Tuami Lasri

Formulation for Complete and Accurate Calibration of Six-Port Reflectometer

An accurate technique for six-port reflectometers calibration is presented in this paper. The method based on a spatial Fourier analysis incorporates nonlinearity and mismatching effects as a part of the calibration procedure. The technique makes use of impedance data distributed on the whole Smith chart to increase the measurement accuracy. A straightforward least square algorithm is used to fully calibrate the six-port reflectometer. Experimental data in the millimeter-wave frequency range is provided to validate the technique.

A 60 Ghz Scanning Near-Field Microscope With High Spatial Resolution Sub-Surface Imaging

We report a 60 GHz (λ = 5 mm) near-field scanning microscope for surface and sub-surface imaging. The sensing evanescent millimeter-wave probe is made of an alumina microstrip line tapered to 7 μm (~ λ/700) to achieve high spatial resolution. The scanning probe microscopy platform provides amplitude and phase-shift mappings of the reflection coefficient. Our microscope demonstrates the ability to achieve subsurface microscale-resolution images of buried structures.

Microwave Liquid Sensing Based on Interferometry and Microscopy Techniques

A microwave technique based on the high spatial resolution of microscopy tools and the unique measurement accuracy of interferometric methods is demonstrated. In particular, we have investigated the sodium chloride concentration in an aqueous solution volume of 144 mm3 at the test frequency of 2.45 GHz. By measuring the reflection coefficient, we have observed a measurement sensitivity of 78 dB/(mol/l) in the range of 0-0.22 mol/l. This method provides a unique approach for high sensitive liquid sensing applications.

Interferometric technique for microwave measurement of high impedances

An interferometric technique for accurate and broadband measurement of microwave impedances is proposed. The method is based on the association of a vector network analyzer and a precise interferometer built up with a power divider, a phase-shifter and an attenuator. Advantages such as simplicity of operation, broadband operation and high accuracy are achieved. The technique can be applied in a wide range of applications. In particular, an experimental demonstration of a near-field microwave microscope operating in liquid media is proposed.

Interferometric Technique for Scanning Near-Field Microwave Microscopy Applications

An interferometric technique for scanning nearfield microscopy applications is proposed. The method is based on the association of a vector network analyzer, an evanescent microwave coaxial probe and a precise interferometer built up with a power divider, a phase-shifter and an attenuator. Advantages such as simplicity of operation, broad frequency band capabilities and high measurement sensitivity are achieved. In particular, a scanning near-field microwave microscope is built and experiments related to the measurement sensitivity in the frequency range 2-6 GHz are demonstrated.

Dual-Band Elliptical Planar Conductive Polymer Antenna Printed on a Flexible Substrate

In this communication, a fully organic dual-band antenna is presented. It consists of a coplanar waveguide coupled to an elliptical monopole antenna designed on a kapton substrate. This antenna is fabricated from a process, based on the use of a conductive polymer (Polyaniline) doped with multiwall carbon nanotubes, that has been optimized for this application. The flexibility of both kapton substrate and doped conductive polymer gives the antenna the ability to be freely crumpled paving the way to body-worn high data rate communications at microwave frequencies. Applications in wireless networks can also be addressed by using this kind of antennas. In this study, a comparison between the performance of an antenna under bending conditions (using a three-dimensional support) and its uncrumpled version is presented. We evaluate the crumpling effect on the resonant frequency, the bandwidth and the radiation patterns. A good agreement is observed between measurements and simulations data, even when the antenna is crumpled.

Geometrical Optics-Based Model for Dielectric Constant and Loss Tangent Free-Space Measurement

A microwave free-space reflection method for determining the complex permittivity of planar dielectric materials is demonstrated. The method makes use of the measurement of the near-field microwave reflection coefficient of a metal-backed sample. The modeling of the structure and its calibration are based on geometrical optics considering spherical electromagnetic waves propagating through the material. The technique that presents a number of features such as low-cost, compactness, robustness, and reliability is a good candidate for industrial applications. As a demonstration, dielectric parameters extraction of building materials is experimentally demonstrated for wireless local area network operations in the 2.45- and 5-GHz bands.

Temperature Measurement by Microwave Radiometry: Application to Microwave Sintering

Temperature is a key parameter in industrial manufacturing, and its control is very often directly related to the quality of the products. Microwave-assisted processing has gained worldwide acceptance in powder technologies, in particular for the sintering of ceramic parts. High-energy efficiency, fast heating rate, and new and improved properties of the materials are typically observed. For example, fully dense bodies could be produced with improved mechanical properties due to the finer grain size. In fast-processing conditions, the system is mostly out of thermal equilibrium. A complex temperature-distribution pattern develops inside the heated parts, which can lead to localized melting or detrimental distortions if it is not under control. Today, none of the available thermometric methods (thermocouples, optical fiber, infrared, etc.) gives access to this volumetric information. We propose the use of microwave radiometry to noninvasively measure and control the temperature during the microwave sintering processes.

Scanning Microwave Near-Field Microscope Based on the Multiport Technology

A multiport based near field high frequency microscope is proposed for local nondestructive evaluation and testing applications. The combination of the multiport technology and near-field microscopy methods present advantages such as low cost, compactness, real-time operation, high spatial resolution and versatility. In particular, experimental demonstrations of a multiport near-field microscope is described in microwave frequency range. The spatial resolution of the instrument is experimentally verified to evaluate the performance of the technique proposed.

Measurement accuracy and repeatability in near-field scanning microwave microscopy

We report on the accuracy and repeatability tests for near-field scanning microwave microscopy applications by associating a network analyzer and an evanescent microwave probe (EMP). A broadband matching network based on an interferometric technique is used to achieve a strong electromagnetic coupling between the probe tip and the material in the frequency range 1-20 GHz. The electromagnetic coupling between the probe and a planar metallic sample is investigated using numerical simulations based on finite element method (FEM). Experimental validations show that the measurement sensitivity is enhanced in the vicinity of the probe tip. Measurement accuracy and repeatability of the system are provided that are instructive and beneficial to further experiments.