Experimental Investigation of Discharge Characteristics and Power Interruption for Fire Prevention from Metal Object in a Microwave Oven

Microwave ovens (MWOs) are widely used in food processing, industrial and medical applications. A metal object placed inside the MWO can cause discharges which could lead to fires. This study investigates a fire prevention approach that detects discharge signals to cut off the power supply with a circuit interrupter, using an aluminum foil ball as a practical and severe metal object sample. Discharge‐emitted electromagnetic (EM) waves were measured using a selective signal detection technique with an ultra‐high‐frequency band antenna during MWO operation, together with light emission images recorded by a digital camera. Two interrupters with different operation times were used: a commercially available solid‐state relay (SSR) and a self‐developed MOSFET type interrupter. The interruption time, defined as the time from discharge signal detection to circuit interruption, was within a few hundred microseconds for the MOSFET type, much faster than the millisecond‐scale SSR. As a result, the discharge duration of the MOSFET type interrupter was reduced by about one order of magnitude compared to the SSR, and neither intense light emission nor flame generation was detected. Therefore, this system, which detects discharge signals to cut off the power supply, successfully prevented ignition caused by a metallic object inside the MWO. © 2026 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.