Tatsuo Yamabuchi

Finite element simulation of non-linear sound wave propagation

Abstract A numerical approach for non-linear acoustic wave propagation is proposed in which a finite element method is used. An approximate equation which can describe the effect of diffraction with reasonable accuracy is derived based on the equations of fluid dynamics. Only the generation of the second harmonic wave is considered, with the higher order harmonics being neglected. Under the assumption of weak non-linearity, a set of uncoupled equations for the primary and secondary wave is discretized in space by a finite element method, and then solved by using the Newmark-β integration scheme for time. Only two-dimensional cases are considered, and some numerical examples are presented for sound propagation along a duct with stepped width, for scattering from a circular rod and for a focusing source in which the diffraction effect is of interest. Some examples of the wave propagation fields are displayed.

Finite element cochlear models and their steady state response

Abstract Numerical cochlear models are constructed by means of a finite element approach and their frequency and spatial responses are calculated. The cochlea is modelled as a coupled fluid-membrane system, for which both two- and three-dimensional models are considered. The fluid in the scala canals is assumed to be incompressible and the basilar membrane is assumed to be a locally reactive impedance wall or a lossy elastic membrane. With the three-dimensional models, the effects are examined of the spiral configuration of the cochlea, of the presence of the lamina and the ligament that narrows the coupling area between the two fluid canals (scala vestibuli and scala tympani), and of the extended reaction of the basilar membrane which cannot be included in case of the two-dimensional models. The conclusion is that these effects on the cochlear response and the inherent mechanism governing the cochlear behaviour are found to be rather secondary.

Boundary element models of the vocal tract and radiation field and their response characteristics

Abstract Accurate vocal tract models become increasingly important for the investigation of speech analysis, synthesis and identification. The geometrical configuration of the vocal tract is determined by the position of the vocal tracts wall in association with the movement of the jaws and the mouth. One-dimensional models cannot provide the direct correspondence of the geometrical shape with its acoustical characteristic properly, taking the wall impedance and the end conditions into account. The vocal tract is a bent tube, and sound radiates to the outer space from the mouth opening. Here we demonstrate more realistic three-dimensional models of the vocal tract and the head made of boundary elements. The vocal tracts transmission responses and the sound field around the head are discussed separately, showing the capability of the boundary element models.

Verification of a logarithmic model for estimation of gas concentrations in a mixture for a tin oxide gas sensor response

Abstract Changes in electrical conductivity due to a reaction occurring between the original adsorbents and the gases present in the surrounding atmosphere were measured for a tin dioxide-based gas sensor. In this study, a model of the gas sensor response using a relationship between the gas concentration in a mixture and the sensor resistance is proposed. The values of coefficients are determined by a least-squares fit of measured data. Using two gas sensors having different characteristics, the concentrations of gases in a mixture can be evaluated. The proposed method has been applied to the evaluation of the gas concentrations in ammonia–ethanol and CO–ethanol mixtures. Furthermore, we verified our model for a gas mixture of carbon monoxide, propane and methane gases, namely for a three-gas system. The results of the present study indicated that the evaluation of gas concentrations in a mixture is feasible using the proposed model of gas sensor response, which can be used as an inexpensive monitor for air pollution.

Verification of Individual Identification Method Using Bioelectric Potential of Plant during Human Walking

In this study, we monitored electromagnetic waves generated by human activity and investigated a method for individual identification by looking at the bioelectric potential of a rubber tree. Four subjects were asked to walk in place at a distance of 60 cm from a rubber tree while we measured variations in the bioelectric potential of the tree as produced by the stepping. The results confirmed that electromagnetic waves generated by a human subject walking in place produce a measurable response in the bioelectric potential of a plant. It was also found that this variation in bioelectric potential varies in synchrony with each subjects walking pace. The spectral envelope of the observed signal was approximated using a straight line and the distribution of the coefficients of this line was plotted. Even for a simple straight-line approximation, we demonstrated that this coefficient distribution varies considerably among individual subjects.

NO2 gas sensor made of porous MoO3 sputtered films

Molybdenum trioxide films were sputter-deposited on quartz substrates at various substrate temperatures and discharge gas pressures. The films were annealed in air at 450°C. Scanning electron microscopy showed that fine flakes were formed in the films deposited at 300°C, while the surface of the films deposited at room temperature was smooth. After annealing, the fine flakes in the former films grew, while in the latter films, a layered structure was formed. X-ray diffraction patterns showed that every film was composed of orthorhombic MoO3 crystallites. The highest sensitivity and the fastest response to NO2 gas were observed in a film with a layered structure, which was deposited at room temperature and a high pressure of 11 Pa. This film was found to be porous and to have a density of 2.8 g/cm3, which is much lower than the bulk density of 4.7 g/cm3.

Finite‐element equivalent circuits for acoustic field

An equivalent electrical circuit results from the process of representing a general three‐dimensional system approximately by the corresponding nondimensional discrete network. The equivalent electrical circuits for acoustic field problems are presented based on the finite‐element approach. Basic equivalent circuits are first developed for a triangular or tetrahedral acoustic element in which the pressure is assumed to change linearly within the element. The circuit of an arbitrary sound field can be obtained simply by connecting these basic elements. The lossy field and the boundary wall with an acoustic impedance are then considered.

Dependence of Composition Distribution of NiTi Sputtered Films on Ar Gas Pressure

The composition distribution of NiTi films formed by dc magnetron sputtering under various conditions was investigated and analyzed using a simulation, where the angular distribution of the sputtered atoms as well as the scattering by Ar gas were considered. The Ti concentration under a low pressure was lower than that in the target, and was higher at the substrate center than at the positions facing the erosion ring. The nonuniformity of the composition was ascribed to the difference between the angular distributions of Ni and Ti. The Ti concentration increased as the pressure increased. This occurs mainly because the deficiency in Ti atoms as an effect of the difference in the angular distributions is suppressed by the scattering. The difference in mass between Ni and Ti is also an important factor in the determination of the composition distribution.

Slit Structure as a Countermeasure for the Thermal Deformation of a Metal Mask

A metal mask used for the pattern formation of sputtered films is sometimes deformed during film deposition, because its temperature increases during deposition. In this study, a slit structure as a countermeasure for the deformation is proposed. The mask investigated is made of 0.3-mm-thick stainless steel and is composed of a frame with many beams running inside the frame. The slits in the structure absorb the thermal expansion of the beams, which results in the relaxation of thermal stress in the beams. The relaxation of the stress is analyzed using the finite element method as well as the theory of beam bending. It was experimentally confirmed that a mask furnished with well-designed slits was not deformed.

Pattern Formation of Sputtered Films by Deposition through Mask

The thickness of the film near the edge of a film pattern formed by sputter deposition through a mask is not uniform, because of the shadowing effect of the side wall of the mask edge. When the effect is large, a sharp pattern can not be obtained. In order to clarify the precision or the sharpness of the film pattern, the distribution of the film thickness near the pattern edge was measured. It was found that the sharpness depended on the position of the pattern edge and the attitude of the side wall of the mask. A mask with bridges was contrived for the formation of an isolated space in a film, and the film deposition under the bridge was observed. It was found that the ratio of the gap between the substrate and the bridge to the bridge width must be larger than 1.0 for the thickness under the bridge to be greater than half the full thickness.