There has recently been an increasing interest in the generation of a sound field that is audible in one spatial region and inaudible in an adjacent region. The method proposed here ensures the control of the amplitude and phase of multiple acoustic sources in order to maximize the acoustic energy difference between two adjacent regions while also ensuring that evenly distributed source strengths are used. The performance of the method proposed is evaluated by computer simulations and experiments with real loudspeaker arrays in the shape of a circle and a sphere. The proposed method gives an improvement in the efficiency of radiation into the space in which the sound should be audible, while maintaining the acoustic pressure difference between two acoustic spaces. This is shown to give an improvement of performance compared to the contrast control method previously proposed.

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We report on the mechanical friction method for a fabrication of a Si nanostructure on a H-passivated Si͑100͒ substrate using an atomic force microscope ͑AFM͒ in a contact mode in air. The bare Si surface region exposed by the mechanical friction between a silicon nitride tip and Si surface was fully oxidized by ambient oxygens. The oxide mask patterns could withstand a selective wet etching process for pattern transfer. The width of the oxide layer formed by an AFM tip was about 200 Å. As the etching time and scan rate were decreased, the oxide line shape was improved. This study also showed that there exists a critical tip force in the removal of a H-passivating layer.

This paper presents a novel, highly sensitive condenser microphone with a flexure hinge diaphragm. We used the finiteelement analysis (FEA) to evaluate the mechanical and acoustic performance of the condenser microphone with a hinge diaphragm. And we fabricated the miniature condenser microphones with area of 1.5 mm x 1.5 mm. From the simulation and measurement results, we confirmed that the maximum displacements at the center of flexure hinge diaphragms are several hundred times, compared with flat diaphragms. Moreover, the miniature microphones have obtained -3 dB bandwidth of nearly 20 kHz by proper design of the flexure hinge diaphragms.

We report on the fabrication of metal nanowires on an insulating substrate using carbon nanotubes as a new kind of mask material. By irradiating Ar+ ions of 300 eV energy on a nanotube-coated Au/Ti thin layer on a SiO2 substrate, Au/Ti nanowires were successfully formed just underneath the nanotube, indicating that the carbon nanotubes had acted as a good mask against the argon ion bombardment. The Au/Ti wire of a few nanometers in width was frequently observed among the wires of various widths. After the formation of the Au/Ti nanowires, the carbon nanotube on the metal nanowire could be removed by atomic force microscope.