Acoustic feature computing apparatus, acoustic feature computing method, and program
A technique for accurately measuring acoustic characteristics of a parametric array is provided. A first calculation unit that calculates a complex amplitude d of an optical phase at a frequency f d from an amount of change φ s of the optical phase caused by demodulated sound S, assuming that q diff (ξ′, η′) is a function defined using a Gaussian beam expansion method, a second calculation unit that calculates a function value q diff (ξ, η) at a point X and a line integral value ∫ L q diff (ξ′, η)dξ′ of the function q diff (ξ′, η) along the optical path L, and a third calculation unit that calculates a complex amplitude p of the demodulated sound with the frequency f d at the point X using the complex amplitude d, the function value q diff (ξ, η), and the line integral value ∫ L q diff (ξ′, η)dξ′ are included.
1 . An acoustic characteristics measurement device comprising
a transducer configured to generate a parametric array to generate demodulated sound S as audible sound in a sound field, the transducer being a substantially circular sound source;
a phase change measurement device configured to measure a phase change of light due to the demodulated sound S;
a light source device configured to emit the light along an optical path toward the phase change measurement device through the sound field; and
a processor configured to execute operations comprising:
where L represents the optical path for the phase change measurement device,
C represents a point at which the optical path L intersects a straight line passing through the transducer and parallel to a propagation direction of the demodulated sound S,
X represents a point on the optical path L at which a distance from the point C is x,
z represents a distance from the transducer to the optical path L,
a represents a radius of the transducer, f d =|f 1 −f 2 | (where f 1 is a frequency of a carrier wave and f 2 is a frequency of a sideband wave) represents a frequency of the demodulated sound S, and
c represents a speed of sound,
calculating a complex amplitude d of an optical phase at the frequency f d from an amount of change φ s of the optical phase caused by the demodulated sound S;
where a function q diff (ξ′, η′) represents a predetermined function using a Gaussian beam expansion method,
calculating a function value of the function q diff (ξ, η) at the point X (where ξ=x/a, η=2z/ka 2 , k 1 =f 1 /c, k 2 =f 2 /c, and k=(k 1 +k 2 )/2 are satisfied) and a line integral value ∫ L q diff (ξ′, η)dξ′ of the function q diff (ξ′, η) along the optical path L; and
calculating a complex amplitude p of the demodulated sound with the frequency f d at the point X using the complex amplitude d of the optical phase at the frequency f d , the function value q diff (ξ, η) at the point X, and the line integral value ∫ L q diff (ξ′, η)dξ′ of the function q diff (ξ′, η) along the optical path L, and the complex amplitude p of the demodulated sound represents an acoustic characteristic of the parametric array with accuracy.
2 . The acoustic characteristics calculation device according to claim 1 ,
wherein the function q diff (ξ′, η′) is a function defined by the following expressions:
q
diff
(
ξ
′
,
η
′
)
=
∑
m
=
1
10
∑
m
′
=
1
10
A
m
A
m
′
q
diff
(
mm
′
)
(
ξ
′
,
η
′
)
q
diff
(
mm
′
)
(
ξ
′
,
η
′
)
=
1
4
r
1
(
mm
′
)
exp
(
-
s
1
(
mm
′
)
r
1
(
mm
′
)
ξ
′2
)
×
[
E
1
(
s
2
(
mm
′
)
r
1
(
mm
′
)
(
r
1
(
mm
′
)
η
′
+
r
2
(
mm
′
)
)
ξ
′2
)
-
E
1
(
s
2
(
mm
′
)
r
1
(
mm
′
)
r
2
(
mm
′
)
ξ
′2
)
]
(where r 1 (mm′) =(k a B k_bm′ +k b B k_am )+i(k a +k b )η′B k_am B k_bm′ , r 2 (mm′) =(k a B k_am +k b B k_bm′ )η′−i(k a +k b ), s 1 (mm′) =(k a +k b ) 2 B k_am B k_bm′ , s 2 (mm′) =−i(k a +k b )k a k b (B k_am −B k_bm′ ) 2 , B k_am =B m (1) /k a +i/δ, B k_bm′ =B m′ (2) /k b +i/δ, k a =k 1 /k, and k b =−k 2 /k are satisfied, and A m , A m′ , B m (1) , B m′ (2) , and δ predetermined constants), and
the calculating the complex amplitude p further comprises generating the complex amplitude p using the following expression:
p
(
ξ
,
η
)
=
1
C
ao
q
diff
(
ξ
,
η
)
∫
L
q
diff
(
ξ
′
,
η
)
d
ξ
′
d
(where C ao is a value determined under a physical condition at a time of measuring a sound field).
3 . A non-transitory recording medium recording a computer-executable program instructions that when executed causes a computer to function as the acoustic characteristics measurement device according to claim 1 .
4 . An acoustic characteristics measurement method comprising:
generating a parametric array, by a transducer, to generate demodulated sound S as audible sound in a sound field, the transducer being a substantially circular sound source;
measuring, by a phase change measurement device, a phase change of light due to the demodulated sound S;
emitting, by a light source device, the light along an optical path toward the phase change measurement device through the sound field;
where L represents the optical path for the phase change measurement device,
C represents a point at which the optical path L intersects a straight line passing through the transducer and parallel to a propagation direction of the demodulated sound S,
X represents a point on the optical path L at which a distance from the point C is x,
z represents a distance from the transducer to the optical path L,
a represents a radius of the transducer, f d =|f 1 −f 2 | (where f 1 is a frequency of a carrier wave and f 2 is a frequency of a sideband wave) represents a frequency of the demodulated sound S, and
c represents the speed of sound,
calculating a complex amplitude d of an optical phase at the frequency f d from an amount of change φ s of the optical phase caused by the demodulated sound S;
where a function q diff (ξ′, η′) represents a predetermined function using a Gaussian beam expansion method,
calculating a function value of the function q diff (ξ, η) at the point X (where ξ=x/a, η=2z/ka 2 , k 1 =f/c, k 2 =f 2 /c, and k=(k 1 +k 2 )/2 are satisfied) and a line integral value ∫ L q diff (ξ′, η)dξ′ of the function q diff (ξ′, η) along the optical path L; and
calculating a complex amplitude p of the demodulated sound with the frequency f d at the point X using the complex amplitude d of the optical phase at the frequency f d , the function value q diff (ξ, η) at the point X, and the line integral value ∫ L q diff (ξ′, η)dξ′ of the function q diff (ξ′, η) along the optical path L, and the complex amplitude p of the demodulated sound represents an acoustic characteristic of the parametric array with accuracy.