Comparative study of radio-frequency and microwave heating for phytosanitary treatment of wood

Radio-frequency (RF) and microwave (MW) heating for phytosanitary treatment of green wood in compliance with international standards for phytosanitary measures no. 15 (ISPM-15) were evaluated and compared to assess treatment time, depth of electromagnetic wave (EMW) penetration and heating uniformity. White oak (Quercus alba) cants (48 cm long with cross-section dimensions ranging from 10 × 10 cm² to 25 × 25 cm²) were heated in a 19 MHz RF or 2.45 GHz MW laboratory oven using an equivalent heating power (3.4 kW). In each specimen, temperature was measured at different depths (distance from the upper face). Specimens were held in the treatment chamber for 2 min after the target temperature of 60 °C was achieved through the profile of the specimen to ensure compliance with the ISPM-15 treatment schedule. Thermal image analyses of treated specimens as well as theoretical depth of penetration for dielectric energy were explored. Wood specimens were also heated using RF at high power (9–11 kW) and results were compared with RF heating at 3.4 kW. For wood with cross-section dimensions of 10 × 10 cm² to 15 × 15 cm², heating rates for RF and MW were relatively similar. However, above 15 × 15 cm², RF heating was more than 40 % faster with greater heating uniformity than MW. The theoretical values derived for depth of penetration and thermal image analyses indicate that RF (19 MHz) penetrates wood more uniformly and is better suited than MW (2.45 GHz) for bulk volume treatments of wood.