Electronic cancelling of acoustic traveling waves

Claim 1

Apparatus for attenuating a selected acoustic wave mode of an acoustic disturbance traveling in a given direction in a medium, said apparatus comprising an input transducer for detecting acoustic wave energy at a first position along the medium to produce an input electric signal, processing means for performing operations on the input signal in electronic circuits to generate first and second output signals at first and second outputs respectively, output transducer means for converting the two output signals to acoustic wave energy and injecting them into said medium at spatially separate positions, said output transducer means comprising a first transducer located at said first position and a second transducer located at a second position in said given direction from the first position, said first and second outputs being coupled to the first and second transducers, respectively; wherein said electronic circuits include summing means having an input from said input transducer, integrating means coupled from the summing means to said second output, first delay means in series with a minus-one circuit coupled from said second output to said first output and also to an input of the summing means, and second delay means coupled from the second output to an input of the summing means; wherein said first and second delay means each provide a given delay time which is equal to the distance between said first and second positions divided by the velocity of the selected acoustic wave mode sensed by the input transducer and injected by said first and second output transducers, the output of the second delay means being a third signal which is equal to the second output signal as a function of time less said given delay; wherein said summing means comprises means to generate a signal which is equal to the sum of the first output signal and third signal subtracted from said input electrical signal, so that its output is an estimate of said acoustic disturbance, and wherein the integrating means forms the integral over time of said estimate.

Claim 6

A method of attenuating an acoustic disturbance traveling in a given direction in a medium, comprising detecting acoustic wave energy at a first position along the medium to produce an input electronic signal, processing the input signal in electronic circuits to generate first and second output signals, and converting the two output signals to acoustic wave energy and injecting them into said medium at spatially separate positions; wherein said processing includes delaying and performing a minus one operation on the second output signal to generate the first output signal, delaying the second output signal to generate a third signal, generating a signal which is equal to the sum of the first output signal and third signal subtracted from the input electronic signal as an estimate of said acoustic disturbance, and integrating the last said signal over time to generate the second output signal.

Claim 7

A method of attenuating an acoustic disturbance traveling in a given direction in a medium, comprising detecting acoustic wave energy at a first position along the medium to produce an input electronic signal, processing the input signal in electronic circuits to generate first and second output signals, and converting the two output signals to acoustic wave energy and injecting them into said medium at spatially separate positions; wherein said processing includes delaying and performing a minus one operation on the second output signal to generate the first output signal, delaying the second output signal to generate a third signal, generating a signal which is equal to the sum of the first output signal and third signal subtracted from the input electronic signal as an estimate of said acoustic disturbance, and integrating the last said signal over time to generate the second output signal.