Method of determining the time-of-flight of an ultrasonic pulse

In a method for determining the time-of-flight of an ultrasound pulse through an examination zone which is disposed between an ultrasound transmitter and an ultrasound receiver which comprises the steps of:

• transmitting an ultrasound pulse through the examination zone;
• receiving the pulse after it has traveled through the examination zone and producing an electrical received signal (s) therefrom;
• periodically sampling the received signal (s) at a predetermined rate 1/T and storing the sequence of samples thus produced;
• measuring the discrete period of time (N*T) between the time of transmission and the time that the sampled received signal reaches a predetermined threshold value;
• calculating a correction factor by:
• comparing the stored sequence of samples of the received signal with sequences of periodic samples of a discrete reference signal (s*), repeatedly shifting the samples of the reference signal by one sample position and again comparing the received signal sequence to the shifted reference signal until a shifted position of the reference signal which produces a best correspondence between the samples of the received signal and the samples of the shifted reference signal is determined, and then choosing the associated shift of the reference signal as the correction factor;
• and adding the correction factor to the interval (n*T) to determine the time-of-flight;
• wherein, as an improvement:
• the reference signal is produced by measuring the mean received value of an ultrasound pulse which is propagated through a homogeneous medium using the same transmitting and receiving apparatus and geometry as are used to measure the examination zone.

In a method for determining the time-of-flight of an ultrasound pulse through an examination zone which is disposed between an ultrasound transmitter and an ultrasound receiver which comprises the steps of:

• transmitting an ultrasound pulse through the examination zone;
• receiving the pulse after it has traveled through the examination zone and producing an electrical received signal (s) therefrom;
• periodically sampling the received signal (s) at a predetermined rate 1/T and storing the sequency of samples thus produced;
• measuring the discrete period of time (N*T) between the time of transmission and the time that the sampled received signal reaches a predetermined threshold value;
• calculating a correction factor by:
• comparing the stored sequence of samples of the received signal with sequences of periodic samples of a discrete reference signal (s*), repeatedly shifting the samples of the reference signal by one sample position and again comparing the received signal sequence to the shifted reference signal until a shifted position of the reference signal which produces a best correspondence between the samples of the received signal and the samples of the shifted reference signal is determined, and then choosing the associated shift of the reference signal as the correction factor;
• and adding the correction factor to the interval (n*T) to determine the time-of-flight;
• wherein, as an improvement:
• the reference signal (s*) has a sampling density which is a factor K larger than sampling of the stored signal (s), and wherein the stored signal is compared with sequences which consist of every K.sup.th sample of the reference signal, and
• the reference signal is produced by measuring the mean received value of an ultrasound pulse which is propagated through a homogeneous medium using the same transmitting and receiving apparatus and geometry as are used to measure the examination zone.