Noise Absorber Research Articles

Causal impedance matching for broadband hybrid noise absorption.

The complementary strengths and weaknesses of passive and active noise control (ANC) methods have motivated many researchers to develop hybrid noise absorbers that integrate both control strategies. The impedance matching technique (IMT) is the most effective for such a purpose. An unsolved problem with available IMT schemes is the a priori reference signal that limits IMT applications. This study proposes the use of the forward wave, available by the two-microphone method, as the reference signal. Due to inevitable errors in wave separation and inlet reflection of the control signal, the absorber becomes a feedback system. A simple and stable ANC is developed for impedance matching without the a priori reference signal. The proposed absorber has an absorption coefficient of 0.9 or above in a frequency range of 60-850 Hz. It is stable in the presence of sensor mismatch and robust with respect to significant variation of inlet boundary conditions.

Improvement of the electromagnetic-noise suppressing features for Fe–Si–Al composite sheets by dc magnetic field biasing

The electromagnetic-noise suppression sheets made of Fe–Si–Al thin flakes embedded in polymer improve their noise suppressing performance appreciably in the magnetic field. We have already confirmed that the transmission characteristics of a microstrip line exhibit a high-frequency suppressing feature when a small piece of the sheet is placed on it [S. Yoshida et al., IEEE Trans. Magn. 37, 2401 (2001)]. In this article we found that this filtering performance is appreciably improved by a dc magnetic field. The effect becomes explicit in a field with intensity higher than a few hundred Oe and rise of the transmission loss becomes much steeper near the frequency of magnetic resonance. An example is that in the field of 1 kOe the 3 dB width of half to the peak of frequency profile of the transmission loss at resonance is reduced to less than a quarter of the one without magnetic field. This improvement brings about a new research subject to develop the high performance electromagnetic noise absorber that is expected to work under the optimized conditions in various digital electronic devices with operation frequencies up to the GHz band.

ごみ焼却灰を利用した軌道用吸音材 : 「ごみは貴重な資源である」の実践をめざして(<特集>エネルギー・資源循環型都市構造と機械工学)

ごみ焼却灰を利用した軌道用吸音材 : 「ごみは貴重な資源である」の実践をめざして(<特集>エネルギー・資源循環型都市構造と機械工学)

フエノール樹脂歯車の機械的特性(第1報)

In this report mechanical properties of phenol resin gears-such as the strength of teeth due to statical and impact tests, abraision resistance and noise absorbing properties, etc.-were studied.Laminate of improved No. 11 base showed the most suitable properties for gear materials for the sizes of these models.The superiority of phenolresin gears to the cast iron gears in bad lubricating conditions, and also the suitable lubricating conditions for phenol resin gears were made clear.