposure with about 15% compared to the sham-exposed group. No other statistically significant differences were found, except for minor changes with little biological significance. The most obvious effect we detected is the increase in mortality rate of the exposed groups with respect to the sham-exposed group after 21 months of exposure at the age of 25 months. This increase even increases when observing rats until the age of 28 months: mortality in exposed groups then reaches almost twice the value observed in the sham-exposed group.

Laboratory UWB GPR system for land mine detection

In this paper, the design and the modeling of an indoor impulse UWB GPR systems (1 GHz - 5 GHz), built in the scope of the HUDEM project, is presented. For an impulse UWB system, a time-domain modeling is an obvious choice. We explain how the antennas can be characterized by their normalized impulse response. By considering the antenna as a convolution operator, we get a mechanism for modeling the whole radar system as a cascade of linear responses, which gives a lot of advantages and possible application. In our research it is used to express the radar range equation in the time-domain, to optimize the antenna configuration and to tune signal- processing algorithms. The deconvolution of the signal source and antenna impulse responses is an ill posed operation. In this paper we present a method for decomposing an A-scan in a linear combination of wavelets, using the Continuous Wavelet Transformations -- by properly choosing the mother wavelet. This technique can also be used to reduce the amount of data for further processing. Finally results obtained by our UWB GPR system are shown. Advantages and shortcomings are discussed.

Migration technique based on the time-domain model of the Ground Penetrating Radar

Migration is a common name for processing techniques that try to reconstruct, from the dat recorded at the surface, the reflecting structures in the sub-surface. Most of the existing migration techniques do not take into account the characteristics of the acquisition system and the ground characteristics. We propose a novel migration method, applicable on Ground Penetrating Radar (GPR) images, that integrates the time domain model of the GPR in the migration scheme. We calculate by forward modeling a synthetic 3D point spread function of the GPR, i.e. a synthetic C-scan of a small point scatterer. The 3D point spread function, containing system characteristics like the waveform of the excitation source, the combined antenna footprint and the impulse response (IR) of the antennas, is then used to deconvolve the recorded data. Results of this migration method on real data obtained by an ultra-wideband GPR system show that the migration method is able to reconstruct the top contour of small targets like AP mines, in some cases even the correct dimensions. The method is also capable of migrating oblique targets into their true position. The migration scheme is not computational intensive and can easily be implemented in real time.

Biological Effects of Microwaves in Acupuncture

Microwave acupuncture is a very interesting field of investigation. The biological effects of microwaves offer general interesting developments, and microwave acupuncture more specifically is rather intriguing, being in the border area of three fields : microwaves, acupuncture, and neurophysiology. The paper will describe the microwave equipment which delivers a set of spectral lines extending from 0.2 to 3.0 GHz, with a maximum power of a few watts. Antalgic effects have been measured in experiments on rabbits. Essentially three methods are compared : absorption of Fentanyl (painkiller), acupuncture effects amplified by electric discharges, and microwave acupuncture.

An analytical small-signal bias-dependent nonuniform model for p-i-n traveling-wave photodetectors

A fully analytical small-signal model is developed for the frequency response of traveling-wave photodetectors. It takes into account the dependence of the equivalent transmission-line admittance on the position, induced by the nonuniform distribution of the optical beam along the traveling direction. Moreover, the influence of the bias voltage on the transit time has been accurately investigated. The model is applied to the design of an InAlAs-InGaAs p-i-n photodetector. Its performances are investigated in term of electrical bandwidth.

First Results of a Long-Term Epidemiological Study on Low-Level Microwave Exposure of Rats

The general public applications of microwaves are essentially the cellular phone and the microwave oven. Some years ago, articles in the national and international press started to express concern about cancer incidences among radar technicians and people housed in the neighborhood of antenna base stations. In this study, a possible link between microwave exposure and the physiological and cellular changes is being evaluated by an epidemiological long-term animal study on 120 rats, for 21 months. In order to assess the possible biological effects of microwaves, we selected among others the following parameters: lymphocytes, monocytes, granulocytes, erythrocytes and blood platelets

Time-domain modeling of UWB GPR and its application to land mine detection

In this paper, the time domain modeling of an indoor impulse UWB GPR systems, built in the scope of the HUDEM project, is presented. For an impulse UWB system, a time-domain modeling is an obvious choice. We explain how the antennas can be characterized by their normalized impulse response. By considering the antenna as a convolution operator, we get a mechanism for modeling the whole radar system as a cascade of linear response, which gives a lot of advantages and possible application. In our research it is used to express the radar range equation in the time-domain, to optimize the antenna configuration and to calculate the point-spread function of the UWB GPR at a given depth. The point-spread function can be used for migration by deconvolving it from the collected data. In this way the migration method takes into account the characteristics of the radar system. Finally, results of this migration method on data obtained by our UWB GPR system are shown.

Experimental evidence of mounting grooves and serration patterns on fin lines characteristics

In this paper, the mounting grooves and serration patterns of fin line circuits are investigated experimentally. Our measurements show that the short-circuit ended mounting grooves degrade seriously the insertion loss of fin lines at the low frequencies of the band. The open ended mounting grooves are found better for fin lines applications and measurements. An improvement of 0.7 dB is observed over the whole band, when the serration patterns of the fin line are placed into the open-ended mounting grooves. These results can be used for measuring the losses and for designing transitions or other fin line circuits.