Fish detect underwater objects by measuring even tiny water velocity changes on their skin through their lateral-line system. Several approaches try to mimic the lateral-line system by hot-wire or electro-mechanical sensor arrays but none has achieved yet an underwater vehicle using a biomimetic lateral-line system for object avoidance, not even in simulation. In this paper we describe construction and properties of low-cost sensors applicable to the task, viz., sensors where a constant current heats thermistors in water flow. With increasing stream velocity, thermal dissipation and thus voltage increases. A glass-bead and a bow protect the thermistors. The small diameter of 0.36mm results in a small time constant and thus allows fast measurements. Sensors are about 1 cm long and consume less than 0.2W so that our small-sized underwater vehicle prototype “Snookie” can carry a whole array of them. We describe the magnitude of velocity changes depending on the distance to an obstacle and show experimentally that a single sensor can already detect underwater objects - so much the better a whole ensemble of them, as in fish.
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