Método de medición de permitividad eléctrica

ilustraciones, fotografías, gráficas, tablasIn this research, a method is presented to measure electrical permittivity, using reflectometry techniques with the help of a vector network analyzer (VNA) and a Vivaldi type antenna developed during the investigation. This method is intended to assist the material identi cation process wirelessly and noninvasively. The method focuses on the UHF frequency band because the measurement equipment, both in the Electromagnetic Compatibility Laboratory of the Universidad Nacional de Colombia as in the Electronic Engineering Laboratory of the Ponti cia Universidad Javeriana showed that in this frequency band, the measurement of electrical permittivity of water behaves stably.En esta investigación, se presenta un método para medir la permitividad eléctrica, utilizando técnicas de reflectometría con la ayuda de un analizador de redes vectoriales (VNA) y una antena tipo Vivaldi desarrollada durante la investigación. Este método está destinado a ayudar al proceso de identi ficación de materiales de forma inalámbrica y no invasiva. El método se enfoca en la banda de frecuencia UHF porque el equipo de medición, tanto en el Laboratorio de Compatibilidad Electromagnética de la Universidad Nacional de Colombia como en el Laboratorio de Ingeniería Electrónica de la Ponti ficia Universidad Javeriana mostró que en esta banda de frecuencia, la medición de la permitividad eléctrica del agua se comporta de manera estable. (Texto tomado de la fuente).MaestríaMagíster en Ingeniería - Ingeniería ElectrónicaElectrónica y circuitos de alta frecuencia, radiofrecuenci

Monitoring thermal ablation via microwave tomography. An ex vivo experimental assessment

Thermal ablation treatments are gaining a lot of attention in the clinics thanks to their reduced invasiveness and their capability of treating non-surgical patients. The effectiveness of these treatments and their impact in the hospital's routine would significantly increase if paired with a monitoring technique able to control the evolution of the treated area in real-time. This is particularly relevant in microwave thermal ablation, wherein the capability of treating larger tumors in a shorter time needs proper monitoring. Current diagnostic imaging techniques do not provide effective solutions to this issue for a number of reasons, including economical sustainability and safety. Hence, the development of alternative modalities is of interest. Microwave tomography, which aims at imaging the electromagnetic properties of a target under test, has been recently proposed for this scope, given the significant temperature-dependent changes of the dielectric properties of human tissues induced by thermal ablation. In this paper, the outcomes of the first ex vivo experimental study, performed to assess the expected potentialities of microwave tomography, are presented. The paper describes the validation study dealing with the imaging of the changes occurring in thermal ablation treatments. The experimental test was carried out on two ex vivo bovine liver samples and the reported results show the capability of microwave tomography of imaging the transition between ablated and untreated tissue. Moreover, the discussion section provides some guidelines to follow in order to improve the achievable performances

EXPERIMENTAL SHIELDING EFFECTIVENESS STUDY OF METAL ENCLOSURE WITH ELECTROMAGNETIC ABSORBER INSIDE

In this paper, the impact of an electromagnetic absorber inside a protective metal enclosure is analyzed. The absorber is put inside the enclosure in order to improve its shielding effectiveness, especially at the first resonant frequency. Different absorber's sheet positions inside the enclosure are analyzed. The absorber sheet dimensions are fitted to correspond the enclosure's walls. The experimental procedure is conducted in a semi-anechoic room. The numerical TLM simulations of the EM filed distribution inside enclosure are conducted in order to consider position of the absorber sheet on different walls

Challenges and Prospects of Vehicle OTA Spherical Near-Field Measurement Probes

This Paper Discusses the Issue of Measuring Probe Indicators for Large-Scale Equipment, Such as Automobiles, under Conditions of Offset Configuration. a Simulation of Spherical Near-Field Measurement based on an Offset Configuration is Presented in This Paper. the Measurement Error is Defined According to the Reference Data Calculated by Spherical Wave Expansion Theory. through Comparative Analysis of the Simulation Results, the Main Reason for the Measurement Error is the Insufficient Coverage of the Probe\u27s Beamwidth. by Adjusting the Probe\u27s Radiation Pattern using Simulation Software, an Optimized Probe that Satisfies Near-Field Measurement Requirements under Meter-Level Offset Conditions is Obtained. Finally, based on the Simulation Results, a Set of Recommended Values for the Main Performance of the Optimized Probe is Provided

Two Alternative Methods to Measure the Radiated Emission in a Reverberation Chamber

One of the most important applications of a reverberation chamber is for radiated power measurement. Two new alternative methods are proposed to measure the radiated power of equipment under test in a reverberation chamber in this paper. Traditionally, as stated in IEC 61000-4-21 standard, this measurement requires two antennas, a signal generator and a spectrum analyzer or receiver. However, it is found that if a signal generator is not available, a vector network analyzer can be used to complete the measurement. Furthermore, if only one antenna is available, by taking advantage of the enhanced backscattering effect, the measurement can still be completed. By incorporating the one- and/or two-antenna methods, the radiation efficiency of antennas is also considered. Measurements have been conducted to verify the proposed methods, the results from these three methods are compared, and a very good agreement is obtained. It is found that the two proposed methods are simpler than the conventional method

Development of novel mechanical diagnostic techniques for early prediction of bone fracture healing outcome

2021 Fall.Includes bibliographical references.To view the abstract, please see the full text of the document

Characterization of Electron Number Density of Rocket Exhaust Plumes Through Microwave Transmissions

Charged rocket plumes generally exceed the length of their source vehicles, and offer lightning a favorable path to ground. Rocket plumes enhance the induced transient currents in flight electronics, and increase the risk of vehicle failure. The affinity of lightning to the plume can be associated with the plume\u27s electrical properties, which are coupled to plasma characteristics including the electron number density. However, the electron number density of rocket plumes is not well-known. In this study, the electron number density is characterized through data from static rocket firings. A model of the plume in finite difference time domain (FDTD) simulations also supports the results. Radio frequency and radar methodologies are used to characterize the plume as a dynamic component of an electrical system, supported by the construction of an RF apparatus that includes the design and manufacture of ultra-wideband antenna arrays. The research estimates electron number density using methods exploiting signal processing techniques in time and frequency domain, but the data suggests that other dynamic elements influence delay and attenuation of the radio signal

UHF Antenna Design for AFIT Random Noise Radar

The design of a small ultra-high frequency (UHF) antenna for an ultra-wideband (UWB) random noise radar (RNR) system was undertaken to improve system bandwidth and reduce overall system size. The Vivaldi dipole antenna class showed the greatest potential for high performance in this specific application. After extensive computer simulation, three designs were built using two printed circuit board antenna construction methods. The antipodal chopped Vivaldi dipole antenna, built with a milling machine, achieved a wider bandwidth and more uniform spectral performance characteristics. Though current results show improvement over the current log-periodic antenna (LPA) used on the system, greater performance could possibly be achieved with higher fidelity construction methods. The chopped Vivaldi dipole antenna can be classified as a highly efficient, electrically small antenna optimized for UWB applications, due to the combination of small size as well as a nearly uniform frequency response and low dispersion in the UHF bandwidth. Though designed for AFIT\u27s Noise Network (NoNET) system, a UHF UWB RNR, the antenna could be applied to a variety of UHF systems looking to optimize the trade-off between size and power budgets