Swimming-type robotic fish are being developed as mobile sensor platforms that have the potential to outperform existing underwater vehicles in terms of manoeuvrability, miniaturisation and silent operation. Conducting polymer actuators are potential candidates for propelling a flapping tail fin for a robotic fish. This study introduces a method for directly measuring the thrust force generated by a polypyrrole (PPy) powered tail fin. The effects of voltage stimulus (waveform shape and frequency) and tail fin shape on the thrust force were determined. A square wave voltage input was shown to generate the highest thrust forces as fast bending actuation was induced. The thrust force tended to decrease at higher operating frequencies as a result of the reduced actuation occurring in the PPy layers. Increases in the tail fin area tended to lower the frequency where the peak in thrust force was achieved. Tail fin shape was also shown to be important to the force-frequency behaviour. When attached to an untethered robotic fish, the swimming speed tended to increase with increasing voltage input frequency. There was also an optimum frequency that enabled the fastest acceleration from rest that happened to be higher than the frequency that gave the peak thrust force. This was presumed to be due to the complicated swimming behaviour involving the side-to-side movement of the fish nose at low flap frequencies. The study provides valuable insight into the means for tailoring polymer actuator performance to achieve maximum fish swimming speeds. Scheme 1. Structure of polypyrrole and its electrochemical oxidation and reduction.

O n lanuary 19, 1975, research and development programs of the U.S. Atomic Energy Commission (AEC) became part of the newly formed Energy Research and Development Administration (ERDA). In this report, since it refers to work done in 1974, most references are to AEC programs.

Eventual development of fusion power reactors could increase the mining, use and disposal of lithium five-fold by the year 2000. This study has investigated potential effects from unusual amounts of lithium in aquatic environments. Freshwater organisms representing a Pacific Northwest salmonid habitat were exposed to elevated concentrations of lithium. Nine parameters were used to determine the incipient toxicity of lithium to rainbow trout (Salmo gairdneri), insect larvae (Chironomus sp.) and Columbia River periphyton. All three groups of biota were incipiently sensitive to lithium at concentrations ranging between 0.1 and 1 mg/L. These results correspond with the incipient toxicity of beryllium, a chemically similar component of fusion reactor cores. A maximum lithium concentration of 0.01 mg/L occurs naturally in most freshwater environments (beryllium is rarer). Therefore, a concentration range of 0.01 to 0.1 mg/L may be regarded as "approaching toxic concentrations" when assessing the hazards of lithium in freshwaters.

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