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JP2011104106

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JP2011104106
PROBLEM TO BE SOLVED: In some cases, the magnitude of an acoustic wave generated with the
attenuation of light decreases, and an output of a desired size can not be obtained from an
electromechanical transducer that receives the acoustic wave. SOLUTION: A control device for
controlling an electro-mechanical transducer according to the present invention comprises:
converting means for converting a current outputted from a first electrode of the electromechanical transducer into a voltage; and a gap between the first electrode and the first
electrode. DC voltage application means for applying a DC voltage to the second electrode
provided, and the DC voltage or the current is converted into a voltage based on elapsed time
information from the time when the light is irradiated to the subject And generating means for
generating a control signal for changing at least one of the conversion ratio at that time.
[Selected figure] Figure 1
Control device and control method of electromechanical transducer, and measurement system
[0001]
The present invention relates to a control device and control method for controlling driving of an
electromechanical transducer, and a measurement system. In particular, the present invention
relates to a control device and control method of a capacitive electromechanical transducer that
receives an acoustic wave generated by a photoacoustic effect, and a measurement system
including the electromechanical transducer.
[0002]
04-05-2019
1
A measurement system that emits light to a subject, generates an acoustic wave (typically an
ultrasonic wave) from the measurement target in the subject by photoacoustic effect, and
receives the generated acoustic wave using an electromechanical transducer There is. Further, as
one form of the electromechanical transducer, there is a capacitive electromechanical transducer
CMUT (Capacitive Micromachined Ultrasonic Transducer) having a feature that the reception
band of acoustic waves is wide. CMUT is produced using the MEMS process which applied the
semiconductor process. Patent Document 1 proposes a method of using a CMUT as an
electromechanical transducer used in a measuring device using a photoacoustic effect.
[0003]
US Patent Application Publication No. 2007/0287912
[0004]
In the measurement system using the photoacoustic effect, in order to generate an acoustic wave
from the subject by the photoacoustic effect, the light source is made to emit light periodically
with a predetermined pulse width, and the subject is irradiated with light.
However, in the case of measuring a subject such as a living body, the irradiated light
exponentially attenuates according to the distance traveled in the subject. Therefore, the
magnitude (sound pressure) of the generated acoustic wave changes depending on the depth at
which the measurement target (for example, a tumor) is present in the subject. When the sound
pressure is small, the sound pressure reaching the electromechanical conversion device may be
lower than the reception sensitivity (minimum receivable sound pressure) originally possessed by
the electromechanical conversion device. In order to avoid this, it is also conceivable to set so as
to always obtain high reception sensitivity, but then, when the sound pressure is large, the signal
is saturated and it becomes impossible to take out the detected signal. Therefore, an object of the
present invention is to provide a control device and control method of a capacitive
electromechanical transducer in consideration of the influence of light attenuation in a subject.
[0005]
The control device according to the present invention has a first electrode and a second electrode
provided with a gap between the first electrode and an acoustic wave generated by light
irradiated to a subject. A control device for controlling an electromechanical transducer
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2
comprising an element for outputting a current from the first electrode by receiving a wave in a
state where a DC voltage is applied to the second electrode, A conversion means for converting a
current output from the first electrode into a voltage, a DC voltage application means for
applying a DC voltage to the second electrode, and a process from the time when the light is
irradiated to the subject And generating means for generating a control signal for changing at
least one of the DC voltage or a conversion ratio at the time of converting the current into a
voltage based on time information.
[0006]
Further, the control method of the present invention includes a first electrode and a second
electrode provided with a gap between the first electrode and light, and light is irradiated to the
subject. A control method for controlling an electromechanical transducer including an element
for receiving an acoustic wave generated by the step of converting current output from the first
electrode into voltage, and DC voltage to the second electrode Applying the DC voltage or the
conversion ratio of the current to the voltage based on the elapsed time information from the
time when the light is irradiated to the subject. And V. changing at least one of the steps.
[0007]
Since the capacitive electromechanical transducer is controlled in consideration of the influence
of light attenuation in the subject, the effect of the reduction in the output of the
electromechanical transducer can be reduced.
[0008]
It is a schematic diagram explaining the measurement system concerning a 1st embodiment.
It is a schematic diagram explaining regarding generation | occurrence | production and
attenuation | damping of light.
It is a schematic diagram explaining the electromechanical transducer which can apply the
present invention.
It is a schematic diagram for demonstrating how to obtain | require a conversion factor. It is a
schematic diagram for demonstrating how to obtain | require a conversion factor. It is a
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3
schematic diagram of a measurement system at the time of providing a reference signal
generating body. It is a schematic diagram explaining the measurement system concerning a 2nd
embodiment.
[0009]
In order to cope with the influence of the reduction of the output of the electromechanical
transducer due to the light attenuation, the present invention uses at least one of the following
two methods. The first is to increase the output from the electromechanical transducer itself by
increasing the required reception sensitivity of the acoustic wave corresponding to the
attenuation of light. This form will be described in the first embodiment. Second, the output from
the electromechanical transducer itself is not adjusted, and the conversion ratio when converting
the current output from the electromechanical transducer into a voltage is increased according to
the attenuation of light. This form will be described in the second embodiment. Thus, in either
form, the influence of the signal output to the external device for generating the image data can
be reduced as the light decays.
[0010]
Hereinafter, the present invention will be described in detail using the drawings. In the present
invention, the acoustic wave includes acoustic waves, ultrasonic waves, and so-called
photoacoustic waves, and is an elastic wave generated inside a subject by irradiating the subject
with light (electromagnetic wave) such as near-infrared light. Indicates
[0011]
First Embodiment In the present embodiment, the drive voltage (DC voltage) applied to the
capacitive electromechanical transducer is changed based on the elapsed time from the time
when the object is irradiated with light, and the reception sensitivity is determined. It is
characterized by changing.
[0012]
FIG. 1 is a schematic view of a measurement system including a control device of an
electromechanical transducer applicable to the present embodiment.
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The present measurement system using the photoacoustic effect emits light 202 to the subject
112 by generating light 202 (pulsed light) from the light source 111 based on the light emission
instruction signal 201. In the object 112, an acoustic wave is generated from the measurement
target (acoustic wave generation source) by the irradiation of the light 202, and the acoustic
wave is received by the electromechanical transducer 101 as an acoustic wave receiver. The
electromechanical conversion device 101 converts the vibration due to the received acoustic
wave into an electric signal (current) 204 and outputs the electric signal (current) to the currentvoltage conversion means 102. The current-voltage conversion unit 102 converts the input
current 204 into a voltage 205, and outputs the voltage 205 to an input unit (for example, AD
conversion or phasing addition processing) of an external device (not shown) for generating
image data. The current voltage conversion means can use a transimpedance circuit as an
example. On the other hand, the elapsed time information generation unit 103 generates
information on elapsed time from the ON signal (for example, the time at the middle of the width
of the pulse) of the light emission instruction signal 201 as the elapsed time information 206.
Output to The control signal generation unit 104 generates a control signal 207 based on the
elapsed time information 206 and outputs the control signal 207 to the DC voltage application
unit 105 that applies a drive voltage (DC voltage) to the electromechanical conversion device
101. The control device for controlling the electro-mechanical conversion device 101 of the
present embodiment includes at least a control signal generation unit 104, a DC voltage
application unit 105, and a current / voltage conversion unit 102. The elapsed time information
generation unit 103 may be incorporated in the control device, or may be incorporated in a
device (a drive control device or the like of the light source 111) other than the control device.
Here, the current voltage conversion unit 102, the elapsed time information generation unit 103,
the control signal generation unit 104, and the DC voltage application unit 105 can be
configured using a PC, a CPU for integration, an FPGA, an analog circuit, or the like. These
components can be disposed in proximity to the electromechanical transducer 101 or can be
disposed in an integrated manner by being integrated on a dedicated control IC chip.
[0013]
Next, generation and attenuation of the light 202 focused on in the present invention will be
described with reference to FIG. In FIG. 2, the horizontal axis in FIG. 2A represents time, the
vertical axis represents the magnitude of the drive signal for driving the light source 111, and the
horizontal axis in FIG. It is the strength of light. The horizontal axis in FIG. 2 (c) is the distance x 1
traveled by the light in the subject, the vertical axis is the light intensity, the horizontal axis in
FIG. 2 (d) is time, and the vertical axis is the electromechanical transducer It is a distance x2 from
103.
04-05-2019
5
[0014]
The light emission instruction signal 201 is a periodic pulse signal as shown in FIG. 2A, and light
is generated from the light source when the light emission instruction signal 201 is ON. The light
source 111 periodically emits light upon receiving the light emission instruction signal 201 (see
FIG. 2B). The light 202 generated by the light source 111 is irradiated to the subject 112. Here,
as shown in FIG. 2C, the light emitted to the subject 112 exponentially decays in light intensity
according to the distance traveled in the subject. In the present invention, the relationship
between the distance x 1 traveled by the light in the object and the light intensity is called the
light attenuation relationship. However, since light travels at a very high speed, it can be
regarded that light has reached any position of the object simultaneously with the generation of
light by the light source.
[0015]
On the other hand, since the acoustic wave generated by the light 202 travels in the subject at a
constant speed, the acoustic wave reaches the electromechanical transducer 101 according to
the distance x2 from the electromechanical transducer 101 to the acoustic wave source. The time
changes (see Fig. 2 (d)). Therefore, it is identified how far away from the electromechanical
transducer 101 the acoustic wave is generated from the elapsed time t from the time when the
light source 111 generates light (the same time as the time when the light is irradiated to the
object). be able to. That is, the position of the acoustic wave generation source in the object 112
is grasped from the relationship of the elapsed time t from the time of light irradiation, the
position of the electromechanical transducer 101, the irradiation position of the light 202, the
position of the object 112, etc. it can. Then, based on the position of the acoustic wave generation
source and the attenuation relationship of light, “the elapsed time from the light irradiation,“
the size of the light wave received by the acoustic wave arriving at the elapsed time t has been
received to generate the acoustic wave The relationship between the light attenuation and the
light attenuation can be derived. Thereby, at the time of elapsed time t, how large the acoustic
wave (ie, the sound pressure) reaches the electromechanical transducer 101, that is, how large
the acoustic wave needs to be received, Can understand In the present embodiment, the output
itself from the electromechanical transducer 101 required in response to light attenuation is
increased to increase the reception sensitivity of the acoustic wave.
[0016]
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6
Here, an electromechanical transducer 101 applicable to the present invention will be described
with reference to FIG. FIG. 3 is a cross-sectional view of the electromechanical transducer 101
and a schematic view of the DC voltage application means 105 and the current voltage
conversion means 102. In the capacitive electromechanical transducer 101, a lower electrode
505 is formed on a substrate 506, and an upper electrode 502 is disposed with the lower
electrode 505 and a gap 504 (usually several tens of nm to 900 nm) interposed therebetween. In
the present embodiment, the upper electrode 502 is formed on the vibrating film 501, and the
vibrating film 501 is supported by the support portion 503 formed on the substrate 506. In the
present invention, the smallest unit that vibrates is referred to as a cell, with the two electrodes
facing each other across the diaphragm 501 and the gap 504 in this way as one set. A
configuration in which a plurality of cells are electrically connected in parallel is called an
element. In FIG. 3, two cells form one element, but the present invention is not limited to this, one
cell may form one element, and a plurality of cells are arranged in a two-dimensional array. It
may be connected in a shape. The elements may be provided in an arbitrary number, and may be
arranged in a two-dimensional array. CMUT, which is an electromechanical transducer, usually
has about 100 to 3000 cells as one element (one pixel), and about 200 to 4000 elements are
two-dimensionally arrayed, and CMUT itself has a size of about 1 to 10 cm It is.
[0017]
The upper electrode used in the present invention is selected from metals selected from Al, Cr, Ti,
Au, Pt, Cu, Ag, Mo, Ta, Ni, AlSi, AlCu, AlTi, MoW, AlCr. At least one of the alloys can be selected
and used. In addition, the upper electrode may be provided on at least one of the upper surface,
the back surface, and the inside of the vibrating film, or when the vibrating film is formed of a
conductor or a semiconductor, the vibrating film itself may serve as the upper electrode. is there.
Moreover, as the lower electrode used in the present invention, the same metal as the upper
electrode can be used. When the substrate is a semiconductor substrate such as silicon, the
substrate may double as the lower electrode.
[0018]
In FIG. 3, the upper electrodes 502 are all electrically connected in the electromechanical
transducer 101, and a plurality of upper electrodes 502 are connected with DC voltage
application means 105. The direct current voltage application unit 105 uniformly applies a
predetermined direct current voltage to the upper electrode 502 so that a desired potential
04-05-2019
7
difference is generated between the lower electrode 505 and the lower electrode 505. Then,
when an acoustic wave is input to the vibrating membrane 501, the vibrating membrane 501
vibrates according to the size of the acoustic wave. In the lower electrode 505, electrostatic
induction occurs due to the vibration of the vibrating membrane 501, and a minute current is
generated. By converting the current value into a voltage value and acquiring it by the currentvoltage conversion means 102 connected to the lower electrode 505 for each element, it is
possible to take out the reception signal of the acoustic wave as a voltage value for each element.
In the present invention, the electrode connected to the current-voltage conversion means 102 is
a first electrode, and the electrode connected to the DC voltage application means 105 is a
second electrode. That is, although in FIG. 3 the lower electrode 505 is the first electrode and the
upper electrode 502 is the second electrode, the current voltage conversion means 102 is
connected to the upper electrode 502 to form the first electrode; May be connected to the lower
electrode 505 as a second electrode.
[0019]
Next, the principle of increasing the reception sensitivity of the acoustic wave required
corresponding to the attenuation of light will be described. When driving a capacitive
electromechanical transducer, a predetermined potential difference is applied between the first
and second electrodes (between the upper and lower electrodes), and the electrostatic film
generated between the electrodes causes the vibrating film 501 to be the substrate 506. It will be
bent to the side. When receiving an acoustic wave, the magnitude of the generated microcurrent
is inversely proportional to the distance between the electrodes and proportional to the potential
difference between the electrodes. Therefore, the potential difference between the electrodes
changes the current generated when the vibrating membrane 501 receives an acoustic wave.
Specifically, when the potential difference between the electrodes is increased, the electrostatic
attractive force is increased, the deflection of the vibrating film 501 is increased, and the distance
between the electrodes is narrowed. In the same vibration when an acoustic wave of the same
size is received, the smaller the distance between the electrodes, the larger the generated current
and the larger the potential difference between the electrodes, and therefore the larger the
generated current. Conversely, if the potential difference between the electrodes is reduced, the
electrostatic attraction is reduced, the deflection of the vibrating membrane 501 is reduced, and
the distance between the electrodes is increased. The larger the distance between the electrodes,
the smaller the generated current and the smaller the potential difference between the electrodes
in the same vibration when an acoustic wave of the same size is received, and the smaller the
generated current.
[0020]
04-05-2019
8
In the present embodiment, the control signal 207 generated by the control signal generation
unit 104 is output to the DC voltage application unit 105. The DC voltage application unit 105
changes the DC voltage applied to the upper electrode 502 so as to correspond to the input
control signal 207. Thereby, the potential difference between the upper and lower electrodes can
be changed, and the required reception sensitivity of the acoustic wave can be changed
corresponding to the light attenuation (the elapsed time from the light irradiation time point). In
other words, this means changing the ratio (conversion coefficient) for converting mechanical
vibration due to the received acoustic wave into current. That is, the control signal generation
unit 104 obtains this conversion coefficient based on the elapsed time t from the light irradiation
time point, generates a control signal 207 corresponding to this conversion coefficient, and
outputs the control signal 207 to the DC voltage application unit 105. Thereby, the influence of
the reduction of the output current from the electromechanical conversion device 101 caused by
the light attenuation is reduced, and finally, the signal (current-voltage conversion shown in FIG.
1) to be output to the external device for generating the image data. The voltage 205) output
from the means 102 is also adjusted.
[0021]
(How to Determine Conversion Coefficient) Next, a conversion coefficient which is a ratio for
converting mechanical vibration due to the received acoustic wave into current will be described.
The conversion coefficient differs depending on the positional relationship between the
irradiation direction of the light 202 and the electromechanical transducer 101. First, the case
where the irradiation direction of the light 202 and the receiving surface of the
electromechanical transducer 101 are opposed will be described using FIG. 4.
[0022]
In FIG. 4, the light source 111 emits light 202 perpendicularly to the subject 112. The
electromechanical transducer 101 is disposed at a position facing the light source 111 with the
subject 112 interposed therebetween. Here, it is assumed that the thickness T of the subject 112
is constant, and the electro-mechanical transducer 101 is disposed without a gap from the
subject 112. In addition, there is no attenuation of the light 202 between the light source 111
and the subject 112.
04-05-2019
9
[0023]
As the light 202 generated from the light source 111 and irradiated to the subject travels in the
depth direction of the subject 112, the light travels exponentially with the light intensity being
attenuated. That is, in the subject 112, the closer to the light source 111, the stronger light
strikes, and the farther it goes, the more the light attenuates and the weaker light strikes. When
an acoustic wave generation source is present at a position of depth d from the light irradiation
surface of the object 112, the intensity φ of the light irradiated to the acoustic wave generation
source can be expressed by the following equation. φ = A × exp (−μeff × d) (1) In the
equation (1), A is a coefficient determined by the light intensity, and μeff is a coefficient
determined by the characteristics of the object 112. Here, since the light travels in the object 112
at a very high speed, it can be considered that the light has arrived at any position in the object
112 at the same timing as the light source 111 emits light. When the materials of the acoustic
wave generation source are of the same nature and size, the magnitude of the acoustic wave
generated by the photoacoustic effect is determined corresponding to the intensity of the
irradiated light. That is, in the subject 112, a strong acoustic wave is generated from the side
closer to the light source 111, and a weaker acoustic wave is generated as it goes farther. That is,
depending on the position where the acoustic wave generation source exists in the subject 112,
the required reception sensitivity is significantly different.
[0024]
Assuming that the magnitude of the acoustic wave generated when the light intensity φ is
irradiated to a substance having a certain structure (acoustic wave generation source) is P, it can
be expressed by the following equation. P = B × φ = B ′ × exp (−μeff × d) (2) Here, B and
μeff are coefficients determined by the acoustic wave generation source. On the other hand,
acoustic waves generated by the photoacoustic effect propagate inside the object 112 in the
direction of the electromechanical transducer 101 and are received by the electromechanical
transducer 101. Since the speed at which the acoustic wave travels through the object 112 is
slower than light, in the electromechanical transducer 101, the one closer to the
electromechanical transducer 101 (the one farther from the light source 111) is received first.
The one far from 101 (closer to the light source 111) will be received later.
[0025]
Here, assuming that the distance from the electromechanical transducer 101 to the acoustic
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10
wave generation source is x and the velocity at which the acoustic wave travels in the object 112
is v, the time t until the acoustic wave reaches the electromechanical transducer 101 is , Can be
expressed by the following equation. t = x / v (3) From these, in the configuration of FIG. 4, the
weak acoustic wave generated by the weak light is received first near the electromechanical
transducer 101, and the electromechanical transducer It can be seen that a strong acoustic wave
generated by strong light is received later at a position far from 101. Therefore, in such a mode,
immediately after the light source 111 emits light, the conversion coefficient is increased (the
reception sensitivity is increased) and the conversion coefficient is decreased (the reception
sensitivity is decreased) as time passes. It is.
[0026]
Further, the depth d from the irradiation surface of the light on the object 112 to the acoustic
wave generation source is expressed by the following equation using the distance x from the
electromechanical transducer and the thickness T of the object 112 Can. d = T−x Formula (4) If
Formula (3) is substituted in Formula (4), it can deform | transform into the following formula |
equation. d = T−v × t (5) Assuming that the magnitude of the acoustic wave generated by the
acoustic wave generation source at a distance d from the irradiation surface of the light on the
object 112 is P ′, P 'Can be expressed by the following equation using P (the size of an acoustic
wave generated when light is not attenuated). P ′ = C × P / x (6) C is a coefficient determined
by the subject 112. Substituting the equations (2) and (5) into the equation (6), the following
equation can be obtained.
[0027]
[0028]
D is a coefficient determined by the light amount of the light source and the photoacoustic effect
of the subject.
Therefore, assuming that the conversion coefficient is K, K can be expressed by the following
equation using the elapsed time t.
[0029]
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11
[0030]
Therefore, as shown in FIG. 4, when the irradiation direction of the light 202 and the receiving
surface of the electro-mechanical transducer 101 face each other, the control signal 207 is
generated based on the conversion coefficient shown in equation (8).
[0031]
Next, as shown in FIG. 5, the irradiation direction of the light 202 does not face the receiving
surface of the electro-mechanical transducer 101, and the irradiation surface of the light on the
object 112 and the receiving surface of the acoustic wave The case where they are arranged on
the same side will be described.
[0032]
In FIG. 5, the light 202 irradiates the object 112 at a predetermined angle, or the light is
irradiated through the optical waveguide in the electromechanical transducer, and the light
irradiation surface and the acoustic wave are received. The faces are placed on the same side of
the subject.
In such a configuration, the strong acoustic wave generated by the strong light is received first
near the electromechanical transducer 101, and the weak acoustic wave generated by the weak
light is far from the electromechanical transducer 101. It will be received later.
Therefore, in this embodiment, immediately after the light source 111 emits light, the conversion
coefficient is reduced (the reception sensitivity is lowered), and the conversion coefficient is
increased (the reception sensitivity is increased) as time passes. is there.
[0033]
Since the electromechanical transducer 101 and the light source 111 are disposed on the same
side, the depth d from the light irradiation surface of the object 112 to the acoustic wave source
and the acoustic wave source to the electromechanical transducer The distance x can be the
same numerical value.
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12
d = x Formula (9) From Formula (9), Formula (3) and Formula (6) can be rewritten to the
following formulas. t = d / v Formula (3 ′) P ′ = C × P / d Formula (6 ′) The subject 112
according to Formula (2), Formula (3 ′), and Formula (6 ′) The size P ′ of the acoustic wave
generated by the acoustic wave generation source at a distance of depth d from the light
irradiation surface can be expressed by the following equation.
[0034]
[0035]
That is, the conversion coefficient K in the present embodiment can be expressed by the
following equation using the elapsed time t.
[0036]
[0037]
Therefore, as shown in FIG. 5, when the surface on the object to be irradiated with light and the
receiving surface of the acoustic wave are disposed on the same side of the object, the control
signal is calculated based on the conversion coefficient K shown in equation (11). Can be
generated.
[0038]
Furthermore, the conversion coefficient K can be determined also when the light 202 is
irradiated from both sides of the subject (not shown).
In this case, K can be expressed by the following equation (12).
[0039]
[0040]
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13
D1 and D2 are coefficients determined by the light amount of the light source and the
photoacoustic effect of the subject.
[0041]
As described above, even if the plane of irradiating the object 112 with the light 202 and the
arrangement position of the electromechanical conversion device 101 are changed, control is
performed based on the elapsed time t from the time of irradiating the object 112 with light. The
signal generation unit 104 can obtain a conversion coefficient (in the present embodiment, a
ratio for converting mechanical vibration due to the received acoustic wave into current).
Then, the control signal 207 corresponding to the conversion coefficient is generated and output
to the DC voltage application unit 105.
The DC voltage application unit 105 changes the DC voltage applied to the upper electrode 502
so as to correspond to the input control signal 207.
Thereby, the potential difference between the upper and lower electrodes can be changed, and
the required reception sensitivity of the acoustic wave can be changed corresponding to the light
attenuation (the elapsed time from the light irradiation time point).
Therefore, it is possible to reduce the influence of the signal 205 (voltage output from the
current-voltage conversion unit 102 in FIG. 1) output to the external device for generating the
image data, as the light attenuates. .
[0042]
(Acquisition of Elapsed Time Information) In the above description, as shown in FIG. 1, the
elapsed time information generation means 103 generates an ON signal (pulse) which the light
emission instructing signal 201 has as a signal instructing the light source to generate light. The
elapsed time information 206 is acquired from the center time of the width of
04-05-2019
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However, as shown in FIG. 6, the reference signal generator 301 for generating the desired
acoustic wave 401 by the light 202 is provided between the electromechanical transducer 101
and the subject 112, and the electromechanical transducer 101 generates the acoustic wave. The
elapsed time information 206 may be acquired from the time when the wave 401 was received.
That is, from the acoustic wave 401 generated by the reference signal generator 301, the
reference signal 402 for generating the elapsed time information 206 is generated.
[0043]
In FIG. 6, the reference signal generator 301 is disposed between the electromechanical
transducer 101 and the subject 112. Specifically, it is preferable to provide the surface of the
object 112 or a plate for keeping the shape of a part of the object constant near the surface of
the object 112 on the surface on which the electro-mechanical transducer 101 is disposed. .
Therefore, the acoustic wave 401 generated by the reference signal generator 301 reaches the
electromechanical transducer 101 ahead of the acoustic wave 203 generated by the subject 112.
The reference signal determination means 302 determines that the acoustic wave 401 generated
by the reference signal generator 301 has reached the electromechanical conversion device 101,
and outputs a reference signal 402 to the elapsed time information generation means 103. The
elapsed time information generation unit 103 generates the elapsed time information 206 based
on the reference signal 402.
[0044]
Here, the determination by the reference signal determination unit 302 will be described. First,
let us consider a state after sufficient time has elapsed since the previous light emission of the
light source 111 and all the acoustic waves 203 generated by the subject 112 have reached the
electromechanical transducer 101. When the light emission instruction signal 201 is input to the
light source 111, the light 202 is output after a slight time delay (delay) from the light source
111. This is because, for the light emission instructing signal 201, it takes some time for the light
source 111 to generate the light 202. Since the speed of light is very high, the output light 202
can be regarded as being emitted to the reference signal generator 301 and the subject 112 in an
instant.
[0045]
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The acoustic wave generated by the light 202 is received from that generated at a position close
to the electromechanical transducer 101. The DC voltage application unit 105 has a switch for
switching between the reception state and the non-reception state of the acoustic wave, and
when receiving the acoustic wave 401 generated by the reference signal generator 301, the
switch is switched to the acoustic wave reception state A current 204 corresponding to the
acoustic wave 401 is output. After this, according to the position of the acoustic wave generation
source, the procedure is such that the current 204 corresponding to the received acoustic wave
is sequentially output. Here, the reference signal determination means 302 determines that the
acoustic wave 401 generated by the reference signal generator 301 has arrived by switching
from the non-reception state to the reception state, and outputs the reference signal 402. As a
result, it is possible to prevent the DC voltage application unit 105 from operating abnormally
due to the influence of noise generated by the light emission of the light source 111 or the like.
[0046]
By using the acoustic wave 401 generated by the reference signal generator 301 as the reference
signal 402 of the elapsed time information generating means 103, the delay until the light source
111 emits light, the light source 111 and the object 112, and the electromechanical transducer
101 It is possible to correct the deviation of the arrival time of the acoustic wave due to the
deviation of the arrangement of.
[0047]
Second Embodiment Next, a second embodiment will be described with reference to FIG.
In the first embodiment, the reception sensitivity is increased by raising the drive voltage (DC
voltage) applied to the electromechanical conversion device 101 in response to the light
attenuation, and the current 204 itself output by the electromechanical conversion device 101 is
increased. Do. That is, in the first embodiment, the conversion coefficient for converting the
vibration by the acoustic wave received by the electromechanical conversion device 101 into a
current is changed based on the elapsed time after the light is irradiated to the object. However,
in the second embodiment, the sensitivity of the electromechanical transducer itself is not
changed, and even if the current 204 output from the electromechanical transducer 101
decreases in response to the attenuation of light, the current-voltage conversion means 102
Increase the rate of conversion to voltage. That is, in the present embodiment, the conversion
coefficient at the time of converting the current into the voltage by the current-voltage
conversion unit 102 is changed based on the elapsed time from the light irradiation. Other than
that, it is the same as the first embodiment.
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[0048]
FIG. 7A shows a schematic view of a measurement system including a control device of the
electromechanical transducer 101 applicable to the present embodiment. As in the first
embodiment, the light source 111 generates light 202 (pulsed light) based on the light emission
instruction signal 201, and the light 202 is irradiated to the subject 112. In the subject 112, the
electromechanical transducer 101 receives an acoustic wave generated by the irradiation of the
light 202. The electromechanical transducer 101 converts the received vibration due to the
acoustic wave into a current 204 and outputs the current 204 to the current-voltage converter
102. On the other hand, the elapsed time information generation unit 103 generates information
on elapsed time from the ON signal (based on the time at the middle of the width of the pulse) of
the light emission instruction signal 201 as the elapsed time information 206. Output. Here, in
the present embodiment, the control signal 207 generated by the control signal generation unit
104 based on the elapsed time information 206 is output to the current-voltage conversion unit
102. Then, the current-voltage conversion unit 102 converts the current 204 input from the
electromechanical conversion device 101 into a voltage 205 at a conversion ratio (conversion
coefficient) based on the control signal 207, and generates an image data, etc. Output to a device
(not shown). The conversion coefficient is the same as the conversion coefficient K shown in the
description of (how to obtain conversion coefficient) in the first embodiment. That is, it can be
obtained from the relationship between the electromechanical transducer 101 and the light
irradiation direction.
[0049]
FIG. 7B shows a configuration diagram of a transimpedance circuit which is the current voltage
conversion means 102 of the present embodiment. 701 is an operational amplifier, 702 is a
variable resistor, 703 is a variable capacitor, 704 is a resistor, and 705 is a capacitor.
[0050]
In FIG. 7B, the operational amplifier 701 is connected to the positive and negative power supplies
VDD and VSS. First, the operation at the time of capacity change detection (at the time of acoustic
wave reception) will be described. The inverting input terminal (−IN) of the operational amplifier
701 is connected to the first electrode (lower electrode 505 in the case of FIG. 3) of the
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electromechanical transducer 101. Further, in the output terminal (OUT) of the operational
amplifier 701, the variable resistor 702 and the variable capacitor 703 connected in parallel are
connected to the inverting input terminal (-IN), and the output signal is fed back. The
noninverting input terminal (+ IN) of the operational amplifier 701 is connected to the ground
terminal (GND) by a resistor 704 and a capacitor 705 connected in parallel. The voltage of the
ground terminal (GND) is an intermediate potential between the positive power supply VDD and
the negative power supply VSS.
[0051]
In this embodiment, the values of the variable resistor 702 and the variable capacitor 703 are
changed based on the input control signal 207 to change the conversion ratio when the currentvoltage conversion means 102 converts current into voltage. Can. Therefore, the control signal
207 generated based on the conversion coefficient can be electrically reflected fast enough
compared to the speed of the sound pressure change due to the light attenuation.
[0052]
The elapsed time from the light irradiation may be acquired from the light emission instruction
signal 201 as in the first embodiment, but the reference signal generator 301 is provided, and
from the time when the acoustic wave from the reference signal generator is received.
Information on elapsed time may be acquired.
[0053]
Also, unlike the present embodiment, adjustment of gain is performed by a preamplifier (variable
gain amplifier: VGA) in front of an AD converter provided in an external device (not shown) from
which the voltage converted by the current voltage conversion means 102 is output. It is also
conceivable to do
However, the acoustic wave generated by the photoacoustic effect has a wide frequency band
and a wide range of output voltage. Therefore, a gain adjustment function may be required in a
range exceeding the maximum gain (amplification factor) of the preamplifier. Therefore, as in the
first embodiment, the form of raising the current 204 output from the electro-mechanical
conversion device 101 or the conversion ratio when converting from current to voltage by the
current-voltage conversion unit 102 as in the second embodiment. By performing at least one of
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the modes in which プ リ ア ン プ is increased, it is possible to use a preamplifier that does not
require gain adjustment or a preamplifier that has a small adjustment range.
[0054]
DESCRIPTION OF SYMBOLS 101 Electromechanical conversion device 102 Current voltage
conversion means 103 Elapsed time information generation means 104 Control signal
generation means 105 DC voltage application means 111 Light source 112 Object 201 Light
emission instruction signal 202 Light 203 Acoustic wave 204 Current 205 Voltage 206 Elapsed
time information 207 Control Signal 501 vibrating film 502 upper electrode 503 support portion
504 gap 505 lower electrode 506 substrate
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