Temperature-dependent dielectric properties of chestnut and chestnut weevil from 10 to 4500 MHz

The dielectric properties of chestnut and chestnut weevil at five temperatures between 20 °C and 60 °C over the frequency range from 10 to 4500 MHz were measured with an open-ended coaxial-line probe and network analyser. The dielectric constants (ε′) of both materials decreased with increasing frequency. The dielectric loss factor (ε″) of chestnut decreased with increasing frequency below about 3000 MHz, and slightly increased above 3000 MHz. The ε″ of chestnut weevil decreased with increasing frequency to a minimum value at about 1000 MHz. Below the turn point, the value of ε″ increased with increasing temperature, and decreased with temperature above that point. The ε′ and ε″ of chestnut and ε′ of chestnut weevil increased with increasing temperature. The penetration depth decreased with the increase of either frequency or temperature. Dielectric heating below 100 MHz might provide practical applications in controlling chestnut weevil due to potential differential heating and sufficient penetration depth. The study offers useful information on dielectric properties of chestnut and chestnut weevil in developing thermal treatments for postharvest disinfestation based on electromagnetic energy.

► Dielectric properties of chestnut and chestnut weevil are frequency and temperature dependent.
► Loss factor of chestnut weevil was much higher than that of chestnut at radio frequency.
► Penetration depth at lower frequencies was larger than at microwave frequencies.
► Dielectric heating below 100 MHz is the practical choice for developing disinfestation of chestnuts.