Extensive simulation experiments have been carried out on the DC and high-frequency characteristics of α-(4H) Silicon Carbide based double-drift (p⁺⁺ p n n ⁺⁺ type) impact avalanche transit time (IMPATT) diodes at two important millimeter-wave window frequencies (35 and 140 GHz). The studies reveal that the IMPATT diode designed at Ka-band (at around 35.0 GHz) may yield an RF power density of 10.72 × 10 ¹² Wm⁻² with an efficiency of 21.5%, whereas the D-band (at around 140.0 GHz) IMPATT is capable of delivering an RF power density of 0.38 × 10 ¹² Wm⁻² with an efficiency of 15.0%. These results are very encouraging to choose SiC as a suitable base material for developing high-power and high-frequency IMPATT ­diodes. ­Impurity charge spikes are introduced in the flatly doped n and p regions of the double-drift diodes in the form of single low-high-low (p ⁺⁺ p p ⁺ p n n ⁺ n n ⁺⁺ type) bump. The effects of this charge bump on the mm-wave characteristics of the double-drift 4H-SiC IMPATTs are analyzed for the first time, through a modified simulation technique. It is interesting to note that the introduction of charge spikes improves the overall performance of the designed diodes at the window frequencies.

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This paper introduces a new functional architecture, together with a direct and efficient method of estimating signal parameters of a single pulse radar, in an electronic warfare digital receiver. The implemented architecture consists of three main units connected through different buffer hierarchy. These units are: Data acquisition and pre-processing unit; data analysis and radar parameter estimation unit; and the human computer interface unit. These units, invoked independently, allowed simple algorithms to be executed concurrently. In the data acquisition unit, the signal is digitized continuously after it is down converted into intermediate frequency signal. This signal is then converted into a video signal which stores radar pulse data upon signal existence. A double threshold noise gate is deployed, together with moving average sampling filter, to refine incoming data steam and avoid multi-triggering problem. In the data analysis unit, the processed radar signal parameters are estimated. This includes the estimation of intermediate ­frequency, pulse width, time of arrival, time of departure, pulse repetition interval and pulse amplitude.

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In medical imaging, image denoising has become a very essential exercise all through the diagnosis. Compromise between the preservation of useful diagnostic information and noise suppression must be respected in medical ­images. One of the ultimate goals of an imaging modality is to provide the clinician with the best possible information needed to make an accurate diagnosis. Ultrasound images suffer from an intrinsic artifact called speckle. Speckle degrades spatial and contrast resolution and obscures the underlying anatomy. Thus, it seems sensible to reduce speckle ­artifacts before performing image analysis, provided the image that might distinguish one tissue from another is preserved. The main goal of this thesis was the development of novel methods for suppression of speckle in medical ultrasound images in the wavelet domain. We have adopted weighted variance for estimating the threshold and multiscale product scheme for thresholding the coefficients. To employ the wavelet interscale dependencies, the adjacent wavelet subbands are multiplied. Multiplying the adjacent wavelet scales would sharpen the important structures while reducing noise. In the multiscale products, edges can be efficiently discriminated from noise. Then, an adaptive threshold was calculated and imposed on the products, instead of on the wavelet coefficients, to identify important features. Fundamentally speckle noise is a signal-dependent one, and so weighted variance of each background pixel was taken into account while calculating threshold. Experiments show that the proposed scheme better suppresses noise and preserves edges than other wavelet-denoising methods. Experiments with synthetic and real ultrasound imagery show that the proposed method improves the signal-to-noise ratio and preserves edge clarity.

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Chaotic dynamics of electronic circuits and systems is attracting the interest of researchers for the last few decades, mainly because of its potential for application in electronic communication systems. Different methods can be proposed to drive a microwave Gunn oscillator into chaotic mode. Among them, an injection-locked Gunn oscillator driven by a weak co-channel signal may be a feasible technique. The present work considers this method through a hardware experiment and finds that under certain conditions of interference strength and detuning, chaotic oscillations of a Gunn oscillator can be observed.

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Computer-aided analytical studies and physical understanding of important characteristics of some commonly used left-handed material (LHM) structures (wire-array and split-ring resonator), to realize negative effective ­permittivity and permeability leading to negative refractive index over a desired frequency band have been reported in this ­paper. The transmission of electromagnetic wave through LHMs and right-handed materials (RHMs) has some ­fundamental differences. This issue of electromagnetic wave transmission through LHM has been characterized, and a ­physical ­insight of the phenomena has also been included. The LHM characterization using computer-aided ­analytical ­modeling shows good agreement with the previous numerical simulation and experimental results reported for such microstructures operating at microwave frequencies.

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Impedance glottography, or electroglottography, is a noninvasive technique for monitoring the variation of the degree of contact between the vibrating vocal cords during voice production. Electrical impedance is sensed using a pair of electrodes placed on either side of the larynx, by injecting a low-level high-frequency current. A wide-band impedance detector circuit has been developed using a precision rectifier based on voltage feedback clamping amplifier and approximately linear-phase lowpass filter. The circuit can be used for obtaining electroglottogram signal for diagnosis of vocal fold disorders.

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