Visualization of microwave energy distribution in a multimode microwave cavity using CoCl2 on gypsum plates

This study provides a facile method to map the microwave field distribution in a multimode microwave cavity. Anhydrous calcium sulfate powder was used to make the gypsum plates that were used as the carrying medium. Cobalt chloride hexahydrate, whose color changes when losing part or all of its crystal waters, was selected as an indicator of the energy absorption. The cobalt chloride aqueous solution at a concentration of 1.6% was absorbed by the dried gypsum plates. After introducing the plates into a microwave field, those areas that receive more microwave energy were preferably heated, resulting in the release of the moisture and consequently the loss of crystal water from the cobalt chloride hexahydrate. The color change on the plate formed a color map indicating the microwave field distribution. This method was used to investigate the energy distribution of a microwave oven by placing single or multiple plates in horizontal or vertical positions at different locations in the cavity.