Closed-loop-controlled atmospheric pressure plasma treatment system

Dielectric barrier discharges (DBD) are used as cold atmospheric-pressure plasma (CAP) sources in many emerging applications in medicine, surface modification, agriculture and environmental protection. Unlike their low-pressure counterparts, CAPs operate in the open air and are subject to inevitable environmental fluctuations, which affect the device performance. Therefore, the strategy used in traditional low-pressure systems of having a tight control environment is not viable for CAPs. As a result, stability, repeatability and control of the discharge properties are the key limitations of current CAP systems.

To mitigate against these undesired fluctuations, an ‘intelligent’ Power Supply Unit (PSU) capable of adjusting the applied electrical field to control the power delivered to the discharge over long periods of time and achieve a stable and repeatable plasma treatment is proposed as part of this thesis. The PSU designed, built and tested is affordable (<£500), and it is shown to improve the stability and control of two different DBD reactors. The PSU can utilise electrical as well as optical signals to adapt the output of the power supply, and a power-controlled and an ozone concentration-controlled operation modes are demonstrated. The PSU is shown to be able to keep the stable performance of DBD reactors for hours at a time, with at least a 4x reduction in fluctuations caused by environmental changes when compared with conventional power supplies.