Tadahiro Kubota

The axial distributions of optical emission and metastable density: comparison between experiments with DC and RF helium glow discharges

The axial distributions of the optical emission intensity and metastable atom density are shown experimentally for DC and RF helium discharges. Significant differences in the cathode glow adjacent to the cathode sheath are perceived between the DC and RF discharges. These differences seem to lead to differences in the consistencies of their cathode sheaths. It is found that the RF glow is caused by a direct excitation of non-thermalized high-energy electrons; on the other hand, the DC glow is caused by a dissociative recombination of old molecular ions and thermalized low-temperature electrons in addition to the former process. A theoretical model of metastable atoms in the cathode glow region is proposed, and the theoretical curves are compared with the experimental results of metastable density distribution. The validity of this model is then assured, at least qualitatively.

Improved RF-driven probe method for RF discharge plasma diagnostics

The authors describe an electrostatic probe technique for radio-frequency (RF) plasmas. The presence of RF potential fluctuations between probe and plasma distorts the Langmuir probe characteristic; it therefore introduces large errors into plasma parameters. The method presented an improved version of that proposed by Braithwaite et al. to remove the effect of an RF fluctuation on probe characteristics. It consists in superimposing the fluctuation of the space potential measured by an emissive probe to the DC voltage applied to the probe. This technique is applied to the measurement of electron temperature and density in 13.56 MHz RF discharges in helium and argon. The results are compared with direct-current (DC) discharge plasmas with identical input power. The electron temperature in the RF plasmas is higher than that in the equivalent DC plasmas and the electron density in the RF plasmas is lower than that in the equivalent DC plasmas.

Subadaptive piecewise linear quantization for speech signal (64 kbit/s) compression

We propose a simple speech compression algorithm using subband division and subadaptive piecewise linear quantization for a voice-mail system. Voice mail is an audio equivalent of sending letters. The main differences are that computer networks deliver the mail and that electronic recording is used instead of letters. Although speech data are stored in a semiconductor memory device, its capacity and the available network capacity are limited. Therefore, it is necessary to compress the data as much as possible. However, there are two conditions to be satisfied. The first is that the reconstructed datum must be understood correctly. Second, we need to identify the sender. Signals with a rate of 64 kbit/s are compressed at a ratio of about 1/9 using the proposed subband division and subadaptive piecewise linear quantization.

Axial Electric Field of He–Ne and He–Ar Gas Mixture Positive Column Plasmas in a Capillary Discharge Tube

The axial electric field of a positive column in a 0.8 mm-I.D. capillary discharge tube was measured for He–Ne and He–Ar gas mixtures at gas pressures from 0.1 to 10 Torr and discharge currents from 10 to 30 mA. The results show no significant percentage neon gas mixture effect on the axial electric field up to 10% neon in the He–Ne mixture. However, if we mix more than 1% of argon in helium, the axial electric field is observed to reduce significantly. The results also show that the axial electric field decreases with increasing percentages of neon and argon in He mixture.

Time-Averaged Electric Field Profiles in a Capacitive Coupling Parallel Plate Electrode RF Discharge Helium Plasma

Time-averaged electric field profiles in a capacitive coupling parallel plate electrode RF discharge with Balun circuit have been measured for a helium plasma. The experiment was conducted at a gas pressure from 0.3 to 3 Torr and RF power from 10 to 30 W. The results show that the time-averaged electric field in the central region of the discharge tube is observed to be relatively uniform for the present range of experimentation except for the gas pressure near 0.7 Torr for higher RF power conditions, where nonmonotonic potential profiles are observed.

The Axial Electric Field of a Positive Column in a Capillary Discharge Tube

The axial electric field of a positive column in capillary discharge tubes was measured for helium, neon, argon, krypton and xenon. The tubes used had diameters of 0.8 and 0.5 mm, the gas pressure was varied from 0.8 to 40 Torr and the discharge current was varied from 10 to 30 mA.

One Approach to Joining Plasma and Sheath

This letter treats the problem of joining plasma and sheath transverse to the discharge axis. The balance equations of plasma are solved from the center of the plasma to the wall. The point joining plasma and sheath is decided so that the sheath equation becomes non-negative. It is thought that the results of this letter will be useful in the analysis of the probe diagnostics, plasma processing, etc.

Real‐time pitch detection with a digital signal processor

Pitch detection is an important and essential technique in speech analysis, synthesis, and so on. There are many methods to extract voice pitch, but it is difficult to perform pitch extraction in real time. This paper describes a simple real‐time pitch detection algorithm which directly estimates the interval between peaks of the waveform. This algorithm consists of the following two parts: one is the peak emphasis of voiced signals and the other is the pitch detection. The peak emphasis is obtained by running a DFS (discrete Fourier series) and a window operation. It is important to determine the peaks for the pitch measurement because the pitch period is obtained by estimating the interval between successive peaks representing the pitch period of the voiced signal. The peaks related to pitch are determined using a few simple rules. Since the voiced signal waveform includes several extra complicated peaks, these rules are constructed taking into account the characteristics of the voiced signal. Other pea...