Francois Boone

Design and Calibration of a Large Open-Ended Coaxial Probe for the Measurement of the Dielectric Properties of Concrete

The subject of this paper is the design and calibration of an open-ended coaxial probe for the nondestructive measurement of the dielectric properties of concrete. Measurements are made between 100-900 MHz, frequencies which are often used in geophysics and civil engineering for ground penetrating radar inspection. The probe is calibrated using measurements on saline solutions in conjunction with three different mathematical techniques for comparative study. Measurements of mortar and concrete specimens having different water/cement ratios were made in order to observe the standard deviations due to their heterogeneous nature. Similar to the case of relatively homogeneous rock specimens (limestone and granite), the standard deviation for heterogeneous concrete samples do not exceed 5%. In addition, the effect of the concretes porosity on its dielectric properties was clearly observed: measured permittivity between 4-4.5 at 900 MHz for porous concrete, and between 6.5-7.5 at 900 MHz for dense concrete.

Application of Jonscher model for the characterization of the dielectric permittivity of concrete

The study of electromagnetic waves propagating in concrete is a complex problem. Understanding the phenomenon of interaction between the wave and the matter is related to the knowledge of the variation process of concretes electromagnetic properties in terms of its physical characteristics. In particular, dielectric permittivity of concrete is affected by moisture content and change in the frequency of the electromagnetic field applied. In this study, we apply the three-parameter Jonscher model (n, χr, e∞) to show the dispersive aspect of the concrete. The validation of this model is carried out through tests on mortar and concrete at the laboratory, on the one hand, and by comparison of the results with data obtained previously by other researchers, on the other hand. The Jonscher model matches very well the experimental measurements of the concrete. At different moisture levels, heterogeneities and porosities, the results obtained are very good. This shows that this model is very effective and very suitable to represent the dielectric properties of concrete.

High-Resistivity Silicon Dielectric Ribbon Waveguide for Single-Mode Low-Loss Propagation at F/G-Bands

In this paper, dielectric ribbon waveguides (DRWs) are designed and characterized to work in the F (90-140 GHz) and G (140-220 GHz) frequency bands. High resistivity silicon (HR-silicon) due to its high transparency in these bands, and its low-cost fabrication process, were selected for the fabrication of these waveguides. The guided modes of DRW are studied using Marcatili and multi-line methods. A design procedure for optimal single-mode propagation was introduced. The wave attenuation inside the waveguide is discussed. Our experiments show that HR-silicon DRW has less than 0.087 dB/cm (0.01 cm-1) of loss over the guiding bandwidth. The designed DRWs were realized using microfabrication techniques. The measurements are in very good agreement with theoretical predictions.

Modelling dielectric-constant values of concrete: an aid to shielding effectiveness prediction and ground-penetrating radar wave technique interpretation

A number of efficient and diverse mathematical methods have been used to model electromagnetic wave propagation. Each of these methods possesses a set of key elements which eases its understanding. However, the modelling of the propagation in concrete becomes impossible without modelling its electrical properties. In addition to experimental measurements; material theoretical and empirical models can be useful to investigate the behaviour of concretes electrical properties with respect to frequency, moisture content (MC) or other factors. These models can be used in different fields of civil engineering such as (1) electromagnetic compatibility which predicts the shielding effectiveness (SE) of a concrete structure against external electromagnetic waves and (2) in non-destructive testing to predict the radar wave reflected on a concrete slab. This paper presents a comparison between the Jonscher model and the Debye models which is suitable to represent the dielectric properties of concrete, although dielectric and conduction losses are taken into consideration in these models. The Jonscher model gives values of permittivity, SE and radar wave reflected in a very good agreement with those given by experimental measurements and this for different MCs. Compared with other models, the Jonscher model is very effective and is the most appropriate to represent the electric properties of concrete.

Electrothermal Mapping of AlGaN/GaN HEMTs Using Microresistance Thermometer Detectors

Self-heating effects in AlGaN/GaN high-electron mobility transistors (HEMTs) can notably reduce electron mobility and produce reliability concerns. Electrothermal characterization and appropriate thermal management are required to address this situation. This letter presents the measurement of channel temperature (T_ch) of GaN HEMTs in multiple bias conditions with a good accuracy. The measurements are executed using the integrated microresistance thermometer detector (μRTD) technique in AlGaN/GaN HEMTs on SiC and sapphire substrates. The integrated Ti/Pt μRTD sensor with linear resistance-temperature characteristic is used to obtain an I_ds-V_ds-T_ch map for each device. Thermal resistances are compared for similar operation conditions, obtaining RTH = 34.7 °C · W^-1 for the HEMT on SiC and RTH = 157.2 °C · W^-1 for the HEMT on sapphire.

Iterative Design Techniques for All-Pole Dual-Bandpass Filters

Two iterative techniques to design all-pole dual-bandpass filters are presented. The oversized aspect of the problem is highlighted and the system is solved by relaxing a parameter, which ensures the convergence. The proposed methods are based on the Remez algorithm and the match points technique. Both methods are applied to design filters by relaxing either a bandpass edge frequency or a ripple level. Also, two examples are presented and demonstrate the speed and accuracy of the proposed techniques.

Nonradiative dielectric (NRD) waveguide diplexer for millimeter-wave applications

In this paper, a T junction and a right angle elbow in Nonradiative dielectric (NRD) guide technology are carefully analyzed. This analysis is based on our mode-matching program combined with a cascading procedure that allows formulating generalized admittance and then generalized scattering matrices. These structures are optimized to reach the maximum power transfer from LSM to LSE mode. Putting these together, a splitter from LSM to LSM mode is created. Two LSM bandpass filters are then designed and added to the previous structure to obtain a diplexer. This diplexer presents two kinds of isolation. The first one can be easily minimized by increasing the order of filters. The second one is defined as a coupling isolation. A new physical topology is then presented to minimize this isolation. Our simulations are compared with HFSS software simulations and results are in very good agreement.

Creating screen‐printed passive components for microwave applications

Purpose – The purpose of this paper is to share valuable information about low‐cost microwave circuit research with academic and industrial communities that work, or want to work, in this field.Design/methodology/approach – Screen‐printing technology has been chosen as the fabrication method because of simplicity and low costs. Different materials and printing parameters were tested in four generations of microstrip lines. After obtaining a satisfactory fabrication method, passive microwave components were printed, assembled, characterized and modeled.Findings – Results demonstrated that the proposed low‐cost method allows fabricating low loss microstrip lines (15.63×10−3 dB/mm at 10 GHz), filters, inductors, and capacitors that work well up to 12 GHz.Research limitations/implications – Model accuracy of inductors and capacitors can be improved. The use of more precise calibration and de‐embedding techniques is necessary. More components can be fabricated and modeled to increase the flexibility and applic...

Concept of Virtual Electric/Magnetic Walls and its Realization With Artificial Magnetic Conductor Technique

In this letter, we present a novel concept of virtual electric/magnetic walls which are formed by combining perfect electric conducting parallel plates and perfect magnetic conducting parallel plates. In practice, the perfect magnetic wall can be replaced with an artificial magnetic conductor surface. Two types of complementary transverse electromagnetic waveguides are built with the virtual electric/magnetic walls. The field distribution in the waveguide was simulated and measured. The existence of virtual electric wall was verified.

Integration of Micro Resistance Thermometer Detectors in AlGaN/GaN Devices

Temperature measurements in AlGaN/GaN high electron mobility transistors are required for proper device design, modeling and achieving appropriate reliability. These measurements usually require sophisticated equipment and extensive calibration. This study evaluates the feasibility of temperature measurements by integration of a Pt resistance thermal detector (RTD) in an “un-gated” transistor and evaluating their electrical interactions. The integrated RTD presents the advantage of being independent of the device. Micro RTD showed a linear response in the calibration interval (0 to 206 °C). Measured temperature values using the micro RTD are in agreement with 3D finite element simulations at multiple bias conditions in the “un-gated” transistor. Measurements show no noticeable electrical perturbation between the device and RTD under simultaneous operation.