Broadband dielectric characterization systems for food materials

A detailed knowledge of the dielectric properties of food materials is vital to any electromagnetic-based treatments, ranging from reheating meals in a domestic microwave oven through to sterilization processes. The uniformity and rate of heating of the food is highly dependent upon the dielectric constant and dielectric loss of the food material, with both parameters being intrinsically temperature-dependent. In this work, we explore various methods for the dielectric characterisation of materials over a wide frequency range (1 MHz to 20 GHz), to cover RF and microwave frequencies, as well as understand the impact of ingredients (e.g. salt, sugar) and temperature on free and bound water resonances. Such a large frequency range gives information that is invaluable when designing future equipment that relies on multi-frequency/broadband microwave heating techniques. The characterization methods of interest are the open-ended coaxial dielectric probe, the broadband dielectric broadband spectrometer, and a custom stripline resonator. Instant mashed potato is used as a food standard, which allowing for a large set of samples to be measured with various moisture contents. When directly compared at 1 GHz, all three methods produced comparable dielectric properties for 20% and 30% potato mixtures.