Abstract
Systems of precisely spaced bubbles, balloons, or air‐filled thin shells in water, in full spaces, or near elastic boundaries, insonified at frequencies close to the fundamental resonance value ω0 (“bubble frequency”) and interacting via multiple scatter may develop true resonant modes or superresonances (SRs). Under SR conditions the pressure amplification relative to the incident field will be of order (kRa)−2, as opposed to (kRa)−1 for single scatter at ω0, kR being the wavenumber in water and a the scatterer radius. For simple configurations this leads to theoretical SR amplifications between 103 and 5 × 103. It is shown here that, in order to observe the SR effect, spacings and volumes must be controlled to 12 or better. Typical pair spacings are of order 13 λacoust or (roughly) multiples thereof. When a bubble/balloon pair is near a thin plate the basic spacing is about one flexure‐wave wavelength and SR amplification becomes very sensitive to the direction of flexure mode arrivals, tending to vanish entirely for angles intermediate between broadside and endfire incidence. [Work supported by ONR.]
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