JP2012134595A - Oscillation device and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric oscillation device in which generation of splitting oscillation can be suppressed.SOLUTION: In the oscillation device, i.e. an electroacoustic transducer 100, a peripheral part of a piezoelectric element 123 is reinforced by a reinforcing member 130. In the splitting oscillation mode, a peripheral part and a central part of an elastic member 122 are deformed in the phases different from each other. Since the peripheral part of the piezoelectric element 123 that becomes a node of the splitting oscillation is reinforced, the rigidity can be enhanced locally. Consequently, the mode of the splitting oscillation can be deformed, and thereby the sound pressure level can be increased.

Description

  The present invention relates to an oscillation device using a piezoelectric vibrator, and an electronic apparatus using the oscillation device.

  In mobile phones, the development of thin and stylish mobile phones that have commercial value such as music playback and hands-free acoustic functions is becoming active. Among these, electroacoustic transducers are highly demanded for being small and thin and having high sound quality. As means for solving these demands, a piezoelectric electroacoustic transducer using a piezoelectric element as a drive source has been developed. Since the piezoelectric electroacoustic transducer utilizes the self-expanding motion of the piezoelectric element, the piezoelectric electroacoustic transducer is thinner than the electrodynamic electroacoustic transducer composed of a magnetic circuit.

  Currently, there are various proposals as the above-mentioned electroacoustic transducer (Patent Document 1).

JP 2008-151666 A

  However, since the piezoelectric electroacoustic transducer has a high mechanical quality factor Q, energy concentrates in the vicinity of the resonance frequency, and the sound pressure level frequency characteristic is uneven. Furthermore, the piezoelectric element has a problem that split vibration occurs in a higher-order vibration mode after the fundamental resonance frequency.

  The divided vibration is a higher-order vibration mode and grows by superimposing the fundamental vibration mode. Here, there is a problem that the vibration modes of the normal phase and the reverse phase overlap locally, and interference (cancelling) occurs when sound waves are emitted, so that the sound pressure level is significantly reduced. For this reason, in an electroacoustic transducer using a piezoelectric element, an epoch-making technique capable of suppressing the occurrence of divided vibrations is required.

  The present invention has been made in view of the above-described problems, and provides a piezoelectric oscillation device capable of suppressing the occurrence of divided vibrations, and an electronic apparatus using such an oscillation device. .

  The oscillation device of the present invention includes a frame-shaped support frame, a flat vibration member supported on the support frame at the outer peripheral portion, an elastic member disposed on at least one surface of the vibration member and having higher rigidity than the vibration member, The piezoelectric element is disposed on at least one surface of the elastic member and expands and contracts when an electric field is applied, and a reinforcing member that reinforces the peripheral edge of the piezoelectric element.

  A first electronic device according to the present invention includes the oscillation device according to the present invention and an oscillation drive unit that causes the oscillation device to output an ultrasonic wave demodulated into an audible sound wave.

  A second electronic device according to the present invention includes an oscillation device according to the present invention, an oscillation drive unit that outputs an ultrasonic wave to the oscillation device, and an ultrasonic detection that detects an ultrasonic wave oscillated from the oscillation device and reflected from a measurement object. And a distance measuring unit that calculates a distance from the detected ultrasonic wave to the measurement object.

  The various components of the present invention do not necessarily have to be independent of each other. A plurality of components are formed as a single member, and a single component is formed of a plurality of members. It may be that a certain component is a part of another component, a part of a certain component overlaps with a part of another component, or the like.

  In the oscillation device of the present invention, the peripheral portion of the piezoelectric element is reinforced by the reinforcing member. In the split vibration mode, the peripheral edge portion and the central portion of the elastic member are deformed at different phases. For this reason, since the peripheral part of the piezoelectric element that becomes a node of the divided vibration is reinforced, the rigidity thereof can be locally strengthened. Therefore, occurrence of divided vibration can be suppressed.

It is a typical longitudinal section front view showing the structure of the electroacoustic transducer which is an oscillation device of an embodiment of the invention. It is a typical top view which shows the structure of an electroacoustic transducer. It is a typical top view which shows the structure of the electroacoustic transducer which is an oscillation apparatus of one modification.

  An electroacoustic transducer 100 that is an oscillation device of the present embodiment will be described below with reference to FIGS. 1 and 2. As shown in FIG. 1, the electroacoustic transducer 100 according to the present embodiment includes a frame-shaped support frame 110, a flat vibration film 121 supported on the support frame 110 at the outer peripheral portion, and vibration that is a vibration member. An elastic member 122 that is disposed on at least one surface of the film 121 and has higher rigidity than the vibration film 121, a piezoelectric element 123 that is disposed on at least one surface of the elastic member 122 and expands and contracts when an electric field is applied, and the periphery of the piezoelectric element 123 And a reinforcing member 130 for reinforcing the part.

  As shown in FIGS. 1 and 2, the reinforcing member 130 is composed of a plurality of shaft-shaped members 131 that are at least more rigid than the piezoelectric elements 123 and are embedded in the periphery of the piezoelectric elements 123. The shaft-shaped members 131 are metal rods. Consists of. The shaft-like member 131 can be used as long as it is a highly rigid metal rod.

  Moreover, in the electroacoustic transducer 100 of this Embodiment, as shown in FIG. 1, the shaft-shaped member 131 is embed | buried from the piezoelectric element 123 to the elastic member 122. As shown in FIG. In the electroacoustic transducer 100 according to the present embodiment, as shown in FIG. 2, the piezoelectric element 123, the elastic member 122, and the vibration film 121 are formed in a concentric planar shape, and the shaft-shaped member 131 is The planar shape is arranged at substantially equal intervals around the periphery of the piezoelectric element 123 having a circular shape.

  More specifically, an electrode layer 124 is also formed on both surfaces of the piezoelectric element 123, and the piezoelectric layer 120 is formed by the electrode layer 124, the piezoelectric element 123, the elastic member 122, and the vibration film 121. A driver circuit 140 that is an oscillation drive unit is connected to such a piezoelectric vibrator 120. When the driver circuit 140 drives the piezoelectric vibrator 120, the piezoelectric element 123 oscillates at an ultrasonic band frequency of 20 kHz or more.

  The shaft member 131 made of a metal rod also penetrates the electrode layer 124. For example, the through hole of the electrode layer 124 is formed with a larger diameter than the shaft member 131, and an insulator is formed in the gap. Thus, the shaft member 131 and the electrode layer 124 are insulated from each other. However, the shaft-shaped member 131 can be used as a connection terminal of the electrode layer 124 by partially connecting the shaft-shaped member 131 to the electrode layer 124.

  In the electroacoustic transducer 100 of the present embodiment, for example, the longitudinal elastic coefficient of the resin vibration film 121 is 1/50 or less of the longitudinal elastic coefficient of the metal elastic member 122, and the elastic member 122 vibrates. The thickness ratio of the film 121 is approximately 3: 1.

The piezoelectric element 123 is not particularly limited as long as it is a material having a piezoelectric effect. However, a material having high electromechanical conversion efficiency, such as lead zirconate titanate (PZT) or barium titanate (BaTiO 3). Materials such as ₃ ) can be used. Moreover, although thickness is not specifically limited, It is preferable that they are 10 micrometers-1 mm.

  When a thin film having a thickness of less than 10 μm is used as a ceramic material which is a brittle material, chipping or breakage occurs due to weak mechanical strength during handling, making handling difficult. In addition, when a ceramic having a thickness exceeding 1 mm is used, the conversion efficiency for converting electrical energy into mechanical energy is remarkably lowered, and sufficient performance as the electroacoustic transducer 100 cannot be obtained. In general, in a piezoelectric ceramic that generates an electrostrictive effect by inputting an electric signal, the conversion efficiency depends on the electric field strength. Since the electric field strength is expressed by the thickness / input voltage with respect to the polarization direction, an increase in thickness inevitably causes a decrease in conversion efficiency.

  In the piezoelectric element 123 of the present invention, an electrode layer 124 is formed on the main surface in order to generate an electric field. Although the material is not particularly limited, for example, silver or silver / palladium can be used. Silver is used as a general-purpose electrode material with low resistance, which has advantages in manufacturing process and cost. Silver / palladium is a low-resistance material with excellent oxidation resistance, so it has advantages from the viewpoint of reliability. is there.

  Moreover, the thickness of the electrode layer 124 is not particularly limited, but the thickness is preferably 1 to 100 μm. If the thickness is less than 1 μm, since the film thickness is thin, it cannot be uniformly formed, and conversion efficiency may be reduced. In addition, when the thickness of the electrode layer 124 exceeds 100 μm, there is no particular problem in manufacturing, but the electrode layer 124 becomes a constraining surface with respect to the ceramic material of the piezoelectric element 123 and the energy conversion efficiency is lowered. There is a point.

  The elastic member 122 is not particularly limited as long as it is a material having a high elastic modulus with respect to a ceramic that is a brittle material such as metal or resin, but a general-purpose material such as phosphor bronze or stainless steel is used from the viewpoint of workability and cost. The Moreover, about thickness, it is preferable that it is 5-1000 micrometers. When the thickness is less than 5 μm, there is a problem that mechanical strength is weak, the function as a restraining member is impaired, and the mechanical vibration characteristics of the vibrators vary between manufacturing lots due to a decrease in processing accuracy.

  The vibration film 121 is not particularly limited as long as the longitudinal elastic modulus is a polymer material of 100 GPa or less, but from the viewpoint of versatility, use of polyethylene terephthalate, polyethylene, urethane, silicone rubber, natural rubber, synthetic rubber, or the like Is possible.

  Further, when the thickness exceeds 1000 μm, there is a problem in that the restraint on the piezoelectric element 123 due to the increase in rigidity is strengthened and the vibration displacement amount is attenuated. In addition, the elastic member 122 of the present embodiment preferably has a longitudinal elastic modulus, which is an index indicating the rigidity of the material, of 1 to 500 GPa. As described above, when the rigidity of the elastic member 122 is excessively low or excessively high, there is a problem that characteristics and reliability are impaired as a mechanical vibrator.

  As a mechanism for generating sound waves, an expansion and contraction motion generated by applying an electric field to the piezoelectric element 123 is used. Moreover, the frequency of an ultrasonic wave is limited to 20 kHz or more. Since the piezoelectric element 123 has a high mechanical quality factor Q, energy is concentrated in the vicinity of the basic resonance, so that a high sound pressure level can be obtained at the basic resonance frequency, but in other frequency bands, the sound pressure is attenuated. End up.

  Since the electroacoustic transducer 100 of this embodiment oscillates an ultrasonic wave limited to a specific frequency, it is rather advantageous in that the mechanical quality factor Q of the piezoelectric element 123 is high. Further, since the basic resonance frequency of the piezoelectric vibrator is affected by the shape of the piezoelectric element 123, when the resonance frequency is adjusted to a high frequency band, for example, an ultrasonic band, it is advantageous for miniaturization.

  The electroacoustic transducer 100 according to the present embodiment oscillates FM (Frequency Modulation) or AM (Amplitude Modulation) -modulated ultrasonic waves, and uses a nonlinear state (sparse / dense state) of air to generate a modulated wave. Sound reproduction is performed based on the principle of a so-called parametric speaker that demodulates and reproduces audible sound. In the electroacoustic transducer 100 of the present embodiment, the piezoelectric element 123 has a configuration limited to oscillation in a high frequency band, and thus can be miniaturized.

  In the above-described configuration, in the piezoelectric electroacoustic transducer 100 of the present configuration, a plurality of shaft-like members 131 are embedded in the peripheral portion of the piezoelectric element 123 serving as a split vibration node, and thus the plurality of shafts It is possible to locally enhance the rigidity by the reinforcing member 130 made of the member 131 and to change the form of the divided vibration. That is, by suppressing the divided vibration, it is possible to suppress the interference of sound waves and increase the sound pressure level.

  In particular, since the shaft-shaped member 131 penetrates the piezoelectric element 123 and the elastic member 122, there is an advantage that the outer shape is not changed. Further, since the elastic member 122 made of a metal plate and the shaft-like member 131 made of a metal rod can be joined, the joining strength between the piezoelectric element 123 and the elastic member 122 can also be increased. Moreover, by performing the insulation treatment locally, it can be used as an electrical connection terminal, and the manufacturability is improved.

  Further, the operation principle of the piezoelectric vibrator 120 of the electroacoustic transducer 100 of the present embodiment utilizes the expansion and contraction motion that occurs when an electric field is applied to the piezoelectric element 123. The oscillation frequency is preferably an ultrasonic band of 20 kHz or more. By setting the oscillation frequency to the ultrasonic band, the piezoelectric vibrator 120 can be miniaturized and the directivity can be controlled using the straightness of the ultrasonic wave. As an application example thereof, the present invention can also be used for a parametric speaker in which an audio signal is conveyed to an ultrasonic wave and demodulated in the air.

  Furthermore, the electroacoustic transducer 100 according to the present embodiment is composed of a resin-made vibration film 121 having a flexible end portion where stress is concentrated during vibration. That is, since the impact energy at the time of dropping can be absorbed by the resin vibration film 121, the dropping strength can be improved.

  Moreover, in the electroacoustic transducer 100 of this structure, the edge part between the support frame 110 and the elastic member 122 is comprised with resin of the vibration film 121. FIG. In other words, the flexible resin vibration film 121 located at the end of vibration expands the movable range of the end, the vibration state becomes closer to a piston shape, and the volume exclusion amount during vibration increases. To do. Since the sound pressure level depends on the volume exclusion amount to the air at the time of vibration, the electroacoustic transducer 100 having this configuration can realize superior characteristics.

  The present invention is not limited to the present embodiment, and various modifications are allowed without departing from the scope of the present invention. For example, in the above embodiment, the piezoelectric element 123, the elastic member 122, and the vibration film 121 are formed in a similar shape and illustrated as being concentrically formed.

  However, like the electroacoustic transducer 200 illustrated as an oscillation device in FIG. 3, the piezoelectric element 123, the elastic member 122, the vibration film 121, and the support frame 110 are formed in a polygonal square similar shape, A shaft-like member 131 that is a reinforcing member 130 may be embedded in the corner portion.

  Moreover, in the said form, the electroacoustic transducer 100 of the monomorph structure in which the piezoelectric vibrator 120 was formed in the single side | surface of the vibration film 121 was illustrated. However, a bimorph structure in which the piezoelectric vibrator 120 is formed on both surfaces of the vibration film 121 can also be implemented (not shown). In that case, by making the diameters of the pair of elastic members different, it is possible to make the structures of the piezoelectric vibrators attached to both surfaces of the vibration film one by one different. In addition, the plate thickness of the pair of elastic members may be different with the same diameter, and the diameter and plate thickness of the piezoelectric element may be different (none is shown).

  Further, in the above embodiment, an electronic apparatus in which the electroacoustic transducer 100 is connected to the driver circuit 140 that is an oscillation driving unit is assumed. However, such an electroacoustic transducer 100, an oscillation drive unit that outputs an ultrasonic wave to the electroacoustic transducer 100, and an ultrasonic wave that is detected from the ultrasonic wave that is oscillated from the electroacoustic transducer 100 and reflected by the measurement object. An electronic device (not shown) such as a sonar that includes a detection unit and a distance measurement unit that calculates a distance from the detected ultrasonic wave to the measurement target can also be implemented.

  Needless to say, the above-described embodiment and a plurality of modifications can be combined within a range in which the contents do not conflict with each other. Further, in the above-described embodiments and modifications, the structure of each part has been specifically described, but the structure and the like can be changed in various ways within a range that satisfies the present invention.

DESCRIPTION OF SYMBOLS 100 Electroacoustic transducer 110 Support frame 120 Piezoelectric vibrator 121 Vibration film 122 Elastic member 123 Piezoelectric element 124 Electrode layer 130 Reinforcing member 131 Axial member 140 Driver circuit 200 Electroacoustic transducer

Claims (9)

A frame-shaped support frame;
A flat vibration member supported at the outer periphery of the support frame;
An elastic member disposed on at least one surface of the vibration member and having a higher rigidity than the vibration member;
A piezoelectric element that is disposed on at least one surface of the elastic member and that expands and contracts by application of an electric field;
A reinforcing member for reinforcing the peripheral edge of the piezoelectric element;
An oscillation device having   2. The oscillation device according to claim 1, wherein the reinforcing member includes a plurality of shaft-like members that are at least more rigid than the piezoelectric element and are embedded in a peripheral portion of the piezoelectric element.   The oscillation device according to claim 2, wherein the shaft-shaped member is made of a metal rod.   The oscillation device according to claim 2, wherein the shaft-like member is embedded from the piezoelectric element to the elastic member. The piezoelectric element, the elastic member, and the vibration member are formed in a concentric planar shape,
5. The oscillation device according to claim 2, wherein the shaft-like members are arranged at substantially equal intervals on a peripheral portion of the piezoelectric element having a circular planar shape. The piezoelectric element, the elastic member, and the vibration member are formed in a polygonal similar planar shape,
The oscillation device according to claim 2, wherein the shaft-shaped member is disposed at a plurality of corners of the piezoelectric element.   The oscillation device according to any one of claims 1 to 6, wherein the piezoelectric element oscillates at a frequency in an ultrasonic band of 20 kHz or more. The oscillation device according to any one of claims 1 to 7,
An oscillation driver for outputting an ultrasonic wave demodulated into an audible sound wave to the oscillation device;
Electronic equipment having The oscillation device according to any one of claims 1 to 7,
An oscillation driver that outputs ultrasonic waves to the oscillation device;
An ultrasonic detector for detecting the ultrasonic wave oscillated from the oscillation device and reflected by the measurement object;
A distance measuring unit for calculating a distance from the detected ultrasonic wave to the measurement object;
Electronic equipment having

Images