Method and apparatus for acoustic attenuation

An apparatus for reducing acoustic radiation from an enclosure containing a fluid, said apparatus comprising:

• (A) one or more sensors for detecting a vibration in a surface of said enclosure, said one or more sensors being adapted to generate signals in response to detected vibration;
• (B) a radiation filter coupled to said one or more sensors, said radiation filter including a signal processor, for assigning weight values to said signals from said one or more sensors, and for generating summation signals therefrom;
• (C) a control unit coupled to said radiation filter, said control unit including a digital processor adapted to perform a cancellation algorithm on the summation signal and a reference signal for calculating cancellation waveforms corresponding to said summation signals, said cancellation algorithm comprising
• (a) means for calculating an estimated phase angle and an estimated frequency from said reference signal;
• (b) means for generating a complex-valued analytic signal representing a first harmonic of the reference signal;
• (c) a demodulating function adapted for performing a complex heterodyning of the analytic signal to generate a demodulated signal;
• (d) a decoupling module adapted for recoupling the demodulated signal by performing a complex vector matrix multiplication with a vector of all degrees of freedom for the demodulated signal and a matrix representing a multi-channel inverse transfer function at the estimated frequency;
• (e) means for converting an output of the complex vector matrix multiplication to a disturbance rejection signal by subjecting the output to an integral control law;
• and
• (f) a remodulating function for converting the disturbance rejection signal back to the estimated frequency;
• and
• (D) a fluid displacement unit in communication with said fluid, and coupled to said control unit for receiving said cancellation waveforms, said fluid displacement unit being capable of imparting, to said fluid, a pressure oscillation corresponding to said cancellation waveforms, to thereby reduce acoustic radiation, said fluid displacement unit comprising a solid state actuator element surrounded by an electroconductive coil, said coil being capable of generating a magnetic field around said actuator element upon application of an electric current, said actuator element being capable of undergoing magnetostriction in response to said magnetic field.