! für die Profis !
Es liegt mir eine Veröffentlichung aus Taiwan vor, die ich gegen einen NDA per Email zusenden kann. Ist in engl...hier der Anfangstext :

A highly accurate multiple-frequency continuous wave ultrasonic range-measuring system for use in
air is described. The proposed system uses a method heretofore applied to radio frequency distance
measurement but not to air-based ultrasonic systems. The method presented here is based upon the
comparative phase shifts generated by three continuous ultrasonic waves of different but closely
spaced frequencies. In the test embodiment to confirm concept feasibility, two low cost 40 kHz
ultrasonic transducers are set face to face and used to transmit and receive ultrasound. Individual
frequencies are transmitted serially, each generating its own phase shift. For any given frequency,
the transmitter/receiver distance modulates the phase shift between the transmitted and received
signals. Comparison of the phase shifts allows a highly accurate evaluation of target distance. A
single-chip microcomputer-based multiple-frequency continuous wave generator and phase detector
was designed to record and compute the phase shift information and the resulting distance, which
is then sent to either a LCD or a PC. The PC is necessary only for calibration of the system, which
can be run independently after calibration. Experiments were conducted to test the performance of
the whole system. Experimentally, ranging accuracy was found to be within 60.05 mm, with a
range of over 1.5 m. The main advantages of this ultrasonic range measurement system are high
resolution, low cost, narrow bandwidth requirements, and ease of implementation.

na denn..viel Vergnügen..hats aber in sich