electroacoustic transducer

Abstract

To provide an electroacoustic transducer capable of achieving nonlinear acoustic output at the lowest possible sound pressure.SOLUTION: An electroacoustic transducer (1) includes a heating element (3) that is a thin film of conductive carbon material, and a thermal insulation layer (22) provided on the back side of the heating element. The heating element is, for example, a graphene thin film. The thermal insulation layer is provided on one surface (21) side of a substrate (2) having a thickness direction along an acoustic radiation direction (D). The thermal insulation layer is made of, for example, porous silicon. A drive control unit (5) is provided so as to apply a drive voltage to the heating element. The drive voltage has a voltage rising waveform in which the voltage rises over time, and a cutoff waveform in which the voltage subsequently falls. In the voltage rising waveform, the voltage rises in steps.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electro-acoustic transducer. [Background technology]

[0002] Acoustic devices such as ultrasonic generators, which have been widely used in industry, are configured to emit sound (i.e., sound waves or ultrasonic waves) by generating mechanical vibrations using the piezoelectric effect, etc. For this reason, it has been difficult for these types of conventional devices to generate sound with waveforms other than sinusoidal.

[0003] In response to this, a sound wave generator using so-called thermoacoustic conversion has been proposed (see, for example, Patent Document 1). Such a sound wave generator is composed of a substrate, a thermal insulating layer (i.e., a heat insulating layer) provided on the substrate, and an electrically driven heating element thin film provided on the thermal insulating layer. By providing a thermal insulating layer such as a porous layer or polymer layer with extremely low thermal conductivity, such a sound wave generator generates sound waves by increasing the temperature change in the air layer on the surface of the heating element thin film. With this configuration, it is possible to obtain a triangular acoustic output waveform. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-239518 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, in the ultrasonic band above 20 kHz, it is known that when the sound pressure exceeds 120 dB, a nonlinear phenomenon occurs, enabling the realization of a highly directional acoustic device (i.e., the parametric effect). However, it is considered undesirable for ultrasonic waves above 115 dB to affect the human auditory organs for a long period of time. Furthermore, as mentioned above, conventional acoustic devices using mechanical vibrations have difficulty generating sound with waveforms other than sinusoidal. For this reason, the use of conventional nonlinear acoustic devices using mechanical vibrations is limited to limited locations, such as train station platforms where there is a high turnover of people. On the other hand, if an acoustic device capable of generating an impulse response were realized, it would be possible to emit nonlinear ultrasonic waves at sound pressures lower than 120 dB. The present invention has been made in consideration of the circumstances exemplified above. That is, the present invention provides, for example, an electro-acoustic transducer that can achieve nonlinear acoustic output at the lowest possible sound pressure. [Means for solving the problem]

[0006] The electroacoustic transducer (1) according to claim 1 comprises: a heating element (3) which is a thin film of a conductive carbon material; a thermal insulating layer (24) provided on the rear side of the heating element; Equipped with picture, The heating element has defects (301) at intervals of 0.9 to 1.1 times the wavelength of the radiated sound. The electroacoustic transducer (1) according to claim 2 comprises: a heating element (3) which is a thin film of a conductive carbon material; a thermal insulating layer (24) provided on the rear side of the heating element; Equipped with The heating element has defects (301) at intervals of 0.9 to 1.1 times the wavelength of the radiated sound, The thermal insulation layer is provided on one surface (21) of a substrate (2) having a plate thickness direction along the acoustic radiation direction (D), A recess (R) opening toward the acoustic radiation direction is provided at a position corresponding to the thermal insulation layer in an in-plane direction perpendicular to the plate thickness direction. There are.

[0007] In addition, in each section of the application documents, each element may be assigned a reference symbol in parentheses. In this case, the reference symbol merely indicates an example of the correspondence between the element and the specific configuration described in the embodiment described below. Therefore, the present invention is not limited in any way by the description of the reference symbol. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a side cross-sectional view showing a schematic device configuration of an electro-acoustic transducer according to an embodiment of the present invention. [Figure 2] 2 is a graph showing impulse response performance of the electroacoustic transducer shown in FIG. 1 together with a comparative example. [Figure 3] 2 is a graph showing an example of an ultrasonic wave radiation waveform in the electroacoustic transducer shown in FIG. 1. [Figure 4A] 10 is a graph showing another example of the waveform of an ultrasonic wave emitted from the electroacoustic transducer shown in FIG. [Figure 4B] 10 is a graph showing another example of the waveform of an ultrasonic wave emitted from the electroacoustic transducer shown in FIG. [Figure 5] 2 is a plan view schematically showing an example of an in-plane shape of the electro-acoustic transducer shown in FIG. 1. FIG. [Figure 6] 1. FIG. 4 is a plan view schematically showing another example of the in-plane shape of the electro-acoustic transducer shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment) Hereinafter, embodiments of the present invention will be described with reference to the drawings. Incidentally, if various modifications applicable to one embodiment are inserted in the middle of a series of descriptions relating to that embodiment, understanding of that embodiment may be hindered. Therefore, the modifications will not be inserted in the middle of a series of descriptions relating to that embodiment, but will be described together after that. Furthermore, the descriptions of the drawings and the corresponding device configurations, functions, or operations described below are simplified for the purpose of concisely explaining the contents of the present invention and do not in any way limit the contents of the present invention. Therefore, it goes without saying that the exemplary configurations shown in the drawings do not necessarily correspond to the specific configurations actually manufactured and sold. In other words, unless expressly limited by the applicant in the prosecution history of this application, the present invention should not be construed as being limited by the descriptions of the drawings and the corresponding device configurations, functions, or operations described below.

[0010] (composition) With reference to FIG. 1 , a schematic configuration of an electroacoustic transducer 1 according to this embodiment will be described. For ease of explanation, a right-handed XYZ Cartesian coordinate system is set so that the Z axis is parallel to the directional axis CA, as shown in the figure. The directional axis CA is an imaginary line along the acoustic radiation direction D of the electroacoustic transducer 1 that emits sound. The directional axis CA is typically an imaginary line that serves as a reference for the directivity of the electroacoustic transducer 1. When a range of directivity, for example, a range in which a predetermined gain or a predetermined acoustic level can be obtained, is represented by a three-dimensional shape such as an approximately conical or spindle shape, the imaginary line corresponds to the imaginary line indicating the axial center of the three-dimensional shape. Specifically, for example, the directional axis CA is the central axis of the sound pressure half-limit angle. Hereinafter, a direction along the directional axis CA, i.e., a direction parallel to the directional axis CA, will be referred to as the "axial direction." Therefore, the axial direction is a direction parallel to the Z axis in the drawing. Furthermore, any direction perpendicular to the axial direction will be referred to as the "in-plane direction." The "in-plane direction" is a direction parallel to the XY plane in the drawing. Furthermore, viewing the electro-acoustic transducer 1 and its components from above in the direction opposite to the Z axis in Fig. 1 is referred to as a "plan view." In other words, the shape of a certain component in a "plan view" corresponds to the shape of the component when it is mapped onto the XY plane in the figure. The shape in a plan view, i.e., the shape in the in-plane direction, is referred to as an "in-plane shape."

[0011] 1, the electroacoustic transducer 1 according to this embodiment has a configuration as a so-called ultrasonic speaker that radiates, i.e., transmits, ultrasonic waves. Specifically, the electroacoustic transducer 1 includes a substrate 2, a heating element 3, electrodes 4, and a drive control unit 5. The configuration of each unit in the electroacoustic transducer 1 according to this embodiment will be described below in order.

[0012] The substrate 2 is a silicon substrate and is provided so that its thickness direction is along the axial direction, i.e., the acoustic radiation direction D. The top surface 21 of the substrate 2, i.e., one of the pair of main surfaces on the acoustic radiation direction D side, is formed in a flat, planar shape. The "main surface" is the surface of a plate-like object that is perpendicular to the thickness direction, and may also be referred to as the "plate surface." In the drawing, the other side of the top surface 21 is omitted for simplicity of illustration.

[0013] A mask layer 22 is provided on the upper surface 21. The mask layer 22 is formed of a SiN film or a SiC film with a thickness on the submicron level. An opening 23 is provided in the mask layer 22. The opening 23 is formed so as to penetrate the mask layer 22. The opening 23 may be formed in a substantially rectangular, circular, elliptical, or polygonal shape in a plan view. A thermal insulation layer 24 made of porous silicon is formed at a position corresponding to the opening 23 in an in-plane direction perpendicular to the thickness direction of the substrate 2. The thermal insulation layer 24 is provided on the upper surface 21 side of the substrate 2 (i.e., at a position facing the upper surface 21). The thermal insulation layer 24 has an in-plane shape corresponding to the in-plane shape of the opening 23. The thermal insulation layer 24 is formed to a thickness of about 10 μm, i.e., to a depth of about 10 μm from the upper surface 21.

[0014] The heating element 3 is a thin film of a conductive carbon material, specifically a graphene thin film, and is provided so as to cover the mask layer 22 and the thermal insulation layer 24. That is, the thermal insulation layer 24 is provided on the back side of the heating element 3 at a position corresponding to the thermal insulation layer 24 in the in-plane direction. In this embodiment, the heating element 3 is formed with a thickness on the sub-nano level or nano level. Then, a recess R that opens toward the acoustic radiation direction D is provided at a position corresponding to the thermal insulation layer 24 in the in-plane direction. The heating element 3 is provided on the inner wall surfaces of the recess R, i.e., the bottom wall surface and side wall surfaces.

[0015] The electrode 4 is provided on the heating element 3 at a position in the in-plane direction where the mask layer 22 is provided. The electrode 4 is a conductive film made of metal or the like. The electrode 4 has a first electrode 41 and a second electrode 42. A recess R is provided between the first electrode 41 and the second electrode 42. The first electrode 41 and the second electrode 42 are electrically connected to a drive control unit 5. The drive control unit 5 applies a drive voltage between the first electrode 41 and the second electrode 42 to pass a current through the portion of the heating element 3 between the first electrode 41 and the second electrode 42.

[0016] (Manufacturing method) A brief description of a manufacturing method for the electroacoustic transducer 1 having the configuration shown in Fig. 1 will be given below. First, a mask layer 22 having openings 23 is formed by patterning a SiN film or SiC film on the upper surface 21 of a substrate 2, which is a silicon wafer. Next, the upper surface 21, which is the silicon wafer surface exposed by the openings 23, is anodized using a mixed solution of hydrofluoric acid and ethanol. This forms a thermal insulation layer 24 made of porous silicon to a predetermined depth from the upper surface 21. Thereafter, a heating element 3 made of a graphene thin film and an electrode 4 made of a metal film are formed. Well-known methods can be used to form the heating element 3 and the electrode 4.

[0017] (effect) Below, an outline of the operation of the configuration of this embodiment will be described together with the effects achieved by the configuration, with reference to the drawings.

[0018] When the drive control unit 5 applies a drive voltage between the first electrode 41 and the second electrode 42, a current flows in the portion of the heating element 3 between the first electrode 41 and the second electrode 42 (i.e., the portion corresponding to the recessed portion R). This generates Joule heat in this portion, and the air is heated in the bottom region of the recessed portion R, i.e., the region schematically shown by the two-dot chain ellipse in the figure. When a drive voltage with a pulsed or AC waveform that generates a pulsed ON state is applied, the air expands in a pulsed or intermittent manner due to heat generation in the ON state, generating compressional waves in the air. These compressional waves in the air generate an acoustic output that is an ultrasonic wave, which is radiated in the acoustic radiation direction D.

[0019] In the electroacoustic transducer 1 according to this embodiment, a thermal insulating layer 24 made of porous silicon, which has low thermal capacity and thermal conductivity, is provided on the back side of the heating element 3, which is made of a thin film of a conductive carbon material such as graphene, which has a low thermal capacity. This allows the heating element 3 to be heated uniformly and rapidly in the on-state. Here, in the heating element 3, heat is rapidly dissipated toward the mask layer 22 in the portion where the mask layer 22, made of a SiN or SiC film with thermal properties similar to those of silicon, is provided as an underlying layer. In contrast, heat is difficult to dissipate in the portion where the thermal insulating layer 24 is provided. As a result, the air layer in the recess R is instantly heated and expands. Furthermore, in the off-state, the heating element 3 made of a thin film of a conductive carbon material such as graphene has a higher thermal conductivity than a thin metal film such as tungsten. This allows heat to dissipate efficiently in the in-plane direction. Furthermore, the thin film thickness reduces the thermal capacity, enhancing its effectiveness. Additionally, the thermal insulating layer 24 made of porous silicon is also made of a silicon lattice, and the thermal conductivity of the silicon portion is greater than that of the air layer, allowing rapid cooling through the silicon portion. Therefore, the heating element 3 is rapidly cooled to the ambient temperature. Therefore, the electroacoustic transducer 1 having such a configuration enables an impulse response, and makes it possible to achieve a nonlinear acoustic output with the lowest possible sound pressure.

[0020] FIG. 2 shows the impulse response characteristics of the electroacoustic transducer 1 according to this embodiment, together with a comparative example. The comparative example has the same configuration as this embodiment, except that a tungsten film is used as the heating element 3. The upper side of FIG. 2 shows the impulse response characteristics of this embodiment, and the lower side shows the impulse response characteristics of the comparative example. In the figure, the dotted waveform indicates the drive voltage, and the solid waveform indicates the microphone voltage. The microphone voltage is the output voltage of a sound pressure detection microphone placed a predetermined distance away from the electroacoustic transducer 1 in the sound radiation direction D. Therefore, there is a time difference between the drive voltage pulse and the generated sound pressure pulse, which corresponds to the propagation time of the ultrasonic waves from the electroacoustic transducer 1 to the sound pressure detection microphone, i.e., the distance from the electroacoustic transducer 1 to the sound pressure detection microphone.

[0021] In the configuration of the comparative example, a tungsten film is used as the heating element 3, so the temperature of the heating element 3, i.e., the heater temperature, decreases relatively slowly when the heater is off. Therefore, both an upward sound pressure peak due to air compression and a subsequent downward sound pressure peak due to air expansion occur, followed by silence. Furthermore, a second upward sound pressure peak occurs because the cooling rate is on the order of μsec due to the heater film thickness being large. In contrast, in this embodiment, the heater temperature decreases rapidly when the heater is off, so only one upward sound pressure peak occurs due to air compression, and neither a subsequent downward sound pressure peak nor a second upward sound pressure peak occurs due to air expansion. Therefore, this embodiment provides better impulse response characteristics than the comparative example.

[0022] Figure 3 shows the response characteristics when a driving voltage having a voltage rise waveform in which the voltage rises over time and a subsequent voltage drop waveform is applied to the heating element 3. In the example shown in Figure 3, the driving voltage was a 15-μs-wide pulse voltage that instantaneously rose from 0 V to a predetermined voltage, then increased the voltage stepwise five times every 1.5 μs, held the voltage constant for 7.5 μs, and then instantaneously dropped to 0 V. In this driving voltage waveform, the step-like portion corresponds to the voltage rise waveform, and the subsequent voltage hold period followed by the falling waveform corresponds to the cutoff waveform. In this case, a sound pressure peak of approximately 7.5 μs was obtained in the rising portion of the compression direction and approximately 2.2 μs in the falling portion, for a total of 9.7 μs. In addition, a sound pressure peak of 5.3 μs was obtained in the expansion direction. The combined duration of the compression and expansion directions was 15 μs, the same as the driving voltage waveform. In the example of Fig. 3, the step-like voltage increase is performed in 1.5 μsec increments, but this step time depends on the power supply frequency and can theoretically be set to 1 nsec or more. On the other hand, if one cycle exceeds 50 μsec, the frequency falls below 20 kHz, which falls into the audible range and is perceived by humans as an abnormal sound, which is undesirable. For this reason, the length of one cycle, i.e., the pulse width of the drive voltage waveform, is preferably 1 nsec to 50 μsec.

[0023] Figure 4A shows the response characteristics when a drive voltage waveform like that shown in Figure 3 is continuously applied to the heating element 3. In the example of Figure 4, the step time is 5 μsec, the voltage hold time is 5 μsec, and the off time is 5 μsec, with one cycle at 50 kHz. In this case, the time required for air expansion is 15 μsec and the time required for compression is 5 μsec. Figure 4B shows the response characteristics when the drive voltage waveform of Figure 4A is modified so that the step-like voltage increase section starts from 0 V. In this case, the time required for air expansion is 14 μsec and the time required for compression is 6 μsec. In this way, modifying the drive voltage waveform can change the nonlinearity of the output ultrasound. At a constant frequency, such a nonlinear waveform can be obtained by increasing the voltage stepwise while providing an off time required to cool the air in contact with the heating element 3.

[0024] According to this embodiment, the efficiency of a local speaker, such as that disclosed in Japanese Patent Publication No. 11-145915 and Japanese Patent No. 4251052, which interferes with nonlinear ultrasonic waves and demodulates the frequency difference between them, can be improved. Here, as disclosed in Japanese Patent Publication No. 4251052, if an ultrasonic waveform is to be nonlinearized using a parametric speaker, a sound pressure of 120 dB or more is required. However, it is considered undesirable for ultrasonic waves of 115 dB or more to affect the human auditory organs for a long period of time. Furthermore, when two ultrasonic waves of 120 dB or more intersect, an audible sound of the difference between the two ultrasonic waves is demodulated, but this is inefficient, resulting in a maximum sound pressure of only about 60 dB. In contrast, according to this embodiment, the nonlinearity of the ultrasonic waves can be arbitrarily set, improving demodulation efficiency and potentially enabling the demodulation of audible sounds of 60 dB or more using ultrasonic waves with a sound pressure lower than 120 dB.

[0025] Second Embodiment The second embodiment will be described below with reference to FIG. 5. In the following description of the second embodiment, differences from the first embodiment will be mainly described. In addition, identical or equivalent parts in the first and second embodiments are denoted by the same reference numerals. Therefore, in the following description of the second embodiment, the description of the first embodiment can be appropriately applied to components having the same reference numerals as those in the first embodiment, unless there is a technical contradiction or a special additional explanation. The same applies to the other embodiments described below.

[0026] In this embodiment, the heating element 3 extends in the X-axis direction in the drawing between the first electrode 41 and the second electrode 42 in a plan view. The heating element 3 also has defect portions 301. The defect portions 301 are portions of the heating element 3 having a higher electrical resistance than the non-defect portions 302, and extend along the width direction of the heating element 3 (i.e., the Y-axis direction in the drawing), which is perpendicular to the film thickness direction and extension direction of the heating element 3. Specifically, the defects constituting the defect portions 301 may be formed by structural defects such as carbon atom defects, substitution of carbon atoms with other atoms, or wrinkles. The non-defect portions 302 are portions different from the defect portions 301, i.e., portions that have no or fewer defects than the defect portions 301, and are formed in a substantially rectangular shape in a plan view. In this embodiment, a plurality of defect portions 301 are disposed at equal intervals between the first electrode 41 and the second electrode 42.

[0027] In this configuration, the defect portions 301 have a higher electrical resistance than the non-defect portions 302, and therefore generate more heat than the non-defect portions 302. As a result, large sound pressure is generated locally in the defect portions 301. By arranging the defect portions 301, which generate large sound pressure, at a predetermined pitch, a predetermined directivity can be obtained due to the interference effect. In this case, it is preferable to provide the defect portions 301 at intervals of 0.9 to 1.1 times the wavelength of the radiated sound.

[0028] (Third embodiment) The third embodiment will be described below with reference to Fig. 6. In the following description of the third embodiment, differences from the second embodiment will be mainly described.

[0029] In this embodiment, linear defect portions 301 are formed in a lattice pattern. That is, non-defect portions 302, each having a substantially rectangular shape in a plan view, are arranged two-dimensionally. With this configuration, two-dimensional directivity can be obtained.

[0030] (Variation) The present invention is not limited to the above-described embodiment. Therefore, the above-described embodiment can be modified as appropriate. Representative modifications will be described below. In the following description of the modifications, differences from the above-described embodiment will be mainly described. Furthermore, the same reference numerals are used for parts that are identical or equivalent to each other in the above-described embodiment and the modifications. Therefore, in the following description of the modifications, the description of the above-described embodiment can be used as appropriate for components that have the same reference numerals as the above-described embodiment, unless there is a technical contradiction or special additional explanation.

[0031] The present invention is not limited to the specific device configurations described in the above embodiments. That is, as mentioned above, the description of the above embodiments has been simplified to concisely explain the contents of the present invention. For this reason, illustrations and descriptions of components that are normally provided in products that are actually manufactured and sold, such as casings, bonding materials, terminals, and wiring, are appropriately omitted in the above embodiments and corresponding drawings.

[0032] The electroacoustic transducer 1 is not limited to a so-called ultrasonic speaker, and may be, for example, a sonic speaker that emits sound waves in the audible range.

[0033] The materials constituting each part are not limited to the above specific examples. For example, the heating element 3 may be made of a carbon material, such as a carbon nanotube or a carbon nanohorn, that is, a nanocarbon material.

[0034] In the above description, multiple components that are formed seamlessly together may be formed by bonding separate members together. Similarly, multiple components that are formed by bonding separate members together may be formed seamlessly together.

[0035] In the above description, multiple components that are made of the same material may be made of different materials, and similarly, multiple components that are made of different materials may be made of the same material.

[0036] It goes without saying that the elements constituting the above-described embodiments are not necessarily essential unless they are particularly expressly stated as essential or are clearly considered essential in principle. Furthermore, when numerical values ​​such as the number, amount, dimensions, and range of components are mentioned, the present invention is not limited to those specific numerical values ​​unless they are particularly expressly stated as essential or are clearly limited to specific numerical values ​​in principle. Similarly, when the shape, direction, positional relationship, etc. of components are mentioned, the present invention is not limited to those shapes, directions, positional relationships, etc. unless they are particularly expressly stated as essential or are clearly limited to specific shapes, directions, positional relationships, etc. in principle.

[0037] The modified examples are not limited to the above examples. For example, any one of the multiple embodiments and any one of the multiple modified examples may be combined with each other as long as there is no technical contradiction. Similarly, one of the multiple modified examples and another one of the multiple modified examples may be combined with each other as long as there is no technical contradiction.

[0038] (Disclosure details) As is clear from the above description of the embodiments and modifications, at least the following aspects are disclosed in this specification. <Point 1> The electroacoustic transducer (1) is a heating element (3) which is a thin film of a conductive carbon material; a thermal insulating layer (24) provided on the rear side of the heating element; It is equipped with: <Point 2> In view point 1, The thermal insulation layer is provided on one surface (21) of a substrate (2) having a plate thickness direction along the acoustic radiation direction (D), A recess (R) that opens toward the acoustic radiation direction is provided at a position corresponding to the thermal insulation layer in an in-plane direction perpendicular to the plate thickness direction. <Point 3> In terms of points 1 and 2, The heating element is a graphene thin film. <Point 4> In terms of points 1 to 3, The heating element has defects (301) at intervals of 0.9 to 1.1 times the wavelength of the radiated sound. <Point 5> In terms of points 1 to 4, The thermal insulating layer is made of porous silicon. <Point 6> In terms of points 1 to 5, Further, a drive control unit (5) is provided to apply a drive voltage to the heating element, The drive control unit applies the drive voltage, which has a voltage rising waveform in which the voltage rises over time and a cut-off waveform in which the voltage then falls, to the heating element. <Point 7> In point 6, The voltage rise waveform has a step-like voltage rise. [Explanation of symbols]

[0039] 1. Electroacoustic transducer 2 boards 21 Top side 24 Thermal insulation layer 3 Heating element 302 Defects 4 electrodes 5 Drive control unit D Sound radiation direction R recess

Claims

1. An electroacoustic transducer (1), a heating element (3) which is a thin film of a conductive carbon material; A thermal insulating layer (24) provided on the rear side of the heating element; Equipped with The heating element has defects (301) at intervals of 0.9 to 1.1 times the wavelength of the radiated acoustic wave. Electroacoustic transducer.

2. An electroacoustic transducer (1), a heating element (3) which is a thin film of a conductive carbon material; A thermal insulating layer (24) provided on the rear side of the heating element; Equipped with The heating element has defects (301) at intervals of 0.9 to 1.1 times the wavelength of the radiated sound, The thermal insulating layer is provided on one surface (21) of a substrate (2) having a plate thickness direction along the acoustic radiation direction (D), A recess (R) opening toward the acoustic radiation direction is provided at a position corresponding to the thermal insulation layer in an in-plane direction perpendicular to the plate thickness direction. Electroacoustic transducer.

3. The heating element is a graphene thin film.

3. The electroacoustic transducer according to claim 1 or 2.

4. The thermal insulation layer is made of porous silicon.

3. The electroacoustic transducer according to claim 1 or 2.

5. Further provided is a drive control unit (5) configured to apply a drive voltage to the heating element, the drive control unit applies the drive voltage to the heating element, the drive voltage having a voltage rising waveform in which the voltage rises over time and a cut-off waveform in which the voltage then falls; 3. The electroacoustic transducer according to claim 1 or 2.

6. The voltage rise waveform has a step-like voltage rise.

6. The electroacoustic transducer according to claim 5.

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