A Cantor multilayer traveling wave applicator for microwave heating: Numerical analysis and design

Abstract

A traveling wave applicator particularly suitable for heating low loss materials is described. The applicator consists of a dielectric Cantor multilayer inserted in a single-mode rectangular metallic waveguide. Field localization phenomenon occurring in the multilayer allows high field amplitude (several times the amplitude of the incident field) to be obtained in a load placed at the center of the applicator. Design examples and numerical characterization of an applicator in WR-284 waveguide operating at 2.45 GHz are presented for cylindrical and planar loads. Results show that the proposed applicator can significantly enhance the effectiveness of the heating process

Cantor dielectric resonators for microwave waveguide applicators

“…This fractal construction consists of an initiator (which is the structure at the zeroth stage of growth) and a procedure generating the structure at the stage of growth M+1 from the one at the stage of growth M. In our case the initiator is a dielectric layer with relative permittivity d and thickness L while the generating procedure consists in removing the middle Rth part (R >1) of the dielectric layers at the stage of growth M leaving air gaps in their places ( a = 1). In this paper resonators at the stage of growth M = 2 will be considered, because they seem to offer a good trade-off between structure complexity and field localization property [Chiadini et al, 2008b[Chiadini et al, , 2014. As shown in Figure 1, at the stage M = 2 the Cantor resonator has a very simple structure consisting of four equal thickness dielectric layers separated by three air gaps with different lengths.…”

“…Equations (1)-(3) indicate that the geometry of the resonator is unambiguously determined fixing two of the three parameters D, L, and R. When inserted in metallic rectangular waveguide, a Cantor resonator exhibits a transmissivity spectrum with forbidden bands and narrow transmission peaks in the single-mode frequency range of the waveguide [Chiadini et al, 2009]. At the frequencies corresponding to the peaks a resonance phenomenon occurs, yielding energy concentration and field localization in the central air gap [Chiadini et al, 2014].…”

“…Numerical simulations showed that the localization factor is lower than that one of unperturbed structure. Nevertheless, the field localization inside the load should allow more efficient heating processes of low loss materials to be performed if their dielectric properties do not dramatically change during the treatment [Chiadini et al, 2014]. Figure 12 show the prototype of applicator realized by inserting a two-stage Cantor dielectric resonator in a 540 mm long WR340 aluminum waveguide with CPR340F flange at both ends.…”

“…On the other hand, microwave heating treatments of low loss materials require high-intensity fields [Metaxas and Meredith, 1993]. For these reason, the potential advantages of using dielectric resonators in microwave heating applicator have been analyzed [Chiadini et al, 2014]. Former investigations focused on the Cantor dielectric resonators because they seem to offer performance better than the perturbed periodic ones [Chiadini et al, 2008a[Chiadini et al, , 2008b.…”

Optimization of HF waves energy source for thermal treatment of building materials

“…HF wave thermal treatment pays an important role in producing heat-insulating building materials due to high inefficiency of the existing convection heating methods which is responsible for the low coefficient of thermal conductivity of heat-insulating materials [5].…”