Three-dimensional Magnetic Induction Tomography: Improved Performance for the Center Regions inside a Low Conductive and Voluminous Body

Magnetic induction tomography (MIT) is a contactless technique that is used to image the distribution of passive electromagnetic properties inside a voluminous body. However, the central area sensitivity (CAS) of this method is critically weak and blurred for a low conductive volume. This article analyzes this challenging issue, which inhibits even faint imaging of the central interior region of a body, and it suggests a remedy. The problem is expounded via two-dimensional (2D) and three-dimensional (3D) eddy current simulations with different transmitter geometries. On this basis, it is shown that a spatially undulating exciter coil can significantly improve the CAS by >20 dB. Consequently, the central region inside a low conductive voluminous object becomes clearly detectable above the noise floor, a fact which is also confirmed by practical measurements. The improved sensitivity map of the new arrangement is compared with maps of more typical circular MIT geometries. In conclusion, 3D MIT reconstructions are presented, and for the same incidence of noise, their performance is much better with the suggested improvement than that with a circular setup.

Characterization and Modeling of Photoconductive GaN Ultraviolet Detectors

In this work high gain GaN photoconductive UV detectors have been fabricated and characterized, and a novel gain mechanism, dominant in these detectors, is described. DC responsivities higher than 103A/W have been measured for an incident power of lW/m2 at room temperature. The photoconductive gain depends directly on the bias voltage and scales with incident power as P−k (k ≈ 0.9) for more than five decades. A decrease of both gain and k parameter with temperature has also been observed. As a consequence of the slow non-exponential transient response, AC gain measurements result in lower values for gain and k parameter, which are frequency dependent. The high responsivity, non-linear behavior and slow non-exponential transient response, are all modeled taking into account a modulation mechanism of the layer conductive volume. Such spatial modulation is due to the photovoltaic response of the potential barriers related to the surface and charged dislocations arrays.

CONTINUOUS CONDUCTIVE VOLUME AFFECTS THE PROPAGATION OF SIGNALS IN DISCRETE SYSTEMS

The effect of a continuous conductive volume on the propagation of signals in discretely coupled nonlinear electronic circuits is presented. Two different coupling mechanisms between the circuits are considered at the same time (through linear resistors and through a continuous conductive volume) trying to mimic the behavior observed in some experiments from cardiac electrophysiology. The effects of the geometry of the conductive medium and the distance from the measuring point to the electronic fiber are studied experimentally.