JP7609296B2 - Ultrasonic Transducers - Google Patents

Description

The present invention relates to an ultrasonic transducer.

JP 2007-142967 A (Patent Document 1) is a prior document that discloses the configuration of an ultrasonic sensor. The ultrasonic sensor described in Patent Document 1 is attached to the inner surface of a vehicle bumper or a plastic part. The ultrasonic sensor has an ultrasonic transducer and a housing. The ultrasonic transducer transmits and receives ultrasonic waves. The housing contains the ultrasonic transducer. The ultrasonic transducer is fixed in contact with the inner surface of the bottom part of the housing, and the outer surface of the bottom part abuts against the inner surface of the vehicle bumper or the plastic part.

An ultrasonic transmission part is formed on a part of the bottom surface of the housing. The ultrasonic transmission part is arranged so as to be in contact with the vehicle bumper or the resin part and the ultrasonic transducer. The ultrasonic transmission part is made of a material different from the material of the housing, and has an acoustic impedance intermediate between the acoustic impedance of the ultrasonic transducer and the acoustic impedance of the vehicle bumper or the resin part. The ultrasonic sensor transmits and receives ultrasonic waves via the ultrasonic transmission part and the vehicle bumper or the resin part.

JP 2007-142967 A

If the vibration area is limited to a narrow range to prevent the angular range of directionality from becoming narrow, the transmission strength and receiving sensitivity of the ultrasound will be reduced.

The present invention has been made in consideration of the above problems, and aims to provide an ultrasonic transducer that can achieve at least one of transmitting high-sound-pressure ultrasonic waves and receiving high-sensitivity ultrasonic waves while suppressing the narrowing of the angular range of directivity.

The ultrasonic transducer according to the present invention comprises an exterior part, a cylinder, an ultrasonic vibrator, and a restraint part. The exterior part has an inner surface. The cylinder is attached to the inner surface. The ultrasonic vibrator is attached to the cylinder and faces the inner surface with a gap therebetween. The restraint part is attached to the inner surface and sandwiches the cylinder with a gap therebetween. When viewed from a first direction perpendicular to the inner surface, the main vibration part, which is a part of the exterior part located inside the cylinder, resonates and vibrates in the opposite phase to the ultrasonic vibrator. When viewed from the first direction, the sub vibration part, which is a part of the exterior part located outside the cylinder and inside the restraint part in a second direction perpendicular to the first direction, resonates and vibrates in a range in which the absolute value of the phase difference with respect to the resonant vibration of the main vibration part is 120° or more and 180° or less.

According to the present invention, it is possible to suppress the narrowing of the angular range of directivity while achieving at least one of the transmission of high sound pressure ultrasound and the reception of high sensitivity ultrasound.

1 is a longitudinal sectional view showing a configuration of an ultrasonic transducer according to a first embodiment of the present invention. 1 is an exploded perspective view showing a configuration of an ultrasonic transducer according to a first embodiment of the present invention. 1 is a cross-sectional view showing a configuration of an ultrasonic vibrator included in an ultrasonic transducer according to a first embodiment of the present invention. 1 is a perspective view showing a displacement state simulated and analyzed using a finite element method when the ultrasonic transducer according to the first embodiment of the present invention transmits or receives ultrasonic waves. FIG. 5 is a cross-sectional view of the ultrasonic transducer of FIG. 4 as viewed from the direction of the arrow VV. 11 is a diagram for explaining the relationship between the area of a vibrating part and directivity. FIG. 1 is a schematic diagram showing a state in which sub-sound sources that vibrate in an antiphase to the main sound source are arranged on both sides of the main sound source. 13 is a graph showing the directivity obtained by simulation analysis using the finite element method when only the main sound source is driven, when the sound pressure ratio between the main sound source and the sub sound source is set to 16:1, and when the sound pressure ratio between the main sound source and the sub sound source is set to 4:1. 13 is a graph showing the change in sound pressure level at an emission angle of 20° when the sound pressure ratio of the sub sound source to the main sound source and the phase difference between the ultrasonic sine wave emitted from the main sound source and the ultrasonic sine wave emitted from the sub sound source are changed. 13 is a graph showing changes in sound pressure level at an emission angle of 40° when the sound pressure ratio of the sub sound source to the main sound source and the phase difference between the ultrasonic sine wave emitted from the main sound source and the ultrasonic sine wave emitted from the sub sound source are changed. 4 is a cross-sectional view showing a resonance mode of a main vibration part simulated and analyzed by using a finite element method in the ultrasonic transducer according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view showing a resonance mode of a sub-vibration part simulated and analyzed using a finite element method in the ultrasonic transducer according to the first embodiment of the present invention. FIG. 11 is a cross-sectional view showing a state in which the resonant vibration of the main vibration part and the resonant vibration of the sub vibration part are in phase, as determined by simulation analysis using the finite element method. FIG. 11 is a graph showing the relationship between the ratio of the difference between the resonant frequency of the main vibration section and the resonant frequency of the sub vibration section to the resonant frequency of the main vibration section, and the phase difference between the resonant vibration of the main vibration section and the resonant vibration of the sub vibration section. 11 is a graph showing the relationship between the ratio of the difference between the resonant frequency of the main vibration section and the resonant frequency of the sub vibration section to the resonant frequency of the main vibration section, and the ratio of the resonant amplitude of the sub vibration section to the resonant amplitude of the main vibration section. FIG. 13 is a plan view showing a restraining portion according to a first modified example. FIG. 11 is a plan view showing a restraining portion according to a second modified example. FIG. 13 is a plan view showing a restraining portion according to a third modified example. FIG. 13 is a plan view showing a restraining portion according to a fourth modified example. FIG. 13 is a plan view showing a restraining portion according to a fifth modified example. FIG. 13 is a plan view showing a restraining portion according to a sixth modified example. FIG. 13 is a cross-sectional view showing a configuration of an ultrasonic transducer according to a seventh modified example. FIG. 13 is a cross-sectional view showing a configuration of an ultrasonic transducer according to an eighth modified example. FIG. 13 is a cross-sectional view showing the configuration of an ultrasonic transducer according to a ninth modified example. FIG. 23 is a longitudinal sectional view showing the configuration of an ultrasonic transducer according to a tenth modified example of the first embodiment of the present invention. FIG. 5 is a longitudinal sectional view showing the configuration of an ultrasonic transducer according to a second embodiment of the present invention. FIG. 11 is an exploded perspective view showing a configuration of an ultrasonic transducer according to a second embodiment of the present invention. FIG. 11 is a longitudinal cross-sectional view showing the periphery of an ultrasonic vibrator of an ultrasonic transducer according to a first modified example of the second embodiment of the present invention. 13 is a perspective view showing a cylindrical body and a metal plate portion of an ultrasonic transducer according to a second modified example of the second embodiment of the present invention. FIG. FIG. 11 is a longitudinal sectional view showing the configuration of an ultrasonic transducer according to a third embodiment of the present invention. FIG. 11 is an exploded perspective view showing a configuration of an ultrasonic transducer according to a third embodiment of the present invention. FIG. 11 is a perspective view showing a metal plate portion and a cylindrical body according to a comparative example. FIG. 2 is a perspective view showing a metal plate portion and a cylindrical body according to the first embodiment. FIG. 11 is a perspective view showing a metal plate portion and a cylindrical body according to a second embodiment. FIG. 11 is a perspective view showing a metal plate portion and a cylindrical body according to a third embodiment. 10 is a graph showing the relationship between the resonance frequency of each of the main vibration section and the sub vibration section and the length of a slit. FIG. 11 is a perspective view showing a cylindrical body and a metal plate portion of an ultrasonic transducer according to a modified example of the third embodiment of the present invention.

Hereinafter, ultrasonic transducers according to each embodiment of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same or corresponding parts in the drawings will be given the same reference numerals, and the description will not be repeated.

(Embodiment 1)
Fig. 1 is a longitudinal sectional view showing the configuration of an ultrasonic transducer according to embodiment 1 of the present invention. Fig. 2 is an exploded perspective view showing the configuration of an ultrasonic transducer according to embodiment 1 of the present invention. As shown in Figs. 1 and 2, an ultrasonic transducer 100 according to embodiment 1 of the present invention includes an exterior part 110, a cylindrical body 120, an ultrasonic vibrator 130, and a restraint part 140.

The exterior part 110 is, for example, a part of the exterior of a vehicle bumper, a computer or smartphone housing, furniture, or a wall of a house. The exterior part 110 has an inner surface 111. The exterior part 110 has a substantially flat plate shape. The exterior part 110 is formed of a resin such as polypropylene. The thickness of the exterior part 110 is, for example, about 1.5 mm.

In the figure, a first direction perpendicular to the inner surface 111 of the exterior portion 110 is shown as the Z-axis direction, a second direction perpendicular to the first direction is shown as the X-axis direction, and a third direction perpendicular to both the first and second directions is shown as the Y-axis direction.

The cylindrical body 120 is attached to the inner surface 111 of the exterior part 110. In this embodiment, one end of the cylindrical body 120 in the first direction (Z-axis direction) is adhered to the inner surface 111 of the exterior part 110. The cylindrical body 120 has a rectangular ring-shaped shape. The cylindrical body 120 has a longitudinal direction along the third direction (Y-axis direction) and a transverse direction along the second direction (X-axis direction). The axial direction of the cylindrical body 120 is along the first direction (Z-axis direction).

The cylindrical body 120 is formed from resin, glass epoxy, metal, or the like. From the viewpoint of suppressing changes in characteristics of the ultrasonic transducer 100 due to temperature changes, it is preferable that the cylindrical body 120 is formed from metal. On the other hand, from the viewpoint of lowering the frequency of the ultrasonic waves transmitted or received by the ultrasonic transducer 100 and from the viewpoint of miniaturizing the ultrasonic transducer 100, it is preferable that the cylindrical body 120 is formed from resin. In this embodiment, the cylindrical body 120 is formed from glass epoxy, which has intermediate properties between metal and resin.

Figure 3 is a cross-sectional view showing the configuration of an ultrasonic vibrator provided in the ultrasonic transducer of embodiment 1 of the present invention. As shown in Figure 1, the ultrasonic vibrator 130 is attached to the cylindrical body 120 and faces the inner surface 111 of the exterior part 110 with a gap therebetween. Specifically, the ultrasonic vibrator 130 is attached to the other end of the cylindrical body 120 in the first direction (Z-axis direction) and faces the inner surface 111 of the exterior part 110 through the internal space of the cylindrical body 120.

As shown in Figures 1 to 3, the ultrasonic transducer 130 is a piezoelectric element including a piezoelectric body 131. As shown in Figure 3, in this embodiment, the ultrasonic transducer 130 includes two stacked piezoelectric bodies 131. The polarization directions Dp of the two piezoelectric bodies 131 are different from each other. Specifically, the polarization directions Dp of the two piezoelectric bodies 131 face each other in the first direction (Z-axis direction). The two piezoelectric bodies 131 are sandwiched between a first electrode 132 and a second electrode 133, and an intermediate electrode 134 is disposed between the two piezoelectric bodies 131. The first electrode 132 and the second electrode 133 are electrically connected to a processing circuit 150 capable of applying an AC voltage. The ultrasonic transducer 130 is a so-called series-type bimorph piezoelectric transducer. The total thickness of the two piezoelectric bodies 131 is, for example, 0.5 mm or more and 0.75 mm or less.

The restraint section 140 is attached to the inner surface 111 of the exterior section 110, and sandwiches the cylindrical body 120 with a gap therebetween. In this embodiment, the restraint section 140 has an annular shape. Specifically, the restraint section 140 has a rectangular annular shape. The restraint section 140 surrounds the cylindrical body 120 from the outside while leaving a gap therebetween. However, it is sufficient that the restraint section 140 sandwiches the cylindrical body 120 with a gap therebetween in the second direction (X-axis direction). One end of the restraint section 140 in the first direction (Z-axis direction) is adhered to the inner surface 111 of the exterior section 110.

The restraint section 140 is formed of a metal such as stainless steel or aluminum, or a highly rigid material such as glass epoxy. By restraining the portion of the exterior section 110 to which the restraint section 140 is attached, the vibration of the sub-vibration section, which will be described later, can be contained within the sub-vibration section and stabilized.

Figure 4 is a perspective view showing a displacement state simulated and analyzed using the finite element method when the ultrasonic transducer according to embodiment 1 of the present invention transmits or receives ultrasonic waves. Figure 5 is a cross-sectional view of the ultrasonic transducer in Figure 4 as seen from the direction of the V-V line arrow. The simulation analysis conditions were as follows: the thickness of the exterior part 110 was 1.5 mm, the thickness of the piezoelectric body 131 was 0.6 mm, the longitudinal dimension of the outer shape of the cylindrical body 120 was 16 mm, the lateral dimension was 6 mm, the thickness was 0.4 mm, and the width of the cylindrical body 120 was 0.5 mm. That is, the longitudinal dimension of the inner shape of the cylindrical body 120 was 15 mm, and the lateral dimension was 5 mm. The width of the restraint part 140 was 2 mm, and the thickness was 3 mm. The distance between the cylindrical body 120 and the restraint part 140 in the second direction (X-axis direction) was 4 mm.

As shown in Figures 4 and 5, the ultrasonic transducer 100 of embodiment 1 of the present invention has a main vibration part 110m, which is a part of the exterior part 110 located inside the cylindrical body 120 when viewed from a first direction (Z-axis direction), and a sub-vibration part 110s, which is a part of the exterior part 110 located outside the cylindrical body 120 and inside the restraint part 140 in the second direction (X-axis direction).

As shown in Figure 5, the main vibration part 110m resonates in an opposite phase to the ultrasonic transducer 130. That is, the displacement direction of the resonant vibration Bm of the main vibration part 110m and the displacement direction of the resonant vibration Bp of the ultrasonic transducer 130 are opposite to each other in the first direction (Z-axis direction).

The sub-vibration unit 110s resonates in a range in which the absolute value of the phase difference with respect to the resonant vibration of the main vibration unit 110m is in the range of 120° to 180°. In other words, the displacement direction of the resonant vibration Bs of the sub-vibration unit 110s and the displacement direction of the resonant vibration Bm of the main vibration unit 110m are opposite to each other in the first direction (Z-axis direction).

Here, we will explain the mechanism by which the effects of the ultrasonic transducer 100 of embodiment 1 of the present invention are achieved.

As shown in Fig. 5, the main vibration section 110m resonates in the opposite phase to the ultrasonic transducer 130, so that the vibration leakage to the periphery of the main vibration section 110m in the exterior section 110 can be reduced as shown in Fig. 4. This makes it possible to prevent the angular range of the directivity of the ultrasonic transducer 100 from narrowing. In addition, in the ultrasonic transducer 100, by exciting the above-mentioned resonant vibration Bs in the sub vibration section 110s, it is possible to prevent the angular range of the directivity of the ultrasonic transducer 100 from narrowing while realizing at least one of the transmission of ultrasonic waves with high sound pressure and the reception of ultrasonic waves with high sensitivity.

First, we will use a simplified model to explain the mechanism by which the main vibration and sub-vibration can prevent the angular range of directivity from narrowing.

Figure 6 is a diagram for explaining the relationship between the area of the vibration part and the directivity. As shown in Figure 6, if we consider that the ultrasonic waves emitted from the vibration part are emitted from multiple point sound sources S arranged at intervals from each other, the difference DL in the path length of the ultrasonic waves emitted in a direction other than 0° at the radiation angle θ between the point sound sources S located at one end and the other end of the vibration part increases as the area of the vibration part increases. Since interference occurs depending on the relationship between this path length difference DL and the wavelength of the ultrasonic waves, basically, the larger the area of the vibration part is and the higher the frequency of the ultrasonic waves is, the narrower the angular range of the directivity becomes.

On the other hand, if the area of the vibrating part is reduced, the narrowing of the angular range of directivity can be prevented, but the sound pressure of the radiated ultrasound will be reduced. Here, we will explain the results of a simulation analysis using the finite element method on the relationship between sound pressure and directivity when sub-sound sources that vibrate in the opposite phase to the main sound source are placed on both sides of the main sound source.

Figure 7 is a schematic diagram showing a state in which sub-sound sources that vibrate in antiphase to the main sound source are placed on both sides of the main sound source. As shown in Figure 7, a simplified model in which sub-sound sources SS that vibrate in antiphase to the main sound source MS are placed on both sides of the main sound source MS was used for simulation analysis using the finite element method.

Figure 8 is a graph showing the directivity analyzed by simulation using the finite element method when only the main sound source is driven, when the sound pressure ratio between the main sound source and the sub sound source is 16:1, and when the sound pressure ratio between the main sound source and the sub sound source is 4:1. In Figure 8, the vertical axis shows the sound pressure level (dB), and the circumferential axis shows the radiation angle (°) from the center of the main sound source. The directivity when only the main sound source is driven is shown by a solid line, the directivity when the sound pressure ratio between the main sound source and the sub sound source is 16:1 is shown by a dotted line, and the directivity when the sound pressure ratio between the main sound source and the sub sound source is 4:1 is shown by a two-dot chain line. Note that in each of the above three cases, the sound pressure level in the front direction at a radiation angle θ = 0° is set to 0 dB, and the transition between the radiation angle θ and the sound pressure level is shown.

As shown in Figure 8, when the sound pressure ratio between the main sound source MS and the sub sound source SS was set to 16:1, the angular range of directivity was wider, and when the sound pressure ratio between the main sound source MS and the sub sound source SS was set to 4:1, the angular range of directivity was even wider.

When the sound pressure ratio between the main sound source MS and the sub sound source SS was set to 4:1, the sound pressure level in the front direction at a radiation angle θ = 0° was low due to interference between the ultrasound emitted from the main sound source MS and the ultrasound emitted from the sub sound source SS, but the sound pressure level was highest when the radiation angle θ was in the range of 20° to 40°.

The change in sound pressure level due to interference varies depending on the sound pressure ratio between the main sound source MS and the sub sound source SS and the phase difference between the ultrasonic sine wave emitted from the main sound source MS and the ultrasonic sine wave emitted from the sub sound source SS.

Figure 9 is a graph showing the transition of the sound pressure level at an emission angle of 20° when the sound pressure ratio of the sub sound source to the main sound source and the phase difference between the ultrasonic sine wave emitted from the main sound source and the ultrasonic sine wave emitted from the sub sound source are changed. Figure 10 is a graph showing the transition of the sound pressure level at an emission angle of 40° when the sound pressure ratio of the sub sound source to the main sound source and the phase difference between the ultrasonic sine wave emitted from the main sound source and the ultrasonic sine wave emitted from the sub sound source are changed.

In Figure 9, the vertical axis shows the sound pressure level (dB) at a radiation angle of 20°, and the horizontal axis shows the sound pressure ratio (%) of the sub sound source to the main sound source. In Figure 10, the vertical axis shows the sound pressure level (dB) at a radiation angle of 40°, and the horizontal axis shows the sound pressure ratio (%) of the sub sound source to the main sound source. In Figures 9 and 10, the sound pressure level in the front direction at a radiation angle θ = 0° is set to 0 dB, and the absolute value of the phase difference between the ultrasonic sine wave radiated from the main sound source and the ultrasonic sine wave radiated from the sub sound source is shown as L1 when it is 90°, L2 when it is 120°, L3 when it is 150°, and L4 when it is 180°.

In each of Figures 9 and 10, when the sound pressure level is higher than when the sound pressure ratio of the sub sound source SS to the main sound source MS is 0%, the angular range of directivity is wider.

As shown in Figures 9 and 10, when the absolute value of the phase difference between the ultrasonic sine wave emitted from the main sound source MS and the ultrasonic sine wave emitted from the sub-sound source SS is 90°, the sound pressure levels at emission angles of 20° and 40° were not higher than when the sound pressure ratio of the sub-sound source SS to the main sound source MS was 0%.

When the absolute value of the above phase difference was 120°, the sound pressure level at a radiation angle of 20° was approximately the same as when the sound pressure ratio of the sub-sound source SS to the main sound source MS was 0%, and the sound pressure level at a radiation angle of 40° was greater than when the sound pressure ratio of the sub-sound source SS to the main sound source MS was 0%.

When the absolute value of the above phase difference was 150° and 180°, the sound pressure level at radiation angles of 20° and 40° was higher than when the sound pressure ratio of the sub sound source SS to the main sound source MS was 0%.

From the above results, it was confirmed that the angular range of directivity is widened when the absolute value of the phase difference between the ultrasonic sine wave emitted from the main sound source MS and the ultrasonic sine wave emitted from the sub sound source SS is in the range of 120° to 180°. For example, when the absolute value of the phase difference between the ultrasonic sine wave emitted from the main sound source MS and the ultrasonic sine wave emitted from the sub sound source SS is 180° and the sound pressure ratio of the sub sound source SS to the main sound source MS is 10% or more, the sound pressure level at a radiation angle of 20° is 2 dB or more higher and the sound pressure level at a radiation angle of 40° is 6 dB or more higher than when the sound pressure ratio of the sub sound source SS to the main sound source MS is 0%.

Next, the vibration modes in each of the main vibration section 110m and the sub vibration section 110s will be described. Figure 11 is a cross-sectional view showing the resonance mode of the main vibration section, which is simulated and analyzed using the finite element method in the ultrasonic transducer according to embodiment 1 of the present invention. Figure 12 is a cross-sectional view showing the resonance mode of the sub vibration section, which is simulated and analyzed using the finite element method in the ultrasonic transducer according to embodiment 1 of the present invention. Figures 11 and 12 are cross-sectional views at the same cross-sectional position as Figure 5.

The ultrasonic transducer 100 according to the first embodiment of the present invention transmits and/or receives ultrasonic waves by the resonance mode of the main vibration part 110m shown in Fig. 11. The ultrasonic transducer 100 according to the first embodiment of the present invention suppresses the narrowing of the angular range of directivity by superimposing the resonance mode of the sub vibration part 110s shown in Fig. 12 on the resonance mode of the main vibration part 110m. In order to efficiently transmit and/or receive ultrasonic waves, the sub vibration part 110s is vibrated resonantly at a frequency near the resonance frequency of the main vibration part 110m.

Figure 13 is a cross-sectional view showing a state in which the resonant vibration of the main vibration part and the resonant vibration of the sub vibration part are in phase, as simulated and analyzed using the finite element method. In Figure 13, the cross-section is taken at the same cross-sectional position as in Figure 5. When the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub vibration part 110s is outside the preferred range, the resonant vibration Bm of the main vibration part 110m and the resonant vibration Bs of the sub vibration part 110s are in phase as shown in Figure 13. In this case, the sound pressure level in the front direction at a radiation angle θ = 0° increases due to interference between the ultrasonic waves emitted from the main vibration part 110m and the ultrasonic waves emitted from the sub vibration part 110s, and the angular range of directivity becomes narrower.

On the other hand, when the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub vibration part 110s is within a suitable range, the phase difference and amplitude ratio between the resonant vibration Bm of the main vibration part 110m and the resonant vibration Bs of the sub vibration part 110s can be set to a desired state, as shown in Figure 5.

First, in order to vibrate the main vibration part 110m in a resonant mode with little vibration leakage, it is required that the main vibration part 110m and the ultrasonic transducer 130 resonate in opposite phases while maintaining the physical balance between them.

In order to maintain the physical balance between the main vibration section 110m and the ultrasonic transducer 130, it is preferable to satisfy the relationship of 0.7CpTp/Cb≦Tb≦1.3CpTp/Cb, where Cb is the sound velocity of the transverse waves of the exterior section 110, Cp is the sound velocity of the transverse waves of the piezoelectric body 131, Tb is the thickness dimension of the main vibration section 110m, and Tp is the thickness dimension of the piezoelectric body 131. The sound velocity Cb of the transverse waves of the exterior section 110 is determined by the material constituting the exterior section 110. The sound velocity Cp of the transverse waves of the piezoelectric body 131 is determined by the material constituting the piezoelectric body 131. When multiple piezoelectric bodies 131 are stacked in the ultrasonic transducer 130, the thickness dimension Tp of the piezoelectric body 131 is the sum of the thicknesses of the multiple piezoelectric bodies 131.

By satisfying the relationship of 0.7CpTp/Cb≦Tb≦1.3CpTp/Cb, the physical balance between the main vibration part 110m and the ultrasonic transducer 130 during vibration can be maintained, and the amplitude of the resonant vibration of the main vibration part 110m can be reduced and vibration leakage can be suppressed. It is more preferable to satisfy the relationship of Tb=CpTp/Cb.

Next, the results of a simulation analysis using the finite element method will be described regarding the relationship between the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub vibration part 110s, and the phase difference between the resonant vibration Bm of the main vibration part 110m and the resonant vibration Bs of the sub vibration part 110s. Figure 14 is a graph showing the relationship between the ratio of the difference between the resonant frequency of the main vibration part and the resonant frequency of the sub vibration part to the resonant frequency of the main vibration part, and the phase difference between the resonant vibration of the main vibration part and the resonant vibration of the sub vibration part. In Figure 14, the vertical axis shows the phase difference (°) between the resonant vibration of the main vibration part and the resonant vibration of the sub vibration part, and the horizontal axis shows the ratio (%) of the difference between the resonant frequency of the main vibration part and the resonant frequency of the sub vibration part to the resonant frequency of the main vibration part.

In addition, as the distance between the cylinder 120 and the restraint portion 140 in the second direction (X-axis direction) increases, the resonant frequency of the sub-vibration portion decreases, and as the distance decreases, the resonant frequency of the sub-vibration portion increases.

14, when the resonant frequency of the sub vibration part 110s is lower than the resonant frequency of the main vibration part 110m, the phase difference between the resonant vibration of the main vibration part 110m and the resonant vibration of the sub vibration part 110s is 0° or more and 80° or less. As shown by the dotted line La, when the ratio of the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub vibration part 110s to the resonant frequency of the main vibration part 110m is 7%, the phase difference between the resonant vibration of the main vibration part 110m and the resonant vibration of the sub vibration part 110s is 120°.

Next, the results of a simulation analysis using the finite element method will be described regarding the relationship between the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub vibration part 110s, and the ratio of the resonant amplitude of the sub vibration part 110s to the resonant amplitude of the main vibration part 110m. Figure 15 is a graph showing the relationship between the ratio of the difference between the resonant frequency of the main vibration part and the resonant frequency of the sub vibration part to the resonant frequency of the main vibration part, and the ratio of the resonant amplitude of the sub vibration part to the resonant amplitude of the main vibration part. In Figure 15, the vertical axis shows the ratio (%) of the resonant amplitude of the sub vibration part to the resonant amplitude of the main vibration part, and the horizontal axis shows the ratio (%) of the difference between the resonant frequency of the main vibration part and the resonant frequency of the sub vibration part to the resonant frequency of the main vibration part.

As shown in Figure 15, the resonant amplitude of the sub-vibrating part 110s is smaller than the resonant amplitude of the main vibrating part 110m. When the resonant frequency of the sub-vibrating part 110s is higher than the resonant frequency of the main vibrating part 110m, the closer the resonant frequency of the sub-vibrating part 110s is to the resonant frequency of the main vibrating part 110m, the larger the resonant amplitude of the sub-vibrating part 110s becomes.

As shown by the dotted line La, when the ratio of the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub vibration part 110s to the resonant frequency of the main vibration part 110m was 7%, the ratio of the resonant amplitude of the sub vibration part 110s to the resonant frequency of the main vibration part 110m was 40%. As shown by the dotted line Lb, when the ratio of the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub vibration part 110s to the resonant frequency of the main vibration part 110m was 20%, the ratio of the resonant amplitude of the sub vibration part 110s to the resonant frequency of the main vibration part 110m was 18%. The larger the ratio of the resonant amplitude of the sub vibration part 110s to the resonant frequency of the main vibration part 110m, the wider the angle range of the directivity can be.

As shown in FIG. 15, when the resonant frequency of the sub-vibration part 110s is higher than the resonant frequency of the main vibration part 110m and the ratio of the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub-vibration part 110s to the resonant frequency of the main vibration part 110m is 7% or more and 20% or less, linearity was observed in the ratio of the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub-vibration part 110s to the resonant frequency of the main vibration part 110m and the ratio of the resonant amplitude of the sub-vibration part 110s to the resonant amplitude of the main vibration part 110m.

As shown in Figures 14 and 15, when the resonant frequency of the sub-vibration part 110s is higher than the resonant frequency of the main vibration part 110m and the ratio of the difference between the resonant frequency of the main vibration part 110m and the resonant frequency of the sub-vibration part 110s to the resonant frequency of the main vibration part 110m is 7% or more and 20% or less, the phase difference between the resonant vibration of the main vibration part 110m and the resonant vibration of the sub-vibration part 110s can be made to be 120° or more and 180° or less, while the resonant amplitude of the sub-vibration part 110s can be made 18% or more and 40% or less of the resonant amplitude of the main vibration part 110m.

Therefore, by changing the distance between the cylinder 120 and the restraint portion 140 in the second direction (X-axis direction) and adjusting the resonant frequency of the sub-vibration portion 110s within a range of 107% or more and 120% or less of the resonant frequency of the main vibration portion 110m, the phase difference between the resonant vibration of the main vibration portion 110m and the resonant vibration of the sub-vibration portion 110s can be set to 120° or more and 180° or less, while appropriately selecting the resonant amplitude of the sub-vibration portion 110s within a range R that is 18% or more and 40% or less of the resonant amplitude of the main vibration portion 110m, thereby widening the angular range of directivity while realizing at least one of the transmission of high sound pressure ultrasound and the reception of high sensitivity ultrasound.

As described above, in the ultrasonic transducer 100 according to embodiment 1 of the present invention, by resonating the sub-vibration unit 110s in a suitable resonant mode without reducing the size of the vibration portion of the main vibration unit 110m, it is possible to suppress the narrowing of the angular range of directivity while achieving at least one of the transmission of high sound pressure ultrasound and the reception of high sensitivity ultrasound.

In this embodiment, the ultrasonic transducer 130 is described as a piezoelectric transducer, but as long as the main vibration section 110m and the sub vibration section 110s can be driven in the same manner, the ultrasonic transducer 130 is not limited to a piezoelectric transducer and may be an ultrasonic transducer that is electrostatically or electromagnetically driven.

In addition, the shape of the restraint section 140 is not limited to a rectangular ring shape, so long as the resonant vibration of the sub-vibration section 110s can be generated in a similar manner. Below, the restraint section of the ultrasonic transducer according to each modified example of embodiment 1 of the present invention is described.

FIG. 16 is a plan view showing a restraint portion according to a first modified example. As shown in FIG. 16, the shape of the restraint portion 140a according to the first modified example is a square ring. FIG. 17 is a plan view showing a restraint portion according to a second modified example. As shown in FIG. 17, the outer shape of the restraint portion 140b according to the second modified example is a square, and the inner shape is a circle. FIG. 18 is a plan view showing a restraint portion according to a third modified example. As shown in FIG. 18, the outer shape of the restraint portion 140c according to the third modified example is a square, and the inner shape is a hexagon. FIG. 19 is a plan view showing a restraint portion according to a fourth modified example. As shown in FIG. 19, the shape of the restraint portion 140d according to the fourth modified example is a ring. FIG. 20 is a plan view showing a restraint portion according to a fifth modified example. As shown in FIG. 20, the shape of the restraint portion 140e according to the fifth modified example is a U-shape. FIG. 21 is a plan view showing a restraint portion according to a sixth modified example. As shown in FIG. 21, the shape of a restraining portion 140f according to the sixth modified example is a pair of straight lines extending in the third direction (Y-axis direction) while being spaced apart from each other in the second direction (X-axis direction).

In this embodiment, the ultrasonic vibrator 130 is a so-called series-type bimorph piezoelectric vibrator, but the ultrasonic vibrator 130 may be another type of piezoelectric vibrator. Below, we will explain the ultrasonic vibrator of the ultrasonic transducer related to a modified example of embodiment 1 of the present invention.

Figure 22 is a cross-sectional view showing the configuration of an ultrasonic transducer according to the seventh modified example. As shown in Figure 22, the ultrasonic transducer 130a according to the seventh modified example is a piezoelectric element including two stacked piezoelectric bodies 131. The polarization directions Dp of the two piezoelectric bodies 131 are the same. The ultrasonic transducer 130a is a so-called parallel type bimorph piezoelectric transducer.

Figure 23 is a cross-sectional view showing the configuration of an ultrasonic transducer according to the eighth modified example. As shown in Figure 23, ultrasonic transducer 130b according to the eighth modified example is a piezoelectric element including four stacked piezoelectric bodies 131. The polarization direction Dp of the two piezoelectric bodies 131 located on the outer side of the four piezoelectric bodies 131 faces one side of the first direction (Z-axis direction), and the polarization direction Dp of the two piezoelectric bodies 131 located on the inner side of the four piezoelectric bodies 131 faces the other side of the first direction (Z-axis direction). Ultrasonic transducer 130b is a so-called multimorph type piezoelectric transducer.

Figure 24 is a cross-sectional view showing the configuration of an ultrasonic transducer according to the ninth modified example. As shown in Figure 24, ultrasonic transducer 130c according to the ninth modified example is a piezoelectric element including one piezoelectric body 131. Specifically, piezoelectric body 131 is sandwiched between a first electrode 132 and a vibration plate 135 made of metal. Ultrasonic transducer 130c is a so-called unimorph type piezoelectric transducer.

Figure 25 is a longitudinal cross-sectional view showing the configuration of an ultrasonic transducer according to a tenth modified example of embodiment 1 of the present invention. As shown in Figure 25, ultrasonic transducer 100a according to the tenth modified example of embodiment 1 of the present invention comprises an exterior part 110, a cylindrical body 120a, an ultrasonic vibrator, and a restraint part 140. Cylinder body 120a has a cylindrical shape with a bottom. Cylinder body 120a is formed of metal. A piezoelectric body 131 is attached to the outer bottom surface of cylinder body 120a, forming an ultrasonic vibrator that is a unimorph type piezoelectric vibrator.

In the ultrasonic transducer 100 according to the first embodiment of the present invention, the main vibration section 110m, which is a portion of the exterior section 110 located inside the cylindrical body 120 when viewed from the first direction (Z-axis direction), resonates in an opposite phase to the ultrasonic transducer 130. The sub vibration section 110s, which is a portion of the exterior section 110 located outside the cylindrical body 120 and inside the restraint section 140 in the second direction (X-axis direction) when viewed from the first direction (Z-axis direction), resonates in a range of 120° to 180° in absolute value of phase difference with respect to the resonant vibration of the main vibration section 110m. This makes it possible to suppress the narrowing of the angular range of directivity while realizing at least one of the transmission of high sound pressure ultrasonic waves and the reception of high sensitivity ultrasonic waves.

In the ultrasonic transducer 100 according to the first embodiment of the present invention, the restraint section 140 has an annular shape. This makes it possible to suppress vibration leakage in the third direction (Y-axis direction) perpendicular to the second direction (X-axis direction) that widens the angular range of directivity.

In the ultrasonic transducer according to the first embodiment of the present invention, the ultrasonic vibrator 130 is a piezoelectric element including a piezoelectric body. This allows the ultrasonic transducer 100 to have a simple configuration.

In the ultrasonic transducer according to the first embodiment of the present invention, the resonant frequency of the sub-vibration unit 110s is higher than the resonant frequency of the main vibration unit 110m, and the ratio of the difference between the resonant frequency of the main vibration unit 110m and the resonant frequency of the sub-vibration unit 110s to the resonant frequency of the main vibration unit 110m is 7% or more and 20% or less. This makes it possible to widen the angular range of directivity while realizing at least one of the transmission of high sound pressure ultrasonic waves and the reception of high sensitivity ultrasonic waves.

In the ultrasonic transducer according to the first embodiment of the present invention, the sound velocity of the shear wave of the exterior part 110 is Cb, the sound velocity of the shear wave of the piezoelectric body 131 is Cp, the thickness dimension of the main vibration part 110m is Tb, and the thickness dimension of the piezoelectric body 131 is Tp, the relationship of 0.7CpTp/Cb≦Tb≦1.3CpTp/Cb is satisfied. This maintains the physical balance between the main vibration part 110m and the ultrasonic transducer 130 during vibration, and reduces the amplitude of the resonant vibration of the main vibration part 110m and suppresses vibration leakage.

In the ultrasonic transducer according to the first embodiment of the present invention, the resonant amplitude of the sub-vibration unit 110s is smaller than the resonant amplitude of the main vibration unit 110m. This prevents the sound pressure level in the front direction at a radiation angle θ = 0° from becoming too low.

In the ultrasonic transducer according to the first embodiment of the present invention, the resonant amplitude of the sub-vibration unit 110s is 18% to 40% of the resonant amplitude of the main vibration unit 110m. This makes it possible to realize at least one of the transmission of ultrasonic waves with high sound pressure and the reception of ultrasonic waves with high sensitivity.

(Embodiment 2)
Hereinafter, an ultrasonic transducer according to a second embodiment of the present invention will be described with reference to the drawings. The ultrasonic transducer according to the second embodiment of the present invention differs from the ultrasonic transducer according to the first embodiment of the present invention in that the cylindrical body and the restraining part are attached to the inner surface of the exterior part via a metal plate part, and therefore the description of the same configuration as the ultrasonic transducer according to the first embodiment of the present invention will not be repeated.

Figure 26 is a longitudinal cross-sectional view showing the configuration of an ultrasonic transducer according to embodiment 2 of the present invention. Figure 27 is an exploded oblique view showing the configuration of an ultrasonic transducer according to embodiment 2 of the present invention. As shown in Figures 26 and 27, an ultrasonic transducer 200 according to embodiment 2 of the present invention comprises an exterior portion 110, a cylindrical body 120, an ultrasonic vibrator 130, a restraint portion 140, and a metal plate portion 250.

Each of the cylindrical body 120 and the restraint portion 140 is attached to the inner surface 111 via a metal plate portion 250 extending along the inner surface 111 of the exterior portion 110. Specifically, a recess 112 is formed in the inner surface 111 of the exterior portion 110. The thickness of the exterior portion 110 at the portion where the recess 112 is formed is, for example, 1 mm. Note that the recess 112 does not necessarily have to be formed in the exterior portion 110.

The metal plate portion 250 is flat. The metal plate portion 250 is attached within the recess 112. When viewed from the first direction (Z-axis direction), the cylinder body 120 is attached to the center of the metal plate portion 250, and the restraint portion 140 is attached to the edge of the metal plate portion 250. The metal plate portion 250 is formed of a metal such as aluminum. The thickness of the metal plate portion 250 is, for example, 0.5 mm.

Each of the main vibration part 110m and the sub vibration part 110s is composed of a thin portion in the exterior part 110 where a recess 112 is formed, and a metal plate part 250.

By adding the metal plate portion 250 to each of the main vibration portion 110m and the sub vibration portion 110s, the sound speed of the transverse waves of each of the main vibration portion 110m and the sub vibration portion 110s increases. On the other hand, the thickness of the main vibration portion 110m is thin. In response to this, the thickness of the piezoelectric body 131 needs to be adjusted. When the thickness of the exterior portion 110 where the recess 112 is formed is 1 mm and the thickness of the metal plate portion 250 made of aluminum is 0.5 mm, it is preferable that the thickness of the piezoelectric body 131 is 1 mm or more and 1.5 mm or less.

Resins such as polypropylene that compose the exterior portion 110 become hard at low temperatures and soft at high temperatures. Therefore, the resonant frequencies of the main vibration portion 110m and the sub vibration portion 110s change depending on the temperature.

In the ultrasonic transducer 200 according to the second embodiment of the present invention, the metal plate portion 250, which has little change in hardness due to temperature, is added to each of the main vibration portion 110m and the sub vibration portion 110s, so that the change in the resonant frequency of each of the main vibration portion 110m and the sub vibration portion 110s due to temperature can be reduced. As a result, the temperature characteristics of the ultrasonic transducer 200 can be stabilized.

In addition, in the ultrasonic transducer 200 according to the second embodiment of the present invention, the thickness of the exterior parts 110 constituting each of the main vibration part 110m and the sub vibration part 110s is reduced, thereby reducing the change in the resonant frequency of each of the main vibration part 110m and the sub vibration part 110s due to temperature. This also stabilizes the temperature characteristics of the ultrasonic transducer 200.

Figure 28 is a longitudinal sectional view showing the periphery of an ultrasonic vibrator of an ultrasonic transducer according to a first modified example of embodiment 2 of the present invention. As shown in Figure 28, in the ultrasonic transducer according to the first modified example of embodiment 2 of the present invention, the internal space formed by the cylindrical body 120 and the metal plate part 250 is filled with a damping material 260 such as silicone. This makes it possible to suppress the emission of unnecessary ultrasonic waves and the occurrence of reverberation on the side opposite the exterior part side. The Young's modulus of the damping material 260 is, for example, 0.1 MPa or more and 100 MPa or less. From the viewpoint of suppressing the emission of unnecessary ultrasonic waves on the side opposite the exterior part side, the Young's modulus of the damping material 260 is preferably 0.1 MPa or more and 0.5 MPa or less, and from the viewpoint of suppressing reverberation, the Young's modulus of the damping material 260 is preferably 10 MPa or more and 50 MPa or less.

Figure 29 is an oblique view showing the cylindrical body and metal plate portion of an ultrasonic transducer according to a second modified example of embodiment 2 of the present invention. As shown in Figure 29, in the ultrasonic transducer according to the second modified example of embodiment 2 of the present invention, the cylindrical body 120 and the metal plate portion 250 are integrally formed. Specifically, the cylindrical body 120 and the metal plate portion 250 are composed of a bottomed cylindrical metal member. In this modified example, vibration leakage from the interface between the cylindrical body 120 and the metal plate portion 250 can be suppressed.

(Embodiment 3)
Hereinafter, an ultrasonic transducer according to a third embodiment of the present invention will be described with reference to the drawings. The ultrasonic transducer according to the third embodiment of the present invention differs from the ultrasonic transducer according to the second embodiment of the present invention in that a slit is formed in the metal plate portion, and therefore the description of the same configuration as the ultrasonic transducer according to the second embodiment of the present invention will not be repeated.

Figure 30 is a longitudinal cross-sectional view showing the configuration of an ultrasonic transducer according to embodiment 3 of the present invention. Figure 31 is an exploded oblique view showing the configuration of an ultrasonic transducer according to embodiment 3 of the present invention. As shown in Figures 30 and 31, an ultrasonic transducer 300 according to embodiment 3 of the present invention comprises an exterior portion 110, a cylindrical body 120, an ultrasonic vibrator 130, a restraint portion 140, and a metal plate portion 350.

In this embodiment, when viewed from the first direction (Z-axis direction), a slit 351 extending along the outer edge of the cylindrical body 120 is formed at a position of the metal plate portion 350 overlapping with the sub-vibration portion 110s. The slit 351 extends in the third direction (Y-axis direction). The slit 351 is formed intermittently in the third direction (Y-axis direction). Specifically, the slit 351 is formed at the center and both ends of the cylindrical body 120 in the third direction (Y-axis direction).

In this embodiment, a slit 352 is formed in the metal plate portion 350, the slit 352 extending in the second direction (X-axis direction) along the outer edge of the cylindrical body 120. The slits 351 and 352 are formed in a substantially rectangular shape when viewed from the first direction (Z-axis direction).

Here, we will explain the results of a simulation analysis using the finite element method on the relationship between the resonant frequencies of the main vibration part 110m and the sub vibration part 110s and the length of the slit 351. Figure 32 is a perspective view showing a metal plate part and a cylindrical body according to a comparative example. Figure 33 is a perspective view showing a metal plate part and a cylindrical body according to a first embodiment. Figure 34 is a perspective view showing a metal plate part and a cylindrical body according to a second embodiment. Figure 35 is a perspective view showing a metal plate part and a cylindrical body according to a third embodiment.

As shown in FIG. 32, the metal plate part 950 according to the comparative example does not have a slit 351. As shown in FIG. 33, the metal plate part 350a according to the first embodiment has a slit 351 with a length of 4 mm formed in the center in the third direction (Y-axis direction). As shown in FIG. 34, the metal plate part 350b according to the second embodiment has a slit 351 with a length of 8 mm formed from the center toward both ends in the third direction (Y-axis direction). As shown in FIG. 35, the metal plate part 350c according to the third embodiment has a slit 351 with a length of 12 mm formed from the center toward both ends in the third direction (Y-axis direction).

Figure 36 is a graph showing the relationship between the resonant frequency of each of the main vibration section and the sub vibration section and the length of the slit. In Figure 36, the vertical axis shows the resonant frequency (kHz) of each of the main vibration section and the sub vibration section, and the horizontal axis shows the length of the slit (mm). The resonant frequency of the main vibration section is shown by a solid line, and the resonant frequency of the sub vibration section is shown by a dotted line.

As shown in Figure 36, the resonant frequency of each of the main vibration part 110m and the sub vibration part 110s decreased as the length of the slit 351 increased. In particular, the resonant frequency of the sub vibration part 110s decreased significantly as the length of the slit 351 increased.

As can be seen from the simulation analysis results, by forming a slit 351 extending along the outer edge of the cylindrical body 120 at a position where the metal plate portion 350 overlaps with the sub-vibration portion 110s when viewed from the first direction (Z-axis direction), the resonance frequency of the sub-vibration portion 110s can be lowered. Therefore, by forming a slit 351 of an appropriate length while reducing the gap between the cylindrical body 120 and the restraint portion 140 in the second direction (X-axis direction), the ultrasonic transducer 300 can be miniaturized while maintaining the resonance frequency of the sub-vibration portion 110s. By reducing the gap between the cylindrical body 120 and the restraint portion 140 in the second direction (X-axis direction), vibration leakage can be reduced.

Figure 37 is an oblique view showing the cylindrical body and metal plate portion of an ultrasonic transducer according to a modified example of embodiment 3 of the present invention. As shown in Figure 37, in an ultrasonic transducer according to a modified example of embodiment 3 of the present invention, the cylindrical body 120 and the metal plate portion 350 are integrally formed. Specifically, the cylindrical body 120 and the metal plate portion 350 are composed of a bottomed cylindrical metal member. In this modified example, vibration leakage from the interface between the cylindrical body 120 and the metal plate portion 350 can be suppressed.

In the above description of the embodiments, combinable configurations may be combined with each other.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

100, 100a, 200, 300 Ultrasonic transducer, 110 Exterior part, 110m Main vibration part, 110s Sub vibration part, 111 Inner surface, 112 Recess, 120, 120a Cylinder, 130, 130a, 130b, 130c Ultrasonic vibrator, 131 Piezoelectric body, 132 First electrode, 133 Second electrode, 134 Intermediate electrode, 135 Vibration plate, 140, 140a, 140b, 140c, 140d, 140e, 140f Restraint part, 150 Processing circuit, 250, 350, 350a, 350b, 350c, 950 Metal plate part, 260 Damping material, 351, 352 Slits.

Claims (10)

an exterior portion having an inner surface;
A cylinder attached to the inner surface;
an ultrasonic transducer attached to the cylindrical body and facing the inner surface with a gap therebetween;
a restraining portion attached to the inner surface and sandwiching the cylindrical body with a gap therebetween;
a main vibration section, which is a portion of the exterior section located inside the cylindrical body when viewed from a first direction perpendicular to the inner surface, resonates in an opposite phase to the ultrasonic transducer,
a sub-vibration portion that is a portion of the exterior portion that is located outside the cylindrical body and inside the restraint portion in a second direction perpendicular to the first direction when viewed from the first direction, resonates and vibrates in a range of an absolute value of a phase difference with respect to a resonant vibration of the main vibration portion that is equal to or greater than 120° and equal to or less than 180° ;
the cylindrical body has a longitudinal direction along a third direction perpendicular to each of the first direction and the second direction, and a transverse direction along the second direction,
The sub vibration section is an ultrasonic transducer arranged on both sides of the main vibration section in the short side direction of the cylindrical body . The ultrasonic transducer of claim 1, wherein the restraint portion has an annular shape. The ultrasonic transducer according to claim 1 , wherein the ultrasonic vibrator is a piezoelectric element including a piezoelectric body. The ultrasonic transducer according to claim 1 , wherein each of the cylindrical body and the restraining portion is attached to the inner surface via a metal plate portion extending along the inner surface. The ultrasonic transducer according to claim 4, wherein a slit is formed extending along the outer edge of the cylindrical body at a position where the metal plate portion overlaps with the sub-vibration portion when viewed from the first direction. A recess is formed on the inner surface,
The ultrasonic transducer according to claim 4 , wherein the metal plate portion is attached within the recess. a resonance frequency of the sub vibration part is higher than a resonance frequency of the main vibration part,
2. The ultrasonic transducer according to claim 1 , wherein a difference between a resonant frequency of the sub vibration section and a resonant frequency of the main vibration section is 7% or more and 20% or less of the resonant frequency of the main vibration section. If the sound velocity of the shear wave of the exterior part is Cb, the sound velocity of the shear wave of the piezoelectric body is Cp, the thickness dimension of the main vibration part is Tb, and the thickness dimension of the piezoelectric body is Tp, then
4. The ultrasonic transducer according to claim 3, which satisfies the relationship: 0.7CpTp/Cb≦Tb≦1.3CpTp/Cb. An ultrasonic transducer according to any one of claims 1 to 8, wherein the resonant amplitude of the sub-vibration part is smaller than the resonant amplitude of the main vibration part. The ultrasonic transducer according to claim 9, wherein the resonant amplitude of the sub-vibration part is 18% or more and 40% or less of the resonant amplitude of the main vibration part.

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