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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 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.

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.

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.

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.

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.

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.