Abstract: An ultrasound receiver includes a hollow cylinder formed primarily from flexible piezoeelectric film, the hollow cylinder having an outer surface, an inner surface, a central axis and a height measured parallel to the central axis. A sensing electrode is formed from conductive material applied to the inner surface, while a grounded electrode is formed from conductive material applied to the outer surface. The hollow cylinder is supported by a support structure configured to allow progagation of vibration waves circumferentially around a major part of the hollow cylinder. The sensing electrode is formed as a strip extending in an extensional direction substantially parallel to the central axis along a major part of the height, the strip subtending at the central axis an angle of not more than 90°.

Abstract: A presentation board digitizer system for large boards preferably employs at least three spaced-apart ultrasound receivers assemblies. A current position of an ultrasound transmitter is assigned as a weighted centroid of time-of-flight position measurements based on at least two pairs of receiver assemblies. The weighting used varies as a function of the position of the transmitter across the board. A preferred structure of an ultrasound receiver assembly for use in the system employs a pair of ultrasound receivers arranged side-by-side in a line perpendicular to the surface of the presentation board. The receivers are connected so as to generate a total output signal corresponding to the instantaneous sum of the ultrasound signals received at each, such that the receiver assembly is most sensitive to ultrasound signals incident from a plane adjacent to the presentation board.

Abstract: A presentation board digitizer system for large boards preferably employs at least three spaced-apart ultrasound receivers assemblies. A current position of an ultrasound transmitter is assigned as a weighted centroid of time of-flight position measurements based on at least two pairs of receiver assemblies. The weighting used varies as a function of the position of the transmitter across the board. A preferred structure of an ultrasound receiver assembly for use in the system employs a pair of ultrasound receivers arranged side-by-side in a line perpendicular to the surface of the presentation board. The receivers are connected so as to generate a total output signal corresponding to the instantaneous sum of the ultrasound signals received at each, such that the receiver assembly is most sensitive to ultrasound signals incident from a plane adjacent to the presentation board.

Abstract: A method and corresponding system for tracking variations in distance D calculated from time-of-flight measurements of a sequence of pulses of a pressure wave oscillation from a transmitter to a receiver identifies a state of synchronous operation by obtaining at least two time-of-flight measurements derived from successive pressure wave pulse which satisfy given synchronicity criteria. Successive time-of-flight measurements are then monitored to identify a shifted time-of-flight measurement which varies by at least half of the wave period from a predicted time-of-flight value calculated from a number of preceding time-of-flight measurements. A shift factor is then identified corresponding to an integer multiple of the wave period by which the shifted time-of-flight measurement must be corrected to obtain a corrected time-of-flight measurement falling within half of the wave period from the predicted time-of-flight value.