Daniel M. Sherman

Electrohydrodynamic Flow Control with a Glow-Discharge Surface Plasma

Multiplee ow diagnostics have been applied to planarpanels covered by strips of glow-discharge surface plasma in atmospheric pressure air generated by the one atmosphere uniform glow discharge plasma. Direct drag measurements, smoke wire and titanium tetrachloride e ow visualization, and boundary-layer velocity proe les were obtained. The plasma generated along streamwise-oriented, symmetric strip electrodes is shown to cause a large increase in drag, whereas the plasma along spanwise-oriented, asymmetric strip electrodes can generate a signie cant thrust. Flow visualization and mean velocity measurements show the primary cause of the phenomena to be a combination of mass transport and vortical structures induced by strong electrohydrodynamic body forces on the e ow, known as paraelectric forcing.

The physics and phenomenology of One Atmosphere Uniform Glow Discharge plasma (OAUGDP) reactors for surface treatment applications

In this paper, we present data on the physics and phenomenology of plasma reactors based on the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP™) that are useful in optimizing the conditions for plasma formation, uniformity and surface treatment applications. It is shown that the real (as opposed to reactive) power delivered to a reactor is divided between dielectric heating of the insulating material and power delivered to the plasma available for ionization and active species production. A relationship is given for the dielectric heating power input as a function of the frequency and voltage at which the OAUGDP™ discharge is operated.

Use of a one atmosphere uniform glow discharge plasma to kill a broad spectrum of microorganisms

The medical, industrial, and food processing industries are constantly in search of new technologies to provide improved methods of sterilization and pasteurization. Proposed techniques must deal with such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, cost, and inefficiency in performance. We report results from a newly invented plasma source, a one atmosphere uniform glow discharge plasma (OAUGDP), which is capable of operating at atmospheric pressure in air and providing antimicrobial active species at room temperature. OAUGDP exposures have reduced log numbers of bacteria (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa), bacterial endospores (Bacillus subtilis and Bacillus pumilus), and various yeast and bacterial viruses on a variety of surfaces. These surfaces included polypropylene, filter paper, paper strips, solid culture media, and glass. Experimental results showed at least a ⩾5 log10 colony forming units (CFU) reduction in bacteria...

Sterilization and plasma processing of room temperature surfaces with a one atmosphere uniform glow discharge plasma (OAUGDP)

A technique for generating active species with the one atmosphere uniform glow discharge plasma (OAUGDP) has been developed and tested in a wide range of potential plasma processing applications, including the sterilization and decontamination of surfaces. The OAUGDP is a non-thermal plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. In addition to directly exposing webs and workpieces to active species by immersion or at the plasma boundary of a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. No vacuum system or batch processing is necessary, and a wide range of applications can be accommodated. This technology is simple, cost-effective and suitable for online treatment of webs and such three-dimensional workpieces as medical instruments. We will report the use of an air OAUGDP to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a remote exposure reactor to sterilize large workpieces 20 cm or more from the plasma-generating region, and a sterilizable air filter.

A remote exposure reactor (RER) for plasma processing and sterilization by plasma active species at one atmosphere

We have developed a remote exposure reactor (RER) in which the active species of air and other gases responsible for sterilization and processing effects are generated on flat panels in a surface layer of one atmosphere uniform glow discharge plasma (OAUGDP). These active species are convected by forced airflow at one atmosphere and near room temperature to a remote exposure chamber in which the workpiece is located. This allows workpieces of any size or shape to be sterilized or processed without direct contact with the plasma. Here, we report operation of the RER as a sterilizer with both single-pass and recirculating active species flow through the remote exposure chamber. We used the RER to reduce the numbers of two genera of microorganisms (Esherichia coli and Staphylococcus aureus) on test samples of polypropylene fabric. When the recirculating airflow configuration was employed, the population both of E. coli and S. aureas cells was reduced by at least five decades after only 25 s of exposure. Tests in the single pass airflow configuration produced similar results, with the E. coli and S. aureas populations decreased by at least four decades after 25 s of exposure.

The transition from a filamentary dielectric barrier discharge to a diffuse barrier discharge in air at atmospheric pressure

A transparent plasma discharge reactor using air was used to investigate the transition from a filamentary dielectric barrier discharge (FDBD) operation regime into the diffuse barrier discharge regime. Recent results of other researchers indicate that the stability of diffuse barrier discharges in nitrogen may be attributed to the lack of a fully formed cathode fall layer when the discharge operates in a regime between the Townsend discharge and a normal glow discharge. We have demonstrated that a diffuse barrier discharge in air exhibits an increased accumulation of electric charge on the electrodes dielectric plates as compared with the FDBD. This may provide a means of stabilizing the discharge in a Townsend-to-glow discharge transition. Unlike operation in nitrogen, a streamer mechanism is involved in the formation of a uniform air plasma, though in a different manner than is associated with the FDBD. Numerous diffuse streamer clusters were observed on pre-charged dielectric plates at the breakdown voltage. Our conclusion is that the macroscopically uniform atmospheric-pressure DBD in air is obtained by the numerous radially expanding streamers that are temporally overlapping.

A polyphase low frequency RF power supply for a one atmosphere uniform glow discharge plasma (OAUGDP)

Summary form only given. A flexible, reliable, and robust RF power supply capable of delivering the frequency and voltage required to energize the One Atmosphere Uniform Glow Discharge Plasma OAUGDP is needed, but off-the-shelf availability of such a RF power supply is quite limited. A RF power supply designed to generate the OAUGDP is composed of a frequency generator, amplifiers, and a transformer. If the power supply is built from several smaller subunits (amplifier and transformer) that combine to supply the RF electrical power rather than just one larger unit, a component failure only implies a partial loss in power, rather than a complete shutdown. By properly choosing the components of the RF power supply, the additional capability to generate a polyphase voltage output and electric field gradients across an array of electrodes is also gained. Our previous OAUGDP aerodynamic research explored only the aerodynamic effects created by the generation of the OAUGD plasma. However another method of OAUGDP plasma formation-polyphase peristaltic acceleration-uses the electric field gradient generated by this RF power supply.

Room temperature sterilization of medical devices with OAUGDP

Summary form only given. The sterilization of complex multicomponent medical devices is difficult due to narrow channels and the presence of optics and electronics. Atmospheric Glow Technologies is pursuing the development of room temperature sterilization of these devices using one atmosphere uniform glow discharge plasma. Studies to date demonstrate the ability to routinely neutralize 6 logs of Bacillus endospores within 10 minutes at room temperature using only the convected exhaust from an air plasma. No liquid or gas additives are required. Since sterilization of medical devices is often hindered by the presence of organic debris, AGT has conducted assays in the presence of 10% bovine albumin serum and 0.65% sodium chloride as an organic matrix simulant. These assays support the ability of the reactive chemical species to penetrate the matrix and neutralize underlying microorganisms. This is particularly evident for plasma created with an increased concentration of oxygen as the input gas. Analyses have verified that exposures of 60 minutes have minimal effect on polymers as assessed with scanning electron microscopy. Ongoing efforts to identify and characterize the reactive chemical species responsible for biological neutralization indicate a role for singlet delta oxygen. The development of OAUGDP for room temperature sterilization could provide an economical sterilization option for small to medium-sized healthcare facilities.

Inactivation of airborne bacterial endospores with OAUGDP

Summary form only given. Atmospheric Glow Technologies (AGT) has developed an innovative means of safeguarding indoor environments using One Atmosphere Uniform Glow Discharge Plasma (OAUGDP/sup TM/). AGT has placed an atmospheric plasma device within HVAC duct work and is using reactive chemical species present in the exhaust from this device to neutralize biological agents captured on filter media. This plasma device, using air only, requires no additives. Importantly, since our design does not impede airflow, those flow rates typical for HVAC systems can be maintained. The biological inactivation achieved by this system is broad-spectrum and includes bacterial endospores. AGT routinely achieves neutralization of 6 logs of Bacillus atrophaeus (formerly B. subtilis variant niger, ATCC 9372) endospores within 5-20 minutes up to 2 feet downstream depending upon airflow parameters. Data correlating biological inactivation with electrical and airflow parameters will be presented. Ongoing research indicates singlet delta oxygen plays a significant role in OAUGDP-based biological neutralization. Liability of microorganisms was assessed using standard plate counts from filter media. All plates were incubated for a minimum of 96 h at 37/spl deg/C in order to accurately quantify any surviving organisms. The ability to provide broad-spectrum reduction of air-borne biological agents indicates that the use of a duct-mounted OAUGDP atmospheric plasma device can provide a reliable, unobtrusive means of protecting high-risk buildings.

Mass spectrometry of active species convected from a one atmosphere uniform glow discharge plasma (OAUGDP) in air

Summary form only given, as follows. The one atmosphere uniform glow discharge plasma (OAUGDP) is capable of operating at one atmosphere in air and other gases, and its active species can be used for the plasma treatment of surfaces. The OAUGDP can he operated in a wide range of geometrical configurations, ranging from a slab plasma between parallel plates, to a plasma layer which can cover an isolated flat or curved surface. The remote exposure reactor (RER) utilizes multiple flat panels covered with a surface layer of OAUGD plasma to generate active species from air, which have been convected distances of 20 cm or more downstream of the last plasma. These active species are capable of sterilizing the surface of materials. Our investigations have shown that the energizing voltage, the RF frequency, the RF power input, the number of panels generating the surface layers of the OAUGDP, and the distance active species are convected from the plasma panels to the workpiece all affect the killing times of microorganisms and other plasma processing effects. The relative concentration of active species in the efflux of the remote exposure reactor is determined by mass spectrometry and reported as a function of the above plasma parameters and the distance from the last plasma generating panel. Such information will be correlated with plasma sterilization data from the RER to learn more about the agents responsible for sterilization.