Improvement of Spatial Uniformity of Nanosecond-Pulse Diffuse Discharges in a Multi-Needle-to-Plane Gap

Large-scale non-thermal plasmas generated by nanosecond-pulse discharges have been used in various applications, including surface treatment, biomedical treatment, flow con- trol etc. In this paper, atmospheric-pressure diffuse discharge was produced by a homemade nanosecond-pulse generator with a full width at half maximum of 100 ns and a rise time of 70 ns. In order to increase the discharge area, multi-needle electrodes with a 3~3 array were designed. The electrical characteristics of the diffuse discharge array and optical images were investigated by the voltage-current waveforms and discharge images. The experimental results showed that the intensity of diffuse discharges in the center was significantly weaker than those at the margins, resulting in an inhomogeneous spatial uniformity in the diffuse discharge array. Simulation of the electric field showed that the inhomogeneous spatial uniformity was caused by the non-uniform distribution of the electric field in the diffuse discharge array. Moreover, the spatial uniformity of the diffuse discharge array could be improved by increasing the length of the needle in the centre of the array. Finally, the experimental results confirmed the simulation results, and the spatial uniformity of the nanosecond-pulse diffuse discharge array was significantly improved.

Performance Evaluation and Effectiveness of the Reverberation Room

This research presents a thorough evaluation of the reverberation room at Acoustics Laboratory in National Institute of Standards(NIS)according to the related international standards.The evaluation aims at examining the room performance and exploring its effectiveness in the frequency range from 125 Hz to 10000 Hz according to the international standard requirements.The room,which was designed and built several years ago,is an irregular rectangular shape free from diffusers.Its volume is about 158.84 m^(3),which meets the requirement of the ISO 354 standard Lmax<1.9V^(1/3).Cut-off frequencies of one and one-third octave are 63 Hz and 100 Hz respectively;however Schroder frequency is 400 Hz.Calculations of cut-off frequency and modal density showed adequate modes that give acceptable uniformity starting comfortably from frequency of 125 Hz.The room has a reverberation time that is suitable for its size over the frequency range of interest.The room sound absorption surface area and its sound absorption coefficient satisfy the criteria given in ISO 3741 and ISO 354.There is an accepted diffuse sound field inside the room due to the standard deviation of measured sound level,which is less than 1.5 dB over all the frequency range.The only exception was 125 Hz which may be due to a lack of diffusivity of the sound field at this frequency.The evaluation proves that the NIS reverberation room is in full agreement with the international standards,which in turns qualifies the room to host measurements inside without concerns.