Ultrasonic device

Abstract

Provided is an ultrasonic device capable of efficiently outputting ultrasonic waves while suppressing transmission unevenness of the ultrasonic waves of each frequency caused by a sound matching layer. The ultrasonic device includes: a vibrating plate, a first surface and a second surface opposite to the first surface being flat surfaces; a sound matching layer disposed on the first surface and in contact with an object; a piezoelectric element disposed on the second surface; and a suppression portion formed in a frame shape and disposed so as to surround the piezoelectric element when viewed from a normal direction on the second surface, the suppression portion suppressing vibration of the vibrating plate, wherein, in a case where a thickness of the sound matching layer is set to t, a sound velocity of the ultrasonic waves is set to V, and a center frequency of the ultrasonic waves transmitted from the first surface is set to f, t ≤ V / f is satisfied.

Description

Technical Field

[0001] This invention relates to an ultrasonic device. Background Technology

[0002] Conventionally, as ultrasonic devices that transmit ultrasonic waves to living organisms, there are known ultrasonic devices that include a substrate with an opening, a vibrating plate that closes the opening, and a piezoelectric element stacked on the side of the vibrating plate opposite to the opening (for example, see Patent Document 1).

[0003] Furthermore, in the ultrasonic device of Patent Document 1, a suppression portion surrounding the piezoelectric element is provided on the side of the vibrating plate opposite to the substrate, i.e., on the side where the piezoelectric element is stacked. This suppression portion defines the vibration area of ​​the vibrating plate by suppressing its vibration. Thus, when a voltage is applied to the piezoelectric element, the portion of the vibrating plate surrounded by the suppression portion vibrates, outputting ultrasonic waves at a frequency corresponding to the area of ​​the region surrounded by the suppression portion.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2015-188208

[0005] However, when the ultrasonic device is brought into contact with objects such as living organisms to transmit ultrasonic waves, air bubbles can enter the interior of the opening and obstruct the transmission of ultrasonic waves.

[0006] To mitigate the influence of air bubbles, it is possible to fill the opening with a sound matching part whose acoustic impedance is close to that of the object to suppress bubble intrusion. However, the sound matching part is wavelength-dependent on the transmittance of ultrasound. If the ultrasound output from the ultrasonic device is to be broadbanded, there is a technical problem that the transmittance of ultrasound will produce wavelength inhomogeneity at each frequency. Summary of the Invention

[0007] The ultrasonic device according to the first aspect of this disclosure comprises: a vibrating plate, a first surface and a second surface opposite to the first surface being flat surfaces; a sound matching layer disposed on the first surface and in contact with an object; a piezoelectric element disposed on the second surface; and a suppression portion formed in a frame shape on the second surface when viewed from the normal direction of the second surface and arranged to surround the piezoelectric element, thereby suppressing the vibration of the vibrating plate, wherein when the thickness of the sound matching layer is set to t, the speed of sound of the ultrasonic wave is set to V, and the center frequency of the ultrasonic wave transmitted from the first surface is set to f, t ≤ V / f is satisfied. Attached Figure Description

[0008] Figure 1 This is a cross-sectional view showing the schematic structure of an ultrasonic device according to one embodiment of the present disclosure.

[0009] Figure 2This is a top view of the ultrasonic device of this embodiment, viewed from the side where the ultrasonic waves are emitted.

[0010] Figure 3 This is a graph showing the change in sound pressure relative to frequency in the ultrasonic device of this embodiment when the frequency of the ultrasonic wave is changed in the range of 1 to 10 MHz with a center frequency of 7 MHz.

[0011] Figure 4 This is a graph showing the change in sound pressure relative to frequency in the ultrasonic device of this embodiment when the frequency of the ultrasonic wave is changed in the range of 11 to 20 MHz with a center frequency of 15 MHz.

[0012] Figure 5 This is a graph showing the change in sound pressure relative to frequency in the ultrasonic device of this embodiment when the frequency of the ultrasonic wave is changed within the range of 0.1 to 1.0 MHz with a center frequency of 0.5 MHz.

[0013] Figure 6 The diagrams compare the schematic structure of a conventional ultrasonic device used as a comparative example with the schematic structure of the ultrasonic device of this embodiment.

[0014] Figure 7 This is a graph showing the relationship between the distance of the suppression section and the normalized radiation impedance.

[0015] Explanation of reference numerals in the attached figures

[0016] 1: Ultrasonic device; 11: Vibrating plate; 11A: First surface; 11B: Second surface; 12: Piezoelectric element; 13: Suppression part; 14: Sealing plate; 15: Sound matching layer; 111: First substrate; 112: Second substrate; 121: First electrode; 122: Piezoelectric layer; 123: Second electrode. Detailed Implementation

[0017] The ultrasonic device according to one embodiment of the present disclosure will be described below.

[0018] Figure 1 This is a cross-sectional view showing the schematic structure of the ultrasonic device 1 according to this embodiment. Figure 2 This is a top view of the ultrasonic device 1 of this embodiment, viewed from the side where the ultrasonic waves are emitted.

[0019] The ultrasonic device 1 is a device that transmits ultrasonic waves to an object, and may also be capable of receiving ultrasonic waves reflected from within the object. Examples of objects include living organisms such as the human body, concrete structures, and fluids flowing in pipes. For example, as an ultrasonic device 1 that outputs ultrasonic waves to a living organism, it can be used to perform ultrasonic therapy on an organ by outputting ultrasonic waves to an organ at a predetermined depth within the living organism. It can also be used as a device to obtain internal tomographic images of a living organism by transmitting ultrasonic waves into it and receiving the ultrasonic waves reflected within it. Furthermore, as an ultrasonic device 1 that outputs ultrasonic waves to a structure, it can be used to investigate the internal structure of a structure non-destructively. As an ultrasonic device 1 that outputs ultrasonic waves to a pipe, it can be used to form ultrasonic-based standing waves within the pipe and capture particles contained in the fluid within the pipe.

[0020] In this embodiment, as an example, an ultrasonic device 1 that outputs ultrasonic waves to a living organism will be described.

[0021] like Figure 1 As shown, the ultrasonic device 1 of this embodiment includes a vibrating plate 11, a piezoelectric element 12, a suppression part 13, a sealing plate 14, and a sound matching layer 15.

[0022] The vibrating plate 11 includes a first substrate 111 and a second substrate 112. The first substrate 111 is, for example, a flat plate-shaped substrate made of a semiconductor substrate such as Si. The second substrate 112 is a substrate stacked on the first substrate 111, for example, a flat plate-shaped substrate made of metal oxides such as SiO2 and ZrO2.

[0023] The side of the first substrate 111 opposite to the second substrate 112 constitutes the first surface 11A of this disclosure. In addition, the side of the second substrate 112 opposite to the first substrate 111 constitutes the second surface 11B of this disclosure, forming an inside-out relationship with the first surface 11A.

[0024] In the following explanation, the direction from the first surface 11A to the second surface 11B, that is, the normal direction of the first surface 11A and the second surface 11B, will be defined as the Z direction. Furthermore, the direction orthogonal to the Z direction will be defined as the X direction, and the direction orthogonal to both the X and Z directions will be defined as the Y direction.

[0025] As described above, the first substrate 111 and the second substrate 112 are flat plate-shaped components, and the first surface 11A and the second surface 11B are also flat surfaces, becoming surfaces parallel to the XY plane. More specifically, the first surface 11A preferably has a surface roughness (arithmetic mean roughness) of at least 10 μm or less. This suppresses diffuse reflection of ultrasonic waves on the first surface 11A, effectively suppressing ultrasonic wave loss at the interface from the ultrasonic device to the sound matching layer 15.

[0026] Here, the first substrate 111 is formed to have a greater thickness than the second substrate 112. The second substrate 112 needs to form the piezoelectric layer 122 of the piezoelectric element 12, which will be described later. For example, when the piezoelectric layer 122 is made of PZT, the piezoelectric layer 122 can be appropriately formed by forming a layer of ZrO2 and SiO2 as the second substrate 112.

[0027] Furthermore, in this embodiment, by providing a second substrate 112 made of metal oxide, the piezoelectric layer 122 can be appropriately formed, but the second substrate 112 can also be removed later. In this case, the vibrating plate 11 is composed only of the first substrate 111, with one side of the first substrate 111 becoming the first side 11A and the other side becoming the second side 11B. Alternatively, the second substrate 112, except for the formation portion of the piezoelectric element 12, can also be removed.

[0028] The piezoelectric element 12 is disposed on the second substrate 112 of the vibrating plate 11, i.e., on the second surface 11B, such as... Figure 1 As shown, it is constructed by stacking a first electrode 121, a piezoelectric layer 122, and a second electrode 123 in the -Z direction. Furthermore, the piezoelectric layer 122 in this embodiment is composed of a perovskite-type transition metal oxide containing Pb, for example, in this embodiment, it is PZT containing Pb, Zr, and Ti.

[0029] Here, in the Z direction, the overlapping portion of the first electrode 121, the piezoelectric layer 122, and the second electrode 123 becomes a movable part that expands and contracts when a voltage is applied between the first electrode 121 and the second electrode 123. By expanding and contracting the piezoelectric element 12, the vibrating plate 11, on which the piezoelectric element 12 is provided, vibrates and outputs ultrasonic waves. Furthermore, if ultrasonic waves are input to the vibrating plate 11, the vibrating plate 11 vibrates, and the piezoelectric layer 122 of the piezoelectric element 12 deforms, thereby generating a potential difference between the upper and lower (±Z sides) electrodes. Therefore, by detecting the potential difference generated between the first electrode 121 and the second electrode 123, the reception of ultrasonic waves can be detected.

[0030] It should be noted that, in Figure 1To simplify the accompanying drawings, an example of setting one piezoelectric element 12 is shown, but it is also possible to use an array of multiple piezoelectric elements 12 along the X and Y directions, or along either the X and Y directions.

[0031] The suppression portion 13 is a component provided on the second surface 11B of the vibrating plate 11, and is made of, for example, a permanent resist. Specifically, when viewed from the Z direction, the suppression portion 13 is formed in the shape of a frame surrounding the outer periphery of the piezoelectric element 12. This suppression portion 13 defines the vibration area of ​​the vibrating plate 11 vibrating due to the piezoelectric element 12 by suppressing the vibration of the vibrating plate 11. That is, in this embodiment, the portion of the vibrating plate 11 surrounded by the suppression portion 13 vibrates, thereby outputting ultrasonic waves.

[0032] The sealing plate 14 is significantly thicker in the Z direction than the vibrating plate 11. It is joined to the vibrating plate 11 via the suppression part 13, thereby strengthening the vibrating plate 11. The suppression part 13 vibrates together with the vibrating plate 11.

[0033] A sound matching layer 15 is disposed on the first surface 11A of the diaphragm 11. In this embodiment, the first surface 11A of the diaphragm 11 is a continuous flat surface, and a sound matching layer 15 of uniform thickness is formed on the first surface 11A. Therefore, unlike the conventional structure in which the sound matching layer is filled into the opening provided in the substrate, the generation of air bubbles can be suppressed.

[0034] In this embodiment, the ultrasonic device 1 can transmit ultrasonic waves to the object in direct contact via the vibration of the vibrating plate 11. However, if the vibrating plate 11 is pressed tightly against the organism without providing the sound matching layer 15, there is a high possibility of space (bubbles) being generated between the rigid vibrating plate 11 and the elastic and soft surface of the organism. Therefore, it is more difficult to press the first surface 11A of the flat vibrating plate 11, which is harder than the organism, tightly against the surface of the organism, and bubbles are easily generated even when using gels or the like. In addition, the vibrating plate 11 may break when pressed against the object.

[0035] Therefore, a sound matching layer 15, which is softer than the vibrating plate 11 and can suppress the generation of bubbles and the breakage of the vibrating plate 11, is provided between the vibrating plate 11 and the organism. In addition, by providing a sound matching layer 15 that is close to the acoustic impedance of the organism as a buffer, the reflection of ultrasound waves at the interface between the vibrating plate 11 and the organism can be suppressed, and ultrasound waves can be appropriately transmitted to the organism.

[0036] Thickness of sound matching layer 15

[0037] Next, the thickness of the sound matching layer 15 will be explained.

[0038] In this embodiment, a living organism is used as the object of study. In this case, it is preferable to set the center frequency of the ultrasound in the range of 0.5 to 15 MHz, depending on the depth of the organ at the diagnostic site. Furthermore, as the ultrasound device 1, it is more preferable to employ a structure that does not set a frequency only corresponding to a specific depth, but allows the frequency of the output ultrasound to be varied within a predetermined frequency range centered on the center frequency.

[0039] Figure 3 This is a graph showing the change in sound pressure relative to frequency when the frequency of an ultrasonic wave is changed within the range of 1 to 10 MHz with a center frequency of 7 MHz. Figure 4 This is a graph showing the change in sound pressure relative to frequency when the frequency of an ultrasonic wave is changed within the range of 11 to 20 MHz with a center frequency of 15 MHz. Figure 5 This is a graph showing the change in sound pressure relative to frequency when the frequency of an ultrasonic wave is varied within the range of 0.1 to 1.0 MHz, with a center frequency of 0.5 MHz. Figures 3 to 5 In the diagram, the solid gray line represents the sound pressure level (0λ) without the sound matching layer 15. Furthermore, when the thickness of the sound matching layer 15 is set to t and the wavelength of the ultrasound is set to λ, the solid line represents the sound pressure level at t = 1.0λ, the dashed line represents the sound pressure level at 1.8λ, the single-dotted line represents the sound pressure level at 0.5λ, and the double-dotted line represents the sound pressure level at 0.25λ.

[0040] exist Figures 3 to 5 In theory, without the sound matching layer 15, ultrasonic waves can be output from the first surface 11A of the ultrasonic device 1 with an ideal sound pressure corresponding to the frequency. However, as mentioned above, without the sound matching layer 15, the highly rigid vibrating plate 11 needs to be pressed directly onto the living organism, which can lead to problems such as damage to the vibrating plate 11 and the generation of air bubbles.

[0041] On the other hand, in the case of forming the sound matching layer 15, such as Figures 3 to 5 As shown, the sound pressure varies according to the frequency of the ultrasound.

[0042] That is, the transmittance of the sound matching layer 15 is wavelength-dependent; for a certain frequency range, the transmittance of ultrasound decreases, meaning the sound pressure of the ultrasound transmitted to the organism decreases. Especially in cases where ultrasound is transmitted from the surface of a organism for ultrasound diagnosis and treatment from shallow to deep depths, broadband ultrasound is sometimes necessary. In such cases, if the sound pressure varies significantly with frequency, it will affect treatment efficiency and diagnostic accuracy, and is therefore not preferred.

[0043] Therefore, in this embodiment, based on the center frequency f of the ultrasonic wave output from the first surface 11A and the speed V of the ultrasonic wave passing through the sound matching layer 15, the thickness t of the sound matching layer 15 is formed to at least satisfy t ≤ V / f. If the wavelength of the ultrasonic wave is set to λ, then V = fλ, therefore, in other words, the thickness t of the sound matching layer 15 satisfies t ≤ 1.0λ.

[0044] For example, in the ultrasonic device 1 where the thickness of the sound matching layer 15 is set to t = 1.8λ, and the center frequency is set to 7MHz, such as Figure 3 As shown, in the vicinity of 6MHz, 8MHz, and 10MHz, the sound pressure level through the sound matching layer 15 changes significantly compared to the case without the sound matching layer 15.

[0045] In contrast, in the ultrasonic device 1 where the thickness of the sound matching layer 15 is set to t = 1.0λ, when the center frequency is set to 7MHz, although the sound pressure through the sound matching layer 15 varies with frequency, the variation in sound pressure through the sound matching layer 15 is smaller in the frequency range of 2–10MHz compared to the case where the thickness of the sound matching layer 15 is set to t = 1.8λ. Similarly, when the center frequency is set to 15MHz, the variation in sound pressure through the sound matching layer 15 is smaller in the frequency range of 11–20MHz compared to the case where the thickness of the sound matching layer 15 is set to 1.8λ. The same applies to the ultrasonic device 1 where the thickness of the sound matching layer 15 is set to t = 0.5λ; the variation in sound pressure through the sound matching layer 15 is smaller regardless of whether the center frequency is set to 7MHz or 15MHz.

[0046] Furthermore, in the ultrasonic device 1 with the thickness of the sound matching layer 15 set to t = 0.25λ, the sound pressure did not change significantly in the frequency range of 0.1 to 20 MHz.

[0047] Therefore, the sound matching layer 15 is preferably formed in a manner that satisfies t ≤ 1.0λ, and more preferably 0.5λ ≤ t ≤ 1.0λ. Thus, regardless of the center frequency, the sound pressure fluctuations caused by the sound matching layer 15 can be suppressed over a wide frequency range.

[0048] Furthermore, V = λf, and in this embodiment, according to the condition t ≤ 1.0λ, V ≥ tf. That is, the condition t ≤ V / f holds. Therefore, the smaller the center frequency f of the ultrasound, the thicker the allowable sound matching layer 15 can be.

[0049] For example, if the center frequency f is set to a smaller 0.5MHz, such as Figure 5As shown, regardless of the thickness t of the sound matching layer 15, the influence of sound pressure fluctuations can be significantly reduced.

[0050] Specifically, if the speed of sound V of the ultrasound is set to V = 1000 m / s and the center frequency f is set to f = 0.5 MHz, then t ≤ 2.0 mm. On the other hand, if the center frequency f is set to f = 15 MHz, then 0.03 mm ≤ t ≤ 0.07 mm.

[0051] That is, by making the thickness t of the sound matching layer 15 0.03mm≤t≤2.0mm, when the target object is a living organism (water), the influence of sound pressure fluctuations can be suppressed, and ultrasonic waves can be efficiently output to the target object.

[0052] The area of ​​the vibrating plate surrounded by the suppression part

[0053] Figure 6 This diagram compares the schematic structure of a conventional ultrasonic device 90, which serves as a comparative example, with the schematic structure of the ultrasonic device 1 of this embodiment.

[0054] In existing ultrasonic devices 90, such as Figure 6 As shown, a plurality of openings 911 are formed on the support substrate 91, and a vibrating plate 92 is provided to close the openings 911. Furthermore, viewed from the Z direction, a plurality of piezoelectric elements 93 are provided on the vibrating plate 92 at positions overlapping with the openings 911, and suppression portions 94 are provided between these piezoelectric elements 93. Similar to the ultrasonic device 1 of this embodiment, a sealing plate 95 is provided on the side of the suppression portion 94 opposite to the support substrate 91. Additionally, a sound matching layer 96 is filled into the openings 911.

[0055] In the comparative example of the ultrasonic device 90, the vibration area of ​​the vibrating plate 92, which is surrounded by the edge of the opening 911 and the edge of the suppression portion 94, is determined. However, compared to this embodiment, the area of ​​the vibration area is determined, and more specifically, the distance between the suppression portions in the short axis direction that determines the frequency is smaller.

[0056] Figure 7 This is a graph showing the relationship between the distance between the suppression sections and the normalized radiation impedance. It should be noted that radiation impedance represents the value of the reaction force caused by the vibration of the piezoelectric element relative to its displacement velocity, i.e., the vibration velocity of the vibrating plate. Furthermore, the normalized radiation impedance is obtained by dividing the radiation impedance by the area of ​​the portion of the vibrating plate 11 surrounded by the suppression section 13 when viewed from the Z-direction, the density of the vibrating plate 11, and the sound velocity in the object.

[0057] In the comparative example of the ultrasonic device 90, the distance between the suppressor parts is less than 100 μm, and the normalized radiation impedance is less than 0.4. For example, when the distance between the suppressor parts is 60 μm, the normalized radiation impedance is about 0.2.

[0058] However, in order to efficiently transmit ultrasonic waves from the ultrasonic devices 1 and 90 to the target object (living organism), it is preferable to further increase the radiation impedance. In contrast, in this embodiment, the normalized radiation impedance is formed to be 0.8 or more and 1.0 or less. Specifically, the distance between the suppressor parts of the ultrasonic device 1 in this embodiment is 200 μm or more, thereby enabling the normalized radiation impedance to be 0.8 or more and 1 or less. For example, when the distance between the suppressor parts is 300 μm, the normalized radiation impedance is 0.95, which is 4.7 times that of the comparative example.

[0059] The effect of this implementation method

[0060] The ultrasonic device 1 of this embodiment includes: a vibrating plate 11, with a first surface 11A and a second surface 11B being flat surfaces; a sound matching layer 15 disposed on the first surface 11A and in contact with an object; a piezoelectric element 12 disposed on the second surface 11B; and a suppression part 13 formed in a frame shape when viewed from the Z direction on the second surface 11B and arranged to surround the piezoelectric element 12, suppressing the vibration of the vibrating plate 11. When the thickness of the sound matching layer 15 is set to t, the sound velocity of the ultrasonic wave passing through the sound matching layer 15 is set to V, and the center frequency of the ultrasonic wave transmitted from the first surface 11A is set to f, t ≤ V / f, that is, t ≤ 1.0λ.

[0061] In such an ultrasonic device 1, by providing a sound matching layer 15, damage to the vibrating plate 11 can be suppressed even when the ultrasonic device 1 is pressed onto a living organism, and the generation of bubbles can also be suppressed. Furthermore, as... Figures 3 to 5 As shown, the ultrasonic device 1 can suppress the non-uniformity of ultrasonic wave transmittance at each frequency based on the sound matching layer 15, and can suppress sound pressure fluctuations over a wide frequency range. That is, it can efficiently transmit ultrasonic waves to the object regardless of the frequency, and can suppress wavelength non-uniformity.

[0062] Furthermore, it is preferable that the thickness of the sound matching layer 15 is 0.5λ≤t≤1.0λ. Therefore, even with the sound matching layer 15, variations in sound pressure can be suppressed over a wide frequency range, enabling the transmission of ultrasonic waves to objects with higher efficiency.

[0063] More specifically, when the target object is a living organism (water), it is preferable to have a sound matching layer thickness t of t ≤ 2 mm. This further suppresses sound pressure fluctuations when the target object is a living organism (water).

[0064] In the ultrasonic device 1 of this embodiment, the standardized radiation impedance obtained by dividing the radiation impedance by the area of ​​the portion of the vibrating plate 11 surrounded by the suppression portion 13 when viewed from the Z direction, the density of the vibrating plate 11, and the sound velocity of the ultrasonic wave is 0.8 or more and 1.0 or less.

[0065] Therefore, ultrasonic waves can be efficiently output from ultrasonic device 1 to the target object.

[0066] Variations

[0067] It should be noted that the present invention is not limited to the above-described embodiments and variations. Structures obtained by variations, modifications, and appropriate combinations of embodiments within the scope of achieving the purpose of the present invention are also included in the present invention.

[0068] In the above embodiments, the object is described as a living organism, but it is not limited to this. For example, the object can be a structure such as concrete, or it can be air.

[0069] In this case, a material having a sound impedance close to that of the object is preferably used as the sound matching layer 15. Furthermore, since the speed of ultrasound passing through different objects varies, the thickness t of the sound matching layer 15, which can suppress sound pressure fluctuations, also varies depending on the object.

[0070] In the above embodiments, as a specific example, when the object is a living organism and the speed of sound V is set to V = 1000 m / s, it is preferable to set the thickness t of the sound matching layer 15 to 2.0 mm or less. However, as mentioned above, when the object is another object with a significantly different speed of sound propagation, the thickness of the sound matching layer 15 varies depending on the object. In this case, it is sufficient to form the sound matching layer 15 with a thickness t of V / 2f ≤ t ≤ V / f. That is, it is sufficient to form the sound matching layer 15 in a manner that satisfies t ≥ 0.5V / f.

[0071] This is a summary of the disclosure.

[0072] The ultrasonic device according to the first aspect of this disclosure includes: a vibrating plate, a first surface and a second surface opposite to the first surface being flat surfaces; a sound matching layer disposed on the first surface and in contact with an object; a piezoelectric element disposed on the second surface; and a suppression portion formed in a frame shape on the second surface when viewed from the normal direction of the second surface and arranged to surround the piezoelectric element, suppressing the vibration of the vibrating plate, wherein when the thickness of the sound matching layer is set to t, the speed of sound of the ultrasonic wave is set to V, and the center frequency of the ultrasonic wave transmitted from the first surface is set to f, t≤V / f is satisfied.

[0073] Therefore, the sound matching layer 15 can suppress the breakage of the diaphragm and the incorporation of air bubbles. In addition, it can suppress sound pressure fluctuations even when the frequency is changed.

[0074] In the ultrasonic device of this method, preferably, the thickness t of the sound matching layer satisfies t≥0.5V / f.

[0075] Therefore, similar to the above methods, it is possible to further suppress sound pressure fluctuations and transmit ultrasonic waves to objects with higher efficiency.

[0076] In the ultrasonic device of this method, it is preferable that the thickness t of the sound matching layer is 2 mm or less.

[0077] Therefore, when the target object is water or a living organism with water as its main component, sound pressure fluctuations can be suppressed, and the transmission efficiency of ultrasound to water and living organisms can be improved.

[0078] In the ultrasonic device of this type, it is preferable that the normalized radiation impedance obtained by dividing the radiation impedance, which represents the force generated by the vibration of the vibrating plate relative to the vibration velocity of the vibrating plate vibrating by the piezoelectric element, by the area of ​​the portion of the vibrating plate surrounded by the suppression part when viewed from the normal direction of the second surface, the density of the vibrating plate, and the sound velocity in the object, is 0.8 or more and 1 or less.

[0079] Therefore, it is possible to send ultrasonic waves to objects with high efficiency.

Claims

1. An ultrasonic device, characterized in that, The ultrasonic device includes: The vibrating plate has a first surface and a second surface on the opposite side of the first surface, which are flat surfaces. A sound matching layer is disposed on the first surface and in contact with the object; A piezoelectric element is disposed on the second surface; as well as The suppression portion, when viewed from the normal direction of the second surface, is formed in a frame shape and arranged to surround the piezoelectric element, thereby suppressing the vibration of the vibrating plate. With the thickness of the sound matching layer set to t, the speed of sound of the ultrasonic wave set to V, and the center frequency of the ultrasonic wave emitted from the first surface set to f, the condition t ≤ V / f is satisfied. The normalized radiation impedance obtained by dividing the radiation impedance by the area of ​​the portion of the vibrating plate surrounded by the suppression part when viewed from the normal direction of the second surface, the density of the vibrating plate, and the sound velocity in the object is 0.8 or more and 1 or less. The radiation impedance represents the force generated by the vibration of the vibrating plate relative to the vibration velocity of the vibrating plate due to the piezoelectric element.

2. The ultrasonic device according to claim 1, wherein, The thickness t of the sound matching layer satisfies t≥0.5V / f.

3. The ultrasonic device according to claim 1, wherein, The thickness t of the sound matching layer is less than 2 mm.

Images