Academic literature on the topic 'Electromagnetic measurements'

This thesis describes the development of electromagnetic sensors to measure the phase transformation in steel as it cools from the hot austenite phase to colder ferritic based phases. The work initially involved investigating a variety of sensing configurations including ac excited coils, C-core arrangements and the adaptation of commercial eddy current proximity sensors. Finally, two prototype designs were built and tested on a hot strip mill. The first of these, the T-meter was based on a C-shaped permanent magnet with a Gaussmeter measuring the magnetic field at the pole ends. Laboratory tests indicated that it could reliably detect the onset of transformation. However, the sensor was sensitive to both the steel properties and the position of the steel. To overcome this, an eddy current sensor was incorporated into the final measurement head. The instrument gave results which were consistent with material property variations, provided the lift off variations were below 3Hz. The results indicated that for a grade 1916 carbon- manganese steel, the signal variation was reduced from 37% to 2%, and the resulting output was related to the steel property variations. The second of these prototypes was based on a dc electromagnetic E-core, with Hall probes in each of the three poles. 'Cold' calibration tests were used to decouple the steel and the lift-off. The results indicated that there was an error of 3-4% ferrite/mm at high ferrite fractions. At lower fractions the error was higher due to the instrument’s insensitivity to lift-off. The resulting output again showed a relationship with varying steel strip properties. ft was also shown that a finite element model could be calibrated to experimental results for a simple C-core geometry such that the output was sensitive to 0.2% of the range. This is required to simulate the sensor to resolve to 10% ferrite.

This thesis develops a novel method to predict radiated emissions measurements. The techniques used are based on standard Electromagnetic Compatibility (EMC) qualification test methods. The empirical data used to formulate the final results was restricted to pertinent data protocol waveforms however the entire method may be applied to any waveforms for which empirical radiated emissions have been measured. The method provides a concise means for predicting worst case radiated emissions profiles based on empirical measured data.<br>M.S.E.E.<br>School of Electrical Engineering and Computer Science<br>Engineering and Computer Science<br>Electrical Engineering

This thesis presents a technology that has been called the Full Time-Domain Electromagnetic Interference measurement systems and its applications. Full TDEMI measurement systems are an implementation of an FFT-based receiver that enables the usage of oscilloscopes for EMI measurements. They follow the virtual instrumentation approach for transforming oscilloscopes into a compliant CISPR 16-1-1 receiver. Full TDEMI measurement systems have been assessed for characterizing their performance using waveform oriented calibration procedures that bridge the gap between direct measurements in the time domain and the processed frequency domain magnitudes. As a result, the conformity of Full TDEMI receivers is attested with respect to the requirements defined in the standards. Full TDEMI systems have advantages over the conventional swept receivers for performing challenging measurements typical of EMI assessments. Time-domain captures enable full spectrum measurements that allow analyzing transient phenomena. The number of channels available in most oscilloscopes enable synchronous measurements that allow recording the EMI using a combination of transducers. Some of the applications of the multichannel EMI measurements are the single stage evaluation of the conducted EMI of all the EUT mains lines, the instantaneous measurement of the common-mode and the differential mode voltage noise, the concurrent conducted and radiated EMI measurements, and the parallelization of multi-antenna radiated emissions testing. Such alternative test methods, have improved the EMC testing process in a variety of industries by reducing the time and the efforts required for performing a complete EMI evaluation due to the following reasons. First, Full TDEMI measurements deliver faster results because the interferences' spectrum is simultaneously estimated for all the weighting detectors. Second, the number of measurement iterations is reduced because of the multichannel possibilities and also because of an agile identification of the worst case emissions. Thirdly, Full TDEMI measurement system are a cost-effective alternative to the real-time spectrum analysers. Full TDEMI measurement systems have extended the state-of-the-art with the expected maximum detector and the empirical interference decomposition. The expected maximum detector is a statistical measure of the most probable level of the peak emissions that is based on a time-frequency modelling of the measured EMI using the extreme value theory. Using the variability information of the EMI level at each frequency bin, the expected maximum detector estimates the equivalent max hold value of a random EMI. The expected maximum detector also provides a model for quantifying the uncertainty of peak detector measurement of stochastic EMI. The Empirical Interference Decomposition is a modified implementation of the Hilbert-Huang transform with time-gating capabilities that allow a heuristic determination of characteristic oscillatory patterns without neither domain transformation nor a predefined set of basis function. The EID has been used successfully for ambient noise cancellation purposes during outdoor EMI measurements, obtaining more than 20 dB of attenuation of the usual broadcasting signals. The fundamentals of the ANC by means of EID is the identification, in the time and in the frequency domain, of intrinsic modes of emissions that area attributable to the EUT while subtracting the residual modes from the measurement results. Applications of the Full TDEMI measurement systems have been published in recognized conferences and journal. From the reasons mentioned before, the Full TDEMI measurement technology has advantages for EMI testing, analyzing and troubleshooting. It provides a complementary approach to the typical measurements entirely focused in the frequency domain and it exhibits a level of maturity that could allow it to be standardized in forthcoming years.<br>Esta Tesis comprende un compendio de contribuciones hechas por el autor al campo de la tecnología de medición de radiofrecuencia para la compatibilidad electromagnética. En particular, esta Tesis presenta una tecnología de sistemas medición de interferencias electromagnéticas completamente basado en dominio del tiempo (Full TDEMI) y algunas de sus aplicaciones más relevantes. Los sistemas de medición Full TDEMI son una implementación de un receptor de medida basado en FFT que permite el uso de osciloscopios para mediciones de interferencias electromagnéticas. Los sistemas de medición Full TDEMI siguen el enfoque de instrumentación virtual para transformar los osciloscopios de propósito general en un receptor de medida completamente funcional y conforme con la norma CISPR 16-1-1. Por un lado, esto es factible debido a las técnicas específicas de procesamiento de señales aplicadas sobre las adquisiciones en el dominio del tiempo utilizando una capa de software dedicada. Por otro lado, los sistemas de medida Full TDEMI se han evaluado exhaustivamente para caracterizar su rendimiento utilizando procedimientos novedosos de calibración orientados a formas de onda que acortan la brecha entre las magnitudes medidas en el dominio del tiempo y las aquellas procesadas en el dominio de frecuencia. Como resultado, se certifica la conformidad de los sistemas completos de medición TDEMI con respecto a los requisitos definidos en los estándares internacionales paramediciones EMI. Además, se ha demostrado que los sistemas de medición Full TDEMI ofrecen ventajas en comparación con los receptores de barrido convencionales para realizar varias medidas desafiantes típicas de las evaluaciones de emisiones electromagnéticas. Por ejemplo, las capturas de dominio de tiempo posibilitan mediciones de espectro completo que permiten un análisis adecuado de fenómenos transitorios. Del mismo modo, la cantidad de canales disponibles en la mayoría de los osciloscopios hace viables múltiples mediciones síncronas que para registrar las perturbaciones interferentes mediante una combinación de transductores. Algunas de las aplicaciones de la medición EMI multicanal son la evaluación de etapa única de la EMI conducida de todas las líneas de alimentación de los equipos bajo prueba (EUT), la medición instantánea del voltaje del ruido en modo común y en modo diferencial, las mediciones concurrentes de la EMI conducida y radiada y la paralelización de los ensayos de emisiones radiadas con múltiples antenas. Tales métodos de prueba alternativos, han mejorado significativamente el proceso de prueba de EMC en una variedad de industrias al reducir la cantidad de tiempo y los esfuerzos necesarios para realizar una evaluación completa del sistema principalmente debido a las siguientes razones. En primer lugar, las mediciones de EMI en el dominio del tiempo arrojan resultados más rápidos porque el espectro de interferencias se estima simultáneamente para todos los detectores de ponderación estándar necesarios para determinar el cumplimiento de los límites máximos de emisiones definidos en las respectivas normas de producto. En segundo lugar, el número de iteraciones de medición se reduce debido a las posibilidades multicanal y también debido a una identificación ágil del peor caso de las emisiones de un EUT que tiene diferentes modos de funcionamiento. En tercer lugar, el sistema Full TDEMI es una alternativa económica y versátil a los analizadores de espectro en tiempo real más avanzados en lo concerniente a mediciones EMI en el rango de pocos gigahertzios. Desde el punto de vista teórico, los sistemas de medición Full TDEMI han extendido el estado del arte, como en el caso de un par de contribuciones denominadas el detector de máximo esperado y la descomposición empírica de interferencias. El detector de máximo esperado es una medida estadística del nivel más probable de las emisiones pico que se basa en un modelado tiempo-frecuencia de las interferencias medidas utilizando la teoría del valor extremo. Usando la información de variabilidad del nivel de interferencia en cada componente de frecuencia, el detector de máximo esperado se puede usar para estimar el valor de retención máximo (max-hold) equivalente de una interferencia aleatoria. El detector demáximo esperado también proporciona un modelo que cuantifica la incertidumbre de lamedición del detector de picos ante interferencias estocásticas. La descomposición de interferencia empírica (EID) es una implementación modificada de la transformada de Hilbert-Huang con capacidades de sincronización de tiempo que permiten una determinación heurística de patrones oscilatorios característicos sin requerir transformación de dominio ni un conjunto predefinido de funciones base. La descomposición de la interferencia empírica se ha utilizado con éxito para la cancelación del ruido ambiental durante prueba de concepto de mediciones de EMI de al aire libre, obteniendo más de 20 dB de atenuación de las señales habituales de radiodifusión. El fundamento de la cancelación del ruido ambiental mediante EID es la identificación, en el tiempo y en el dominio de la frecuencia, de los modos de emisión intrínsecos que son atribuibles al EUT al restar los modos residuales (ruido ambiental) de los resultados de medición. Las contribuciones mencionadas se distribuyen en cuatro artículos de revista. Los resultados de medición complementarios y las aplicaciones de los sistemas de medición Full TDEMI también se han publicado en conferencias notables en el área. Por los motivos antes mencionados, la tecnología Full TDEMI tiene ventajas significativas para los ensayos, el análisis y la resolución de problemas de EMI. Asimismo, proporciona un enfoque complementario a las mediciones típicas completamente enfocadas en el dominio de la frecuencia y exhibe un nivel de madurez que podría permitir su estandarización en los próximos años.

Various optical microscopy techniques have been developed for micrometer level imaging of biological tissue samples. Among those techniques, confocal imaging provides superior image contrast and high resolution with a modest system cost. Confocal microscopy allows vertical optical sectioning (imaging a section perpendicular to the surface of tissue) or horizontal optical sectioning (imaging a section parallel to the surface of tissue) and provides high-resolution tissue morphology that is analogous to conventional histopathology images. This has brought up a tremendous potential for guiding surgical biopsies and in vivo non-invasive diagnosis of diseases such as cancer. The challenge in moving microscopic imaging modalities into clinical applications is miniaturization into a form of hand-held devices or catheters for endoscopic applications. In this thesis, micro-fabrication techniques such as Microelectromechanical Systems (MEMS) fabrication process and laser micromachining have been employed to develop magnetic actuators. The actuators are then used to move lenses and optical fibers in order to scan a laser beam across a sample. Lens and fiber actuators are integrated in catheter and hand-held devices for confocal thickness measurement and optical sectioning imaging of biological samples. Thickness measurement is performed by scanning the focal point of a microlens across the thickness of thin films or layered biological tissues and collecting the intensity signal of the single scattering light reflected back from the samples as a function of lens position. A catheter was developed and thickness measurements of polymer layers and biological tissues were demonstrated. The device has optical resolution of 32 µm with expanded uncertainty of measurement of 11.86 µm. Lens and fiber optic actuators have been coupled to form two-dimensional imaging devices. Direct and real-time vertical and horizontal cross-sectional imaging of biological samples has been demonstrated. Vertical imaging is performed by transverse (X-axis) and axial (Z-axis) scanning of a focused laser beam using an optical fiber and a microlens actuator respectively. Horizontal imaging is done by a 2-axis fiber optic scanner. All the developed actuators are driven by electromagnetic forces and require low driving voltages. Confocal imaging of biological samples, with lateral resolution of 1.55 µm, has been demonstrated.

Thesis (M.S. in Physics)--Naval Postgraduate School, March 2007.<br>Thesis Advisor(s): Brett Borden, Gamani Karunasiri. "March 2007." Includes bibliographical references (p. 97-99). Also available in print.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California<br>The US Army Research Laboratory has been involved in the design and implementation of electromagnetic gun technology for the past several years. One of the primary factors of this research is an accurate assessment of in-bore structural loads on the launch projectiles. This assessment is essential for the design of mass-efficient launch packages for electromagnetic guns. If not properly accounted for, projectile failure can result. In order to better understand the magnitude of the in-bore loads, a data-recorder was integrated with an armature and on-board payload that included tri-directional accelerometers and magnetic field sensors. Several packages were launched from an electromagnetic railgun located at Aberdeen Proving Ground, MD. Substantial effort was placed on soft-catching the rounds in order to facilitate data recovery. Analysis of the recovered data provided acceleration and magnetic field data acquired during the launch event.