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This paper describes the design and detection of mechanically actuated micro whistles not equipped with any electronics. When actuated, the micro whistle generates an ultrasonic tone above the audible range. A set of 3 or more microphones in the near record this tone and the position of the whistle is calculated from the time differences of the arrivals of the acoustic signals at the different microphones. Theoretically it is possible to get an accuracy of one wave length (1.7 cm).The micro whistles are fabricated by ultrasonic hot embossing of thermoplastic foils at low-cost and their overall size is approximately 1 cm. In experiments the positions of whistles up to now were measured in a 2 m × 2 m area with an accuracy of less than 10 cm.

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