Low-temperature atmospheric pressure plasma jets (APPJs) have a number of biomedical uses but their potential has been restricted by the limitation of their physical reach. A new article introduces a microwave-driven APPJ (MAPPJ) design that can overcome these limitations and offer advantages in biomedical applications.

APPJs typically use a quartz tube to stabilize their gas flow, which confines the majority of the plasma jet within the tube, making it difficult to use in applications where the plasma needs to interact with an outside object. To address this, Fu et al. developed an MAPPJ based on a complex coaxial transmission design, with one gas channel through the outer transmission line acting as the quartz tube that restricts the plasma, and a separate gas channel through the inner transmission line where the plasma is. The flow for each transmission line can then be adjusted via the driving microwave source to control the length, width and temperature of the plasma jet. As a result, the jet is entirely exposed and can interact with outside objects.

The researchers used a custom-designed microwave source and a complex transmission line structure where the inner conductor of the outer line also acts as the outer conductor of the inner line. This method makes it possible to operate at low temperature and high atmospheric pressure with high efficiency with little thermal radiation.

The ability to touch object surfaces, such as human skin, creates new possibilities for biomedical applications. “With the development of low-temperature plasma jets, the applications of plasmas used in biomedical fields would be extended for use not only as a surgery knife, but also for skin treating, sterilization, and cancer therapy,” said author Wenjie Fu.

Source: “A high efficiency low-temperature microwave-driven atmospheric pressure plasma jet,” by Wenjie Fu, Chaoyang Zhang, Cong Nie, Xiaoyun Li, and Yang Yan, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5108538.