Research On Low-temperature Microwave Plasma System

Due to the characteristics of high electron temperature and low gas temperature,lowtemperature plasma has been widely studied in the fields of medical surgery,sterilization,wound healing and material surface treatment,etc.microwave plasma has received more and more attention because of better safety,higher electron density and other excellent properties compared with traditional high voltage DC or radio frequency plasma.Especially with the development of solid-state microwave devices,the low-temperature microwave plasma system can be greatly reduced in size and can be hand-held,thereby further expanding the application prospects of the low-temperature microwave plasma systems.The low-temperature microwave plasma system mainly consists of three parts: microwave source,impedance adjuster and plasma source.This dissertation aims to develop a more stable,efficient,and miniaturized low-temperature microwave plasma system.New struture of plasma jet,automatic impedance macher,the control of the microwave plasma jet and the characteristics of both continuous and modulated microwave plasma plume are investigated.Besides,the application of low-temperature microwave plasma in sterilization is explored.The main research contents are:1.A new handheld microwave plasma torch with a dual coaxial composite structure is proposed.Through the simulation study of microwave field and airflow distribution,a new plasma jet is designed and tested? the plasma jet is able to generate a stable filamentary low-temperature plasma plume directly in the atmosphere without the traditional quartz glass tube protection under the dual-channel argon gas condition? the design method of the plasma jet and the operating conditions as well as the characteristic parameter of the generated plasma are measured in the paper.The experimental results show that the proposed plasma jet has high efficiency,can be hand-held with arbitrary rotation,the plasma jet length can be controlled,and the plasma plume generated by this jet has low temperature,can be touched by hand,and the electron temperature is in the range of 0.6 1e V.2.For the plasma impedance fluctuation in different gases,gas flow rates,microwave power and other operating conditions,the impedance measurement system and automatic impedance matching system applicable to low-temperature microwave plasma system are studied and designed.A three-probe based microwave impedance real-time detection algorithm is derived and established to realize measurement of microwave impedance.The results show that the atmospheric pressure plasma jet is inductive as a whole,and the impedance of microwave plasma jet at different powers will vary substantially,while the effect of changing the airflow on the plasma impedance is small,which lays the basic data for the impedance matching of the subsequent source-torch integrated ultra-compact plasma jet.In addition,the radius and insertion depth of the triple pin were simulated and studied,the mechanical and circuit of the three-pin adjuster have been designed and realized.Reaults shows that the single deployment time was less than 2s at the operating frequency of 2.45 GHz,and the average voltage standing wave ratio after deployment was less than 1.2,which reached the advanced level of similar products.3.The variation characteristics of low-temperature microwave plasma have been studied under different power,ionized gas,and air flow rate.The plasma length,emission spectrum,and electron temperature were investigated by digital imaging,infrared imaging,and emission spectrum diagnosis.The results show that the plasma produced by this low-temperature microwave plasma system can be controlled stably by microwave power and air flow rate,and the electron temperature of the plasma remains stable under different microwave powers.In addition,the modulated microwave plasma were also investigated.The modulated microwave excited plasma was controlled by different modulation parameters,including duty cycle and modulation frequency.The results demonstrate that the modulated microwave plasma differs in all aspects from the continuous microwave plasma,and the modulated microwave plasma jet was torn at specific modulation parameters.In addition,new phenomena of unripped modulated microwave plasmas tearing when touching the surface of an object are observed.This controlled tearing can increase the contact area of a single plasma jet when treating materials,thus showing potential for application in large area sample treatment.4.The application of microwave low-temperature plasma jets in sterilization was carried out using the developed plasma jet.Agar with E.coli,S.aureus and yeast was treated for different time,times and areas.The results showed that the cold plasma had a very strong disinfection effect on all the above mentioned strains,demonstrating a promising application in medical disinfection.