Method and device for improved measurement of ultrasound propagation time difference

A method for measuring a propagation time difference, comprising:

• transmitting an ultrasound pulse at a transmission reference instant into a spatial region;
• receiving an ultrasound pulse corresponding to the transmitted ultrasound pulse from the spatial region;
• and
• determining a propagation time difference by:
• providing a coarse time difference by comparing the transmission reference instant with an envelope of the received ultrasound pulse, for at least two cycles of sending and receiving which are carried out with mutually opposite directions of transmission;
• providing a fine time difference by comparing the transmission reference instant with an instantaneous variation of the received ultrasound pulse, for the at least two cycles of sending and receiving which are carried out with mutually opposite directions of transmission;
• providing (i) a combination of the fine time differences for the opposite directions of transmission as a first individual combination, and (ii) a combination of the coarse time differences for the opposite directions of transmission as a second individual combination;
• and
• providing the propagation time difference as a combination of the first and second individual combinations.

A propagation time difference measuring device, comprising:

• a transmitter configured to transmit ultrasound pulses in two mutually opposite directions of transmission;
• an output for emitting, for each transmitted ultrasonic pulse, a signal describing the transmitted ultrasound pulse including an envelope and a carrier frequency;
• an input for receiving ultrasound pulses corresponding to the transmitted ultrasound pulses;
• a time-detection device configured to detect a propagation time difference using the received ultrasound pulse and a transmission time reference of the transmitted ultrasound pulse, wherein the time-detection device includes:
• a coarse comparator configured to compare the transmission time reference with an envelope of the received ultrasound pulse, the coarse comparator providing a coarse time difference between the transmitted ultrasound pulse and the received ultrasound pulse as the result;
• a fine comparator configured to compare the transmission time reference with the instantaneous amplitude of the received ultrasound pulse, the fine comparator providing a fine time difference between the transmitted ultrasound pulse and the received ultrasound pulse as the result;
• an individual-combination device connected to the coarse comparator and the fine comparator to receive and combine the coarse and fine time differences provided by the coarse comparator and the fine comparator, wherein the individual-combination device is configured to combine the coarse time differences of opposite directions of transmission to form a first individual combination and to combine the fine time differences of opposite directions of transmission to form a second individual combination;
• and
• a second combination device connected to the individual-combination device to receive and combine the first and second individual combinations of the coarse and fine time differences, wherein the second combination device is further connected to a result output which outputs a signal describing the combined first and second individual combinations as a propagation time difference.