| Research Abstract |
In the theoretical investigation of ultrasound transmission enhancement, we introduce a concept of "effective reflection coefficient" and obtain the enhancement condition precisely for ultrasound to transmit through the layered structures from the solid substrate into a liquid. As a result, the resonant transmission of ultrasound is analogous to the transmission through the quarter-wave plate. We also relate the dispersion relation for the waves in the finite-size layered structure closely to the effective reflection coefficient. Furthermore, we propose a novel definition of the group velocity for the ultrasound frequencies which are in the stop band of dispersion relation. In the experimental investigation, because we are not able to obtain the ultrasound transducer having the same acoustic impedances as those of solids, the quarter-wave-plate-like resonant transmission is not directly observed. We are now preparing to detect it directly. The verification of the novel group velocity i
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s also left for further experimental-investigation. At the beginning of our project, we have a prediction that the thermal resistance between solid and liquid is reduced by the layered structures. However, the theoretical analysis shows that the resistance is not reduced by the layered structures even if the resonance makes the transmission rate be unity.
For the taste sensing as an instance of chemical sensors, we investigate the ultrasound velocities in various taste solutions. We have also tried to detect more complicated tastes making use of the power spectrum of ultrasound which travels in the cell containing the taste solutions and is reflected at an end of the cell. From these observations, we have found that the amplitudes, the velocities, and the power spectra of travelling ultrasound have features characteristic of the taste solutions. Furthermore, the method of self-organizing neural network is applied to the power spectra. From these experimental data, we can distinguish the chemical substances in the taste solutions. This method gives us feasibility for a novel kind of taste sensing. However, the taste sensing has the psychological and physiological aspects. Therefore, we have to include these aspects in the taste sensing as well as the physical and chemical aspects of ultrasound methods. These problems are our new-themes for further investigation of the taste sensing. Less
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