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Yasuno Y.,Kobayasi Institute of Physical Research
Proceedings of Meetings on Acoustics | Year: 2010

The electret condenser microphone (ECM) has become an important component for various consumer equipment systems because of its stable sensitivity and frequency characteristics and its success in achieving small size and high sensitivity. A previous report described the method to design a microphone with stable temperature characteristics. The quality of the silicon material for the diaphragm was pointed out as important for improving robustness. Recently, microphones using micro-electro-mechanical systems (MEMS) have been practically applied and widely used for mobile equipment, such as cellular phones. The major reason for adopting MEMS is that a re-flow soldering process can be used in production, in addition to having desirable features such as being small and thin. However, almost no electret types have been commercialized since a guaranteed 300-degree C heat resistance is required. This report presents a new trial electret silicone microphone that contains a SiO2 thin-film electret. The report also evaluates the heat resistance of a SiO2 electret, the temperature stability of a silicon diaphragm, and the temperature change of sensitivity and frequency characteristics compared with those of a conventional ECM and the microphone for measurement. © 2010 Acoustical Society of America. Source

Yoshimura J.,Kobayasi Institute of Physical Research
40th International Congress and Exposition on Noise Control Engineering 2011, INTER-NOISE 2011 | Year: 2011

The sound reduction index of a solid glass pane depends strongly on boundary conditions attributable to a low internal loss factor. The sound reduction index can be calculated precisely using Cremer's theory and the total loss factor of the system (estimated experimentally or theoretically) at and above the critical frequency. Below the critical frequency, Sewell's mass law accounts for the effects of panel size on forced-wave transmission. The internal loss factor and bending stiffness of laminated glass vary with temperature, and they also have frequency dependence. Generally, the sound reduction index is calculated using Cremer's expression: the theta (angle of incidence) from 0 to 78° is integrated under the assumption of field incidence. However, there are discrepancies in the critical frequency region, especially in the case of a small thick glass pane. At and above the critical frequency, the incidence at the grazing angle to the system has to be taken into account. The incident angle limitation for an ISO test opening was estimated by the calculations comparison between experimental data and predicted the sound reduction index using them for laminated glass panes at various temperatures. Source

Mabuchi Y.,Tokyo University of Science | Nakajima T.,Tokyo University of Science | Furukawa T.,Tokyo University of Science | Furukawa T.,Kobayasi Institute of Physical Research | Okamura S.,Tokyo University of Science
Applied Physics Express | Year: 2011

We investigated the polarization enhancement in 60-nm-thick vinylidene fluoride/trifluoroethylene (VDF/TrFE) films without thermal annealing by applying repeated bipolar electric pulses. The remnant polarization was 8.4mC/m2 in as-spin-coated films and increased to up to 45mC/m 2 when 105 pulses were applied. Although the remnant polarization was half and the coercive field twice those of annealed films, the electrically treated film had a markedly smoother surface than the annealed film. Finally, a 15-nm-thick ferroelectric VDF/TrFE film with low conductivity was fabricated by electric treatment; annealed films with the same thickness experienced a severe short-circuit problem originating from the surface roughness. © 2011 The Japan Society of Applied Physics. Source

Ishii H.,Tokyo University of Science | Nakajima T.,Tokyo University of Science | Takahashi Y.,Tokyo University of Science | Furukawa T.,Tokyo University of Science | Furukawa T.,Kobayasi Institute of Physical Research
Applied Physics Express | Year: 2011

Polarization switching dynamics at extremely high electric fields were measured for a 50-nm-thick ferroelectric vinylidene fluoride/trifluoroethylene copolymer film. Using a fast-rise voltage pulse with minimal duration, we obtained a switching time of as fast as 2 ns at an electric field of 800 MV/m without electrical breakdown. Departure from an exponential law toward a power law was detected above 300 MV/m. Distorted switching curves due to limited voltage rise time were shown to be reproducible by means of nonlinear superposition © 2011 The Japan Society of Applied Physics. Source

Sakagami K.,Kobe University | Yairi M.,Kajima Technical Research Institute | Toyoda E.,Kobayasi Institute of Physical Research | Toyoda M.,Kansai University
Acoustics Australia | Year: 2013

A microperforated panel (MPP) is usually placed with a rigid-back wall to form a Helmholtz resonator with its hole and the air-back cavity. However, the authors have so far proposed an MPP space sound absorber without any backing structure. In the previous studies, as a basic form of such an MPP space absorber, multiple-leaf MPP structures without a back wall were proposed, and were theoretically and experimentally examined. In order to provide more unrestricted usage and designs for an MPP space absorber, the authors have also proposed a three-dimensional MPP space absorber, called a cylindrical MPP space absorber (CMSA). The CMSA was shown to exhibit resonance peak absorption and additional low frequency absorption. In this paper, another alternative of a three-dimensional MPP space absorber, a rectangular MPP space absorber (RMSA) is proposed. Its sound absorption performance is discussed using experimentally measured results. The results show sound absorption characteristics similar to a CMSA, and an RMSA can be effectively used if properly designed. Source

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