Alexander L. Taube

Measuring the dielectric properties of wood at microwave frequencies

A method for measuring the dielectric permittivity of thick pieces of wood is presented together with a description of the software required to extract the dielectric parameters from the measured quantities via the solution of a transcendental equation in the complex plane. This specific experimental method was adopted as it is suitable for extension to measurements at elevated temperatures and pressures. The measuring procedure, the numeric scheme, and a general analysis of the solutions are demonstrated by a series of measurements conducted on soda lime glass. First results of Blue Gum (Eucalyptus globulus) wood measurements are also presented and reveal a strong dependence of the dielectric permittivity on the electric field direction and sample moisture content.

Moisture Monitoring of Corrugated Board During Microwave Processing

Non-contact moisture content measurement of corrugated board on-line, possess significant production advantages which ratify superior productivity and quality control in the corrugated board manufacturing processes. This paper discusses the specific theoretical and practical aspects of microwave moisture content measurements and gives some experimental data obtained from moisture content measurements of typical cardboard materials used in the corrugated board industrial production processes. Regulating the pre-prescribed level of the moisture content during manufacturing is an imperative parameter for drying. The method proposed utilises part of microwave heating energy to control moisture content of the process. The correlation equation between absorbed power and moisture content was determined, in order to program the controlling hardware feeding the drying power.

Non-destructive evaluation using variable frequency microwaves

Microwave assisted Non-Destructive Evaluation (NDE) technologies have been utilised in industry for materials characterization and quality assessment. This paper discusses the potential of using broadband variable frequency microwaves (2.5−18 GHZ) for diagnosing materials integrity, especially during processing in resonant cavities. The technique is compared to conventional microwave based NDE. Details regarding system configuration with on-line process control and volumetric quality control capabilities are included for microwave curable epoxy test pieces. The principles of microwave interactions with these materials are explained and experimental findings presented.

Microwave resonance plasma source for surface modification technologies at atmospheric pressure

This paper extends the range of applications for microwave energy to create a plasma source based on the resonance phenomenon and operated at atmospheric pressure. The atmospheric-pressure process is advantageous for plasma-assisted coating deposition and plasma surface treatment. The novel Microwave Resonance Plasma Torch (MRPT) using the tunable TM/sub 013/ mode cylindrical resonant cavity and working at 2.45 GHz was tested for surface engineering applications. The MRPT was successfully approved with different carrier gases (N/sub 2/, Ar, He) for creation of thermal plasma. The feasibility of using the Microwave Resonance Plasma Torch for nitriding/oxinitriding of Ti, 304 and 316 stainless steel, and 5140 steel with pure N/sub 2/ and with air (the mixture of N/sub 2/ 78 vol%+O/sub 2/ 21 vol%) was confirmed.

A numerical determination of the temperature distribution within a bonded paper web in a waveguide

In this research, a numerical approach is used to study the temperature distribution within a bonded paper web and the outcome compared against experimental technique. The chosen parameters would enable a thorough understanding of the temperature distribution occurring within a bonded paper web. The method of false transient was used to accelerate the numerical convergence and the equations were discretised with central difference in both time and space. The numerical estimates were analogous to the experimental data generated using a waveguide.