longer than the cavity used, and thus made use of near-field effects and not electromagnetic waves. (Commercial microwave ovens use wavelengths only 1% as long.) In agriculture, RF dielectric heating has been widely tested and is increasingly used as a way to kill pests in certain food crops after harvest, such as walnuts still in the shell. Because RF heating can heat foods more uniformly than is the case with microwave heating, RF heating holds promise as a way to process foods quickly. In medicine, the RF heating of body tissues, called diathermy, is used for muscle therapy Heating to higher temperatures, called hyperthermia therapy, is used to kill cancer and tumor tissue. RF heating is used in the wood industry to cure glues used in plywood manufacturing, fingerjointing, and furniture construction. RF heating can also be used to speed up drying lumber. Microwave heating Microwave heating, as distinct from RF heating, is a sub-category of dielectric heating at frequencies above 100 MHz, where an electromagnetic wave can be launched from a small dimension emitter and guided through space to the target. Modern microwave ovens make use of electromagnetic waves with electric fields of much higher frequency and shorter wavelength than RF heaters. Typical domestic microwave ovens operate at 2.45 GHz, but 915 MHz ovens also exist. This means that the wavelengths employed in microwave heating are 0.1 cm to 10 cm. This provides for highly efficient, but less penetrative, dielectric heating. Although a capacitor-like set of plates can be used at microwave frequencies, they are not necessary, since the microwaves are already present as far field type EM radiation, and their absorption does not require the same proximity to a small antenna as does RF heating. The material to be heated (a non-metal) can therefore simply be placed in the path of the waves, and heating takes place in a non-contact process which does not require capacitative conductive plates. Microwave volumetric heating Microwave volumetric heating is a commercially available method of heating liquids, suspensions, or solids in a continuous flow on an industrial scale. Microwave volumetric heating has a greater penetration depth, of up to , which is an even penetration through the entire volume of the flowing product. This is advantageous in commercial applications where increased shelf-life can be achieved, with increased microbial kill at temperatures lower than when using conventional heating systems. Applications of microwave volumetric heating