In the biological research of fish and marine animals, ultrasonic transmitters (pingers) are used to perform ultrasonic biotelemetry. In this method, the size of the pinger is limited to the size that can be attached to the fish or other marine animal. In such a system, a highly efficient ultrasonic biotelemetry system would be needed for use in the ocean, because there is a high level of underwater ambient noise, especially in temperate and tropical areas. We investigated four parameters that determine the performance of this system with the goal of designing the optimum ultrasonic biotelemetry system. The first parameter, the long distance between the pinger and the receiver, determines the transmitting frequency needed. The second, the battery life, requires an effective transducer and a low power dissipation circuit. The third, minimizing of the pinger size, requires the selection of optimal microelectronics components. The last, a high level of recognition, depends on the signal processing method of the transmitting system. We were able to achieve over 1,000-meter transmission. Using two small battery (SR626SW 32-mAh), the system could operate for 240 days with transmission every 30 seconds. The pinger was 10 mm diameter and 40 mm long. To achieve high signal recognition against the ambient noise and to avoid the collision of the pinger against solid material that might damage it, we used a maximum length (M) sequence signal and correlation processing in the receiving system. The system consisted of the tiny pinger and high-performance receiving equipment including the transducer. The pinger could transmit the pinger identification by M sequence signal and the depth information at each repetition interval. The receiver processed the correlation of the received M sequence signal from the pinger using an FPGA (Field-Programmable Gate Array) chip and calculated the direction of the pinger.

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