Nonlinear propagation acoustics of dual-frequency wide-band excitation pulses in a focused ultrasound system.
In this article, acoustic propagation effects of dual-frequency wide-band excitation pulses in a focused ultrasound system are demonstrated in vitro. A designed and manufactured dual-frequency band annular array capable of transmitting 0.9/7.5 MHz center frequency wide-band pulses was used for this purpose. The dual-frequency band annular array, has been designed using a bi-layer piezo-electric stack. Water tank measurements demonstrate the function of the array by activating the low- and high-frequency layers individually and simultaneously. The results show that the array works as intended. Activating the low- and high-frequency layers individually, results in less than -50 dB signal level from the high- and low-frequency layers respectively. Activating both layers simultaneously, produce a well defined dual-frequency pulse. The presence of the low-frequency pulse leads to compression, expansion, and a time delay of the high-frequency pulse. There is a phase shift between the low- and high-frequency pulse as it propagates from the array to the focus. This makes the latter described effects also dependent on the array configuration. By varying the low-frequency pressure, a shift of up to 0.5 MHz in center frequency of a 8.0 MHz transmitted high-frequency pulse is observed at the array focus. The results demonstrate the high propagation complexity of dual-frequency pulses.
Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Olav Kyrres Gate 9, N-7489 Trondheim, Norway. svein-erik.masoy@ntnu.no
Svein-Erik
SE
Måsøy
Øyvind
Ø
Standal
Jochen M
JM
Deibele
Sven Peter
SP
Näsholm
Bjørn
B
Angelsen
Tonni F
TF
Johansen
Thor Andreas
TA
Tangen
Rune
R
Hansen
D004867:Equipment Design; D017711:Nonlinear Dynamics; D014465:Ultrasonics / Q000295:instrumentation* / Q000379:methods*; D014867:Water
D014867:Water