A Be-Al composite diaphragm for a loudspeaker with high performance is developed by a simple and dry process using a vacuum deposition method. The diaphragm with a double layered structure consists of an aluminum foil (JIS-5052) substrate and a beryllium thin film deposited on the concave side of the substrate. The Young's modulus of a Be film deposited at a substrate temperature of 500℃ reaches 2. 2-2. 4×10^<11>N/m^2 comparable to that of a rolled Be sheet. Be deposit thikness is determined through the calculated relationship by finite element method between high frequency resonace ƒ_H of a loudspeaker and thicknesses. the ƒ_H of 26mm diameter dome-type loudspeaker with a Be (30μm thick)-Al (15μm) composite and a Be (30μm) deposit diaphragm (without substrate) are 42kHz and 44kHz, respectively. In the same way for a 66mm diameter diaphragm, the ƒ_H with a Be (70μm)-Al (22μm) composite and a Be (70μm) deposit diaphragm are 14kHz and 16kHz. There is little difference in characteristics of frequency response and of harmonic distortion between the Be-Al composite and the Be deposit diaphragm loudspeaker. And Be-Al composite diaphragm has some merits such as large mechanical strength because of Al-substrate and low manufacturing cost.
Finite element method has successfully applied to analyzing the axisymmetric vibrations of piezoelectric circular rod, in which the electric field is assumed to be constant. When the distance between the electrodes becomes longer so that the longitudinal and flexural vibrations are to be excited, the assumption is no longer valid. In the present paper, two types of FEM model to cope with the situation are proposed. In the first model, nodal potentials of an element are taken into account to express the arbitrary distribution of the electric field. The second model is a thin rod assumption, the electric displacement is taken to be constant. The formulation and computer programs are developed based on these two models. The natural frequencies, the corresponding modes, potential distributions and input admittance at the electrical terminales are calculated. The calculated results of input admittance are compared with the measured ones and the analytical solution. It is found that the first FEM model where the electric fields are unconstrained is capable to simulate the vibrators of any length/diameter ratio as expected, while the second model can be applied to a slender vibrator of the length/diameter of two for its lowest mode.
When using the pulse reflection method to scan for cylindrical objects such as mines buried in seafloor sediment, a model experiment was performed to study the characteristics of waves reflected from a cylinder representing the scanning object, and also the waves reflected from swarm of pebbles and seafloor surface, which may be considered noise. The results are obtained as a function of the beam width of the ultrasonic waves used in the scanning. If the cylinder is inclined at an angle of about 10°, when the beam width is about 0. 5∼0. 8 of the length of the cylinder the image resembles that which would be imaged by two discrete objects located at the ends of the cylinder; when the beam width is reduced to 0. 3 the length of the cylinder or less, the image improves, more nearly resembling a single body the approximate length of the cylinder. Next, the possibility of using a region of narrow beam width near the focal point of an array of concave transducers is investigated. It is shown by experiments that the use of narrow-beam sound waves produced by an array of concave-surface transducers improves the resolution and image quality.