WO2024095808A1 - Spr ultrasonic sensor and ultrasonic measurement system - Google Patents

Abstract

An SPR ultrasonic sensor 110 comprises a prism 111 that allows a laser beam to pass therethrough and a metallic membrane 112 that reflects a laser beam. In the ultrasonic sensor, surface plasmon resonance is generated when a laser beam is incident on the metallic membrane 112, and the resonance angle is shifted when the metallic membrane 112 is irradiated with an ultrasonic wave. The ultrasonic sensor is characterized in that the metallic membrane 112 is formed only on a portion of a first surface 111A such that the area of a laser-beam irradiation spot formed on said surface 111A includes a metallic area and a non-metallic area.

Description

SPR-type ultrasonic sensor and ultrasonic measurement system

The present invention relates to an SPR type ultrasonic sensor and an ultrasonic measurement system equipped with the SPR type ultrasonic sensor.

Conventionally, sensors that utilize surface plasmon resonance (SPR) are known, such as those described in Patent Documents 1 to 4.

The sensor described in Patent Document 1 includes a prism, a metal film formed on one side of the prism, and a sound receiving layer formed on the surface of the metal film. A porous material such as dried silica gel is used for the sound receiving layer. According to the sensor described in Patent Document 1, the change in the refractive index of the sound receiving layer caused by sound pressure can be detected by the change in the resonance angle of the surface plasmon resonance.

The sensor described in Patent Document 2 comprises a prism, a metal film formed on one side of the prism, and a force receiving layer formed on the surface of the metal film. The force receiving layer is made of a porous material such as dried silica gel, similar to the sound receiving layer described in Patent Document 1. According to the sensor described in Patent Document 2, the change in the refractive index of the force receiving layer caused by an external force can be detected by the change in the resonance angle of the surface plasmon resonance.

The sensor described in Patent Document 3 includes a glass plate and a metal thin film spot formed on the light reflecting surface of the glass plate. This sensor is intended for use with a light source that emits incoherent light, such as an LED lamp. As described in Patent Document 3, the light emitted from an LED cannot be focused to a size as small as the laser light from a laser diode, regardless of the optical system used. For this reason, when an LED is used, a reflectance curve with a broad peak is observed. Therefore, in the sensor described in Patent Document 3, the metal thin film spot is made to a size that fits within the LED spot image projected onto the light reflecting surface, thereby making the peak of the reflectance curve sharp. As a result, the sensor described in Patent Document 3 can measure the resonance angle of surface plasmon resonance with high accuracy.

The sensor described in Patent Document 4 includes a transparent piezoelectric substrate, a first thin-film metal electrode provided on a first surface of the transparent piezoelectric substrate, a second thin-film metal electrode provided on the first surface of the transparent piezoelectric substrate, and an attenuated total reflection (ATR) coupler disposed adjacent to the second thin-film metal electrode. The sensor described in Patent Document 4 can improve measurement sensitivity compared to a sensor that does not include an attenuated total reflection (ATR) coupler.

FIG. 12 shows a conventional SPR type ultrasonic sensor 410 used in the research of the present inventor. FIG. 12(A) is a front view of the SPR type ultrasonic sensor 410, and FIG. 12(B) is a plan view of the SPR type ultrasonic sensor 410.

As shown in FIG. 12(A), the SPR ultrasonic sensor 410 includes a prism 411 that transmits laser light, and a metal film 412 that totally reflects the laser light incident at a predetermined angle. The prism 411 is a triangular prism, and has a first surface 411A that is rectangular in plan view. As shown in FIG. 12(B), the metal film 412 is formed over the entire first surface 411A. Also, as shown in FIG. 12(B), an irradiation spot area of the laser light is formed on the first surface 411A.

In the SPR ultrasonic sensor 410, laser light penetrates the metal film 412, resonating with the surface plasmon wave and generating surface plasmon resonance. When ultrasonic waves are irradiated onto the metal film 412, the ultrasonic waves change the refractive index near the surface of the metal film 412, shifting the resonance angle. In other words, ultrasonic waves can be indirectly detected by detecting the reflected light of the laser light reflected by the metal film 412.

Incidentally, photoacoustic methods used for 3D measurements of biological tissues and various physical properties require wideband measurements because the ultrasonic waves generated depend on the physical properties of various tissues. The SPR ultrasonic sensor 410 is capable of wideband measurements, but when the irradiation spot area of the laser light is under certain conditions, a problem occurs in that the measurement sensitivity of the ultrasonic waves decreases when the frequency of the ultrasonic waves increases and the wavelength of the ultrasonic waves becomes shorter. For this reason, there is a demand for improving the frequency characteristics of sensitivity in conventional SPR ultrasonic sensors 410.

In addition, previous research by the inventors of this application has shown that by reducing the irradiation spot diameter of the laser light, the measurement sensitivity in the high frequency band is improved and the frequency characteristics are improved. However, in order to change the irradiation spot diameter of the laser light according to the frequency of the ultrasound, control of the external optical system is required. Also, as shown in Figure 12 (B), the irradiation spot area is always elliptical, which is unsuitable for accurate ultrasound measurement.

JP 2010-245599 A JP 2013-120145 A Japanese Patent Application Laid-Open No. 9-257697 JP 2008-513772 A

The present invention was made in consideration of the above circumstances, and its objective is to provide an SPR type ultrasonic sensor and ultrasonic measurement system that can improve the frequency characteristics of sensitivity with a relatively simple and inexpensive configuration.

In order to solve the above problems, the SPR type ultrasonic sensor according to the present invention comprises:
a prism having a first surface and transmitting laser light;
a metal film formed on the first surface and configured to reflect the laser light;
The SPR type ultrasonic sensor generates surface plasmon resonance by the incidence of the laser light on the metal film, and shifts a resonance angle when the metal film is irradiated with ultrasonic waves,
The metal film is characterized in that the laser light irradiation spot area formed on the first surface includes a metal area where the metal film is present and a non-metal area where the metal film is not present, and the ultrasonic irradiation area formed on the first surface includes the metal area.

In the SPR type ultrasonic sensor,
The metal film is also formed outside the irradiation spot area,
When the metal region within the irradiation spot region is defined as a sensing region, the area of the sensing region can be configured to increase or decrease when the irradiation spot region is translated on the first surface.

In the SPR type ultrasonic sensor,
The metal film may be formed discretely on the first surface so as to form a plurality of circles and/or polygons having different areas when the first surface is viewed in a plan view.

In the SPR type ultrasonic sensor,
The metal film may be formed on the first surface so that it has a triangular and/or trapezoidal shape when viewed in a plane, and the height direction of the triangle and/or trapezoid extends beyond the irradiation spot area.

In the SPR type ultrasonic sensor,
A blocking film for preventing the ultrasonic waves from entering the prism may be formed in an area of the first surface where the metal film is not formed.

In the SPR type ultrasonic sensor,
The metal film may have a protective film formed on the surface thereof to prevent oxidation. For example, the protective film may be a film containing gold.

In order to solve the above problems, an ultrasonic measurement system according to the present invention includes:
a laser light irradiation unit that irradiates laser light;
An ultrasonic generator that generates ultrasonic waves;
an SPR type ultrasonic sensor comprising a prism having a first surface and a metal film formed on the first surface, wherein the laser light is incident on the metal film to generate surface plasmon resonance, and the metal film is irradiated with the ultrasonic wave to shift a resonance angle;
a laser beam receiving unit that receives the laser beam reflected at an interface between the metal film and the prism;
An ultrasonic measurement system comprising:
the metal film is formed only on a portion of the first surface,
the laser light irradiation unit irradiates the laser light such that an irradiation spot region of the laser light formed on the first surface includes a metal region in which the metal film is present and a non-metal region in which the metal film is not present,
the ultrasonic generator generates ultrasonic waves when irradiating the laser light such that the metallic region is included in an irradiated region of the ultrasonic waves formed on the first surface;
The ultrasonic waves are irradiated to the metal film without passing through a sound receiving layer for improving the measurement sensitivity of the ultrasonic waves.

In the ultrasonic measurement system,
The metal film is also formed outside the irradiation spot area,
When the metal region within the irradiation spot region is defined as a sensing region, the area of the sensing region can be configured to increase or decrease when the irradiation spot region is translated on the first surface.

In the ultrasonic measurement system,
The metal film may be formed discretely on the first surface so as to form a plurality of circles and/or polygons having different areas when the first surface is viewed in a plan view.

In the ultrasonic measurement system,
The metal film may be formed on the first surface so that it has a triangular and/or trapezoidal shape when viewed in a plane, and the height direction of the triangle and/or trapezoid extends beyond the irradiation spot area.

In the ultrasonic measurement system,
The SPR type ultrasonic sensor may be configured such that a blocking film for suppressing the ultrasonic waves from entering the prism is formed in an area of the first surface where the metal film is not formed.

In the ultrasonic measurement system,
A container for containing a sample solution and for placing the SPR ultrasonic sensor in the sample solution is further provided.
The ultrasonic generator may be configured to include an ultrasonic transducer that irradiates the ultrasonic waves into the sample solution.

In the ultrasonic measurement system,
the SPR type ultrasonic sensor is disposed so that a measurement target including a light absorber is in contact with the side of the metal film opposite to the first surface,
The ultrasonic generator may output pulsed light to the measurement object and generate the ultrasonic waves from the light absorber due to a photoacoustic effect.

The ultrasonic measurement system includes:
The device may be configured to include a moving mechanism that moves the SPR ultrasonic sensor to move the irradiation spot area in a parallel manner on the metal film.

The ultrasonic measurement system includes:
The laser control unit may be configured to control the laser light irradiation unit to move the irradiation position of the laser light, thereby moving the irradiation spot area in a parallel direction on the metal film.

The present invention provides an SPR type ultrasonic sensor and ultrasonic measurement system that can improve the frequency characteristics of sensitivity with a relatively simple and inexpensive configuration.

1 is a diagram showing an ultrasonic measurement system according to a first embodiment. 1A is a front view of a first embodiment of an SPR type ultrasonic sensor (without a blocking film), FIG. 1B is a plan view, and FIG. 1C is a plan view showing a sensing region. 1A and 1B are diagrams showing an SPR type ultrasonic sensor (with a blocking film) of a first embodiment, in which (A) is a plan view and (B) is a cross-sectional view taken along line BB of (A). 1A is a diagram showing a shift in the resonance angle when ultrasonic waves are applied, and FIG. 1B is a diagram showing a change over time in the amplitude of the AC component of reflected light. FIG. 1 is a diagram showing an experimental sample of effect confirmation experiment 1. FIG. 13 is a diagram showing the experimental results of effect confirmation experiment 1. 10A to 10C are diagrams showing an SPR type ultrasonic sensor of a second embodiment, in which (A) is a front view, (B) is a plan view, and (C) is a plan view showing a sensing region. 13A to 13C are diagrams showing an SPR type ultrasonic sensor of a third embodiment, in which (A) is a front view, (B) is a plan view, and (C) is a plan view showing a sensing region. FIG. 13 is a diagram showing an experimental sample of effect confirmation experiment 2. FIG. 13 is a diagram showing the experimental results of effect confirmation experiment 2. FIG. 13 is a diagram showing an ultrasonic measurement system according to a second embodiment. 1A and 1B are diagrams showing a conventional SPR type ultrasonic sensor, in which (A) is a front view and (B) is a plan view.

Below, an embodiment of an SPR type ultrasonic sensor and an ultrasonic measurement system according to the present invention will be described with reference to the attached drawings.

[First embodiment]
1 shows an ultrasonic measurement system 100 according to a first embodiment of the present invention. The ultrasonic measurement system 100 includes an SPR ultrasonic sensor 110 according to the first embodiment of the present invention, a laser light transmitting and receiving unit 120, an ultrasonic generator 130, and a container 140 that contains a sample solution.

The SPR ultrasonic sensor 110 includes a prism 111 and a metal film 112. The laser light transmitting/receiving unit 120 includes a laser light emitting unit 121, a laser light receiving unit 122, and a display unit 123. The ultrasonic generator 130 includes an ultrasonic light emitting unit 131 and an ultrasonic control unit 132.

Prism 111 is made of a material (glass in this embodiment) that transmits the laser light irradiated from laser light irradiator 121. As shown in FIG. 2(A), prism 111 has a first surface 111A on which metal film 112 is formed, and has an entrance area for laser light (incident light) and an exit area for laser light (reflected light) on a surface different from first surface 111A. Prism 111 in this embodiment is a triangular prism with a triangular cross section, but as long as metal film 112 can be provided, it may be a semicircular prism with a semicircular cross section or a prism of another shape.

The metal film 112 is made of a metal or alloy that reflects the laser light incident at a predetermined incident angle θ (e.g., equal to or greater than the critical angle). In this embodiment, silver is used. A protective film such as an anti-oxidation film can be provided on the silver surface (the surface opposite to the first surface 111A). The metal film 112 is formed directly on the first surface 111A by deposition, sputtering, or the like. The above protective film can be, for example, a film containing gold. However, the protective film is not limited to a film containing gold, and a film containing a metal material other than gold or silver (the material of the metal film 112) or a film containing a resin material can be used as long as it has an anti-oxidation effect.

2B, the metal film 112 is formed only on a portion of the first surface 111A so that it has a circular shape when the first surface 111A is viewed in a plan view. The thickness of the metal film 112 is about 50 nm in this embodiment, but can be changed as appropriate within the range of, for example, 10 nm to 100 nm, as long as it can cause surface plasmon resonance in the SPR ultrasonic sensor 110.

The laser light irradiation unit 121 is configured to irradiate the interface between the metal film 112 and the prism 111 with continuous-wave laser light at a single wavelength. In this embodiment, the laser light irradiation unit 121 irradiates visible laser light of 532 nm, but it is preferable to change the wavelength of the laser light appropriately depending on the materials of the metal film 112 and the prism 111. The laser light irradiation unit 121 may irradiate laser light of other wavelengths as long as surface plasmon resonance can be generated in the SPR ultrasonic sensor 110. Note that since laser light is coherent light, the irradiation spot area described below can be made smaller than incoherent light such as LED light.

As shown in FIG. 2(C), the laser light irradiated from the laser light irradiating unit 121 forms an elliptical irradiation spot area L1 on the first surface 111A. Note that the irradiation spot area in the present invention is the area irradiated with the laser light, and is defined by the full width at half maximum (FWHM) of the intensity distribution of the laser light. The irradiation spot area L1 includes a metal area where the metal film 112 is present, and a non-metal area where the metal film 112 is not present. Only the metal area within the irradiation spot area L1 becomes the sensing area of the SPR ultrasonic sensor 110.

The SPR ultrasonic sensor 110 may include a blocking film 113, as shown in FIG. 3. FIG. 3A is a plan view of the SPR ultrasonic sensor 110 including the blocking film 113, and FIG. 3B is a cross-sectional view taken along line B-B in FIG. 3A.

The blocking film 113 is made of a material (e.g., a foam such as urethane) that prevents ultrasonic waves from penetrating the prism 111. The blocking film 113 is formed in an area of the first surface 111A of the prism 111 where the metal film 112 is not formed. In FIG. 3, the blocking film 113 is made to be the same thickness as the metal film 112, but the blocking film 113 may be thinner or thicker than the metal film 112. Furthermore, the blocking film 113 may be formed only in an area of the first surface 111A where the metal film 112 is not formed and where ultrasonic waves are irradiated (e.g., area U1 in FIG. 2(C)).

When ultrasonic waves enter the prism 111, there is a risk that the ultrasonic waves may adversely affect the laser light passing through the prism 111 (such as causing the optical paths of the incident light and reflected light to shift), but the blocking film 113 can prevent such adverse effects.

The laser light receiving unit 122 is configured to receive the laser light (reflected light) reflected at the interface between the metal film 112 and the prism 111. The laser light receiving unit 122 includes, for example, a photodiode and an amplifier provided after the photodiode. The laser light receiving unit 122 outputs a signal corresponding to the reflected light to the display unit 123.

The display unit 123 is configured to display the waveform of the reflected light received by the laser light receiving unit 122. Although details will be described later, since an AC component corresponding to the ultrasonic wave is superimposed on the waveform of the reflected light, the display unit 123 displays at least the AC component (AC waveform). The display unit 123 includes, for example, an oscilloscope.

The ultrasound irradiation unit 131 is configured to irradiate ultrasound to the surface of the metal film 112 (the surface opposite the first surface 111A) through the sample solution under the control of the ultrasound control unit 132. The ultrasound irradiation unit 131 is an ultrasound transducer that generates ultrasound based on an electrical signal.

In this embodiment, the metal film 112 is irradiated with focused ultrasonic waves, but ultrasonic waves propagating in the sample solution may be incident on the metal film 112 without being focused. That is, the ultrasonic irradiation area is a part of the first surface 111A or the entire first surface 111A. A part of the first surface 111A is an area including metal areas and non-metal areas, or an area of only metal areas. When focused ultrasonic waves are irradiated, the focused ultrasonic waves form a circular irradiation area U1 on the first surface 111A that is larger than the irradiation spot area L1 of the laser light. In this embodiment, ultrasonic waves are irradiated in an arrangement facing the SPR ultrasonic sensor 110, but if the ultrasonic waves are incident on the metal film 112, it is not necessary to irradiate ultrasonic waves in an arrangement facing the SPR ultrasonic sensor 110. That is, the positional value relationship between the SPR ultrasonic sensor 110 and the ultrasonic irradiation unit 131 can be changed as appropriate.

The ultrasonic control unit 132 is configured to apply an electrical signal (in this embodiment, an AC voltage signal) to the ultrasonic control unit 132 to control the ultrasonic irradiation unit 131. The ultrasonic control unit 132 can change the frequency of the ultrasonic waves irradiated by the ultrasonic irradiation unit 131 by changing the frequency of the electrical signal. The ultrasonic control unit 132 includes, for example, a function generator.

The storage unit 140 has an outer wall through which the laser light passes, and is configured to place the entire SPR ultrasonic sensor 110 and at least a part of the ultrasonic irradiation unit 131 in the sample solution. The storage unit 140 is provided with a holding mechanism (not shown) for holding the SPR ultrasonic sensor 110 and the ultrasonic irradiation unit 131 so that the laser light is reflected at the interface between the metal film 112 and the prism 111, and ultrasonic waves are irradiated onto the surface of the metal film 112. The storage unit 140 also has a moving mechanism (not shown) for moving the position of the SPR ultrasonic sensor 110. The moving mechanism will be described later.

In the SPR ultrasonic sensor 110, when laser light is incident on the interface between the metal film 112 and the prism 111 at a predetermined incident angle θ (for example, equal to or greater than the critical angle), an evanescent wave is generated at the interface. When the wave number of the evanescent wave matches the wave number of the surface plasmon wave generated on the surface of the metal film 112, surface plasmon resonance occurs.

The wave number of the surface plasmon wave depends on the medium (in this embodiment, the specimen solution) adjacent to the surface of the metal film 112. When the ultrasound irradiation unit 131 irradiates the surface of the metal film 112 with ultrasound through the specimen solution, the density of the specimen solution changes due to the compression and decompression of the ultrasound, the refractive index of the specimen solution changes, and the wave number of the surface plasmon wave changes. As a result, the conditions for surface plasmon resonance change and the resonance angle shifts. The resonance angle is the incident angle θ at which the reflectance is smallest.

Figure 4(A) shows the reflectance curve of the laser light. In the figure, A is the reflectance curve when the part of the ultrasound with zero sound pressure reaches the metal film 112, B is the reflectance curve when the part of the ultrasound with positive sound pressure (dense part) reaches the metal film 112, and C is the reflectance curve when the part of the ultrasound with negative sound pressure (sparse part) reaches the metal film 112. Figure 4(B) also shows the waveform of the reflected light when the incident angle θ of the laser light is θ = X1.

From Figure 4 (A), it can be seen that when the specimen solution on the surface of the metal film 112 is pressurized by the positive sound pressure of the ultrasound, the reflectance curve shifts to the right, and when the specimen solution on the surface of the metal film 112 is depressurized by the negative sound pressure of the ultrasound, the reflectance curve shifts to the left. Also, from Figure 4 (B), it can be seen that the fluctuation in the reflectance curve due to the pressurization and depressurization of the ultrasound appears as an AC component (fluctuation in the amplitude value of the reflected light) in the waveform of the laser light (reflected light).

However, in reality, the wavefront of the ultrasonic waves that reach the metal film 112 is not a perfect plane, so the sound pressure distribution on the surface of the metal film 112 is not uniform. For example, the sound pressure of the ultrasonic waves will be maximum in one area of the metal film 112, whereas the sound pressure of the ultrasonic waves will not be maximum in another area of the metal film 112. In other words, the phase of the arriving ultrasonic waves differs at each part of the surface of the metal film 112. The effect of such ultrasonic phase distribution becomes greater the larger the area of the sensing region and the higher the frequency and shorter the wavelength of the ultrasonic waves.

As shown in FIG. 12, in a conventional SPR ultrasonic sensor 410 in which the metal film 412 is formed over the entire first surface 411A, the elliptical laser light irradiation spot area becomes the sensing area as it is. For this reason, in the conventional SPR ultrasonic sensor 410, the measurement sensitivity of the ultrasonic waves is reduced due to the influence of the major axis of the ellipse, and the waveform itself also changes, making it impossible to perform accurate measurements.

In contrast, in the SPR ultrasonic sensor 110 according to this embodiment, the irradiation spot area L1 includes metal areas and non-metal areas, and only the metal areas in the irradiation spot area L1 become the sensing area. Therefore, compared to the conventional SPR ultrasonic sensor 410, the area of the sensing area can be made smaller. Also, the sensing area is circular, and is not affected by shape. Furthermore, when the SPR ultrasonic sensor 110 includes a blocking film 113, ultrasonic waves can be more accurately detected as AC components of the laser light (reflected light).

As described above, the SPR ultrasonic sensor 110 and ultrasonic measurement system 100 according to this embodiment can improve the frequency characteristics of sensitivity with a relatively simple and inexpensive configuration. Furthermore, since the ultrasonic measurement system 100 is an optical measurement system, it does not require cables, etc., and since it is configured by simply placing the small SPR ultrasonic sensor 110 inside the housing 140, there is little effect of the SPR ultrasonic sensor 110 disturbing the sound field inside the housing 140.

<Effectiveness Confirmation Experiment 1>
Next, Effect Confirmation Experiment 1 will be described. Fig. 5 shows a front view and a plan view of an experimental sample for Effect Confirmation Experiment 1. Fig. 5(A) shows a conventional SPR type ultrasonic sensor 410', and Figs. 5(B) to (D) show SPR type ultrasonic sensors 110-1 to 110-3 according to this embodiment. Effect Confirmation Experiment 1 is an experiment for confirming the effect of the ultrasonic measurement method according to this embodiment using the SPR type ultrasonic sensors 110-1 to 110-3.

The SPR ultrasonic sensor 410' shown in FIG. 5(A) has the same configuration as the SPR ultrasonic sensor 410 shown in FIG. 12, except that a protective film 414 is formed on the surface of the metal film 412. The metal film 412 is a silver film with a thickness of 31 nm, and the protective film 414 is a gold film with a thickness of 5 nm. In plan view, the metal film 412 and the protective film 414 have a long side length of 14.1 mm and a short side length of 10 mm.

The SPR ultrasonic sensors 110-1 to 110-3 shown in Figures 5(B) to (D) have the same configuration as the SPR ultrasonic sensor 110 shown in Figure 2, except that a protective film 114 is formed on the surfaces of the metal films 112-1 to 112-3. The metal films 112-1 to 112-3 are silver films with a thickness of 31 nm, and the protective film 114 is a gold film with a thickness of 5 nm. The first surface 111A of the prism 111 has a long side length of 14.1 mm and a short side length of 10 mm.

The SPR ultrasonic sensors 110-1 to 110-3 have the same configuration, except for the areas of the metal films 112-1 to 112-3 and the protective film 114 in a plan view. The area of the protective film 114 is the same as the area of the corresponding metal films 112-1 to 112-3. Note that the area of the protective film 114 does not necessarily have to be the same as the area of the metal films 112-1 to 112-3, and may be larger than the area of the metal films 112-1 to 112-3.

The metal film 112-1 of the SPR ultrasonic sensor 110-1 shown in FIG. 5(B) is a circle with a diameter of 1.0 mm in a plan view. The metal film 112-2 of the SPR ultrasonic sensor 110-2 shown in FIG. 5(C) is a circle with a diameter of 0.8 mm in a plan view. The metal film 112-3 of the SPR ultrasonic sensor 110-3 shown in FIG. 5(D) is a circle with a diameter of 0.6 mm in a plan view.

In effect confirmation experiment 1, the ultrasonic measurement method according to this embodiment was carried out using the ultrasonic measurement system 100 shown in FIG. 1. However, instead of the SPR ultrasonic sensor 110, the SPR ultrasonic sensors 110-1 to 110-3 shown in FIGS. 5(B) to (D) were used. For comparison, the ultrasonic measurement method was also carried out using the SPR ultrasonic sensor 410' shown in FIG. 5(A).

The ultrasonic measurement method includes a preparation step, an irradiation step, and a light receiving step. The content of each step is the same regardless of whether SPR type ultrasonic sensor 410', SPR type ultrasonic sensor 110-1, SPR type ultrasonic sensor 110-2, or SPR type ultrasonic sensor 110-3 is used. Therefore, each step will be explained below using the example of using SPR type ultrasonic sensor 110-1.

In the preparation step, the SPR ultrasonic sensor 110-1 is placed in the storage section 140, and the laser light emitting section 121, the laser light receiving section 122, and the ultrasonic wave emitting section 131 are also placed. The laser light emitting section 121 is placed outside the storage section 140 so that the laser light is irradiated to the interface between the metal film 112-1 and the prism 111 at an incident angle θ (in this experiment, θ = 56.05 [deg]). The laser light receiving section 122 is placed outside the storage section 140 so that it receives the laser light (reflected light) reflected at the interface. At least the tip of the ultrasonic wave emitting section 131 is placed inside the storage section 140 so that ultrasonic waves are irradiated to the surface of the metal film 112-1 through the sample solution and the protective film 114.

In this experiment, water (refractive index 1.335) was used as the specimen solution in the storage section 140. A continuous wave laser (CW laser) with a laser light wavelength of 532 [nm] and a laser diameter of 1.26 [mm] was used as the laser light irradiating section 121. A convergent type ultrasonic transducer (ultrasonic transmitter) with a spot diameter (full width at half maximum) of 1.75 [mm] was used as the ultrasonic irradiating section 131.

In the irradiation step, with the SPR ultrasonic sensor 110-1 placed in the housing 140 (the state at the end of the preparation step), the laser light irradiation unit 121 irradiates laser light toward the metal film 112-1 of the SPR ultrasonic sensor 110-1, and the ultrasonic irradiation unit 131 irradiates ultrasonic waves. As a result, an elliptical irradiation spot area L1 caused by the laser light and a circular spot area (not shown) caused by the ultrasonic waves are formed on the first surface 111A of the prism 111. Both areas include the area of the metal film 112-1 (metal area), i.e., the sensing area S11.

In this experiment, the irradiation spot area L1 has a major axis of 2.09 mm and a minor axis of 1.26 mm. The ultrasonic spot area has a diameter (full width at half maximum) of 1.75 mm. The irradiation spot area L1 and the ultrasonic spot area are common to the cases of Figs. 5(A) to (D). On the other hand, the sensing area is different for each of Figs. 5(A) to (D). In Fig. 5(A), the irradiation spot area L1 is the sensing area S10 as it is. In Fig. 5(B), a circular area with a diameter of 1.0 mm (area of metal film 112-1) is the sensing area S11. In Fig. 5(C), a circular area with a diameter of 0.8 mm (area of metal film 112-2) is the sensing area S12. In Fig. 5(D), a circular area with a diameter of 0.6 mm (area of metal film 112-3) is the sensing area S13.

In addition, in this experiment, a 5 MHz sine wave pulse wave (one wave) is input as an input signal from the ultrasound control unit 132 to the ultrasound irradiation unit 131. Such a 5 MHz pulse wave has a wide band of frequency characteristics around 5 MHz. The 5 MHz pulse wave used in this experiment contains components with sufficient amplitude in the frequency band of 2 to 8 MHz. For this reason, it is possible to obtain measurement values in the above frequency band by frequency analysis. Note that the ultrasound control unit 132 can also generate a continuous sine wave, so it is also possible to adopt a continuous sine wave as the input signal.

In the light receiving step, the laser light receiving unit 122 receives the reflected light of the laser light reflected at the interface between the metal film 112-1 and the prism 111, and obtains information (amplitude data) regarding the amplitude value of the AC component of the reflected light. The light receiving step is performed in parallel with the irradiation step.

Figure 6 (A) shows amplitude data of the AC component of the reflected light received by the laser light receiving unit 122 in the light receiving step (waveforms A to D). Waveform A is the waveform of the AC component of the reflected light reflected at the sensing area S10 of the SPR ultrasonic sensor 410'. Waveform B is the waveform of the AC component of the reflected light reflected at the sensing area S11 of the SPR ultrasonic sensor 110-1. Waveform C is the waveform of the AC component of the reflected light reflected at the sensing area S12 of the SPR ultrasonic sensor 110-2. Waveform D is the waveform of the AC component of the reflected light reflected at the sensing area S13 of the SPR ultrasonic sensor 110-3.

For comparison, FIG. 6(A) also shows the amplitude data of the ultrasound (ultrasonic pulse of 5 MHz) output by the ultrasound irradiation unit 131 (waveform E). The ultrasound was observed by placing a needle-type ultrasonic transducer (calibration hydrophone) in place of the SPR ultrasonic sensors 110-1 to 110-3 inside the housing unit 140. The effective diameter of the calibration hydrophone is 1.00 mm.

As can be seen from FIG. 6(A), waveforms B to D are slightly different in the shape of the negative first peak compared to waveform E, but overall they are almost identical to waveform E. From this, it can be seen that the ultrasonic measurement method according to this embodiment can detect the ultrasonic waves output by the ultrasonic irradiation unit 131 as an AC component of the laser light (reflected light) received by the laser light receiving unit 122.

FIG. 6(B) shows the frequency characteristics of the AC component of the reflected light received by the laser light receiving unit 122. Graphs A to D shown in FIG. 6(B) were obtained by performing frequency analysis on the waveforms A to D shown in FIG. 6(A), respectively. Note that the frequency analysis performed in this embodiment is a known technique, so a description of it will be omitted here.

In FIG. 6(B), the amplitude value of the ultrasonic waves directly detected by the calibration hydrophone is set to 1. As can be seen from FIG. 6(B), B to D have amplitude values exceeding 1 in the frequency range of 4 MHz or more. Furthermore, B to D have larger amplitude values than A. Therefore, according to the ultrasonic measurement method of this embodiment, it is possible to improve the measurement sensitivity in the same range compared to using a calibration hydrophone, and it is possible to improve the measurement sensitivity compared to the conventional ultrasonic measurement method using the SPR type ultrasonic sensor 410'. Note that the results of this experiment are only an example, and the present invention is not limited to the above conditions described in Effect Confirmation Experiment 1.

[Modification of SPR type ultrasonic sensor]
In the ultrasonic measurement system 100 according to the first embodiment, an SPR type ultrasonic sensor 210 of a second form or an SPR type ultrasonic sensor 310 of a third form described below can be used instead of the SPR type ultrasonic sensor 110 of the first form.

<Second embodiment of SPR type ultrasonic sensor>
7 shows a second embodiment of an SPR type ultrasonic sensor 210. The SPR type ultrasonic sensor 210 includes a prism 211 and a metal film 212. The prism 211 has the same configuration as the prism 111 of the first embodiment.

As shown in FIG. 7(A), the metal film 212 is made of a metal or alloy that reflects the laser light incident at a predetermined angle. In this embodiment, silver is used. A protective film such as an oxidation prevention film can be provided on the surface of the silver. The metal film 212 is formed directly on the first surface 211A of the prism 211 by deposition, sputtering, or the like.

As shown in FIG. 7B, the metal film 212 is formed discretely only on a part of the first surface 211A so that the first surface 211A is viewed in plan as a plurality of (four in this embodiment) circular metal films 212a-212d with different areas. The thickness of the metal film 212 is about 50 nm in this embodiment, but can be changed as appropriate within a range of, for example, 10 nm to 100 nm, as long as it can cause surface plasmon resonance in the SPR ultrasonic sensor 210. In addition, a blocking film made of a material that prevents ultrasonic waves from penetrating the prism 211 may be formed in an area of the first surface 211A where the metal film 212 is not present. The blocking film has the same configuration as the blocking film 113 in the first embodiment.

As shown in FIG. 7(C), the laser light irradiated from the laser light irradiator 121 forms an elliptical irradiation spot area L2 on the first surface 211A. The irradiation spot area L2 includes a metal area where the metal film 212 (metal film 212a in FIG. 7(C)) is present, and a non-metal area where the metal film 212 is not present. The metal area within the irradiation spot area L2 becomes the sensing area of the SPR ultrasonic sensor 210. In addition, the ultrasonic waves irradiated from the ultrasonic irradiator 131 form a circular irradiation area U2 on the first surface 211A that includes the metal films 212a to 212d.

The movement mechanism of the storage unit 140 in FIG. 1 moves the SPR ultrasonic sensor 210, thereby moving the irradiation spot area L2 in parallel to its short axis direction. In other words, the movement mechanism can select the sensing area from among the four metal films 212a to 212d without moving the laser light irradiation unit 121 and the ultrasonic irradiation unit 131, and without changing the area of the irradiation spot area L2.

For example, when the frequency of the ultrasonic waves is relatively low, the S/N ratio can be improved by using the metal film 212a, which has a large area, as the sensing region. On the other hand, when the frequency of the ultrasonic waves is relatively high, the effect of the phase difference of the ultrasonic waves can be reduced and the measurement sensitivity can be improved by using the metal film 212d, which has a small area, as the sensing region.

As described above, by using the second form of SPR ultrasonic sensor 210, it is possible to improve the frequency characteristics of sensitivity with a relatively simple and inexpensive configuration, and furthermore, it is possible to easily change the area of the sensing region. Note that in the SPR ultrasonic sensor 210, the number of metal films 212 is not limited to four. Also, the arrangement of the metal films 212 may be arranged in a two-dimensional array.

Furthermore, when changing the area of the sensing region, the irradiation spot region L2 may be moved in parallel to its short axis direction by controlling the irradiation position of the laser light from the laser light irradiation unit 121 (which may include control to move the laser light irradiation unit 121 itself) without moving the SPR type ultrasonic sensor 210. In this case, the movement mechanism of the storage unit 140 becomes unnecessary, but a laser control unit that controls the irradiation position of the laser light irradiation unit 121 is required, and the laser light receiving unit 122 may also need to be moved depending on the optical path of the reflected light.

<Third Form of SPR Type Ultrasonic Sensor>
8 shows an SPR type ultrasonic sensor 310 of the third embodiment. The SPR type ultrasonic sensor 310 includes a prism 311 and a metal film 312. The prism 311 has the same configuration as the prism 111 of the first embodiment.

As shown in FIG. 8(A), the metal film 312 is made of a metal or alloy that reflects the laser light incident at a predetermined angle. In this embodiment, silver is used. A protective film such as an oxidation prevention film can be provided on the surface of the silver. The metal film 312 is formed directly on the first surface 311A of the prism 311 by deposition, sputtering, or the like.

As shown in FIG. 8B, the metal film 312 is formed only on a part of the first surface 311A so that it forms a triangle when the first surface 311A is viewed in a plan view. The thickness of the metal film 312 is about 50 nm in this embodiment, but can be changed as appropriate within a range of, for example, 10 nm to 100 nm, as long as it can cause surface plasmon resonance in the SPR ultrasonic sensor 310. Also, a blocking film made of a material that prevents ultrasonic waves from penetrating the prism 311 may be formed in an area of the first surface 311A where the metal film 312 is not present. The blocking film has the same configuration as the blocking film 113 in the first embodiment.

As shown in FIG. 8(C), the laser light irradiated from the laser light irradiating unit 121 forms an elliptical irradiation spot area L3 on the first surface 311A. The triangular metal film 312 is formed only on a part of the first surface 311A so that its height extends into the minor axis direction of the irradiation spot area L3. The irradiation spot area L3 includes a metal area where the metal film 312 is present and a non-metal area where the metal film 312 is not present. The metal area within the irradiation spot area L3 becomes the sensing area of the SPR type ultrasonic sensor 310.

As in the second embodiment, the movement mechanism of the storage unit 140 in FIG. 1 moves the SPR ultrasonic sensor 310 to move the irradiation spot area L3 in parallel to its short axis direction. In other words, the movement mechanism can continuously change the sensing area without moving the laser light irradiation unit 121 and the ultrasonic irradiation unit 131, and without changing the area of the irradiation spot area L3.

For example, when the frequency of the ultrasonic waves is relatively low, the area of the sensing area can be increased and the S/N ratio improved by moving the irradiation spot area L3 toward the base side of the triangular metal film 312. On the other hand, when the frequency of the ultrasonic waves is relatively high, the area of the sensing area can be reduced and the measurement sensitivity improved by moving the irradiation spot area L3 to the opposite side from the base side of the triangular metal film 312.

As described above, by using the third form of SPR ultrasonic sensor 310, it is possible to improve the frequency characteristics of sensitivity with a relatively simple and inexpensive configuration, and furthermore, it is possible to easily and continuously change the area of the sensing region. In addition, in the SPR ultrasonic sensor 310, in order to measure the distribution of ultrasonic waves on the first surface 311A, multiple triangular metal films 312 may be arranged in the long axis direction of the irradiation spot region L3.

Furthermore, when changing the area of the sensing region, as in the second embodiment, the irradiation position of the laser light from the laser light irradiation unit 121 may be controlled (which may include control to move the laser light irradiation unit 121 itself) without moving the SPR type ultrasonic sensor 310, thereby moving the irradiation spot region L3 in parallel in its short axis direction.

<Effectiveness Confirmation Experiment 2>
Next, a description will be given of Effect Confirmation Experiment 2. Fig. 9A shows a front view and a plan view of an SPR type ultrasonic sensor 310' which is an experimental sample of Effect Confirmation Experiment 2.

The SPR ultrasonic sensor 310' has the same configuration as the SPR ultrasonic sensor 310 shown in FIG. 8, except that a metal film 312' is provided instead of the metal film 312. The metal film 312' is a silver film with a thickness of 48 nm, and when the first surface 311A is viewed in plan, it is a trapezoid with an upper base of 0.5 mm, a lower base of 4 mm, and a height of 10 mm. The first surface 311A has a long side length of 28.2 mm and a short side length of 20 mm.

In the effect confirmation experiment 2, the ultrasonic measurement method according to this embodiment was carried out using the ultrasonic measurement system 100 shown in FIG. 1. However, instead of the SPR type ultrasonic sensor 110, an SPR type ultrasonic sensor 310' was used.

As explained in Effect Confirmation Experiment 1, the ultrasonic measurement method according to this embodiment includes a preparation step, an irradiation step, and a light receiving step. In Effect Confirmation Experiment 2, the preparation step, the irradiation step, and the light receiving step were performed in each of the states A, B, and C shown in FIG. 9(B). Each step is common to Effect Confirmation Experiment 1, so a description of the common parts will be omitted here.

In the irradiation step, an elliptical irradiation spot area L4 formed by the laser light and a circular spot area (not shown) formed by the ultrasonic waves are formed on the first surface 111A of the prism 311. The irradiation spot area L4 has a major axis of 4.35 mm and a minor axis of 1.26 mm. The ultrasonic spot area has a diameter (full width at half maximum) of 1.76 mm.

The movement mechanism of the storage section 140 in FIG. 1 can translate the irradiation spot area L4 by moving the SPR type ultrasonic sensor 310'. In other words, the movement mechanism can change only the area of the sensing area without moving the laser light irradiation section 121 and the ultrasonic irradiation section 131, and without changing the area of the irradiation spot area L4 and the area of the ultrasonic spot area. In effect confirmation experiment 2, the area of the sensing area is largest in state A, and is smallest in state C.

Figure 10 (A) shows amplitude data of the AC component of the reflected light received by the laser light receiving unit 122 in the light receiving step (waveforms A to C). Waveform A is the waveform of the AC component of the reflected light in state A of Figure 9 (B). Waveform B is the waveform of the AC component of the reflected light in state B of Figure 9 (B). Waveform C is the waveform of the AC component of the reflected light in state C of Figure 9 (B).

FIG. 10(A) also shows the amplitude data of the ultrasound (ultrasonic pulse of 5 MHz) output by the ultrasound irradiation unit 131 (waveform D), as in Effect Confirmation Experiment 1. Waveform D is the waveform of the ultrasound detected directly by the calibration hydrophone, as in Effect Confirmation Experiment 1. The effective diameter of the calibration hydrophone is 1.00 mm.

As can be seen from FIG. 10(A), waveforms A to C are slightly different from waveform D in the shape of the rising edge and the first negative peak, but overall they are almost identical to waveform D. This shows that the ultrasonic measurement method according to this embodiment using the SPR ultrasonic sensor 310' can detect the ultrasonic waves output by the ultrasonic irradiation unit 131 as an AC component of the laser light (reflected light) received by the laser light receiving unit 122.

Figure 10(B) shows the frequency characteristics of the AC component of the reflected light received by the laser light receiving unit 122. Graphs A to C shown in Figure 10(B) were obtained by performing frequency analysis on waveforms A to C shown in Figure 10(A) in the same manner as in Effect Confirmation Experiment 1.

In FIG. 10(B), the amplitude value of the ultrasonic waves directly detected by the calibration hydrophone is set to 1. As can be seen from FIG. 10(B), A and B have reduced measurement sensitivity in the frequency range of 4 MHz or more, whereas C, which has the smallest sensing area, does not have reduced measurement sensitivity. In other words, according to the ultrasonic measurement method of this embodiment using the SPR ultrasonic sensor 310', the frequency characteristic of sensitivity can be improved by setting the sensing area to state C when the frequency is 4 MHz or more.

Therefore, the ultrasonic measurement method according to this embodiment preferably includes a moving step of moving the laser light irradiation spot area L4 and the ultrasonic spot area in parallel on the first surface 111A. In the moving step, for example, the moving mechanism (controller of the moving mechanism) of the storage section 140 preferably compares the frequency of the ultrasonic waves output by the ultrasonic irradiation section 131 with a preset frequency (e.g., 4 MHz), and moves the SPR ultrasonic sensor 310' according to the magnitude relationship between the frequency and the set frequency, thereby increasing or decreasing the area of the sensing region. Note that the results of this experiment are merely an example, and the present invention is not limited to the above conditions described in Effect Confirmation Experiment 2.

[Second embodiment]
11 shows an ultrasonic measurement system 200 according to the second embodiment of the present invention. The ultrasonic measurement system 200 includes an SPR ultrasonic sensor 210 of the second embodiment, a laser light transmitting and receiving unit 220, and an ultrasonic generator 230.

The SPR type ultrasonic sensor 210 is arranged so that the surface of the metal film 212 is in direct contact with the specimen 240. The specimen 240 corresponds to the "measurement object" of the present invention, and includes a light absorber 241. Note that in the ultrasonic measurement system 200, the first type SPR type ultrasonic sensor 110 or the third type SPR type ultrasonic sensor 310 can be used instead of the second type SPR type ultrasonic sensor 210.

The laser light transmitting/receiving unit 220 includes a laser light emitting unit 221, a laser light receiving unit 222, a display unit 223, and a laser control unit 224. The laser light emitting unit 221, the laser light receiving unit 222, and the display unit 223 have the same configuration as the laser light emitting unit 121, the laser light receiving unit 122, and the display unit 123 of the first embodiment. The laser light emitting unit 221 forms an elliptical irradiation spot area L2 on the first surface 211A of the prism 211, as shown in FIG. 7(C), for example.

The laser control unit 224 is configured to control the irradiation position of the laser light from the laser light irradiation unit 221. Specifically, the laser control unit 224 controls the laser light irradiation unit 221 to move the irradiation position of the laser light so that the irradiation spot area L2 moves parallel to its short axis direction. Regarding the movement of the irradiation position of the laser light, the laser light irradiation unit 221 itself may move under the control of the laser control unit 224, or only the irradiation direction of the laser light may be finely adjusted. In either case, the laser control unit 224 can adjust the area of the sensing area without changing the area of the irradiation spot area L2 by moving the irradiation spot area L2 parallel to the short axis direction.

For example, by using the metal film 212a with a large area as the sensing region, the S/N ratio can be improved, while by using the metal film 212d with a small area as the sensing region, the effect of the phase difference of the ultrasonic waves can be reduced and measurement sensitivity can be improved.

The ultrasonic generator 230 is configured to output pulsed light (e.g., pulsed light in the femtosecond or picosecond range) toward the subject 240. That is, the ultrasonic generator 230 of this embodiment includes a pulsed light irradiator that outputs pulsed light. When the pulsed light output from the ultrasonic generator 230 is irradiated onto the light absorber 241 included in the subject 240, the light absorber 241 generates ultrasonic waves due to the photoacoustic effect. When the ultrasonic waves due to the photoacoustic effect reach the sensing region of the SPR ultrasonic sensor 210, the ultrasonic measurement system 200 can detect the ultrasonic waves as AC components of the laser light (reflected light).

As described above, the ultrasonic measurement system 200 according to this embodiment can improve the frequency characteristics of sensitivity with a relatively simple and inexpensive configuration, and furthermore, can easily and continuously change the area of the sensing region.

When changing the area of the sensing region, the irradiation spot region L2 may be moved in parallel in the short axis direction by moving the SPR ultrasonic sensor 210 on the surface of the subject without moving the laser light irradiation position of the laser light irradiation unit 221. In this case, the laser control unit 224 is not necessary, but a movement mechanism for moving the SPR ultrasonic sensor 210 is required.

　Although the various forms of the SPR type ultrasonic sensor and the various embodiments of the ultrasonic measurement system according to the present invention have been described above, the present invention is not limited to the above forms and embodiments.

The SPR ultrasonic sensor according to the present invention is an SPR ultrasonic sensor that has a first surface, includes a prism that transmits laser light, and a metal film formed on the first surface that reflects the laser light, and generates surface plasmon resonance when the laser light is incident on the metal film, and shifts the resonance angle when ultrasonic waves are irradiated onto the metal film. The configuration of the metal film can be modified as appropriate as long as it is formed only on a portion of the first surface so that the irradiation spot area of the laser light formed on the first surface includes a metal area where the metal film is present and a non-metal area where the metal film is not present.

For example, since the metal region of the present invention is a region containing a metal film that generates surface plasmon resonance upon incidence of laser light, the non-metal region of the present invention may contain a metal that does not generate surface plasmon resonance upon incidence of laser light.

The metal film 112 in the first form is formed only on a part of the first surface 111A so that it is circular when the first surface 111A is viewed in a plan view, but it may be a shape other than circular (e.g., polygonal) as long as the sensing area can be made smaller than the irradiation spot area L1.

The metal film 212 of the second form may be formed to have a plurality of polygons with different areas when the first surface 211A is viewed in a plan view. The metal film 312 of the third form may be formed to have a trapezoid when the first surface 311A is viewed in a plan view, and to have a height direction that extends beyond the minor axis direction of the irradiation spot area L3. In other words, the metal film of the second or third form may be formed to have any shape as long as the area of the sensing area increases or decreases with the parallel movement of the irradiation spot area.

In the above embodiment, a system has been described that includes either a movement mechanism or a laser control unit as a configuration for moving the irradiation spot area in parallel on the metal film, but it may also include both a movement mechanism and a laser control unit, or the irradiation spot area may be moved in parallel using a configuration other than these.

The SPR type ultrasonic sensor according to the present invention can improve the frequency characteristics of sensitivity without using a sound receiving layer for improving the measurement sensitivity of ultrasonic waves. The sound receiving layer for improving the measurement sensitivity of ultrasonic waves is, for example, the sound receiving layer described in Patent Document 1 or the force receiving layer described in Patent Document 2 described in the prior art.

100, 200 Ultrasonic measurement system 110, 210, 310 SPR type ultrasonic sensor 111, 211, 311 Prism 112, 212, 312 Metal film 120, 220 Laser light transmitting/receiving unit 121, 221 Laser light irradiating unit 122, 222 Laser light receiving unit 123, 223 Display unit 224 Laser control unit 130, 230 Ultrasonic generator 131 Ultrasonic irradiating unit 132 Ultrasonic control unit 140 Container unit 240 Specimen 241 Light absorber

Claims (16)

1. a prism having a first surface and transmitting laser light;
   A metal film (excluding those having a sound receiving layer for improving measurement sensitivity of ultrasonic waves) formed on the first surface and reflecting the laser light;
   an SPR type ultrasonic sensor that generates surface plasmon resonance by the incidence of the laser light on the metal film and shifts a resonance angle when the metal film is irradiated with ultrasonic waves,
   The SPR type ultrasonic sensor is characterized in that the metal film is formed only on a part of the first surface such that an irradiation spot area of the laser light formed on the first surface includes a metal area where the metal film is present and a non-metal area where the metal film is not present, and such that an irradiation area of the ultrasonic wave formed on the first surface includes the metal area.
2. The metal film is also formed outside the irradiation spot area,
   2. The SPR type ultrasonic sensor according to claim 1, wherein when the metal region within the irradiation spot region is defined as a sensing region, the area of the sensing region increases or decreases when the irradiation spot region is translated on the first surface.
3. 3. The SPR type ultrasonic sensor according to claim 2, wherein the metal film is discretely formed on the first surface so as to form a plurality of circles and/or polygons having different areas when the first surface is viewed in a plan view.
4. 3. The SPR type ultrasonic sensor according to claim 2, characterized in that the metal film is formed on the first surface so as to have a triangular and/or trapezoidal shape when the first surface is viewed in a plane, and so that the height direction of the triangle and/or trapezoid extends beyond the irradiation spot area.
5. 3. The SPR type ultrasonic sensor according to claim 2, wherein a blocking film is formed in an area of the first surface where the metal film is not formed, for suppressing the ultrasonic waves from entering the prism.
6. 3. The SPR type ultrasonic sensor according to claim 2, wherein a protective film for preventing oxidation is formed on the surface of the metal film.
7. 7. The SPR type ultrasonic sensor according to claim 6, wherein the protective film is a film containing gold.
8. a laser light irradiation unit that irradiates laser light;
   An ultrasonic generator that generates ultrasonic waves;
   an SPR type ultrasonic sensor comprising a prism having a first surface and a metal film formed on the first surface, wherein the laser light is incident on the metal film to generate surface plasmon resonance, and the metal film is irradiated with the ultrasonic wave to shift a resonance angle;
   a laser beam receiving unit that receives the laser beam reflected at an interface between the metal film and the prism;
   An ultrasonic measurement system comprising:
   the metal film is formed only on a portion of the first surface,
   the laser light irradiation unit irradiates the laser light such that an irradiation spot region of the laser light formed on the first surface includes a metal region in which the metal film is present and a non-metal region in which the metal film is not present,
   the ultrasonic generator generates ultrasonic waves when irradiating the laser light such that the metallic region is included in an irradiated region of the ultrasonic waves formed on the first surface;
   An ultrasonic measurement system, characterized in that the ultrasonic waves are irradiated to the metal film without passing through a sound receiving layer for improving measurement sensitivity of the ultrasonic waves.
9. The metal film is also formed outside the irradiation spot area,
   The ultrasonic measurement system of claim 8, characterized in that when the metal area within the irradiation spot area is defined as a sensing area, the area of the sensing area increases or decreases when the irradiation spot area is translated in parallel on the first plane.
10. The ultrasonic measurement system according to claim 9, characterized in that the metal film is discretely formed on the first surface so as to form a plurality of circles and/or polygons having different areas when the first surface is viewed in a plane.
11. The ultrasonic measurement system of claim 9, characterized in that the metal film is formed on the first surface so as to have a triangular and/or trapezoidal shape when the first surface is viewed in a plane, and so that the height direction of the triangle and/or trapezoid extends beyond the irradiation spot area.
12. 10. The ultrasonic measurement system according to claim 9, wherein the SPR type ultrasonic sensor has a blocking film formed in an area of the first surface where the metal film is not formed, for suppressing the ultrasonic waves from entering the prism.
13. A container for containing a sample solution and for placing the SPR ultrasonic sensor in the sample solution,
    10. The ultrasonic measurement system according to claim 9, wherein the ultrasonic generator comprises an ultrasonic transducer that irradiates the ultrasonic wave into the sample solution.
14. the SPR type ultrasonic sensor is disposed so that a measurement target including a light absorber is in contact with the side of the metal film opposite to the first surface,
    10. The ultrasonic measurement system according to claim 9, wherein the ultrasonic generator outputs pulsed light to the measurement object to generate the ultrasonic waves from the light absorber by a photoacoustic effect.
15. 14. The ultrasonic measurement system according to claim 13, further comprising a moving mechanism for moving the SPR ultrasonic sensor to move the irradiation spot area in a parallel manner on the metal film.
16. The ultrasonic measurement system according to claim 13, further comprising a laser control unit that controls the laser light irradiation unit to move the irradiation position of the laser light, thereby moving the irradiation spot area in a parallel direction on the metal film.

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