# Wearable Plasma Pads for Biomedical Applications
## 3 Results and Discussion  
### Description of the Plasma Pad  
The plasma pad introduced in this paper was produced in the form of a wearable device with a flexible thin-film plasma sheet and an electric power unit. Figure 1 shows a schematic of the overall concept of the plasma pad system, including the wearable power-supply unit stored in a band-type pocket. Electrical power is supplied to the pad through a cable with a connector, and the connector is detachable for pad disposal. After the system has been charged with the secondary battery of the power-supply unit, it can be used in a wireless form without external power; therefore, the patient can move freely while wearing the plasma pad system. Although plasma is generated in the voids of the gauze space between the skin and the film surface, the plasma pad has good electrical safety. In addition, it is protected from low temperature thermal damage as the film surface constantly maintains a temperature below 40 \({}^{\circ}\)C.  
A schematic of the plasma film layers and the discharge of the flexible plasma pad are shown in Figure 2a. A sinusoidal voltage of 50 kHz and 1.1 kV rms is applied to the high-voltage electrode. The cold plasma is readily generated even on a curved flexible surface, as shown in Figure 2a, and no electrical problems are evident when the flexible pad is attached to the skin. To confirm the formation of the ROS and RNS generated in the discharge, the plasma pad surface light was analyzed by optical emission spectroscopy in the wavelength range of 200-900 nm (Figure 2b). The identification of these emission lines was performed according to previous reports [32; 33]. The strongest emission peaks were the nitrogen lines at 316 nm, 337 nm, and 358 nm. It should be noted that emission lines from OH (309 nm) and N\({}_{2}^{+}\) (391 nm) appeared, but their intensities were very weak. These emission spectra indicate that the processed chemical and physical reaction produced various ROS such as NO, OH, and O\({}_{2}\) via the plasma pad. Figure 2c shows the variation of temperature inside the plasma pad versus the operating time under the same operating conditions of \(\beta\) = 100% and \(\beta\) = 50. The temperature was measured using a thermocouple inside the pad attached to the skin. Temperature saturating occurred at 50 \({}^{\circ}\)C for \(\beta\) = 100% and at 38.6 \({}^{\circ}\)C for \(\beta\) = 50% after 10 min. During a long-run test of several hours for stability and safety at an operating voltage of 1.1 kV, failures, such as thermal deformation of the film, were not observed, but slight erosion-staining due to plasma on the ground electrode was noted. Concerns about safety and failure due to aerial ozone or thermal heat can be readily reduced through use of the power control for voltage modulation. Figure 1: Schematic illustration of the wearable plasma pad kit and photographs of the thin-film plasma pad discharge. An important issue could be the adjustability of aerial ozone to maintain an allowable concentration below 0.08 ppm and an ozone odor detection threshold below 0.03 ppm [34; 35]. Figure 2d shows the assessment of ozone concentration in aerial space over the plasma pad with voltage modulation for power control during plasma generation. Figure 2d shows ozone concentration versus duty ratio at distances of d = 10 cm and d = 20 cm. When \(\beta\) = 100%, the ozone concentration is slightly \(>\)0.10 ppm. When \(\beta\) < 50%, the concentration is \(<\)0.05 ppm, nearly below odor detection level. Figure 2d shows the possibility of ozone control in the plasma pad. Even if the concentration over the plasma surface was 0.10 ppm at a distance d = 10 cm with \(\beta\) = 100%, the measured level was \(<\)0.05 ppm with the pad attached to the skin. In this study, the use of medical gauze is a distinctive feature of the plasma pad. While the pad is attached to skin, plasma is generated in the gauze between the pad and the skin. The medical gauze plays the role of a spacer, securing a void space for the generation of plasma.