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The authors present a resonant permittivity measurement method which works over a large microwave frequency domain, with a very small volume sample of dielectric material. The cell is a helical resonator having many modes of resonance. The shifts of resonance frequency and Q-factors are better interpreted with a bilinear function which depends on the complex permittivity of the material than by applying the classical perturbation formula. Results concerning two different catalysts which are used in the coupling oxidation methane reaction are given as a function of the temperature and the frequency to illustrate the correlation of both data sets and the differences in catalytic mechanisms.

This paper presents an equation for calculating the effective complex permittivity of a two-component mixture made with particles of medium 2, dispersed in host medium 1. The geometrical density function which describes the mixture is deduced from the distribution function of relaxation times for the case of medium 2 consisting of metallic particles, by assuming that the dielectric response of the mixture follows the universal dielectric response.

The role of electromagnetic heating in batchwise dyeing processes has been investigated. It has been shown that electromagnetic heating offers smoother and more homogeneous heating profiles than are possible with many conventional techniques.

Using the modulated scatterer technique allows us to measure the electromagnetic field in an applicator. The design of a new sensor modulated at 25 Hz is described. The operating conditions and the performance are presented.The sensor can be used for measuring high microwave electric fields up to 10 kV/m in an industrial applicator supplied by any industrial magnetron.

As a consequence of the BERGMAN - MILTON theory, which expresses the effective permittivity of a two phase mixture with an integral of a density function, it has been possible to evaluate the local electrical field strength inside a heterogeneous mixture. The developed formula can be used advantageously for modeling the local temperature inside a ceramic material during its microwave sintering.

The authors have studied the drying of cellulose particles under microwave irradiation. They consider the drying rate, temperature and complex permittivity of cellulose under various experimental conditions. A simple model is proposed, based on a first order kinetics law, the rate constant of which depends linearly on the square of the applied electric field. They suggest that water is directly removed from the surface of cellulose by an electromagnetic field independently of the temperature.

By simultaneously measuring the total input and reflected power and the intensity of the local field inside a resonant applicator, it is possible first to estimate the effective microwave field to which the material is exposed, and second, to control the microwave energy dissipated in the heated or transformed material. The instantaneous dielectric behaviour depending on the temperature or on the fields, or on the transformation stage, is also derived. Some characteristic curves, which illustrate thermal hysteresis during a given heating process are shown.

A closed-groove guide type cavity is described. Its resonance mode is a quasi-unique TE11 mode. A large diameter cylindrical dielectric sample may be introduced into the cavity still conserving a high quality factor which is a necessary condition in order to obtain a large field amplification factor.The field profile along the sample axis is adjustable and may be asymmetric. Coupling devices are discussed and experimental details are given.

Direct calorimetric evaluation of the microwave loss of dielectrics is possible for granular materials. A cylindrical sample is heated by the microwave field of an incident wave in a rectangular guide and simultaneously cooled by a gas flowing through the bed.A mathematical model describing the energy balance and the heat transfer between the microwaves, the materials and the gas is proposed. It is shown that it is possible to determine, simultaneously, the temperature of the material and its microwave dielectric loss from the measurement of the exhaust gas temperature when thermal equilibrium occurs.

The behaviour of a material in a microwave field is di-rectly related to the temperature dependence of the imaginary part of the permittivity of a material. According to the conditions of thermal evacuation chosen, for example convection, its heating is either stable or unstable. For some materials, a critical temperature can be defined which represents an upper limit beyond which the heating is unstable whatever the convective heat transfers. The optimal conditions which can be obtained through the use of an automatic regulation of the heating are, as a consequence, determined. The microwave heating of EPDM rubber is treated as an example.

A groove guide cell for Stark modulation spectroscopy has been constructed and tested. This structure with quasi-unique mode propagation between two isolated plates is well adapted to application of a modulation voltage. The insertion losses are low (0.6 dB for a 3-m-long cell, and R band) and the cell is free of internal reflection. A metallic casing enclosing the plates acts as a shield against electrical interference, prevents low-voltage breakdown, and reduces wall adsorption of the gas. The performance of the cell is not affected by temperature variation (-80 degrees to 25 degrees C). A high sensitivity has been obtained by converting the cell into a 3-m-long, high-Q cavity. This type of cell appears to particularly recommend itself for use in intensity measurements, broadband spectroscopy, analytical studies, and high frequency range work.