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An atmospheric pressure low power microwave-induced air plasma source at 2.45 GHz is presented in this Letter. The device was capable of self-igniting air and generating plasma with only 50 W microwave input power and without any extra trigger. Its sustaining power was as low as 10 W, and the gas temperature of plasma tail flame measured by a fiber optic thermometer was about 32 °C. Spectroscopic measurements showed strong O H (A 2 Σ + → X 2 Π) bands at 306–310 nm and oxygen atomic lines O I (3p5P → 3s5S) at 777.1 nm and O I (3p3P → 3s3S) at 844.6 nm. N O − γ (A 2 Σ + → X 2 Π r) from 200 to 300 nm was also detected in this air plasma jet. This portable plasma apparatus offers potential for air plasma applications in the biomedical fields. [ABSTRACT FROM AUTHOR]

This paper investigated the influence of gas humidity (1%, 3%, 8%, 10%, and 12%) on the characteristics of a microwave-induced atmospheric plasma jet. The plasma discharge was generated by a microwave solid-state source with a H2O–Ar mixture gas flow of 8.1 L/min. The variation in energy efficiency, O and OH concentrations, rotational temperature of heavy species, shapes of plasma plumes with different humidities, and microwave input powers were recorded and analyzed. The results showed that the concentrations of O and OH increase monotonously with gas humidity at higher input powers while they fluctuate with gas humidity at lower input powers. With an increase in the H2O/Ar ratio from 1% to 12%, the energy efficiency of the plasma generator decreases, and the plasma plumes become shorter and thinner. The rotational temperature of plasma at the nozzle also showed positive correlation with increasing humidity. Adding more input power would make all the values of these parameters increase. This paper is supposed to be helpful for the research of the interaction mechanism of mix gas plasma and microwave power and for improving the effect of plasma treating biomedical materials. [ABSTRACT FROM AUTHOR]

This article investigated the discharge characteristics of Ar plasma sustained by a coaxial plasma jet under different microwave frequencies (433 MHz, 915 MHz, 2450 MHz, and 5800 MHz). Clear distinctions of the discharge characteristics such as excitation and plasma-sustaining power, shape, electron number density, electron temperature, and so on were experimentally obtained under these operating frequencies. The results demonstrated that microwave powers at different frequencies could excite distinct particles. The higher the microwave frequency, the lower the excitation and the plasma-sustaining power. However, these powers did not decline linearly to the increase in microwave frequency. The Ar plasma at a frequency of 5800 MHz exhibited an upside-down "bell" shape and a larger cross section, while those at other three frequencies seemed to have thin and long plumes. The investigation also revealed that the electron temperature increased and then decreased, while the electron number density and gas temperature elevated monotonously with increasing frequency. This study is intended to be helpful in determining the optimal frequency and design microwave plasma sources for certain applications. [ABSTRACT FROM AUTHOR]

A 2450-MHz microwave-induced room-temperature atmospheric-pressure plasma jet (RTAPPJ) based on a coaxial structure is proposed for applications of plasma biomedicine. This device is a simple structure with small size, low-power requirement and high controllability. It can induce an argon discharge at atmospheric pressure with as low as 15-W microwave power. The optical emission spectrum of the RTAPPJ shows various highly reactive radicals such as OH and O. The appropriate operation condition can reduce the temperature at the downstream of the flame to be around 30 °C. This portable device is designed to be suitable to manipulate different medical treatments. [ABSTRACT FROM AUTHOR]