Silvio Kühn
Ferdinand-Braun-Institut
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Publication
Featured researches published by Silvio Kühn.
Plasma Sources Science and Technology | 2010
Silvio Kühn; Nikita Bibinov; Roland Gesche; Peter Awakowicz
A new miniature high-frequency (HF) plasma source intended for bio-medical applications is studied using nitrogen/oxygen mixture at atmospheric pressure. This plasma source can be used as an element of a plasma source array for applications in dermatology and surgery. Nitric oxide and ozone which are produced in this plasma source are well-known agents for proliferation of the cells, inhalation therapy for newborn infants, disinfection of wounds and blood ozonation.Using optical emission spectroscopy, microphotography and numerical simulation, the gas temperature in the active plasma region and plasma parameters (electron density and electron distribution function) are determined for varied nitrogen/oxygen flows. The influence of the gas flows on the plasma conditions is studied. Ozone and nitric oxide concentrations in the effluent of the plasma source are measured using absorption spectroscopy and electro-chemical NO-detector at variable gas flows. Correlations between plasma parameters and concentrations of the particles in the effluent of the plasma source are discussed. By varying the gas flows, the HF plasma source can be optimized for nitric oxide or ozone production. Maximum concentrations of 2750 ppm and 400 ppm of NO and O3, correspondingly, are generated.
Journal of Applied Physics | 2010
H. E. Porteanu; Silvio Kühn; Roland Gesche
We examine the applicability of the Langmuir-type of characterization for atmospheric pressure plasma jets generated in a millimeter-size cavity microwave resonator at 2.45 GHz. Wide range I-V characteristics of helium, argon, nitrogen, air and oxygen are presented for different gas fluxes, distances probe-resonator, and microwave powers. A detailed analysis is performed for the fine variation in the current around the floating potential. A simplified theory specially developed for this case is presented, considering the ionic and electronic saturation currents and the floating potential. Based on this theory, we conclude that, while the charge carrier density depends on gas flow, distance to plasma source, and microwave absorbed power, the electron temperature is quite independent of these parameters. The resulting plasma parameters for helium, argon, and nitrogen are presented.
IEEE Transactions on Microwave Theory and Techniques | 2010
Armin Liero; Mike Dewitz; Silvio Kühn; Nidhi Chaturvedi; Jijun Xu; Matthias Rudolph
Recently, GaN-based low-noise amplifiers (LNAs) were shown to provide high ruggedness together with low noise figure. Since no limiter is required to protect the input, these LNAs allow for simplified receiver architectures. This paper presents an in-depth analysis of the recovery time of a highly rugged LNA. Recovery time is measured in the time domain, and an analytical approximation is developed that allows to estimate and optimize recovery. A new measurement setup is established in order to determine the impact of the overdrive pulse on LNA gain. An X-band LNA is shown as an example. It survives input overdrive powers of up to 46 dBm under pulsed and 40 dBm under continuous wave conditions, with a noise figure of 2.8 dB. Extremely short recovery times below were simulated and measured.
Plasma Sources Science and Technology | 2012
R Bussiahn; Roland Gesche; Silvio Kühn; Klaus-Dieter Weltmann
The Integrated Microwave Atmospheric Plasma Source (IMAPlaS) operating with a microwave resonator at 2.45 GHz driven by a solid-state transistor oscillator generates a core plasma of high temperature (T > 1000 K), therefore producing reactive species such as NO very effectively. The effluent of the plasma source is much colder, which enables direct treatment of thermolabile materials or even living tissue. In this study the source was operated with argon, helium and nitrogen with gas flow rates between 0.3 and 1.0 slm. Depending on working gas and distance, axial gas temperatures between 30 and 250 °C were determined in front of the nozzle. Reactive species were identified by emission spectroscopy in the spectral range from vacuum ultraviolet to near infrared. The irradiance in the ultraviolet range was also measured. Using B. atrophaeus spores to test antimicrobial efficiency, we determined log10-reduction rates of up to a factor of 4.
IEEE Transactions on Plasma Science | 2009
Horia-Eugen Porteanu; Silvio Kühn; Roland Gesche
Plasma conductivity is of general interest for both fundamental research and specific applications. For this purpose, plasma equivalent impedance and complex conductivity are measured at 2.2 GHz, at pressures between 1 and 103 mbar, as a function of microwave power in a slot-type resonator, predominantly capacitively coupled to plasma. The plasma impedance is self-adjusting, maintaining a quasi-constant microwave amplitude. The sign of the imaginary part of the impedance (or conductivity) depends on pressure and, consequently, on electron density. The reactive part becomes significant if the Debye length is comparable with the size of the resonator and the plasma frequency is close to the microwave driving frequency.
international microwave symposium | 2010
Christian Bansleben; Silvio Kühn; Wolf-Joachim Fischer
This work was motivated by the idea to monitor the input impedance of differential front-ends of passive RFID-transponders depending on their power-consumption. Different methods readily available in state-of-the-art network analyzers are compared with regard to the special demands imposed by passive RFID front-ends. At this the correct stimulation of the DUT appears to be the major issue of conventional methods. Hereupon a new approach is proposed which for the first time combines the proper stimulation of differential, RF-powered devices with the data aquisition of differential mixed-mode S-parameters in temporal resolution. The new measurement method is applied to a 2.45GHz RFID transponder showing detailed mixed-mode results of its power-up behavior.
international conference on plasma science | 2009
Horia Porteanu; Silvio Kühn; Roland Gesche
Micarowave field breakdown conditions in gases are important whenever using plasma in pulsed mode. The plasma properties during the steady state regime are different from those during the ignition time.
international conference on plasma science | 2009
M. Kettlitz; R. Kozakov; Silvio Kühn; Roland Gesche; Horia-Eugen Porteanu
High pressure metal halide plasma (HID) lamps as compact light sources are characterized by high efficiency, excellent color rendering and long lifetime. Usually the lifetime is mainly influenced by electrode erosion leading to wall blackening and a reduction of the luminous flux. Therefore it is of actual research interest to have an electrodeless power input into HID lamps. More then ten years ago there was a high power electrodeless sulfur lamp with a microwave excitation commercially available1. New trends with lower power HID units below 50 W including research on electrodeless HID lamps could expand the field of application and break into new markets. This work discusses the high frequency power input and the plasma behavior in high pressure lamps2,3. Therefore several lamp geometries and lamp fillings were tested. The lamps were made of quartz and ceramics containing Ar as an ignition gas and several metal halides as light emitting substances. The lamps were ignited by an external high voltage pulse and operated in a special resonator configuration at frequencies around 2.45 GHz. The main energy input by inductive coupling was varied between 5 and 30 W. The power supply was built on a semiconductor basis. Input power, spectral distribution in the visible spectral range and vessel temperature were observed by a vector network analyzer, a fiber spectrometer and an infrared camera respectively. To enhance the vapor pressure of the additives, the lamps were also operated in a vacuum chamber. Variations in the filling, the input power and the wall temperature lead to changes in the spectral output, color temperature, color rendering and to changes in the coupling with the circuit. Further experiments are planed to study the influence of other resonator configurations and lamp shapes.
IEEE Microwave and Wireless Components Letters | 2009
Ibrahim Khalil; Silvio Kühn; Armin Liero; Roland Gesche
This letter presents a novel gate bias configuration for GaN HEMTs that ensures a safe operation of this kind of device by protecting the gate from forward turn-on. The bias circuit includes a simple series diode in the DC path that blocks any positive current from the gate, in other words it restricts the gate diode of the device to operate in forward bias. The new bias circuit ensures a safe operating condition of FET/HEMT transistors during forward turn-on while not hampering or degrading performance under normal operating condition.
international conference on plasma science | 2008
Horia-Eugen Porteanu; Silvio Kühn; Roland Gesche
Air, He, and Ar plasmas are analyzed at different pressures between 102-105 Pa. COMSOL simulation is used to approximate the value of plasma conductivity. Electron density is calculated for a scattering time tau of about 10-11 s, which is very close to the critical density, for which plasma frequency equals the microwave frequency. This might explain the sign change of the imaginary part of conductivity.