Focused ultrasound split-foci control using spherical-confocal-split array with dual frequency of fundamental and harmonic superimposition
A spherical-confocal-split array with dual frequency of fundamental and harmonic superimposition includes: array elements which are spherically confocal, whose quantity is an even number, wherein a half of the array elements operate with a lower frequency, and the other half of the array elements operate with a higher frequency; both the lower frequency and the higher frequency are MHz high-frequencies; each of the array elements corresponds to a frequency drive; array element beams don't superimpose outside the focal region; each of the array elements is connected to a channel amplifier ( 3 ) through corresponding impedance matching ( 2 ); and a multi-channel waveform controller ( 4 ) is connected to the channel amplifier ( 3 ) for controlling amplitudes and phases of all channels. The dual-frequency spherical sectorial split array is able to generate split multi-foci of the focal plane with the dual frequencies; and control strong interference of transient cavitation clouds at the adjacent foci.
1. A method of focused ultrasound split-foci control using spherical-confocal-split array with dual frequency of fundamental and harmonic superimposition, which is based on a dual-frequency confocal superimposed focused ultrasonic spherical splitting array, comprising steps of: using spherical sector array elements or spherical rectangle array elements as array elements which are spherically confocal; controlling the array elements to emit dual frequencies at chosen phases for generating focal plane split multi-foci which extend a size of a radial focal region, so as to have a larger focal region than with a single-focus; wherein under dual frequency of second-harmonic superimposition, a sound pressure at the radial focal region is controlled to be higher than a cavitation threshold;
wherein a method for controlling amplitude phases of the array elements comprises steps of:
defining an array element width as Δw, defining an array element height as Δh, and defining an array element area as ΔA; setting an origin of an xyz coordinate at a top point of a spherical cap with a wave beam direction along a z-axis; reckoning a sound pressure p m of an m-th array element with Reyleigh-Sommerfeld integral, which is calculated with an equation obtained by superimposing N rectangles:
p
m
=
j
ρ
ck
2
π
u
m
∑
n
=
1
N
F
n
Δ
A
R
n
e
-
(
α
+
j
k
)
R
n
sin
c
kx
sn
Δ
w
2
R
sin
c
ky
sn
Δ
h
2
R
.
(
1
)
(1)
wherein each array element m is divided into N squares with same projected areas, then sound pressures at all points of a focal plane are calculated by the equation (1);
wherein in the equation (1), P m (x, y, z) is a complex sound pressure, j=√{square root over (−1)}, ρ and C are respectively a media density and a sound velocity, k=ω/c is a wave number, u m is a surface particle velocity of the m-th array element, which is used as an array element driving signal; wherein parameter calculation are as follows:
parameters are:
R
n
=
(
z
-
z
n
)
2
+
(
y
-
y
n
)
2
+
(
x
-
x
n
)
2
(
2
)
R
=
z
2
+
(
y
-
y
n
)
2
+
(
x
-
x
n
)
2
(
3
)
R
PP
2
=
R
SP
2
-
(
x
n
2
+
y
n
2
)
(
4
)
R
n
=
R
+
1
R
(
R
SP
2
-
zR
SP
+
z
)
R
PP
-
x
n
2
+
y
n
2
2
)
(
5
)
x
sn
=
x
-
z
-
R
SP
R
PP
x
n
(
6
)
y
sn
=
y
-
z
-
R
SP
R
PP
y
n
.
(
7
)
2. A method of focused ultrasound split-foci control using spherical-confocal-split array with dual frequency of fundamental and harmonic superimposition, which is based on the spherical-confocal-split array with the dual frequency of fundamental and the harmonic superimposition, comprising steps of:
using spherical ring array elements as array elements which are spherically confocal; and
applying dual frequencies, and controlling a ratio of a high-frequency sound power and a low-frequency sound power, wherein the superimposition of two frequency pressures results in split foci along beam axial within confocal region, and the maximal peak intensity of split foci is larger than the sum of two frequency intensities of the high-frequency sound power and the low-frequency sound power; or
applying a dual frequency of third-harmonic superimposition, and controlling the ratio of the high-frequency sound power and the low-frequency sound power; when a phase shift is 60°, obtaining maximum superimposed wave positive peak values and negative peak values;
wherein a method for controlling amplitude phases of the array elements comprises steps of:
defining an array element width as Δw, defining an array element height as Δh, and defining an array element area as ΔA; setting an origin of an xyz coordinate at a top point of a spherical cap with a wave beam direction along a z-axis; reckoning a sound pressure p m of an m-th array element with Reyleigh-Sommerfeld integral, which is calculated with an equation obtained by superimposing N rectangles:
p
m
=
j
ρ
ck
2
π
u
m
∑
n
=
1
N
F
n
Δ
A
R
n
e
-
(
α
+
j
k
)
R
n
sin
c
kx
sn
Δ
w
2
R
sin
c
ky
sn
Δ
h
2
R
.
(
1
)
wherein each array element m is divided into N squares with same projected areas, then sound pressures at all points of a focal plane are calculated by the equation (1);
wherein in the equation (1), P m (x, y, z) is a complex sound pressure, j=√{square root over (−1)}, ρ and C are respectively a media density and a sound velocity, k=ω/c is a wave number, u m is a surface particle velocity of the m-th array element, which is used as an array element driving signal; wherein parameter calculation are as follows:
parameters are:
R
n
=
(
z
-
z
n
)
2
+
(
y
-
y
n
)
2
+
(
x
-
x
n
)
2
(
2
)
R
=
z
2
+
(
y
-
y
n
)
2
+
(
x
-
x
n
)
2
(
3
)
R
PP
2
=
R
SP
2
-
(
x
n
2
-
y
n
2
)
(
4
)
R
n
=
R
+
1
R
(
R
SP
2
-
zR
SP
+
z
)
R
PP
-
x
n
2
+
y
n
2
2
)
(
5
)
x
sn
=
x
-
z
-
R
SP
R
PP
x
n
(
6
)
y
sn
=
y
-
z
-
R
SP
R
PP
y
n
.
(
7
)