Development of hand-held needle–ring–ring self-excited plasma device

Copper is deposited in the holes of two perforated printed circuit boards to form copper rings with a width of 1.5 mm, a thickness of 1.6 mm, and diameters of 10 and 7 mm, respectively. The resulting structures form ground electrodes. A plate with a diameter of 10 mm is placed above a plate with a diameter of 7 mm to ensure that the distance between the two electrode rings is 2.5 mm. Meanwhile, a tungsten needle with a diameter of 1.1 mm is placed 6 mm directly above the coaxial position of the 7 mm diameter plate as the needle electrode. The needle–ring–ring electrode structure is designed to achieve stable synchronous discharge from each unit. The shell of the device is made using 3D printing technology. The displacement of active substances on the agar plate by the needle–ring–ring self-excited plasma jet is visualized using the starch–potassium iodide reagent. The results indicate that the device produces a better sterilization effect than traditional sterilizing devices and that no hollow, annular, unsterilized part is produced. In addition, the macroscopic temperature of the self-excited emission stream is detected. The human body detects no obvious burning or tactile sensation from the plasma.