HIGHER HARMONICS OF VIBRATING GAS-FILLED MICROSPHERES .1. SIMULATIONS

The acoustic behaviour of an ideal gas bubble in water is considered a nd the equation of motion is extended to model an Albunex microsphere. Calculations reveal large differences in non-linear behaviour between ideal gas bubbles and Albunex microspheres, due to the additional res toring force of, and friction inside, the shell that surrounds the Alb unex microsphere. Simulations with the Albunex contrast agent further reveal that the optimal driving frequency is 1 MHz, resulting in a sec ond harmonic that is 20 dB below the first harmonic at an acoustic pre ssure of 50 kPa. The difference increases to 25 dB for a driving frequ ency of 2 MHz.