A quantitative imaging method is proposed based on microwave measurements where a direct inversion in real space is employed. The electrical properties of penetrable objects are reconstructed using a resolvent kernel in the forward model, which is extracted from calibration measurements. These measurements are performed on two known objects: the reference object (RO) representing the scatterer-free measurement and the calibration object representing a small scatterer embedded in the RO. Since the method does not need analytical or numerical approximations of the forward model, it is particularly valuable in short-range imaging, where analytical models of the incident field do not exist while the fidelity of the simulation models is often inadequate. The experimentally determined resolvent kernel inherently includes the particulars of the measurement setup, including all transmitting and receiving antennas. The inversion is fast, allowing for quasi-real-time image reconstruction. The proposed technique is demonstrated and validated through examples using simulated and experimental data. Its performance with noisy data is also examined. The concept of experimentally determined resolvent kernel in the forward model may be valuable in other imaging modalities such as ultrasound, photonic imaging, electrical-impedance tomography, etc.

We present a light emitting diode (LED)-based ultramini digital micromirror device projector with a size of 75 mm x 67 mm x 42 mm and a weight of 338 g. The LED illuminator inside this projector makes it possible to achieve a volume of 18 cm(3) by using a dichroic filter and a collimating lens. The illumination system consists of high uniformity of 93% through a microlens array as a homogenizer. A total internal reflection prism is also used to reduce the size of both the illumination system and the telecentric projection lens. A projection lens system with an ultrasmall track of 42 mm, including a high modulation transfer function value of 0.4 at 46.2 line pairs/mm, an optical distortion of only 0.25 %, and a television distortion of 0.01%, is designed. Through the above superior specification, we can produce a 20 in. (51 cm) color display comparable in brightness to a laptop with a contrast of 3700:1. The device is compact and suitable for personal use.

The influence of the size of an n-electrode and a current blocking layer (CBL) on the thermal and electrical characteristics of a vertical-injection GaN-based light emitting diode (LED) chip is investigated by numerical simulation. The predicted forward voltages are quite consistent with previous experimental data. The coupled thermal and electrical effects affect the performance of a LED chip. For cases without a CBL, the variation in current density and temperature distributions in the active layer, and the forward voltage and Joule heating percentage of the LED chip increase as the n-electrode width (L) decreases. The current crowding and temperature of the hot spot are very significant, although the wall-plug efficiency (WPE) is the highest one obtained for L=100μm . The better width of the n-electrode in terms of the uniformity of temperature, current density distribution, WPE, and forward voltage may be the case where L=200μm . The insertion of a CBL into a 600×600μm chip leads to greater uniformity in the distribution of the current density in the effective light-emitting area when L=500μm . A more uniform temperature distribution in the active layer occurs when L=200μm , while the case when L=300μm has the maximum WPE.

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