The five-year Master of Engineering Programme in Dependable Aerospace Systems, with dependability as its silver thread, started at Mälardalen University (MDH) in 2015. This paper presents selected ideas behind the creation of the programme, together with some preliminary analysis of current results and suggested enhancements for the programme’s fourth and fifth years.
This paper compares two dominant Ultra Wide Rand(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.
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 FDTDscheme. This constitutes an electromagnetic scattering problem where a lumped sinusoidal current source, as a source ofelectromagnetic radiation, is included inside the boundary. Confined within the boundary, a specific kind of AbsorbingBoundary 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 FDTDscheme. First, the domain of the problem is chosen to be the free-space without any obstacles. In the second part of thecomputer implementations, a PEC surface is included as the obstacle. The numerical instability of the algorithms can berather easily avoided with respect to the Courant stability condition, which is frequently used in applying the general FDTDalgorithm.
Scattering theory has had a major roll in twentieth century mathematical physics. Mathematical modeling and algorithms of direct,- and inverse electromagnetic scattering formulation due to biological tissues are investigated. The algorithms are used for a model based illustration technique within the microwave range. A number of methods is given to solve the inverse electromagnetic scattering problem in which the nonlinear and ill-posed nature of the problem are acknowledged.
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.
In this paper an experimental prototype of a robot controlled data acquisition system for microwave imaging is presented, where the transmitting and receiving antennas are immersed in a water-tank. The scattered field from the object under test is acquired by using the robot and scanning a single receiving antenna in cylindrical or half spherical coordinates, while the transmitting antenna is fixed at one position with possibilities to be manually moved to different positions. Careful design and construction of the system has given accurate measurements of incident and total field with a SNR of 45dB. A validation of the robot system is performed by comparing measured and computed data for a sunflower oil object.In this paper an experimental prototype of a robot controlled data acquisition system for microwave imaging is presented, where the transmitting and receiving antennas are immersed in a water-tank. The scattered field from the object under test is acquired by using the robot and scanning a single receiving antenna in cylindrical or half spherical coordinates, while the transmitting antenna is fixed at one position with possibilities to be manually moved to different positions. Careful design and construction of the system has given accurate measurements of incident and total field with a SNR of 45dB. A validation of the robot system is performed by comparing measured and computed data for a sunflower oil object.
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 [Keith D. Paulsen and Paul M. Meaney, \Alternative Breast Imaging", The Springer International Series in Engineering and Computer Science, 778, 2005]. The image reconstruction involves a nonlinear inverse scattering problem, which consists to retrieve the dielectric prop- erties of the biological object from the measured scattered field, for an applied incident field. Consequently, the solution is highly sensitive to model errors in the incident field. This paper focus on the impact of this model error on the reconstructed quantitative image using a °exible robotic microwave imaging system, developed at MAalardalen University, together with an itera- tive Newton-Kantorovich (NK) algorithm. This study is conducted during the development of the imaging system and the first quantitative images of a breast phantom are obtained. The robotic microwave imaging system is developed as a °exible experimental platform for biomedical imaging, where one of the applications is breast imaging. Using a robot controlled system the scattered field can be measured with a single transmitting/receiving antenna-pair, thus avoiding the mutual coupling that occur when an antenna-array is used. The scattered field is, herein, measured around a breast phantom, along a circular arc, in the horizontal plane with vertically polarized monopole antennas, considering a two dimensional transverse magnetic case (2D-TM). The radiated field from the transmitting antenna is modeled as a vertical polarized cylindrical wave in the numerical incident field model of the NK algorithm, where images with both the real- and imaginary permittivity profile of the breast phantom are obtained. In this study, two di®erent monopole antenna designs are compared with the numerical incident field model. The di®erence between the antennas is the ground-plane design, where the first setup uses 4 wires forming a horizontal cross as a ground-plane. By varying the length of the wires and angel between the transmitting and receiving antenna the incident electromagnetic field is changed and could be modified to best fit the simulated field. The second setup uses a circular ground plane which will give a more rotational symmetric radiation pattern in the horizontal plane and a better match when comparing measured fields with computed values. The comparison is done directly with the numerical incident field model, as well as the computed and measured scattered field, and finally the impact on the reconstructed images by the NK algorithm are compared, using measured data from both antennas. The results show how the antenna selection impacts the error between the measured incident field and the numerical model, and how the quantitative image of an inhomogeneous object is a®ected by this model error.
In order to create human tissue phantoms for a microwave imaging system, a method to determine the complex permittivity is needed. For this reason a cavity perturbation method has been analyzed and used to perform measurements characterizing the complex permittivity of different fluid mixtures. Results show good agreement on single frequency between the measurement with the reentrant cavity and references. However the complex part of the final material mixture mimicking human tissue are higher than expected, which makes 1.2-propylene glycol inappropriate as a human tissue phantom material. The cavity perturbation method is still a suitable method for measuring liquids and with more work it might even be reliable for gel-based materials.
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 applicator's capability.
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 system for either direct use of diffraction phenomena or indirect use by computational methods for female breast tumor detection is described. The excitation device is a single external non-contacting, sectioned single turn loop, creating an axial magnetic field directed into the breast. A circulating current is created inside it and the diffracted field is directly sensed.
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.
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.
A system and method, as well as sub assemblies thereof, for detection of dielectric irregularities/inhomogeneities inside an object under study (OUS) be means of electromagnetic energy are disclosed. The system comprises a loop/cylinder emitter configured to be located close to the OUS with its axis of symmetry directed towards the OUS. A feeding line feeds the emitter with an alternating current at an operating frequency to cause a magnetic field therein, which in turn will induce a propagating electromagnetic field in the OUS. In order to reduce propagating fields outside of the OUS, the circumference of the emitter is smaller than the free-space wavelength corresponding to the operating frequency, and the feeding line has a characteristic impedance that is smaller than 20 Ohm.
A new and comparatively small type of open-ended microwave applicators has been disclosed. They are for example suitable for transmission into and reception from contacting objects such as protruding human bodyparts for inhomogeneity detection by tomographic methods. The applicators according to the invention are of the dielectric-filled open-ended ridged rectangular TE10 type, with an insert filling the ridge and having a higher permittivity than the surrounding space. The shape of the insert can be as a frustrum pyramid towards the opening. The overall design promotes narrow beamwidths and minimises nearfields and surface wave excitation.
Forskningsområdet mikrovågsavbildning inom medicinen introducerades redan på 1980-talet av Larsen och Jacobi [1]. Objektet var en hundnjure nedsänkt i en mikrovågsabsorberande vätska (bolus) för att undvika störningar och direkt koppling mellan de två roterande antennmatriserna. Man fann att intressant mikrovågskontrastverkan kunde uppnås i biologiska objekt. Fördelar jämfört med mammografi är ex.vis att strålningen är helt ofarlig och att man kan »se» närmare revbenen. Nackdelen är att detaljbilden blir sämre om objektet är stort. Ett relativt enkelt sådant system har utvecklats på MDH [2]. System av denna typ innefattar krav på omfattande matematiska beräkningar för att få fram en bild. Idag anses den ledande utvecklingen ske av Meaney [3] som nu även tar fram ett system på Chalmers i Göteborg. System för stroke- och hjärnblödningsdetektion är under utveckling hos EMTensor i Österrike [4,5] och Medfield diagnostics i Göteborg [6]. Problemen med direkt vågutbredning med s.k. ytvågor längs skallytan blir stora eftersom man inte kan sänka ned skallen i vätska. Absorberande s.k. bolusar och även viss metallisk avskärmning (»huva») används av EM Tensor. En forskningsgrupp under Abbosh [7] har i laboratoriemiljö helt utan störningar lyckats uppnå vissa resultat utan bolusanvändning. Typiska antenner är modifierade kommunikationsantenner och man använder ett spektrum av frekvenser. Återigen blir systemen beräkningsintensiva. På MDH utvecklas f.n. två olika system. Det första har tredimensionella antenner och speciella åtgärder för eliminering av ytvågorna [8] samt kräver matematiska beräkningar som alla de föregående. Det andra bygger på en annan princip: polariserad direktdetektion av den. s.k. diffraktionen från exv. hjärnblödningsområdet och användning av vad som inte är antenner i vanlig mening [9]. Endast mycket enkel bildbehandling krävs, inte heller statistisk träning krävs för framtagning av slutdata så som tillämpas i exv. oljeindustrin för bestämning av olja/vatten/gas med mikrovågsteknik. Sammanfattningsvis karaktäriseras området av ett flertal aktiviteter, varav några pågått i många år. Orsaker till tidsutdräkterna är dels givetvis de allmänna svårigheterna med mikrovågsavbildning, men en ytterligare orsak är att mikrovågsvetenskapen och tekniken i sig är tvärvetenskaplig. En konsekvens av detta är att man inte tillräckligt tidigt ägnat sig åt de speciella ytvågs- och diffraktionsfenomen som kan förbättra mätresultaten.
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.