Abstract-A numerical method and experimental technique for microwave imaging of inhomogeuons bodies is presented. This method is based on the interpretation of the diffraction phenomena and leads to tomographic reconstruction of the body under investigation. Various nnmerical examples are given on spatial impulse response, recognition of dielectric rods, inhomogeneous bodies, and simulated human arm. Different experimental results on dielectric rods and isolated animal organs are also given.

-This short paper points out the realizability of a method suitable for quasi reaf-time coherent microwave tomography for biomedical applications.I.

Fig. 2. Isolation versus frequency for passband VSWR = 1.05, fCO= 3.3 GHz, the resistances of the diodes when forward biased (or at high power) for case I and case II, are 2.47 and 1.0 Q respectively. each and one series inductance of 1.9 nH, realized by a short coaxial high-impedance line length. At forward bias or at high power level, the capacitances Cl and C3 will be replaced by the resistances of the diodes. Let us assume that the resistance of each diode is 2.470. The isolation of the switch/limiter is crdculated using~BCD matrices [4] and is given by al = 10log [451 .26+ 2902~2 ] dB (1) where~is the frequency in GHz. al is plotted against frequency as shown in Fig. z Case II: Inductance as the First Element (Fig. 2) For the same specifications as in case I, the low-pass filter elements values are gl = 0.6181, gz =1.2026, g~=1.4130, g4 = 1.2026, and g~= 0.6181. Therefore, L1=L5=~=l.49nH gz-=1.16pF C2 = C4 = znfco~o L = g3zo 3-=3.4nH. 2 ?rfco Therefore, the required switch/limiter with passband VSWR of 1.05 will consist of two diodes with capacitances of 1.16 pF each and three series inductances (1.49 nH at the input, 3.4 nH in between the diodes, and 1.49 nH at the output) realized by short coaxial high-impedance line lengths. At forward bias or high power level, the capacitances C2 and Cl are replaced by diode resistances. In order to compare the merits of the circuits in cases I and II, we have to take p-in diodes of the same cutoff frequency jC. Assuming the same value for reverse-and forward-biased series resistances, we have~C= l/2 TClRl =1/29rC2R2. Therefore, R2 = (C1/C2)Rl =1.0~. Where RI (= 2.47 Q) and R z are the forward-biased series resistances of each diode in case I and case II, respectively. The isolation a2 is calculated using A BCD matrices and is given by [1]

The relative transparency of biological materials to high-frequency electromagnetic waves has encouraged the development of new systems for imaging. This report describes experiments of microwave tomography conducted on a prototype. The object to be analyzed is submerged in water and is illuminated by a plane wave. The total electric field is analyzed by a microwave camera. The recorded data are then processed numerically in order to reconstruct the image that corresponds to the distribution of equivalent currents in a defined plane of a section. Experiments have been conducted on isolated kidneys with and without perfusion. The influence of the perfusing solution temperature has also been studied. These experiments show the potential of this system, especially through the correlation between microwave images and the biological structures. They also confirm previous results concerning spatial resolution and depth of exploration. Finally, the results demonstrate the influence of temperature and support the applicability of this imaging system in non-invasive thermometry, especially for clinical hyperthermia.

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