In this paper, 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 into the load of up to 80% compared to the bolus-based setup that achieved less than 0.1% effectiveness. 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 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.

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 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.

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 $\varepsilon^{\prime}=19.35$ and $\sigma=0.009S/m$ 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.

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.

Microwave heating involves a large number of partially separable electromagnetic phenomena. This chapter provides a review of the evolution of microwave ovens, state-of-the-art descriptions, and many quantitative examples of these, e.g., on Brewster modes, generalized cavity mode theory, edge overheating, the exploding egg effect, and surface wave effects. Two test methods are also given.

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. Key words: Diffraction, magnetic field, applicator, internal inhomogeneity.

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.

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 noncontacting 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.

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 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 ε' = 30 its diameter becomes 40 mm instead of 150 mm for the airfilled version. Additionally and importantly, the dynamic range of the loss factor ε" is 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.

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.

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 Iossy 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.

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.

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 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.