Yoshinori Hama

New concept of an electromagnetic usage for contactless communication and power transmission in the ocean

We demonstrate a new concept of an electromagnetic usage in the sea. The concept is characterized by sharing one pair of transmitting and receiving antennas for contactless communication and power transmission. The antennas are designed as electromagnetic (EM) high-Q resonators and the lowest resonant frequency is used for power transfer. The higher frequency band is used for signal communications. Using this concept, the efficiency of power transfer can be relatively high and the high transmission rate can be possible. A s a test trial for verifying the above concept, a measurement system is set up and the power transfer and signal quality are evaluated. The results show the power efficiency can be over 40%, and the transmission rate can be 20 Mbps via sea-water of the 5 cms thickness. The proposed concept can be used to realize a compact and maintenance-free wireless usage between different underwater systems, such as autonomous underwater vehicles (AUVs), remotely-operated vehicles (ROVs) and mother ships.

Tonpilz Piezoelectric Transducer with a Bending Piezoelectric Disk on The Radiation Surface

In recent years, it has become necessary to use wide-band signals in various kinds of signal processing and communication technology fields. One of these is the field of underwater acoustic technology, and therefore wide-band transducers are needed in this field. To address this need, we developed a Tonpilz piezoelectric transducer with a bending piezoelectric disk on the radiation surface of the front mass. This transducer was designed by providing a bending piezoelectric disk on the radiation surface of the front mass of a conventional Tonpilz piezoelectric transducer to enable it to generate in two resonance modes: the longitudinal vibration resonance mode and the bending vibration resonance mode of the bending disk. Coupling these two resonance modes makes it possible to achieve low-frequency transmission, and wide-band signals can be attained by adjusting the phase in the two modes. We obtained the optimum design dimensions of the transducer through analysis using the finite element method (FEM), and constructed a prototype based on the analysis. Experiments verified that the measured results for the prototype correspond well to the simulation results and that the bandwidth can be widened without changing the external size of the conventional transducer.

Low-Frequency Synthetic Aperture Sonar System

An experimental synthetic aperture sonar system is developed, and a set of cruises is also conducted. The primary purpose of the system is to confirm the validity of the motion compensation technique, which combines the use of both the DPC algorithm and the motion sensor. The experiment clearly shows the effectiveness of this combination, resulting in the successful estimation of underwater motion errors and the formation of synthetic aperture images.

Long distance high efficient underwater wireless charging system using dielectric-assist antenna

We demonstrated a long-distance high-efficient underwater wireless charging system, which composed of a wireless power transfer antenna and a charging unit. To suppress the seawater conductor loss, which has a high conductivity of ~4 S/m, we analyzed underwater near field EM characteristics and designed dielectric-assist radiative antenna in a magnetic type. It is found that the propagation is dominantly guided by eddy current and low-frequency-operation is suitable from this analysis. The designed antenna size is 24 cm × 24 cm × 1.5 cm. Using this antenna in the sea, high efficiency of 60% through over 10 cm of sea water was achieved. The charging unit composed of a matching circuit, a rectifier, a DC-DC converter and a battery charging circuit. The wireless charging system achieved transmission distance of 5 cm and system efficiency of approximately 50%.

LOW-FREQUENCY SOUND SOURCE WITH DUAL BENDING RADIATION SURFACES

A disk bender sound source with dual radiation surfaces is designed based on the finite element method (FEM) analysis and an equivalent circuit analysis. The results of these analyses results exhibit that the sound source has a low-frequency and high-power radiation capacity and is capable of operating at ten times the normal atmospheric outer water pressure. The sound source comprises of two bending resonators. Each resonator consists of a metal disk and many piezoelectric ceramic segments. Each ceramic segment is firmly bonded to a depression on the metal disk with an epoxy resin adhesive. The sound source has external dimensions of about 80 cm diameter, 9 cm thickness and weighs 130 kg. The resonant frequency obtained is 115 Hz at a depth of 50 m, and the maximum sound pressure level successfully achieved is more than 200 dB re 1 µPa at 1 m. For the purpose of using the sound source at great depths, a pressure-compensation method, in which the inner cavity of the sound source is filled with compressed gas, is theoretically investigated.

Investigation of Disk Bender Low-Frequency Projector with Dual Radiation Surfaces

A low-frequency disk bender projector with dual radiation surfaces was designed on the basis of finite element method (FEM) analysis and equivalent circuit analysis, in order to devise a miniature light weight projector with a high sound pressure level. These analyses suggest that a low-frequency, high-power, miniature and light weight projector can be realized. A trial projector was produced and evaluated. The resonant frequencies for the projector in air and water were 1315 Hz and 970 Hz, respectively. Experimental maximum transmitting voltage sensitivity was 132.2 dB re 1 µPa/V at 1 m.