Gas-filled bubble sound source

1. A sound source, comprising:

a bubble configured to be filled with a gas;

a volume velocity actuator configured to perturb the gas within the bubble by changing the volume of gas within the bubble, wherein the volume velocity actuator is disposed within the bubble, the volume velocity actuator comprising an electro-mechanical motor comprising a plurality of pistons symmetrically moving in opposite directions with a closed space between the pistons, wherein the volume velocity actuator is configured to change the volume and pressure inside the bubble proportionally to a control signal; and

a processing circuit configured to provide a control signal to the volume velocity actuator to cause the volume velocity actuator to perturb the gas within the bubble at a frequency defined by the control signal.

2. The sound source of claim 1 , wherein the bubble comprises an elastic material.

3. The sound source of claim 1 , wherein the bubble has a resonant frequency and the volume velocity actuator has a resonant frequency, wherein the bubble resonant frequency and the volume velocity actuator resonant frequency are about the same.

4. The sound source of claim 1 , further comprising a controllable gas source configured to increase and decrease a volume of gas within the bubble.

5. The sound source of claim 4 , further comprising a sensor configured to sense sound generated by the bubble and to transmit a sensed signal to the processing circuit, wherein the processing circuit is configured to adjust the controllable gas source to keep a resonance frequency of the bubble approximately equal to a frequency of the sensed sound.

6. The sound source of claim 5 , wherein the processing circuit is configured to detect a phase difference between the sensed signal and the control signal and to adjust the controllable gas source based on the phase difference.

7. The sound source of claim 5 , wherein the processing circuit is configured to control the sound source to perform a linear sweep of frequencies, wherein the processing circuit is further configured to adjust the controllable gas source to keep the resonance frequency approximately equal to a frequency of the sensed sound across at least a portion of the linear sweep of frequencies.

8. A method of generating underwater sound waves, comprising:

providing an elastic bubble filled with a gas into an underwater environment;

perturbing the gas within the bubble using a volume velocity actuator, wherein the volume velocity actuator is disposed within the bubble, the volume velocity actuator comprising an electro-mechanical motor comprising a plurality of pistons symmetrically moving in opposite directions with a closed space between the pistons, wherein the volume velocity actuator is configured to change the volume and pressure inside the bubble;

controlling the perturbing of the gas within the bubble to emit sound waves over a plurality of frequencies; and

controlling a resonance frequency of the bubble to approximately equal a radiated signal of the bubble.

9. The method of claim 8 , wherein the controlling further comprising generating a digitally synthesized signal waveform and providing the signal waveform to an actuator source.

10. The method of claim 8 , wherein the resonance frequency of the bubble is controlled by adjusting a volume of gas within the bubble.

11. The method of claim 8 , wherein the controlling further comprises perturbing the gas to emit sound waves over a linear sweep of frequencies and controlling a resonance frequency of the bubble to approximately equal a frequency of sensed sound across at least a portion of the linear sweep of frequencies.