Magnus Otterskog

Modelling of propagation environments inside a scattered field chamber

Measurements on communication devices for evaluation of diversity and/or MIMO concepts must be made in the real environment or in a model of the real propagation environment. As a first step towards a complex, physical environment model the plane wave angular distribution, incident on the device under test (DUT), is altered in order to model plane wave angular distributions of real environments. Here a specialized reverberation chamber called the scattered field chamber (SFC) is used to create a source of Rayleigh faded plane waves and a shielded anechoic box with apertures is used to alter the angular distribution of the plane waves incident on the DUT. According to the measurements made, the model seems to be able to produce data that show agreement with measurements made on real propagation environments.

Experiments and numerical modelling of contacting antenna applicators at a free space head model

Microwave absorbing boluses or similar are impractical, particularly in stroke emergencies, since the creation of surface waves around the head dominating over the internal signal paths is then a problem. The performance of miniaturised ridged waveguide applicators in the frequency interval 1 to 3 GHz designed for the application of breast cancer detection are used in this study, slightly modified, on head models for investigation of disturbing surface waves.

Antenna applicator design for microwave imaging of the interior of human breasts

In this paper we introduce a waveguide antenna applicator design intended to be placed on the surface or in close proximity to a human breast for imaging purposes. Hence, the antenna needs to be compact for easy placement. The design process is carefully carried out dividing the antenna applicator into separate parts, allowing closer analysis towards improved synthesis. A mode applicator antenna was concluded to be necessary, employing a TE10 mode type with minimized near-field and surface (Zennek) wave excitation. Numerical simulations have been used throughout and show that the proposed ridged waveguide antenna is capable of fulfilling the design requirements and the performance goals. Modelling has been carried out using a scenario with a simple breast model and confirms the applicators capability.

Antenna applicator concepts using diffraction phenomena for direct visualization of brain hemorrhages

Direct use of diffraction phenomena at an irregularity in a lossy object such as a head is described. The source is an external magnetic field directed into the skull, creating a circulating current inside the object by which surface waves are avoided. The receiving E-field probe is a 3D resonant structure being selectively sensitive to the desired deflected electric field component from the surface.

A multi-layered head phantom for microwave investigations of brain hemorrhages

A head phantom for microwave investigations is developed. It consists of a skull bone with realistic dielectric properties of cancellous and cortical bone. The skull phantom is filled with liquids and semi-solids that dielectrically represent the white/gray matter and blood, respectively.

Antenna Modeling Issues in Quantitative Image Reconstruction Using a Flexible Microwave Tomography System

Quantitative microwave imaging has been extensively studied in the past years as an alternative technique in biomedical imaging, with a strong potential in early stage breast can- cer detection [Ke ...

Breast tumour detection by two microwave antenna principles

A comparison between breast tumour detection with a traditional lossy coupling medium based system and a system without coupling medium is performed, by numerical modelling and experimentally. While a system with lossy coupling medium offers surface wave reduction and protection from surrounding sources and obstacles it also demands good permittivity matching of the coupling medium to the breast tissue under investigation, as well as a high performance measurement system with a dynamic range exceeding 100 dB. The system without coupling medium offers possible direct detection of inhomogeneities with transmission losses of about 50…60 dB. The proposed contacting antenna system however needs further development in order to reduce stray fields and adoption to realistic breast tissue properties.

Experimental comparison study of UWB technologies for static human detection

This paper compares two dominant Ultra Wide Band(UWB) radar technologies Impulse and M-sequence for static human being detection in free space. The hardware and software platform for each system is described separately. These two radar platform performances are tested in real conditions and the results show that M-sequence UWB radar is better suited for detecting the static human target in larger distances.

A study of different fabrics to increase radar cross section of humans.

This purpose of the study was to increase the visibility on radar for unprotected pedestrians with the aid of conducting fabric. The experiment comprised measurements of four types of fabric to determine the radio frequency properties, such as radar cross section (RCS) for the vehicle radar frequency 77 GHz and transmission (shielding) in the frequency range 3-18 GHz. Two different thicknesses of polypyrrole (PPy) nonvowen fabric were tested and one thickness for 30 % and 40 % stainless steel fabrics respectively. A jacket with the thinner nonvowen material and one with 40 % steel were tested and compared to an unmodified jacket in the RCS measurement. The measurement showed an increase in RCS of 4 dB for the jacket with the 40 % steel lining compared to the unmodified jacket. The transmission measurement was aimed at determining the fabric with the highest transmission of an incoming radio wave. The 30 % steel fabric and the two thicknesses of the nonvowen fabrics were tested. One practical application is for example the use of radar reflective material in search and rescue (SAR) clothes. The study showed that the 30 % steel fabric was the best candidate for further RCS measurements.

Solution of two-dimensional electromagnetic scattering problem by FDTD with optimal step size, based on a semi-norm analysis

To solve the electromagnetic scattering problem in two dimensions, the Finite Difference Time Domain (FDTD) method is used. The order of convergence of the FDTD algorithm, solving the two-dimensional Maxwell’s curl equations, is estimated in two different computer implementations: with and without an obstacle in the numerical domain of the FDTD scheme. This constitutes an electromagnetic scattering problem where a lumped sinusoidal current source, as a source of electromagnetic radiation, is included inside the boundary. Confined within the boundary, a specific kind of Absorbing Boundary Condition (ABC) is chosen and the outside of the boundary is in form of a Perfect Electric Conducting (PEC) surface. Inserted in the computer implementation, a semi-norm has been applied to compare different step sizes in the FDTD scheme. First, the domain of the problem is chosen to be the free-space without any obstacles. In the second part of the computer implementations, a PEC surface is included as the obstacle. The numerical instability of the algorithms can be rather easily avoided with respect to the Courant stability condition, which is frequently used in applying the general FDTD algorithm.