JP6579323B2 - Ultrasonic generator - Google Patents

Description

  The present invention relates to an ultrasonic wave generating element.

  Research is being conducted on ultrasonic examinations that generate ultrasonic waves toward a subject and image reflected waves reflected from the subject. According to this ultrasonic inspection, it is possible to inspect a state of the body that cannot be visually recognized, damage to an object, and the like. For example, to observe the structure of an organ, fill the internal organ of the subject with water, insert an ultrasonic generator and an ultrasonic receiver in the organ, and generate ultrasonic waves in the water of the organ. Let Then, the reflected wave reflected from the inner surface of the organ is received by the ultrasonic receiving unit and imaged, whereby the structure of the organ can be observed. In this case, it is necessary to appropriately select the frequency according to the distance from the ultrasonic wave generating element and the ultrasonic wave receiving unit to the inner surface of the organ and the material of the surface of the organ.

  A piezoelectric element such as PZT (Lead Zirconate Titanate) is known as a general ultrasonic wave generating element (for example, Non-Patent Document 1). Further, a heat-induced ultrasonic wave generating element that generates an airborne ultrasonic wave by a thermal action from the porous silicon surface to air is known (for example, Non-Patent Document 2).

W. Manthey, N. Kroemer, and V. M / a / gori, "Ultrasonic transducers and transducer arrays for applications in air" Measurement Science and Tehnology, No. 3, pp. 249-261, 1992. H. Shinoda, et al., Nature, vol400, 1999, p.853-p.855

  However, in the case of Non-Patent Document 1, in order to generate ultrasonic waves, it is necessary to vibrate the structure with the ultrasonic wave generating element, so that there is a problem that the usable frequency is limited to the vicinity of the resonance frequency. . Moreover, in the case of the said nonpatent literature 2, there existed a problem that it was difficult to generate | occur | produce an ultrasonic wave in media, such as water with a large specific heat and being hard to thermally expand.

  Then, an object of this invention is to provide the ultrasonic wave generation element which can be used for a wider use.

An ultrasonic wave generating element according to the present invention includes an internal medium that applies ultrasonic waves to an external medium when the volume is changed by heat, and a heater that heats the internal medium .
An ultrasonic generating element according to the present invention includes an internal medium that is a liquid that imparts ultrasonic waves to an external medium when the volume is changed by heat, and a thin film that seals a surface of the internal medium. Has an insulating property.

  According to the present invention, the frequency of the ultrasonic wave can be appropriately changed by appropriately changing the period for expanding the volume of the internal medium, and the ultrasonic wave in a wider frequency band can be efficiently applied to the external medium. Can be used for a wider range of applications.

It is a perspective view showing the whole ultrasonic generating element composition concerning this embodiment. It is an exploded perspective view showing the whole ultrasonic generating element composition concerning this embodiment. FIG. 3A is a longitudinal cross-sectional view showing a manufacturing process of an ultrasonic wave generating element according to this embodiment step by step, FIG. 3A is a stage in which a metal layer is formed on a substrate, FIG. 3B is a stage in which a heater is formed, and FIG. FIG. 3D is a diagram showing a stage where a film is formed, and FIG. 3D is a stage where an internal medium is dropped. It is a longitudinal cross-sectional view which shows the use condition of the ultrasonic wave generation element which concerns on this embodiment. It is a figure used when demonstrating operation | movement of the ultrasonic wave generation element which concerns on this embodiment. It is a graph which shows the result of having investigated the influence which the specific heat of an internal medium has on sound pressure. It is a graph which shows the result of having investigated the influence which the heat permeability of a board | substrate has on sound pressure. It is a perspective view which shows schematic structure of the apparatus used for experiment. It is a graph which shows the relationship between an input voltage and a sound pressure. It is a graph which shows the result of having investigated the difference of the sound pressure by the presence or absence of a generation part.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(overall structure)
An ultrasonic generation element 10 shown in FIG. 1 is formed on a substrate 12, and includes a heater 14 and a generation unit 16 provided on the heater 14, and applies ultrasonic waves to an external medium 17. The substrate 12 is not particularly limited, and for example, a glass substrate or a glass composite substrate can be used. Incidentally, the glass composite substrate is formed by stacking cut glass fibers and impregnating with an epoxy resin. The substrate 12 preferably has a low thermal permeability. The heater 14 is connected to the AC power source 19 at the electrode 22, and heats the generating unit 16 with an AC voltage applied by the AC power source 19. The external medium 17 is not particularly limited, and may be air or water.

  As shown in FIG. 2, the generator 16 includes an internal medium 18 provided on the heat generating part 24 of the heater 14 and a thin film 20 that seals the surface of the internal medium 18. The heating part 24 is preferably provided with a heater wire so that the generated Joule heat can be efficiently transmitted to the internal medium 18, and the shape is not particularly limited. In the case of the present embodiment, the heat generating portion 24 includes an annular first heater wire portion 25 and an annular second heater formed concentrically with the first heater wire portion 25 and having an outer diameter smaller than that of the first heater wire portion 25. And a line portion 27.

The internal medium 18 is preferably composed of a gas or a liquid whose volume is changed by heat and whose acoustic impedance matches that of the external medium 17. Further, the internal medium 18 preferably has a specific heat smaller than that of the external medium 17 and a coefficient of thermal expansion larger than that of the external medium 17. More specifically, for example, when the external medium is water, the internal medium 18 preferably has a specific heat smaller than that of water (4.2 (kJ / kgK)). Moreover, it is preferable that a thermal expansion coefficient is larger than 2.1 * 10 <^-4> (K <^-1> ). The internal medium 18 preferably has a bulk elastic modulus larger than that of the external medium 17, for example, the volume elastic modulus of water (2.2 GPa).

  Furthermore, it is more preferable that the internal medium 18 has a small heat capacity and a high heat transfer characteristic. The internal medium 18 may be a liquid that does not boil (volatilize) and does not solidify (solidify) in the operating temperature range.

  Examples of the internal medium 18 include water (boiling point: 100 ° C., melting point: 0 ° C.), silicon oil (in the case of HIVAC F-4 manufactured by Shin-Etsu Chemical Co., Ltd., boiling point: 250 ° C. or more, melting point: −35 ° C.), Can include glycerin (boiling point: 290 ° C, melting point: 18 ° C), acetone (boiling point: 56 ° C, melting point: -95 ° C), alcohol (in the case of ethanol, boiling point: 78 ° C, melting point: -114 ° C), etc. . That is, the operating temperature range is limited by the internal medium 18, and specifically, is a temperature range that is lower than the boiling point of the internal medium 18 and higher than the melting point. The internal medium 18 is preferably electrically insulated from the heater 14. To insulate from the heater 14, an insulating internal medium 18 may be used. An insulating film may be formed between the heater 14 and the internal medium 18.

  As the thin film 20, an organic film, a metal film, or the like can be used. For example, a polyparaxylene (trade name parylene) film or a silicon film can be used.

  In the case of the present embodiment, the heater 14 is formed on the substrate 12, the sealed space is formed by the thin film 20 on the heat generating portion 24 of the heater 14, and the sealed medium is filled with the internal medium 18. Yes. In order to keep the internal medium 18 on the heat generating part 24, a hydrophobic film 26 may be provided on the substrate 12 so as to surround the heat generating part 24 of the heater 14. The hydrophobic film 26 is formed in a ring shape so as to be concentric with the first heater wire portion 25 on the outside of the first heater wire portion 25 using, for example, a hydrophobic amorphous fluororesin (for example, CYTOP (registered trademark)). Can be formed.

(Production method)
A method for manufacturing the ultrasonic generator 10 configured as described above will be described with reference to FIG. First, the metal layer 28 is formed on the substrate 12 (FIG. 3A). Next, the heater 14 having the heat generating portion 24 is formed by forming the metal layer 28 in a predetermined shape using a pattern (FIG. 3B). Next, a hydrophobic film 26 is formed so as to surround the periphery of the heat generating portion 24 (FIG. 3C). Next, for example, silicon oil is dropped on the heat generating portion 24 as the internal medium 18. Then, the internal medium 18 stays on the heat generating part 24 by the hydrophobic film 26 provided around the heat generating part 24 (FIG. 3D). By forming the thin film 20 on the internal medium 18 thus provided and sealing the surface of the internal medium 18, the ultrasonic wave generating element 10 can be obtained (FIG. 4). In the case of this embodiment, the thin film 20 is formed under vacuum. Therefore, bubbles are excluded in the space where the internal medium 18 is sealed. That is, the dissolved gas is excluded from the internal medium 18.

  As described above, the ultrasonic wave generating element 10 according to this embodiment can be manufactured. In the case of the present embodiment, the thin film 20 is illustrated as being formed only on the surfaces of the hydrophobic film 26 and the internal medium 18, but the present invention is not limited to this, and other than the range surrounded by the hydrophobic film 26. The thin film 20 may be formed on the entire surface of the substrate 12.

(Action and effect)
Next, the operation and effect of the ultrasonic wave generating element 10 according to this embodiment will be described. First, an AC voltage V is applied to the heater 14. The AC voltage V can be expressed as shown in FIG. 5, where V ₀ is the maximum value, ω is the angular velocity, and t is the time.

When the AC voltage V is applied, the heater is heated by resistance. That is, Joule heat Q is generated from the heater. This Joule heat Q is periodically generated according to the cycle of the AC voltage. Joule heat Q, when the maximum value and Q _0, can be expressed as shown in FIG.

The internal medium 18 is heated by the Joule heat Q generated periodically in this way. As a result, the internal medium 18 periodically expands and contracts. Due to the expansion and contraction of the internal medium 18, vibration is transmitted to the external medium 17 through the thin film 20. Thereby, ultrasonic waves can be applied to the external medium 17. At this time, the pressure P applied to the external medium 17 by heat is as shown in FIG. 5, and becomes the initial pressure P ₀ and the sound pressure P ₁ . At this time, an ultrasonic wave having a frequency of 2ωt and double the input voltage is generated.

  As described above, the ultrasonic generating element 10 according to the present embodiment applies ultrasonic waves to the external medium 17 by thermally expanding the internal medium 18. Therefore, since the frequency of the ultrasonic wave can be changed as appropriate by appropriately changing the cycle of thermally expanding the internal medium 18, it is possible to generate ultrasonic waves in a wider frequency band than in the past.

  In addition, in the case of an ultrasonic wave generation element using a conventional piezoelectric material, there is a reverberation of the vibration of the material, so that a short pulse cannot be generated.

  On the other hand, since the ultrasonic wave generating element 10 according to the present embodiment generates a pressure wave and the material and the medium do not vibrate, reverberation does not occur and a short pulse ultrasonic wave can be easily generated.

  Furthermore, in the case of the present embodiment, the ultrasonic generating element 10 is configured such that the internal medium 18 is made of liquid, so that the acoustic impedance matches the water as the external medium 17, so that the ultrasonic wave is efficiently transmitted to the external medium. 17.

  Therefore, since the ultrasonic wave generation element 10 can efficiently apply ultrasonic waves in a wide frequency band to the liquid external medium 17, it can be used for a wider range of applications.

  Further, in the space in which the internal medium 18 is sealed, bubbles that hinder the transmission of heat and sound are eliminated. Therefore, the ultrasonic wave generating element 10 can generate ultrasonic waves efficiently.

  In the present embodiment, a liquid is used as the internal medium 18. As liquids that can be used as the internal medium 18, sound pressure was measured for pure water, glycerin, and silicon oil (HIVAC F-5, manufactured by Shin-Etsu Chemical Co., Ltd.) having different specific heats. The specific heat is 4.2 (kJ / kgK) for pure water, 2.4 (kJ / kgK) for glycerin, and 1.3 (kJ / kgK) for silicon oil. The ultrasonic waves were generated using an element in which the heater 14 was simply formed on the substrate 12 shown in FIG. 3B. The heater 14 had a thickness of 150 nm, the diameter of the first heater wire portion 25 was 2.3 mm, the diameter of the second heater wire portion 27 was 1.7 mm, and the electric resistance was 15.2Ω. The sound pressure used was an apparatus in which the internal medium 18 and the element were placed in a water tank, and a hydrophone (Brüel Care Co., Model 8103) was installed at a position 20 mm away from the element.

  An AC voltage of 50 kHz was applied to the heater 14 of the element, and the sound pressure of a 100 kHz ultrasonic wave was measured. The result is shown in FIG. In the figure, the vertical axis represents sound pressure and the horizontal axis represents input power. From this result, it was confirmed that silicon oil has the highest energy efficiency. From this, it was found that the lower the specific heat as the internal medium 18 is more preferable.

In this embodiment, the substrate 12 can be a glass substrate or a glass composite substrate. The heat permeability is 1.5 × 10 ³ {J / (m ² s ^1/2 K)} for the glass substrate and 7.82 × 10 ² {J / (m ² s ^1/2 K) for the glass composite substrate. }. A heater 14 was formed on each substrate 12 in the same manner as described above, and the sound pressure was measured. The result is shown in FIG. In the figure, the vertical axis represents sound pressure and the horizontal axis represents input power. From this result, it was confirmed that the glass composite substrate was higher in energy efficiency. From this, it was found that the substrate 12 preferably has a lower thermal permeability.

  Next, the ultrasonic wave generating element 10 according to the present embodiment was manufactured by the procedure shown in the “manufacturing method”, and the sound pressure was measured. A glass composite substrate having a thickness of 1 mm is used as the substrate 12. The thickness of the substrate 12 is 150 nm, the diameter of the first heater wire portion 25 is 2.3 mm, and the diameter of the second heater wire portion 27 is 1.7 mm. A heater 14 having a resistance of 15.2Ω was formed. A hydrophobic film 26 was formed with CYTOP (registered trademark, manufactured by Asahi Glass Co., Ltd.), and silicon oil was dropped as the internal medium 18. Finally, a parylene film having a thickness of 1 μm was formed as a thin film 20 on the surface of the inner medium 18 by a chemical vapor deposition (CVD) method, and the surface of the inner medium 18 was sealed.

  As shown in FIG. 8, the ultrasonic generator 10 was placed in a water tank 30 containing water, and a hydrophone (Type 8103, manufactured by Brüel & Kjær) was placed 20 mm away from the surface of the substrate 12. The heater 14 was connected to an AC power source 19. The 35 kHz AC voltage of a function generator (not shown) was amplified 10 times with an operational amplifier (Apex technology, PA 09A) (not shown), and the sound pressure of water when applied to the heater 14 was measured. The result is shown in FIG. In this figure, the vertical axis on the left is applied voltage, the vertical axis on the right is sound pressure, and the horizontal axis is time. From this figure, it was confirmed that an ultrasonic wave of 70 kHz can be obtained by applying an AC voltage of 35 kHz.

  Furthermore, the sound pressure of ultrasonic waves having a frequency of 50 kHz to 150 kHz obtained by setting the frequency of the alternating voltage input to the ultrasonic generator 10 to 25 kHz to 75 kHz was measured. For comparison, the sound pressure was measured in the same manner for elements formed in the same manner except that the generator 16 was not provided. The result is shown in FIG. In the figure, the vertical axis represents sound pressure, and the horizontal axis represents frequency. In this figure, “□” is the result of the ultrasonic wave generation element 10 provided with the generation part 16, and “◯” is the result of the element not provided with the generation part 16. From this figure, it was confirmed that the ultrasonic wave generating element 10 can obtain a sound pressure about three times as large as that of the element not provided with the generating unit 16. From this, it was found that the ultrasonic wave generating element 10 can generate ultrasonic waves more efficiently by providing the generator 16.

(Modification)
The present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope of the gist of the present invention.

  Although the case where the internal medium 18 is a liquid has been described in the present embodiment, the present invention is not limited to this, and may be, for example, a gel or a gas.

  In this embodiment, the case where the internal medium 18 is heated by resistance heating of the heater 14 has been described. However, the present invention is not limited to this, and the internal medium 18 is resistance-heated by directly applying a voltage to the internal medium 18. It is good.

  The ultrasonic generator 10 may be configured to have directivity by making the film into a lens shape, making the substrate 12 into a parabolic shape, or arranging a plurality of ultrasonic generators 10 in an array. Good.

DESCRIPTION OF SYMBOLS 10 Ultrasonic generator 12 Substrate 14 Heater 17 External medium 18 Internal medium 20 Thin film

Claims (12)

An internal medium that applies ultrasonic waves to the external medium by changing the volume due to heat ;
An ultrasonic generator, comprising: a heater for heating the internal medium . 2. The ultrasonic wave generating element according to claim 1, wherein when the external medium is a liquid, the internal medium is a substance whose acoustic impedance matches that of the external medium. The internal medium is a liquid;
The ultrasonic generator according to claim 1, further comprising a thin film that seals a surface of the internal medium. The ultrasonic generating element according to claim 3, wherein the internal medium has a specific heat smaller than that of the external medium and a thermal expansion coefficient equal to or higher than a thermal expansion coefficient of the external medium. The ultrasonic generating element according to claim 3, wherein the internal medium has a bulk elastic coefficient larger than that of the external medium. The ultrasonic generator according to claim 3, wherein the internal medium has an insulating property. The ultrasonic generating element according to claim 3, wherein the internal medium does not boil and does not solidify in a use temperature range. 4. The ultrasonic wave generating element according to claim 3, wherein an internal medium from which dissolved gas is excluded is used. An internal medium that is a liquid that imparts ultrasonic waves to the external medium by changing the volume by heat;
A thin film that seals the surface of the internal medium,
The ultrasonic generating element, wherein the internal medium has an insulating property. The ultrasonic generator according to claim 9 , wherein the internal medium is a liquid that is directly heated by supplied electric energy. The ultrasonic generator according to any one of claims 3 to 10 , wherein the thin film is a parylene film. The ultrasonic generating element according to claim 1, wherein the internal medium undergoes a phase change between a liquid and a gas by heat.

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