Roberto Olmi

The Polyacrylamide as a Phantom Material for Electromagnetic Hyperthermia Studies

The Polyacrylamide gel is suggested as a new and convenient material for simulating the electrical behavior of biological tissues in experimental studies of heat deposition by electromagnetic means. The advantages of Polyacrylamide are: 1) excellent optical transparency, 2) solid elastic, 3) easily shaped into complex forms, 4) readily prepared with a complete range of highly reproducible values of electrical parameters, which can also be combined to simulate various different tissues in complex structures. The material is also low-cost and readily available.

Use of polyacrylamide as a tissue-equivalent material in the microwave range

The use of polyacrylamide gel to simulate biological tissues at microwave frequencies is presented. Formulation and preparation procedures are discussed. Measurements of complex permittivity in the range from 0.75 to 5.5 GHz, together with its temperature sensitivity, are reported. Thermal and optical properties have also been measured: the polyacrylamide is transparent and may be used as a phantom material in designing and testing applicators for microwave hyperthermia and for dosimetry studies.<<ETX>>

Non-destructive permittivity measurement of solid materials

An open-coaxial probe suitable for measuring the permittivity of solid materials has been designed and tested. The peculiar structure of the probe allows an easy and firm contact with the surface of the material under measurement, resulting in highly reliable and reproducible dielectric measurements. The permittivity measurement is absolute, as the calibration procedure - based on a genetic algorithm - does not require the use of dielectric standards. The measurement system - including the probe, a network analyser, and the numerical code to determine the permittivity from reflection measurements - have been tested on solid materials of known properties, and used for determining the dielectric characteristics of several types of wood.

Dielectric properties of wood from 2 to 3 GHz.

Many applications of microwave energy to wooden materials have been developed in the lastfew decades, both for treatment and for diagnostic purposes. All these applications require a reliable estimation of the permittivity of the wood species of interest, which is the physical parameter ofcrucial importance in the absorption of electromagnetic energy. This paper presents results obtained in the dielectric characterization of five wood species in the frequency range from 2 to 3 including the ISM frequency of 2.45 GHz. Permittivity was measured by an open-ended coaxial-line probe of new design on wood samples conditioned at several moisture levels. The influence of the natural variability of wood characteristics on the measured pennittivity was also investigated by a suitable experimental setup consisting of a poplar table including both sapwood and heartwood regions. Finally, a theoretical discussion on the meaning of a scalar measurement on anisotropic dielectrics is conducted in terms of an isotropic-equivalent permittivity, which is related to the permittivity tensor of the dielectric material.

Thickness-independent measurement of the permittivity of thin samples in the X band

A method is proposed for measuring the complex permittivity of thin materials. The method allows us to simultaneously measure the permittivity and thickness of the material, allowing us in particular to obtain a meaningful estimate of the average thickness of natural materials. The measuring system consists of a section of rectangular waveguide, operating in the X band and modified to accommodate the material under measurement, and two standard impedance loadings (short-circuit and matched load). Two reflection coefficient values, measured by a vector network analyser at the input of the waveguide sample-holder, allow the determination of the parameters of interest by means of a numerical procedure employing a genetic algorithm. The method has been tested on certified dielectric materials and preliminary results are presented concerning paper and thin cardboard.

High permittivity patch radiator for single and multi-element hyperthermia applicators

A compact, low-profile patch radiator which is the base element for efficient, small-size applicators suitable for superficial hyperthermia is described. The design criteria and the technological processes involved are presented. The electromagnetic characteristics of the patch element are outlined, and possible application of the radiator are discussed.<<ETX>>

Phantom characterization of applicators by liquid-crystal-plate dosimetry

A method for the determination of the SAR distribution produced by an electromagnetic applicator for localized hyperthermia is described. The procedure for SAR evaluation consists of recording the time evolution of the temperature inside a polyacrylamide phantom by means of thermochromic liquid crystal sheets inserted in it. The technique allows a complete characterization of applicators in a very broad frequency range, using power levels of the order of those needed in real treatments. Criteria for the minimum phantom size and the maximum time duration of the characterization procedure are indicated, which allow a reliable determination of the effective field size and penetration depth of the applicator.

Exposure of workers to intense RF electric fields that leak from plastic sealers.

This paper presents the results of an environmental investigation in a plastic-ware industry using RF sealers. Environmental measurements have demonstrated the presence of strong electric fields the intensity of which: reaches significant levels from the health-protection point of view only in proximity to the applicators; often exceeds the maximal levels allowed by all standards (including the most permissive) for short duration exposures, especially in the region of the hands. Results of a cross-sectional study on the health of 63 female workers are related to the observed RF exposure. A statistically significant correlation was found to exist between RF exposure and some minor health effects--eye irritation, upper limb paresthesias, and vitreous body disorganization.

Monitoring alcoholic fermentation by microwave dielectric spectroscopy.

The dielectric properties of water solutions of ethanol and sugar are investigated in the microwave region with the objective of setting up a method for the quality control of the fermentation process of alcoholic beverages. Alcoholic fermentation is the process by which carbohydrates, in particular sugar, are converted by the yeast into alcohol. During that process several other byproduct compounds are produced, including a significant amount of carbon dioxide. The fermentation stage is of fundamental importance in the production of alcoholic beverages because some of the by-products’ components have a considerable effect on the flavour, aroma, and other characteristic properties of the beverages. The on-line monitoring of the fermentation process can thus be very useful for controlling the timing and the development of the process in order to correct it earlier if deviations from “normality” occur. Dielectric spectroscopy is shown to be suitable for such a task, being able to discriminate between the initial water-sugar mixture and the final water-alcohol solution and making it possible to detect the production of carbon dioxide during fermentation. A case-study consisting of the monitoring of the primary fermentation of beer by dielectric spectroscopy is presented and discussed.

A PORTABLE MICROWAVE SYSTEM FOR WOODWORM DISINFESTATION OF ARTISTIC PAINTED BOARDS

Microwave power can be effectively used for disinfesting wooden objects of woodworms. Disinfestation is achieved by heating woodworms inside wood above their lethal temperature values.A prototype of a portable microwave system suitable for treating small and delicate wooden objects is described. The system, working at 2.45 GHz, used a commercial magnetron, a radiative applicator, and a non-contacting thermometer to monitor the temperature of the painted surface. A flow of air is blown through the applicator to cool the irradiated surface. A treatment bench has been set up to heat painted boards in controlled conditions. The applicator is placed on the rear side of the board, while the painted side is monitored by means of an infrared the to maintain its temperature below safe levels (e.g. 50–55 °C).Results concerning the effect of microwave heating on several specimens infested by woodworms in all metamorphical stages (egg, pupa and larva) are reported and discussed. Preliminary results about possible det...