Nature-Inspired Acoustic Sensor Projects

3-D qualitative tracking sonar - Five 40 kHz Murata transducers are configured as a center transmitter flanked by a pair of receivers lying along the horizontal axis and a pair of receivers lying along the vertical axis. Interrogation pulses are transmitted every 10 milliseconds. Simple logic determines which receiver in each pair detects an echo first. For example, if the top receiver detects an echo before the bottom receiver, the object must lie above the sensor horizon. A solenoid then activates a downward-directed air jet to move the sensor upward. A similar operation occurs for the leftright determination. A moving object traveling less than pi2 radianssecond relative to the sensor is tracked by the sonar. This sensor is nonlinear in sensing and control, resulting in a limit cycle about the bearing and elevation of the object. Damping fins make the mechanical system response behave as a first-order system and simplify the control of the sensor. The determination of object location is made qualitatively, by identifying first arrival echoes. Hence, no triangulation computations are performed. Advantages of this approach include 1. The sonar works over the union of the transmitterreceiver echo detection regions, which is larger than the intersection required for triangulation. Triangulation methods require that two transducers detect echoes and, hence, operate only over the intersection of the transmitterreceiver regions. 2. The sonar reacts with the arrival of the first echo, the arrival of the echo to the other receiver in the pair being irrelevant. Since the sensor does not need to wait for the other echo, correction occurs as fast as possible.