Radiation from a submerged thermoacoustic source

Radiation of sound from a submerged and freely flooded tube, closed at one end and open at the other, follows well-known relationships if the exit dimension is much smaller than a wavelength. If the tube is instead filled with a gas and submerged in water, the radiated power is higher than that of the flooded tube for the same internal acoustic pressure. If the density-sound-speed product, pc, is much higher in the liquid than in the gas, as would normally be the case, then the radiated power is greater by the factor l/0.36(ka)², where k is the wave number in the water and a is the tube radius. This provides an ideal setting for construction of an underwater acoustic source using a standing-wave thermoacoustic driver since this driver is force limited rather than displacement limited. The performance is ultimately limited by the hydrostatic pressure and the dimensions of the tube.