Microwave Near-Field Imaging of Electric Fields in a Superconducting Microstrip Resonator

We describe the use of a cryogenic near-field scanning microwave microscope to image microwave electric fields from superconducting and normal-metal microstrip resonators. The microscope employs an open-ended coaxial probe and operates from 77 to 300 K in the 0.01-20 GHz frequency range with a spatial resolution of about 200 mm. We describe the operation of the system and present microwave images of Cu and Tl2Ba2CaCu2O8 microstrip resonators, showing standing wave patterns at the fundamental and second harmonic frequencies.Comment: 9 pages, 3 eps figure

Combined thickness and permittivity measurement of layers using an open-ended coaxial probe

The purpose of this thesis is to develop a method for estimating both the thickness and permittivity of layers simultaneously utilizing an open-ended coaxial probe. One possible application of this method is the detection and characterization of deposits inside pipelines; examples are gas hydrate deposits in multiphase petroleum transportation. The hydrates forming can result in deposits on the interior surface of the piping and may restrict the flow of the production, it is thus necessary to monitor the layer thickness of the deposits to prevent any obstruction of flow, and the permittivity can tell us something about the composition of the deposits. The open-ended coaxial probe is a coaxial line that is a cut-off section of the transmission line. Permittivity measurements with the open-ended coaxial probe rely on analyzing the reflection of the electromagnetic wave from the probe-sample boundary. The open-ended coaxial probe is known to become radiating at high frequencies when the probe dimensions are comparable to the wavelength in the material under test. When measuring on samples with a finite thickness, this may result in additional reflections from the sample boundary interfering with the main reflection. If the applied permittivity model assumes an infinite thickness, the additional reflection may result in artifacts in the measured permittivity. Typically, this effect will be stronger at some frequencies due to resonance effects, which is seen as an unwanted measurement error. The resonance amplitude and frequency depend on the layer thickness, the permittivity of the layer/backing material and the probe dimensions. This thesis shows that by comparing the measured permittivity spectra with a matrix of finite element simulation, we can estimate both the layer thickness and material by comparing the measured data against the simulations. The simulations were verified by measuring liquids with known dielectric properties. The unwanted resonances manifest as artifacts in the permittivity spectra and increase the accuracy of the comparison. With the methods proposed in the thesis, we can also determine when the resonances occur for a given material, layer thickness, and frequency.Masteroppgave i fysikkMAMN-PHYSPHYS39

Traitement des arythmies cardiaques par ablation micro-onde

A comparative study of four open-ended coaxial probe models for permittivity measurements of lossy dielectric/biological materials at microwave frequencies -- Experimental setup for dielectric measuremetns -- Modeling of the open-ended coaxial probe -- Experimental results on saline solutions -- Sensitivity to the calibration media of the virtual line model and the capacitive model -- Correction des discontinuités lors des mesures de la permittivité complexe à l'aide d'une sonde coaxiale -- Catheter ablation : infarcted myocardium has a higher electrical conductivity at rf frequencies but the same complec permittivity at microwave frequencies in comparison with normal cardiac tissue -- A microwave ablation system to treat cardiac arrhythmia

Development of a Transmission-Based Open-Ended Coaxial-Probe Suitable for Axillary Lymph Node Dielectric Measurements

We assess the feasibility of a transmission-based open-ended coaxial-probe for tissue dielectric properties estimation. The ultimate goal is to use it for axillary lymph node dielectric measurement, which is not trivial when applying the state-of-the-art reflection-based open-ended coaxial-probe. The proposed technique consists in placing the material under test between two opposite open-ended coaxial-probes and record the transmission coefficient. We numerically assess three coaxial probe configurations, in order to ensure adequate transmission and sensing volume. The final setup allows for enough propagation through a 5mm sample (which will be sufficient for the measurements of axillary lymph nodes), while confining the sensing volume to the region of interest. Experimental tests on two materials of different permittivity ranges showed good agreement between the measured and numerical transmission coefficient. Moreover, we observed that the transmission coefficient can highlight the contrast between materials with different dielectric properties. The promising initial results motivate the further application of the method to the case of axillary lymph nodes.info:eu-repo/semantics/acceptedVersio

Frequency Following Imaging of Electric Fields from Resonant Superconducting Devices using a Scanning Near-Field Microwave Microscope

We have developed a scanning near-field microwave microscope that operates at cryogenic temperatures. Our system uses an open-ended coaxial probe with a 200 mm inner conductor diameter and operates from 77 to 300 K in the 0.01-20 GHz frequency range. In this paper, we present microwave images of the electric field distribution above a Tl2Ba2CaCu2O8 microstrip resonator at 77 K, measured at several heights. In addition, we describe the use of a frequency-following circuit to study the influence of the probe on the resonant frequency of the device.Comment: 4 pages, postscript file with 6 figures conference proceeding for the Applied Superconductivity Conference 199

Permittivity-Based Water Content Calibration Measurement in Wood-Based Cultural Heritage: A Preliminary Study

In this work, the dielectric permittivity of four kinds of wood (Fir, Poplar, Oak, and Beech Tree), used in Italian Artworks and structures, was characterized at different humidity levels. Measurements were carried out using three different probes connected to a bench vector network analyzer: a standard WR90 X-band waveguide, a WR430 waveguide, and an open-ended coaxial probe. In particular, we investigated the dispersion model for the four wood species, showing how a log-fit model of the open-ended data presents a determination coefficient R2 > 0.990 in the 1–12 GHz frequency range. This result has proven helpful to fill the frequency gap between the measurements obtained at different water contents with the two waveguide probes showing an R2 > 0.93. Furthermore, correlating the log-fit vertical shift with the water content, it was possible to find a calibration curve with a linear characteristic. These experimental results will be helpful for on-site non-invasive water monitoring of wooden artworks or structures. Moreover, the final results show how the open-ended coaxial probe, with a measurement deviation lower than 7% from the waveguide measurements, may be used directly as a non-invasive sensor for on-site measurements

Imaging Microwave Electric Fields Using a Near-Field Scanning Microwave Microscope

By scanning a fine open-ended coaxial probe above an operating microwave device, we image local electric fields generated by the device at microwave frequencies. The probe is sensitive to the electric flux normal to the face of its center conductor, allowing different components of the field to be imaged by orienting the probe appropriately. Using a simple model of the microscope, we are able to interpret the system's output and determine the magnitude of the electric field at the probe tip. We show images of electric field components above a copper microstrip transmission line driven at 8 GHz, with a spatial resolution of approximately 200 $\mu$m.Comment: 10 pages, 3 eps-figures, accepted by Appl. Phys. Let

Sensing depth analysis of open-ended coaxial probe for skin cancer detection

Inherent dielectric properties discrepancy between different tissues have long been of interest to researchers in order to improve medical diagnostic approaches and therapeutic technologies. Hence, determination of the dielectric properties for biological tissues is keystone to develop an innovative medical system. Widely, the dielectric properties of biological tissues have been determined by utilizing slim form open-ended probes. Although, the method is superior to other dielectric property measurement techniques in several aspects, the mea- surement procedure suffers from equipment-related and tissue- related errors. Sensing depth, which is one of the confounders can be associated with both equipment- and tissue-related errors. In this work, we performed the preparation of skin mimicking phantom and conducted a series of experiments on a two-layer configuration consisting of the prepared phantom and a liquid (olive oil). Furthermore, the sensing depth of the 2.2mm aperture open-ended coaxial probe was analyzed at five different frequencies. The results obtained show that the sensing depth of biological tissues strongly depends on the operation frequency. We also observed that the sensing depth decreases at higher frequencies and this is a property can be utilized in tackling thin multi-layered structures problem such as skin cancer detection

Effectiveness of microwave technique in early detection of breast abnormalities

In this paper, a breast phantom of CIRS Model 010A contains various known masses and sizes is studied. A measurement of S11 signals is taken at few locations on a breast surface using an open-ended coaxial probe. The obtained signals permit the extraction of the dielectric property of the masses. The result has shown that the smallest size detected through this probe is approximately 0.20 mm, small enough to be detected at early stage breast abnormality growth. This method undoubtedly recognizes the presence and location of possible abnormalities such as benign and malignant tissues. Although the model does not contain malignant tissues, this study demonstrates the viability of detecting small breast tumors using this approach. Index Terms - Breast abnormalities, dielectric properties, microwave technique, open-ended coaxial probe

Microwave dielectric spectroscopy of renal calculi: A large scale study on dielectric properties from 500 MHz to 18 GHz

Inherent dielectric property discrepancy between biological anomalies and healthy tissue enables the microwave diagnostic and therapeutic technologies. To reveal this discrepancy, microwave dielectric properties of many different biological tissues are tabulated. Although the dielectric properties of biological tissues are well documented in the literature, the knowledge on microwave dielectric property behavior of the renal calculi is limited. This work presents ultra wideband dielectric properties of three renal calculi types between 500 MHz to 18 GHz to pave the way for possible application of microwave technologies for diagnosis, treatment, and prevention of urolithiasis. Microwave dielectric spectroscopy is performed on a total of 66 natural stone samples with open-ended coaxial probe technique. The samples belong to three commonly diagnosed renal calculi categories, namely calcium oxalate, cystine, struvite. Analysis of variance (ANOVA) test is performed on fitted Cole-Cole parameters and it was concluded that there is a statistically significant difference between the dielectric properties of the renal calculi types. A patient-to-patient statistical test is also performed and it was concluded that there is no statistical difference between the samples belonging to the same renal calculi category. To this end, based on the relative permittivity discrepancy between the renal calculi types, the category of renal calculi can be identified by measuring the dielectric properties of renal calculi with open-ended coaxial probe technique