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.

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 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.