STOP BANDS FOR CUBIC ARRAYS OF SPHERICAL BALLOONS

The acoustic band structures have been computed for cubic arrays of sp herical hydrogen balloons in air. Stop bands are obtained for the face -centered-cubic (fee) and body-centered-cubic (bcc) lattices, however, there is no band gap for the simple cubic lattice. These gaps are lar gest for a volume fraction of similar to 38% and, at low balloon press ure (1.10 atm) and small latex wall thickness (10(-3) times the inner radius), the corresponding gap/midgap ratios are about 0.2 for the fee and 0.1 for the bcc structure. As the pressure or wall thickness incr eases, the stop bands diminish and ultimately vanish. (C) 1997 Acousti cal Society of America.