Transducer assembly for generating focused ultrasound
Systems and devices are provided for generating focused ultrasound pulses based on a transducer assembly having a piezoelectric layer coupled to an acoustic lens. In some example embodiments, the piezoelectric layer is a composite piezoelectric material having an acoustic impedance configured to match the acoustic impedance of the acoustic lens. The acoustic lens may be formed from aluminum, or an alloy thereof, and may have a distal surface having a non-spherical profile for producing a focal region that is smaller than an equivalent spherical lens. The acoustic lens may have an f-number less than unity. In some embodiments, the acoustic lens is coated with a polymer acoustic impedance matching layer that is compatible with deposition via chemical vapor deposition, such as a p-xylylene based polymer. In some embodiments, the acoustic lens is formed from aluminum or an alloy thereof, and the polymer acoustic impedance matching layer is a Parylene layer.
1. An ultrasound system for generating focused ultrasound and performing histotripsy, the ultrasound system comprising:
an ultrasound transducer assembly including:
a piezoelectric layer;
an acoustic lens having a proximal surface and a curved distal surface, wherein the proximal surface is attached to the piezoelectric layer; and
an acoustic impedance matching layer coating the curved distal surface of the acoustic lens; and
driver circuitry operably connected with the ultrasound transducer assembly, wherein the driver circuitry is configured to deliver electrical pulses with a voltage and operating frequency configured to generate ultrasound pulses that produce cavitation within water;
wherein an acoustic impedance of the piezoelectric layer resides within plus or minus 40% of an acoustic impedance of the acoustic lens; and
wherein the acoustic lens has an f-number of less than two; and further
an intermediate layer is provided between the acoustic lens and the piezoelectric layer, wherein an acoustic impedance of the intermediate layer is less than the acoustic impedance of the acoustic lens and the acoustic impedance of the piezoelectric layer.
2. The ultrasound system according to claim 1 wherein the acoustic lens comprises aluminum.
3. The ultrasound system according to claim 2 wherein the acoustic lens is formed from an aluminum alloy.
4. The ultrasound system according to claim 2 wherein the acoustic lens comprises at least 85% aluminum by weight.
5. The ultrasound system according to claim 1 wherein the curved distal surface of the acoustic lens is non-spherical.
6. The ultrasound system according to claim 5 wherein the curved distal surface of the acoustic lens is elliptical.
7. The ultrasound system according to claim 1 wherein an f-number of the acoustic lens is less than unity.
8. The ultrasound system according to claim 1 wherein the acoustic impedance matching layer is formed from a polymer compatible with chemical vapor deposition.
9. The ultrasound system according to claim 1 wherein the acoustic impedance matching layer comprises an p-xylylene based polymer.
10. The ultrasound system according to claim 9 wherein the acoustic impedance matching layer comprises Parylene C.
11. The ultrasound system according to claim 1 wherein the acoustic impedance matching layer comprises polyimide.
12. The ultrasound system according to claim 1 wherein the acoustic impedance matching layer comprises a fluoropolymer.
13. The ultrasound system according to claim 1 further comprising an integrated ultrasound imaging transducer.
14. The ultrasound system according to claim 13 wherein the integrated ultrasound imaging transducer is coaxially supported relative to an axis of the acoustic lens within an aperture defined within the acoustic lens.
15. The ultrasound system according to claim 13 wherein a distal end of the integrated ultrasound imaging transducer is recessed within an aperture defined within the acoustic lens.
16. The ultrasound system according to claim 1 wherein the intermediate layer is an adhesive layer bonding the acoustic lens to the piezoelectric layer.
17. The ultrasound system according to claim 16 wherein the adhesive layer is an epoxy layer.
18. The ultrasound system according to claim 1 wherein an acoustic power spectrum thereof comprises a peak having an associated frequency that is dependent on the thickness of the intermediate layer.
19. The ultrasound system according to claim 18 wherein an intensity of the peak is also dependent on the thickness of the intermediate layer.
20. The ultrasound system according to claim 18 wherein the acoustic impedance matching layer is a quarter wave matching layer corresponding to the frequency associated with the peak in the acoustic power spectrum.
21. The ultrasound system according to claim 1 wherein the intermediate layer has a thickness between 15 and 50 microns.
22. The ultrasound system according to claim 1 wherein the intermediate layer has a thickness between 50 and 200 microns.
23. The ultrasound system according to claim 1 wherein the intermediate layer has a thickness of at least 20 microns.
24. The ultrasound system according to claim 1 wherein the intermediate layer has a thickness of at least 50 microns.
25. The ultrasound system according to claim 1 wherein a thickness of the intermediate layer is configured to effect an increase in peak emitted acoustic power in an acoustic power spectrum of the ultrasound system by a factor of at least ranging between two and three relative to an equivalent ultrasound system absent of the intermediate layer.
26. The ultrasound system according to claim 1 wherein a thickness of the intermediate layer is configured to effect an increase in peak efficiency in an acoustic efficiency spectrum of the ultrasound system by at least between 20% and 40% relative to an equivalent ultrasound system absent of the intermediate layer.
27. The ultrasound system according to claim 1 wherein the operating frequency corresponds to a frequency associated with the peak in the acoustic power spectrum.
28. The ultrasound system according to claim 1 wherein an intensity of a peak is also dependent on the thickness of the intermediate layer.
29. The ultrasound system according to claim 1 wherein the acoustic impedance matching layer is a quarter wave matching layer corresponding to a frequency associated with the peak in the acoustic power spectrum.