Takashi Sudo

Emission characteristics of dispenser cathodes with a fine-grained tungsten top layer

Abstract In order to improve the emission stability of the Ir-coated dispenser cathode under ion bombardment, a fine-grained tungsten top layer was applied on the substrate porous tungsten plug before Ir coating. The emission characteristics were studied after being assembled in a CRT gun. Cathode current was measured under pulse operation in a range of 0.1–9% duty. Remarkable anti-ion bombardment characteristics were observed over the range of 1–6% duty. The improved cathode showed 1.5 times higher emission current than that of a conventional Ir-coated dispenser cathode at 4% duty. AES analysis showed that the recovering rates of surface Ba and O atoms after ion bombardment were 2.5 times higher. From these results it is confirmed that the Ir coated cathode with a fine-grained tungsten top layer is provided with a good tolerance against the ion bombardment.

A study on single-channel non-stationary noise suppression for cardiac sound

In recent years, the need for health care continues to grow, thereby leading to the widespread use of home-oriented health care and medical equipment. An example of the same is the use of the digital stethoscope. Our research aims to accurately monitor a users cardiac status 24 hours a day at any location using a wearable device with an in-built digital stethoscope. A presently existing challenge is that the cardiac sound monitored with digital stethoscopes is often mixed with ambient noise or overlapped with vibrations from body movement. This study investigated a means to suppress sudden non-stationary noise from a single-channel stethoscope signal. We propose a method in which we assume the excitation signal to be a non-stationary noise component in the linear prediction analysis. Compared with the spectral subtraction method, which continually updates the noise spectrum, our method improves the spectrum distortion by 2.0 dB, and improves the degree of noise suppression by 4.6 dB.

Spectrum selective nonlinear echo suppression based on the amount of linear echo cancellation

When acoustic echo cancellation or suppression is applied to hands-free communications in cellular phones, it is important for it to be robust against echo path variation and to suppress highly nonlinear echo at low cost. This paper proposes the spectrum selective nonlinear echo suppression (SS-ES) approach as a solution to these issues. SS-ES is characterized by selecting either a spectrum of the residual signal from an adaptive filter or a spectrum of the sending input signal depending on the contribution from linear echo cancellation in an adaptive filter. In the SS-ES approach, the results of objective evaluation show that the average ERLE is approximately 1.2-2.7 dB, the average LSD is approximately 0.19-0.62 dB, and the PESQ values is approximately 0.36-0.53 better than the conventional methods under conditions of echo path variation and double-talk.