Method and apparatus to monitor conduction of sonic waves in an acoustically conductive medium

System to monitor conduction of sonic waves in an acoustically conductive medium, comprising

• means (7) generating signals of a sonic, or ultrasonic frequency;
• frequency modulating means (6) connected to said signal generator means (7) to provide frequency-modulated signals;
• transmitter transducer means (2) located at a transmitting location and transmitting the generated frequency-modulated signals to the medium to be supervised to introduce frequency-modulated sonic-type vibrations in said medium;
• receiver transducer means (3) located at a receiving location receiving vibrations from said medium transmitted therein by said transmitter transducer means (2) and providing an electrical received signal;
• frequency demodulator means connected to the receiving transducer means (37);
• time detector means (10, 11) connected to both said generator means (7) and said receiving transducer means (3) and determining the relative temporal change between the modulation, and demodulation envelope of the transmitted, and received waves, respectively, to evaluate change in the group velocity of the waves in the medium;
• and alarm generating means to provide an alarm when the temporal relationship of the modulation between transmitted and received signals as determined by the time detector means (10, 11) changes beyond a predetermined level.

Method of monitoring conduction of sonic-type wave in an acoustically conductive medium, in which wave-type signals are generated;

• the generated wave-type signals are applied to the medium at a transmitting location by a transmitter applying sonic-type signals to the medium;
• the transmitted sonic-type signals are received from the medium by a receiver at a receiving location;
• and an alarm signal is generated when a predetermined change in the characteristic of said generated signal with respect to said received signal is detected;
• comprising the steps of:
• generating at least two sonic-type waves of slightly different frequency;
• applying said waves to the medium so that said waves will propagate in the medium and generate interferences to obtain propagation of the waves in the medium subject to the group velocity phenomenon;
• receiving said at least two waves;
• analyzing the interference wave or waves resulting from interference of the at least two waves due to the group velocity phenomenon;
• and determining change in the interference wave to obtain an indication of disturbance of, or in the medium.

System to monitor conduction of sonic waves in an acoustically conductive medium having dispersion comprising

• means (7) generating at least two signals of a sonic or ultrasonic frequency, the at least two signals being of slightly different frequency;
• transmitter-transducer means (2) located at the transmitting location and transmitting said generated waves to the medium to be supervised in the form of sonic-type signals propagating in the medium, to obtain propagation of the waves therein subject to the group velocity phenomenon;
• receiver transducer means (3) located at a receiving location receiving vibrations from said medium transmitted therein by said transmitter-transducer means and providing an electrical received signal;
• demodulator means connected to the receiver transducer means and demodulating the received signal;
• time detector means (10, 11) connected to both said generator means (7) and said receiver transducer means and determining relative temporal change of the demodulated signal to evaulate change in the group velocity of the waves in the medium;
• and circuit means providing an output signal when the temporal relationship of said at least two transmitted waves and said received signal, as determined by said time detector means, changes beyond a predetermined level.