Focusing dielectric slabs for the optimization of heating patterns in single mode microwave applicators

[Display omitted] •Specific temperature distributions are difficult to obtain in microwave applicators.•Dielectric slabs with adjustable positions are proposed as focusing lenses.•Numerical and experimental results are provided for a TE101 rectangular cavity.•The slabs allow the optimization of heating patterns with great flexibility.•Their effect is illustrated on plastic preforms with a predefined heating pattern. A new approach based on dielectric slabs with adjustable position is proposed as near-field focusing lenses inside a single-mode microwave applicator to provide specific temperature distributions within a material heated by microwaves. Numerical and experimental results in a TE101 rectangular cavity at 915 MHz have been used to evaluate the capability of these focusing dielectrics to optimize the temperature profile of Polyethylene terephthalate (PET) preforms. Measurements of the temperature profile on the preforms verified the strong effect of the slabs on the electric field distribution, allowing the optimization of the heating patterns with great flexibility. The successful application applied to PET preforms with different sizes and geometries showed the versatility of this approach which can be extended to the application of other type of loads and microwave cavities.