An Ultra Wide Band (UWB) radar is used to measure the backscattering of a human and a human phantom. The choice of material and shape for the human phantom is discussed. The dielectric properties of the material (wet sand) used in the experiment are measured by a retromodeling technique and also calculated by mixture formulas. The appropriate frequency choice for the application is discussed.
An Ultra Wide Band(UWB) radar is used to measure the cross section of a human phantom indifferent polarizations of the receiver antenna. The choice of material and shape for the human phantom is discussed. The material used in the experiment(wet sand) dielectric properties measured by a retromodeling technique and then calculated by mixture formulas. The appropriate frequency choice for the application is discussed.
This paper presents an experimental comparison study of human movement and presence detection in different environments using ultra-wide-band (UWB) M-Sequence radar. The benchmarking measurements are made in an anechoic chamber and repeated in an open office environment. The wave forms of the background noise and scattered amplitudes of a human body are measured and compared. The result is analyzed and discussed. A set of detection algorithms and filters which are developed to track the human movement and presence is presented and the tracking results in these two environments are compared to each other.
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.
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.
We present significant improvements on in particular our transmitting applicator and its performance. This is a crucial component of our system for direct detection of internal inhomogeneities such as breast tumors and brain hemorrhages by a special transmitting applicator and specially polarized receiving applicators. The operating frequency is about 1 GHz. The transmitting applicator is unique by no need to contact the object under study (OUS) and does not generate any surface waves at it. The primary field has properties behaving as from a magnetic monopole. The overall system allows direct detection without a need for phase measurements, which provides the possibility of using a simple microwave generator and simple rectification and position registration of the received signals. The receiving 3D contacting applicator contains a high-permittivity ceramic and is resonant in order to provide the desired field polarization sensitivity. The desired system properties are achieved by optimized use of the orthogonality properties of the primary magnetic, induced electric, and diffracted electric fields.
The most accurate dielectric measurements are made by resonant cavity methods, the circular TM010 type being the simplest and most common. However, an airfilled such cavity at 1 GHz needs to be 250 mm in diameter. There is another problem as well: its limited applicability with very lossy samples, due to a too low Q value. This paper describes the development and properties of a metalized zirconia ceramic cavity for use at about 1 GHz. With its permittivity εⲠ= 30 its diameter becomes 40 mm instead of 150 mm for the airfilled version. Additionally and importantly, the dynamic range of the loss factor εⳠis greatly expanded. The calibration procedure using numerical retromodelling is described and a measurement example of a ternary alcohol mixture is carried out. The accuracy is also estimated.
Hitherto described microwave modalities for detection of internal inhomogeneities in human tissues such as breasts and heads are by image reconstruction, requiring time-consuming computational resources. The method developed at MDH is instead based on the use of a magnetic field transducer, creating an essentially circular electrical field. This is in turn diffracted by the dielectric inhomogenity and that signal is received by an E-field sensor in an appropriate position. The transmitting applicator is unique by no need to contact the object under study (OUS) and does not generate any surface waves at it. The primary field has properties behaving as coming from a magnetic monopole. The receiving 3D contacting applicator contains a high-permittivity ceramic and is resonant in order to provide the desired field polarisation sensitivity. The desired system properties are achieved by optimized use of the orthogonality properties of the primary magnetic, induced electric, and diffracted electric fields.
We present modified antenna-like devices - applicators - for direct detection of internal inhomogeneities such as breast tumours and brain haemorrhages, at a frequency about 1 GHz. This direct detection provides the possibility of using a simple microwave generator and simple rectification and position registration of the received signals. Direct readouts are thus possible, without any massive computing resources as with tomographic imaging. The transmitting applicator is non-contacting and in free air close to the object. It generates an essentially quasistatic axial magnetic field which induces a circular electric field in the tissue. The receiving 3D contacting applicator contains a high-permittivity ceramic and is resonant. Its mode field provides the desired polarisation sensitivity and filters out the main electric field. The overall system sensitivity for detection of internal inhomogeneities is accomplished by optimised use of the orthogonality of the primary magnetic, induced electric, and diffracted electric fields. When developments are completed, the system will replace or complement existing commercial technologies at a low cost.
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.
Measurements of electric and electromagnetic field for safety controls are made by E field probes, typically with scaling in power flux density, indicating what would be true only for plane propagating waves. This presentation addresses the fact that such measurements at microwave frequencies have to be at a minimum distance from the nearest accessible part of the equipment emitting the field, and describes the different rationales for the validity of the 50 mm distance used since many years with e.g. microwave ovens and industrial equipment. – Since the emission of electric field energy dominates over that from the magnetic field in high frequency equipment, almost quasistatic E field emission conditions occur, resulting in a much weaker power absorption in human tissues than assumed in the existing safety standards. The phenomena are quantified, and a relaxation of the E field emission limits in industrial standards is proposed for such non-radiating conditions, as is a 150 mm minimum measurement distance in combination with barriers, etc., hindering access. – In induction equipment, the quasistatic magnetic fields instead dominate, and there is again a much weaker power absorption in human tissues than assumed in the existing safety standards. Some methods for safety assessments will be given in the oral presentation only, due to the limited space in this manuscript.
The tendency of arch-trapped microwave propagation at curved surfaces is a kind of diffraction which needs more attention in the development of measurement systems, from the oil industry to the investigations using antenna applicator systems for biological objects. We develop equations for propagation in very lossy substances in metal pipes. Similar such propagation occurs at the periphery of rounded objects in air, where also surface wave effects occur and can cause measurement problems. We show a modified contacting antenna applicator minimizing arch-trapped as well as surface waves.
Hitherto described microwave modalities for detection of internal inhomogeneities in human tissues such as breasts and heads are by image reconstruction, requiring time consuming computational resources. The method developed at MDH is instead based on the use of magnetic field transducer, creating an essentially circular electrical field. This is in turn diffracted by the dielectric inhomogeneity and that signal is received by an E-field sensor in an appropriate position.
Various medical and industrial equipment types with electric fields having frequencies in the range 13 to 40 MHz have a long history. The relative simplicity of the generators and applicators (i.e. the assembly which is adapted for the treatment) have led to equipment manufacturing by many small companies having insufficient knowledge about human exposure hazards. The international regulations on maximum allowed exposure are not well-developed and mainly concern limits of the measured electric field, so-called reference levels, which are set to low values considered to be safe under all possible conditions. – Quite some scientific work on the field characteristics has been carried out since the 1970’s, the goal in many cases having been to motivate further research grants rather than assisting industry in improving safety by proposing more detailed regulations. In particular, researchers have used the electric field strengths as measured, without consideration of the field curvature and decay rate from the equipment, and by also using a too simplistic approach to the “power flux density” of the field emission. – As a consequence of the above, it is estimated that over 90 % of today’s operational equipment does not fulfill these simple regulations. In spite of that, very few incidents or accidents are reported. – New ongoing work by the International Electrotechnical Commission (IEC; committee 27) is now explaining this. The work is based on advanced numerical modelling of typical kinds of equipment and humans in different postures of arms and hands. Some results will be demonstrated and indicate that from five to more than twenty times stronger fields can be accepted under conditions of limited direct access to the energised equipment parts such as electrodes and rails, and proper design of the system grounding.
In this article, we present an air-based approach to irradiate the female breast with electromagnetic microwave radiation by means of contactless evanescent near-field coupling for medical applications. A suitable transducer, so-called applicator, is presented, designed to create a TE-polarized evanescent field at approximately 4 GHz, reducing stray radiation and other unwanted first-order interactions at the breast surface without the need for a dielectric bolus liquid. Initial numerical investigations showed that the applicator setup achieves a 20-dB higher signal-to-clutter ratio (SCR) than a comparable bolus-based setup when applied to a simple high-adipose breast phantom. In the case of a low-adipose test load, the SCR could not be readily attributed to the presence of a tumor, yet it was found that under realistic conditions, the applicator setup achieves a significantly higher power transmission Effectiveness (EFF) into the load of up to 80% compared to the bolus-based setup that achieved less than 0.1% EFF. Experimental measurements of the applicator show a change of resonance frequency of less than 2% for load permittivities ranging from 1 to 80, enabling the applicator to be used for a wide span of patient-specific dielectric breast properties.
In this paper, we present the latest design of a magnetic field applicator designed to expose a dielectric body to electromagnetic microwave radiation by means of a magnetic near-field for microwave imaging purposes. Numerical simulations show that unwanted surface waves created from electric fringing fields of the applicator can be separated from the desired fields inside the breast due to their different polarizations. The applicator working principle is demonstrated in an experimental measurement setup with three different tissue-mimicking loads. A propagating electromagnetic wave is invoked directly inside the load based on its dielectric properties, leading to a decreasing reflection coefficient with increasing load permittivity, which could be verified in numerical simulations and experimental measurements.
A common problem in microwave imaging of human body parts is the creation of unwanted surface waves due to permittivity mismatch between the object under test (OUT) and the surrounding space. These waves propagate more easily along the surface of the OUT and can overshadow the desired signal from an inner inhomogeneity (e.g. a tumor). Submerging the OUT into a matching bolus liquid has proven to reduce surface waves, yet also to increase the overall signal attenuation. In this paper we present a novel applicator concept that can be used to effectively illuminate the human breast without the need for such a bolus liquid. Electromagnetic simulations show that the applicator creates almost no surface waves even if placed 1 mm away from a simplified breast model. An estimation of the applicator performance in a realistic measurement scenario is made using a detailed breast model from the UWCEM Numerical Breast Phantoms Repository in the simulation.
In this study we present a permittivity measurement technique based on retro-modelling of a resonant cavity in the frequency range from 2.2 to 2.6 GHz that allows for a more arbitrary sample shape than traditional cavity perturbation techniques. It is shown that the resolution of the retro-modelling technique can be improved if the invoked modes in the sample and in the surrounding cavity space are of different type or indexation, a condition that must clearly be avoided in classical perturbation techniques. The measurement method was applied to a ceramic sample of unknown permittivity which was retro-modelled to "0 = 19.35 and = 0.009 S/m with a remaining combined error of geometry and permittivity deviations between measurement and simulation of <0.1% in frequency and 22% in Q-value at the target resonance. This technique will allow us to identify suitable dielectric materials to improve the feed efficiency of our magnetic field applicator which is currently being developed for microwave breast cancer detection.
In this paper, we investigate if external resonances created at a spherical tumor model can be utilized to increase the contrast between the tumor and background field in a simple microwave breast imaging scenario. Numerical simulations are being performed for two cases, low-adipose and high-adipose average breast tissue, exhibiting high and low permittivity and dielectric losses, respectively. The electric field is probed along the breast surface with and without a spherical tumor model present, and the relative tumor signal with respect to the background field is separated into a surface-normal and surface-parallel component. It is shown that in the high-adipose case, an external spherical resonance is created at the tumor, whereas no clear resonance occurs in the low-adipose case. In both cases is the contrast between the tumor signal and the background field stronger in the surface-normal than in the surface-parallel component. The external tumor resonance could directly be observed in the high-adipose case as a decrease of field strength close to the tumor if placed in close proximity to the breast surface.
In this paper, we present a numerical simulation scenario to estimate the signal strength of a tumor in a microwave detection scenario containing a magnetic near-field applicator and a quarter-wave dipole as transmitter and receiver, respectively. Two different receiver orientations are tested on two different breast phantoms representing high-adipose and low-adipose bulk breast tissue. The tumor signal strength is estimated by subtracting the received signals acquired with and without a tumor being present. The results indicate that in the horizontally aligned receiver case, the presence of a tumor can be estimated from the receiver positions exhibiting the highest difference signals. The strongest difference signals however do not occur at the frequency of operation but below. The other cases are not conclusive, but a stronger tumor signal was received with the horizontally aligned receiver than with the vertically aligned one throughout.