Approved for public release; distribution is unlimited / This report discusses the theory, design, implementation and testing of a personal computer-based Multi-Frequency Modulation (MFM) packet communications system. Transmitter/receiver programs provide software drivers for D/A and A/D boards and perform symbol encoding, modulating, demodulating and decoding. The design and construction of a polarity coincidence correlator for receiver packet synchronization is presented. Experimental results show that the implemented MFM communication system conforms to theoretical analysis with acceptable bit error. Results also show the MFM can be uniquely adapted to a specific channel. / http://archive.org/details/implementationof00gant / Lieutenant, United States Navy

This thesis considers the feasibility of using the electromagnetic techniques to monitor the wear of the refractory base of a glass-making furnace. The research focuses in building a system that is able to provide measurements of the distance to the molten glass in this demanding high temperature application. The main challenge in this project is to eliminate the effect of the refractory supporting steel structure and still be able to detect and exploit a much smaller signal from the molten glass. In order to differentiate between the molten glass and the steel supports, a multi-coil, multi-frequency technique was proposed, studied and implemented in this research.

The inverse source problem for the Helmholtz equation is studied. An unknown source is to be identified from the knowledge of its radiated wave. The focus is placed on the effect that multi-frequency data has on establishing uniqueness. In particular, we prove that data obtained from finitely many frequencies is not sufficient. On the other hand, if the frequency varies within an open interval of the positive real line, then the source is determined uniquely. An algorithm is based on an incomplete Fourier transform of the measured data and we establish an error estimate under certain regularity assumptions on the source function. We conclude that multi-frequency data not only leads to uniqueness for the inverse source problem, but in fact it contributes with a stability result for the reconstruction of an unknown source.

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Future microprocessor poses many challenges to its dedicated power supplies, the voltage regulators (VRs), such as the low voltage, high current, fast load transient, etc. For the VR designs using multiphase buck converters, one of the results from these stringent challenges is a large amount of output capacitors, which is undesired from both a cost and a motherboard real estate perspective. In order to save the output capacitors, the control-loop bandwidth must be increased. However, the bandwidth is limited in the practical design. The influence from the switching frequency on the control-loop bandwidth has not been identified, and the influence from multiphase is not clear, either. Since the widely-used average model eliminates the inherent switching functions, it is not able to predict the converter's high-frequency performance. In this dissertation, the primary objectives are to develop the methodology of high-frequency modeling for the buck and multiphase buck converters, and to analyze their high-frequency characteristics. First, the nonlinearity of the pulse-width modulator (PWM) scheme is identified. Because of the sampling characteristic, the sideband components are generated at the output of the PWM comparator. Using the assumption that the sideband components are well attenuated by the low-pass filters in the converter, the conventional average model only includes the perturbation-frequency components. When studying the high-frequency performance, the sideband frequency is not sufficiently high as compared with the perturbation one; therefore, the assumption for the average model is not good any more. Under this condition, the converter response cannot be reflected by the average model. Furthermore, with a closed loop, the generated sideband components at the output voltage appear at the input of the PWM comparator, and then generate the perturbation-frequency components at the output. This causes the sideband effect to happen. The perturbation-frequency components and the sideband components are then coupled through the comparator. To be able to predict the converter's high-frequency performance, it is necessary to have a model that reflects the sampling characteristic of the PWM comparator. As the basis of further research, the existing high-frequency modeling approaches are reviewed. Among them, the harmonic balance approach predicts the high-frequency performance but it is too complicated to utilize. However, it is promising when simplified in the applications with buck and multiphase buck converters. Once the nonlinearity of the PWM comparator is identified, a simple model can be obtained because the rest of the converter system is a linear function. With the Fourier analysis, the relationship between the perturbation-frequency components and the sideband components are derived for the trailing-edge PWM comparator. The concept of multi-frequency modeling is developed based on a single-phase voltage-mode-controlled buck converter. The system stability and transient performance depend on the loop gain that is affected by the sideband component. Based on the multi-frequency model, it is mathematically indicated that the result from the sideband effect is the reduction of magnitude and phase characteristics of the loop gain. With a higher bandwidth, there are more magnitude and phase reductions, which, therefore, cause the sideband effect to pose limitations when pushing the bandwidth. The proposed model is then applied to the multiphase buck converter. For voltage-mode control, the multiphase technique has the potential to cancel the sideband effect around the switching frequency. Therefore, theoretically the control-loop bandwidth can be pushed higher than the single-phase design. However, in practical designs, there is still magnitude and phase reductions around the switching frequency in the measured loop gain. Using the multi-frequency model, it is clearly pointed out that the sideband effect cannot be fully cancelled with unsymmetrical phases, which results in additional reduction of the phase margin, especially for the high-bandwidth design. Therefore, one should be extremely careful to push the bandwidth when depending on the interleaving to cancel the sideband effect. The multiphase buck converter with peak-current control is also investigated. Because of the current loop in each individual phase, there is the sideband effect that cannot be canceled with the interleaving technique. For higher bandwidths and better transient performances, two schemes are presented to reduce the influence from the current loop: the external ramps are inserted in the modulators, and the inductor currents are coupled, either through feedback control or by the coupled-inductor structure. A bandwidth around one-third of the switching frequency is achieved with the coupled-inductor buck converter, which makes it a promising circuit for the VR applications. As a conclusion, the feedback loop results in the sideband effect, which limits the bandwidth and is not included in the average model. With the proposed multi-frequency model, the high-frequency performance for the buck and multiphase buck converters can be accurately predicted. / Ph. D.

Cette thèse contient deux matières différentes. Dans la première partie, deux cas sont considérés. L'un est le modèle plus lisse de la plaque mince et l'autre est les équations des limites elliptiques avec des données limites incertaines. Dans cette partie, les convergences stochastiques des méthodes des éléments finis sont prouvées pour chaque problème.Dans la deuxième partie, nous fournissons une analyse mathématique du problème inverse linéarisé dans la tomographie d'impédance électrique multifréquence. Nous présentons un cadre mathématique et numérique pour une procédure d'imagerie du tenseur de conductivité électrique anisotrope en utilisant une nouvelle technique appelée Tentomètre de diffusion Magnéto-acoustographie et proposons une approche de contrôle optimale pour reconstruire le facteur de propriété intrinsèque reliant le tenseur de diffusion au tenseur de conductivité électrique anisotrope. Nous démontrons la convergence et la stabilité du type Lipschitz de l'algorithme et présente des exemples numériques pour illustrer sa précision. Le modèle cellulaire pour Electropermécanisme est démontré. Nous étudions les paramètres efficaces dans un modèle d'homogénéisation. Nous démontrons numériquement la sensibilité de ces paramètres efficaces aux paramètres microscopiques critiques régissant l'électropermécanisme. / This thesis contains two different subjects. In first part, two cases are considered. One is the thin plate spline smoother model and the other one is the elliptic boundary equations with uncertain boundary data. In this part, stochastic convergences of the finite element methods are proved for each problem.In second part, we provide a mathematical analysis of the linearized inverse problem in multifrequency electrical impedance tomography. We present a mathematical and numerical framework for a procedure of imaging anisotropic electrical conductivity tensor using a novel technique called Diffusion Tensor Magneto-acoustography and propose an optimal control approach for reconstructing the cross-property factor relating the diffusion tensor to the anisotropic electrical conductivity tensor. We prove convergence and Lipschitz type stability of the algorithm and present numerical examples to illustrate its accuracy. The cell model for Electropermeabilization is demonstrated. We study effective parameters in a homogenization model. We demonstrate numerically the sensitivity of these effective parameters to critical microscopic parameters governing electropermeabilization..

The application of high frequency ultrasound is the key to higher resolution intravascular ultrasound (IVUS) images. The need to further improve the IVUS spatial resolution may drive the transducer center frequency even higher than the current 40 MHz range. However, increasing the center frequency may be challenging as it leads to stronger scattering echoes from blood. The high level of blood scattering echoes may obscure the arterial lumen and make image interpretation difficult. Blood backscatter levels increase with transmission center frequency at a much greater rate compared to arterial tissue. These different frequency dependencies provide a potential method to distinguish blood from tissues by means of multi-frequency processing techniques. To obtain a good blood-tissue contrast with sufficient signal-to-noise ratio, a system with a wider bandwidth is highly desirable. The method described in this paper is based on the ratio of the received signal power between the high (60 MHz) and low (25 MHz) frequency ranges from a novel 40 MHz wideband IVUS catheter. In this paper we will present our in vitro experiment work on porcine blood and a tissue-mimicking arterial wall. Results of multi-frequency processing indicate that blood, at higher frequencies, has a greater backscatter power that is 8X greater than arterial tissue, suggesting this technique will provide a greater contrast between the blood-wall lumen boundary for coronary imaging.

In the past, the suspended sediment concentration (SSC) was mainly measured by the optical backscattering device (OBS) and water sample filtration. However, there has been a new development that user is based on the acoustics backscattering (ABS) to measure the SSC in the world. The acoustic instruments have some advantages that the optical ones do not have. For example, acoustic instruments are not effected by high turbidity, biofouling and high viscosity in the water. Acoustic instruments have high spatial and temporal resolutions. And they can immediately indicate the SSC changes than the water sample filtration method. Therefore, in this study we used the multi-frequency acoustics instrument (AQUAscat-1000) to investigate the relations of the suspended sediment size and concentration to the acoustic characteristics. The results are separated into two parts: (1) The calibration process in the flume. (2) The acoustic results in the field experiment. In the first part, we examined the range of preferred bin size with respect to the different frequencies as well as the condition in the flume, and determine that conclude the 20 mm is the best range for our case. In addition, the gain should be used when the maximum SSC is less than 100 mg/l and vice versa. Therefore, in the field case around the river mouth, the signal gain should be turned off due to high concentrations. According to the sensitivity of the backscatter intensity of different frequencies to the suspended particle sizes, multiple frequencies are needed to derive the SSC when the sediment size becomes smaller. The last point in this part is the comparison of the results between the acoustics and optical instruments. When the suspended particles in the water column are transparent, the optical measurement of the SSC is underestimated, but the acoustic method is not. The result of the field experiment in 2009 showed that the AQUAscat-1000 is a better instrument to quantify SSC than the optical instruments. The SSC increase caused by the bottom sediment re-suspension was due to the wave shear. In the 2011 experiment, although the acoustic results overestimated the SSC at some points but they still had higher relation and significance with water sample data than the optical measurements. The SSC increase caused by the bottom sediment re-suspension was due to the current shear.

Radio Frequency Identification, RFID, is a wireless identification method which uses electromagnetic fields in order to communicate with electronic tags in the vicinity. In recent years, in conjunction with the digitalization of society, RFID has become a popular method for digital identification. RFID, as a method for digital identification, is often used for credit card payments in store, access control to locked rooms and renting books at libraries. As a result of RFID growing rapidly, different frequencies have emerged. In order to benefit from different frequencies, a multi frequency RFID-reader was designed. The purpose of this study was to examine which difficulties arise in the development of a small multi frequency RFID-reader. This study shows that a small multi frequency RFID-reader lacks the conditions that are required to reach the read distance specified in available research. Furthermore, the study shows it is difficult to read different tags simultaneously without the use of a RTOS or a multicore processor.

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