Underwater acoustic lenses are used as a beamformer for underwater imaging. However, lenses have aberrations, causing blur or distortion to acoustic images. A thin aspherical single lens is effective for aberration correction without attenuation or reflection of the sound wave. We have designed hyperbolic and aplanatic Fresnel lenses made of silicone rubber. However, the Fresnel lenses were too thin and soft to retain their shape. In this study, we designed acrylic covers to maintain the shape of Fresnel lenses, and we evaluated the effects of the covers on the convergence property by calculations and experiments. The covers were designed on the basis of wave theory. The optimal thickness was determined to be half of the wavelength in the cover. As a result, the covers did not effect the location of focal points. The covered aplanatic Fresnel lens showed an almost uniform gain in the range from 0 to 20°; however, the gain was lower than that of the uncovered lens. The covered hyperbolic Fresnel lens produced almost the same shape of the sound distribution as the uncovered hyperbolic Fresnel lens but with a lower gain than that of the uncovered lens at all incident angles. In conclusion, the covers decreased the lens gain but did not affect the angular properties. Thus, the covers are expected to contribute to practical applications using Fresnel lenses.
This paper describes an experiment whose goal is to assess the role of temporal and amplitude variations in sonically simulating the act of walking over a bump or a hole. In particular, it has been investigated whether the timing between heel and toe and the timing between footsteps, as well as variations in the amplitude of heel and toe affect the perception of walking on unflat surfaces. Forty five subjects participated to three between-subjects experiments where they were asked to interact with a desktop system simulating bumps, holes and flat surfaces by means of auditory cues. Results show that it is possible to simulate a bump or a hole by only using temporal information in the auditory modality. Furthermore results show that the proposed amplitude variations are not sufficient to provide the information concerning uneven surfaces.
As a factor to characterize the sound of an electric guitar, it is thought that a characteristic of the pickup contributes most. The pickups most often used are classified roughly into single-coil models and humbucking models. The single-coil pickup is made by winding the thin wires with several thousand turns of coils around six polarizing pole pieces each corresponding to a string of the guitar, and the change in the magnetic reluctance owing to the string vibration that causes the change in the magnetic flux is transformed into an electrical signal. The humbucking pickup is composed of one magnetic circuit with two single-coil pickups, and made to be in phase electrically and out of phase magnetically for the purpose of removing circumference magnetic noise. In this paper, the response of the humbucking pickup excited by a string vibration set up by a real commercial solid body electric guitar is analyzed, and a simulation result is shown to agree with an actual measured value with sufficient precision. In addition, the response of the humbucking pickup imitated with two single-coil pickups is compared with the single-coil pickup and some additional considerations in the characteristics have been gained through analysis.
The analysis of the road humps influence on traffic noise is based on ASJ RTN-Model 2008 of noise emission. A single hump decelerates each vehicle and decreases noise emission. Unfortunately, the subsequent accelerations bring about an increases in noise emission. A series of humps lowers the average vehicle speed and, under certain conditions, reduces traffic noise level. It is shown that this reduction is a function of two variables: the distance between two successive humps and the vehicle speed in the absence of humps.
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