JP4997545B2 - Ultrasonic element - Google Patents

Description

  The present invention relates to an ultrasonic element used for detecting an object and measuring a distance by generating an ultrasonic wave.

For example, the conventional ultrasonic element used for an ultrasonic sensor etc. is disclosed by the following patent document 1, for example.
In an ultrasonic element, in order to enable high-precision measurement and remote measurement, it is desired to increase the reproduction sound pressure.

FIG. 5 is a cross-sectional view showing a structure of a general ultrasonic element. In the figure, the piezoelectric ceramic 1 is a piezoelectric material that expands and contracts when an electric signal is supplied from a terminal 5.
The metal plate 2 is coupled to the piezoelectric ceramic 1 and is a member that bends and vibrates as the piezoelectric ceramic 1 expands and contracts.
The resonator 3 is coupled to the central portion of the metal plate 2 and is a member that vibrates with bending vibration of the metal plate 2.
The holding material 4 is a member that holds the piezoelectric ceramic 1.
The terminal 5 is a member that takes in an electric signal from the outside and supplies the electric signal to the piezoelectric ceramic 1.
The base 6 is a member that fixes the holding material 4 and the terminal 5. 7 is a case.

Next, the operation will be described.
When an electric signal is supplied from the terminal 5, the piezoelectric ceramic 1 acquires a driving force by a piezoelectric phenomenon and vibrates and expands.
When the piezoelectric ceramic 1 starts stretching vibration, the metal plate 2 bends and vibrates with the stretching vibration of the piezoelectric ceramic 1, and the resonator 3 vibrates with the bending vibration of the metal plate 2 to generate ultrasonic waves.

The vibration system of the ultrasonic element composed of the piezoelectric ceramic 1, the metal plate 2, and the resonator 3 exhibits several resonance phenomena, and has a level on the sound pressure frequency characteristic of the ultrasonic element at several frequencies at which resonance occurs. A high peak is formed.
The ultrasonic element is driven at a certain peak frequency at which the sound pressure level is high, and operations such as object detection and distance measurement are performed at that frequency.

FIG. 6 is an explanatory diagram showing typical sound pressure frequency characteristics of the ultrasonic element.
Two peaks of the sound pressure due to the resonance described above are usually conspicuous. If the lower first peak frequency is f ₁ and the second second peak frequency is f ₂ , the peak frequencies f ₁ , f ₂ Is present in the ultrasonic band outside the human audible band, and generally uses a peak frequency f ₁ having a high sound pressure.
When the sound pressure characteristics and the vibration characteristics are analyzed in order to investigate the operation mechanism of the two sound pressure peaks, the two sound pressure peaks exhibit approximately the same resonance vibration mode as the resonator 3 undergoes axisymmetric vibration.
That is, in the vibration state of the two sound pressure peaks, the vibration displacement of the resonator 3 is relatively large compared to the vibration displacement of the metal plate 2 and the piezoelectric ceramic 1. For example, the amplitude of the outer peripheral portion of the resonator 3 is It becomes twice or more the outer periphery of the plate 2.

FIG. 7 is an explanatory diagram showing the vibration state of the vibration system, and particularly shows the vibration of the resonator 3 in an enlarged manner.
In contrast to the stationary state (a) of the resonator 3, (b) is a vibration mode representing a plus state at the maximum amplitude of the resonator 3, and (c) represents a minus state at the maximum amplitude of the resonator 3. It is a vibration mode.
As is clear from FIG. 7, the resonator 3 coupled to the central portion of the metal plate 2 having a relatively small displacement causes an axially symmetric vibration in which the amplitude increases toward the periphery, thereby causing a bending vibration.
At this time, the periphery of the resonator 3 is fluttering, and this vibration state is called “flap vibration”.
In the above vibration state, two peaks also appear in the frequency response characteristics, and the vibration mode at that time almost coincides with the actually measured vibration mode, and exhibits the sound pressure characteristic in which the two peaks are dominant.

Next, when the vibration state of the metal plate 2 (+ piezoelectric ceramic 1) is considered in detail, a phenomenon as shown in FIG. 8 occurs.
8A exaggerates the displacement in the vibration mode of the first peak, and FIGS. 8B and 8C show the positive state and the negative state of the vibration mode of the same resonator 3 as in FIG. State.
Moreover, (d) and (e) of FIG. 8 (A) show the vibration state of the metal plate 2 corresponding when the resonator 3 is in the plus state (b) and the minus state (c).
However, the metal plate 2 and the piezoelectric ceramic 1 in FIG. 8 (A) are represented by a single solid line and are displayed ignoring the thickness.

The vibration state of the metal plate 2 is close to the primary axisymmetric vibration mode of the disc. That is, the central portion of the metal plate 2 vibrates at the maximum displacement, and one vibration node exists at a position about 70% of the diameter.
In FIG. 8A, the holding member 4 is disposed at the node position in the first-order axisymmetric vibration mode.
At the first peak, as shown in FIG. 8A, a flap vibration in which the outer peripheral vibration of the resonator 3 and the outer peripheral vibration of the metal plate 2 are in opposite phases occurs.
In such a vibration state, the sound radiated by the vibration of the metal plate 2 and the resonator 3 is in reverse phase, and the sound wave flows from dense to sparse due to its nature. The reverse phase action at the outer peripheral edge causes a sound wraparound phenomenon, and the sound pressure level on the sound axis at the peak frequency f ₁ decreases (see FIG. 6).

On the other hand, FIG. 8B enlarges and exaggerates the amplitude in the vibration mode of the second peak, and FIGS. 8B and 8C show the positive state of the vibration mode of the resonator 3 same as FIG. It is a minus state.
Moreover, (d) and (e) of FIG. 8 (B) show the vibration state of the metal plate 2 corresponding when the resonator 3 is in the plus state (b) and the minus state (c).
The vibration state of the metal plate 4 is a vibration that substantially translates in the vertical direction of the drawing sheet.
At the second peak, as shown in FIG. 8B, the outer periphery vibration of the resonator 3 and the outer periphery vibration of the metal plate 2 vibrate in the same direction, and a flap vibration in which the displacement is in phase occurs.
In such a vibration state, the sound radiated by the vibration of the metal plate 2 and the resonator 3 is in phase, so that the sound is not weakened as in the first peak.

JP-A-8-322100 (paragraph number [0019], FIG. 1)

  Since the conventional ultrasonic element is configured as described above, at the first peak, a flap vibration is generated in which the vibration of the outer peripheral portion of the metal plate 2 vibrates in a phase opposite to that of the outer peripheral portion of the resonator 3. Thereby, since the sound radiated from the outer peripheral portion of the metal plate 2 cancels the sound radiated from the resonator 3, there is a problem that the peak sound pressure level is lowered.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an ultrasonic element that can prevent a decrease in peak sound pressure level and obtain acoustic characteristics of a high sound pressure level. To do.

An ultrasonic element according to the present invention includes a metal plate that bends and vibrates with the expansion and contraction vibration of the piezoelectric material, a resonator that vibrates with the bending vibration of the metal plate, and a holding material that holds an outer peripheral end of the metal plate. The guide is provided on the outer periphery of the holding material while allowing the holding material to expand and contract in the vibration direction of the metal plate and restricting the movement of the holding material in the direction perpendicular to the vibration direction of the metal plate .

According to the present invention, the guide is provided on the outer peripheral portion of the holding material while allowing the holding material to expand and contract with respect to the vibration direction of the metal plate while restricting the movement of the holding material with respect to the direction perpendicular to the vibration direction of the metal plate. Therefore, it is possible to prevent lateral shaking while supporting vertical vibration of the vibration system, to prevent a decrease in peak sound pressure level, and to obtain acoustic characteristics with a high sound pressure level.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram showing a structure that is a premise of an ultrasonic element according to Embodiment 1 of the present invention. In the figure, a piezoelectric ceramic 11 is a piezoelectric material that expands and contracts when an electric signal is supplied from a terminal 15. is there.
The metal plate 12 is coupled to the piezoelectric ceramic 11 and is a member that bends and vibrates as the piezoelectric ceramic 11 expands and contracts.
The resonator 13 is a member that is coupled to the central portion of the metal plate 12 and vibrates with bending vibration of the metal plate 12.
The holding member 14 is a member that holds the outer peripheral end of the metal plate 12.
The terminal 15 is a member that takes in an electric signal from the outside and supplies the electric signal to the piezoelectric ceramic 11.
The base 16 is a member that fixes the holding member 14 and the terminal 15. Reference numeral 17 denotes a case.

Next, the operation will be described.
When an electric signal is supplied from the terminal 15, the piezoelectric ceramic 11 acquires a driving force by a piezoelectric phenomenon and vibrates and expands.
When the piezoelectric ceramic 11 starts stretching vibration, the metal plate 12 bends and vibrates along with the stretching vibration of the piezoelectric ceramic 11, and the resonator 13 vibrates along with the bending vibration of the metal plate 12 to generate ultrasonic waves.

FIG. 4 is an explanatory view showing a concept that is a premise of the ultrasonic element according to the first embodiment of the present invention. In particular, FIG. 4A shows the first peak in the case where the diameter of the holding material 14 is made larger than that of the conventional ultrasonic element (see FIGS. 5 and 8) and the outer peripheral edge of the metal plate 12 is held. It represents the vibration state.
At the first peak, assuming that the holding member 14 holds the outer peripheral edge of the metal plate 12, assuming that it vibrates in the resonance mode as shown in FIG. 8A, as shown in FIG. A vibration state in which the central portion of the vibration system including the plate 12 and the resonator 13 has a maximum amplitude is obtained.
Since the resonator 13 that plays an important role in the sound radiation efficiency is coupled to the central portion of the vibration system (the central portion of the metal plate 12), the amplitude is larger than that in the state of FIG. As a result, the sound pressure at the first peak increases.

The conventional ultrasonic element holding material 4 is made of a hard material, but FIG. 4B shows a holding material 14 in which a soft material is used instead of the holding material 4 (holding). The material 14 is composed of, for example, a urethane foam material, and has a second peak vibration state when using a spring property that expands and contracts in the vibration direction (sound radiation direction) of the metal plate 12. Represents.
However, the holding position of the holding material 14 is assumed to be a position for holding the piezoelectric ceramic 11 as in the case of the holding material 4 in the conventional ultrasonic element (see FIG. 5) for the convenience of the following comparative explanation.

Since the holding material 14 has a spring property that expands and contracts in the vibration direction of the metal plate 12, the degree of expansion and contraction of the holding material 14 is higher than that in the state of FIG. 8B in which the vibration is limited by the holding material 4. The displacement of the whole vibration system that vibrates up and down in the figure increases. As a result, the sound pressure at the second peak also increases.
In this way, considering that the translational movement of the vibration system is increased by the expansion and contraction of the holding material 14 in the vibration direction of the metal plate 12, the holding material 14 of the ultrasonic element that holds the outer peripheral end of the metal plate 12. In the second peak, the same vibration as in FIG. 4B occurs, but also in the first peak, the holding material 14 softly holds the metal plate 12, so that the vibration due to the resonance of the resonator 13 increases and decreases. A translational motion will be added.

FIG. 2 is an explanatory view showing a vibration state in which a translational motion is applied.
As shown in FIG. 2, the translational motion is added to the original resonance mode occurring at the first peak, so that the vibration system has a large displacement even at the first peak. As a result, the sound pressure level is also increased and the acoustic characteristics are improved.

Also, since the hold member 14 is configured to hold the outer peripheral edge of the metal plate 12 to the bending vibration along with the stretching vibration of the piezoelectric ceramic 11, thereby preventing a decrease in peak sound pressure level, a high sound pressure level The effect which can acquire an acoustic characteristic is produced.
Also, since the hold member 14 has a spring property that expands and contracts in the vibration direction of the metal plate 12, and vibration system overall displacement is increased, there is also an effect that the sound pressure at the second peak is increased.

In the above description, the material of the holding material 14 is a urethane foam material. However, the material of the holding material 14 is not limited to the urethane foam material, and any material can be used as long as sufficient expansion and contraction can be expected. For example, the holding member 14 may be configured by a coiled spring or the like.
Further, the cross-sectional shape of the holding member 14 is not limited to a ring shape or a cylindrical shape, and may be a cross-sectional area that changes in the vertical direction or a polygonal cross section such as a square.

FIG. 3 is a block diagram showing the structure of the ultrasonic element according to the first embodiment of the present invention. In the figure, the same reference numerals as those in FIG.
The guide 18 is provided on the outer peripheral portion of the holding material 14 and allows the holding material 14 to expand and contract with respect to the vibration direction of the metal plate 12, while restricting the movement of the holding material 14 with respect to the direction perpendicular to the vibration direction of the metal plate 12. It is.

In the first embodiment, it is assumed that the holding material 14 is made of, for example, a ring-shaped urethane foam material. However, as shown in FIG. 3, for example, the outer peripheral end of the metal plate 12 is formed into a thin cylindrical rod shape. The support material 14 may be configured to be supported at multiple points (four points in the example of FIG. 3).
In the example of FIG. 3, the guide 18 restricts the movement of the outer periphery of the holding member 14, and functions to prevent lateral shaking while supporting vertical vibration of the vibration system.

As is apparent from the above, according to the first embodiment, the holding material 14 is allowed to expand and contract with respect to the vibration direction of the metal plate 12, while the holding material 14 is moved relative to the direction perpendicular to the vibration direction of the metal plate 12. Since the limiting guide 18 is provided on the outer peripheral portion of the holding member 14, the lateral vibration is prevented while supporting the vertical vibration of the vibration system, and the sound pressure at the second peak is reduced without causing deterioration of the acoustic characteristics. There is an effect that can be enhanced.

It is a block diagram which shows the structure used as the premise of the ultrasonic element by Embodiment 1 of this invention. It is explanatory drawing which shows the vibration state to which the motion translated up and down is added. It is a block diagram which shows the structure of the ultrasonic element by Embodiment 1 of this invention. It is an explanatory view showing a person thinking of the ultrasonic device according to the first embodiment of the invention. It is sectional drawing which shows the structure of a general ultrasonic element. It is explanatory drawing which shows the typical sound pressure frequency characteristic of an ultrasonic element. It is explanatory drawing which shows the vibration state of a vibration system. It is explanatory drawing which shows the displacement in the vibration mode of a 1st and 2nd peak.

  1 Piezoelectric Ceramic, 2 Metal Plate, 3 Resonator, 4 Holding Material, 5 Terminal, 6 Base, 7 Case, 11 Piezoelectric Ceramic (Piezoelectric Material), 12 Metal Plate, 13 Resonator, 14 Holding Material, 15 Terminal, 16 Base , 17 cases, 18 guides.

Claims (1)

Piezoelectric material that expands and contracts when a voltage is applied, a metal plate that is coupled with the piezoelectric material, flexibly vibrates with the expansion and contraction vibration of the piezoelectric material, and a central portion of the metal plate, In an ultrasonic element comprising a resonator that vibrates with bending vibration and a holding material that holds an outer peripheral end of the metal plate, and the holding material has a spring property that expands and contracts in the vibration direction of the metal plate. A guide is provided on the outer peripheral portion of the holding material while allowing the holding material to expand and contract with respect to the vibration direction of the metal plate and restricting movement of the holding material with respect to a direction perpendicular to the vibration direction of the metal plate. ultrasonic element.

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