Luc Dubois

Complete three-dimensional modeling of new microstrip-microslot applicators for microwave hyperthermia using F.D.T.D. method

Describes a complete 3D modeling using the finite difference time domain (FDTD) method of a new generation of external applicators for microwave hyperthermia used at either at 434 MHz or 915 MHz without any modifications. With this new model, it is possible to obtain theoretical results concerning the variations of the reflection coefficient as a function of frequency, the power deposition inside the heated lossy tissues and the heating patterns. Experimental electromagnetic and thermal characteristics are presented and compared with the theoretical results obtained with the 3D method.<<ETX>>

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.

Temperature Measurement by Microwave Radiometry

Temperature is an important parameter in the industrial world. For example, temperature control is of a greater concern in food processing industry for safety reasons as well as for product quality. Recently, microwave processing of powder metallurgical bodies has been shown to be very promising. Fully dense bodies with improved mechanical properties could be produced due to finer grain size. In the field of the sintering of materials, a control of the temperature inside heated parts is necessary to avoid local melting or distortions. The medical field is another sector particularly interested in non invasive techniques for the measurement of human temperature. In fact, the corporal temperature is proved to be a pertinent parameter in the scope of diagnosis, monitoring of many pathologies and for the posology of some medicines. None of the current methods for measuring temperature (thermocouples, optic fibers, infrared, etc...) give by a non-invasive way continuous temperature information. So, microwave radiometry brings a neat solution to measure and control non-invasively temperature inside a dissipative material. This paper is concerning the design and the realization of specific radiometric sensors in order to measure and control temperatures from a non-invasive way by microwave radiometry either in industrial or in medical applications.

1 to 220 GHz Complex Permittivity Behavior of Flexible Polydimethylsiloxane Substrate

Coplanar transmission lines (CPW) are realized on polydimethylsiloxane (PDMS) substrate in order to characterize its complex permittivity, from 1 to 220 GHz. By varying the complex permittivity, the propagation constant of the PDMS-CPW calculated with full wave software is matched to those extracted by de-embedding techniques using S-parameters measurements. The real permittivity evolves from 2.9 to 2.55 while the loss tangent increases slowly to reach 0.048 at 210 GHz.

Design and modeling of a specific microwave applicator for the treatment of snoring

One of the main objectives of using microwaves in medical applications is to make use of the therapeutic effects resulting from the interaction between electromagnetic waves and biological tissues in order to obtain a local heating. For this purpose, a large number of devices have been designed and tested for various medical applications. We present in this paper the results concerning the design and the modeling of an applicator developed for the treatment of snoring using microwaves.

Local measure of the electromagnetic field in magnetic resonance coils: How do simulations help to disentangle the contributions of the electric and magnetic fields?

The development of probes for Nuclear Magnetic Resonance (NMR) spectroscopy of metabolites, biomolecules or materials requires the accurate determination of the radio-frequency (RF) magnetic field strength, B1, at the position of the sample since this RF-field strength is related to the signal sensitivity and the excitation bandwidth. The Ball Shift (BS) technique is a commonly employed test bench method to measure the B1 value. Nevertheless, the influence of the RF electric field, E1, on BS is often overlooked. Herein, we derive, from Maxwell equations, an analytical expression of the BS, which shows the contribution of both the electric and magnetic energies to the BS value. This equation shows that the BS allows quantifying the B1 field strength only in regions where the electric energy is small with respect to the magnetic one. The numerical simulations of electromagnetic (EM) field and energy prove that this condition is fulfilled at 100.5MHz inside the electrically balanced coil of a double-resonance 1H/X 4mm Magic Angle Spinning (MAS) probe since for that circuit, the center of the coil is an antinode for the B1 standing wave and a node for the E1 one. We also show that the simulated BS values agree well with the experimental ones. Conversely, NMR experiments show that the contribution of the electric energy to BS becomes significant when the X channel of this probe is connected to a frequency splitter. In that case, the use of BS method to estimate the B1 value is compromised.

Design and modeling of multipatches planar applicators for microwave hyperthermia

Describes a new type of external planar applicator with several patches which have been developed for microwave hyperthermia controlled by microwave radiometry. The possibility to obtain larger heating patterns than with the single patch applicators is clearly focused by the theoretical results which are presented and verified by experimental measurements.<<ETX>>

Modeling of planar annular applicators for microwave thermotherapy

In order to improve the external applicators used for microwave thermotherapy controlled by microwave radiometry in medical applications, we propose specific annular planar applicators developed for the heating. The final goal of this study is the realization of a honeycomb network for the treatment of larger areas and greater volumes.

Miniature sensor for measurement and control of temperatures by microwave radiometry in medical applications

In order to improve non-invasive measurement microwave radiometry in medical and industrial applications, we propose a new generation of sensors realized from a metallic sheet laid on a dielectric substrate. It allows the realization of sensors of small sizes and very light weight for medical applications such as neonates temperature control.

Non invasive Determination of Temperature Trajectories During a Defrosting Process using Microwave Radiometry

The control of the freezing or defrosting velocity is an important parameter in food industries, for the improvement of product quality. In this paper, radiometric measurements, a noninvasive method, are shown to be effective to follow the defrosting of foodstuff. We describe experiments and the radiometric device used. Simulations based upon the combined algorithms FDTD - heat transport equation are used to predict the radiometric temperature trajectories during the defrosting process by introducing the temperature dependent media. The comparisons between experimental and theoretical results are presented and analyzed.