JPS5924598B2 - piezoelectric bimorph vibrator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric bimorph vibrator used in a sounding body, and more particularly to a cantilever piezoelectric bimorph vibrator for a speaker in which the shape of the vibrator is specified and reproduction frequency characteristics are improved.

A piezoelectric speaker whose driving source is a piezoelectric bimorph vibrator is
Due to their thinness and low power consumption, various attempts have been made to put them into practical use as a substitute for conventional dynamic speakers and for reproducing synthesized voices and melodies.

However, since piezoelectric speakers utilize the mechanical resonance of a piezoelectric vibrator, the lower limit frequency for sound reproduction is at most 1000H.
It is only about z, and there is a need for even lower frequencies.

In particular, for audio reproduction, a reproduction capability of up to about 3000 Hz is required to improve the clarity of the audio, but this has been considered extremely difficult to achieve with conventional piezoelectric speakers.

Therefore, by specifying the shape of the piezoelectric vibrator, this invention aims to create a piezoelectric bimorph vibrator that, when assembled into a piezoelectric speaker, can significantly lower the lower limit of low frequency reproduction and flatten its frequency characteristics. do.

In other words, the present invention provides a piezoelectric bimorph vibrator with a cantilevered configuration in which one end of a vibrator is fixed, for example, a piezoelectric plate of a similar shape is attached to a rectangular metal plate, and the other end is used as a vibrating tip. The basic idea is to partially provide a protrusion on the vibrating tip that is longer in the length direction than the connection point with the diaphragm, and preferably the vibrating tip side is wider than the fixed side. In addition, the coupling point with the diaphragm is placed on the auxiliary vibration part that protrudes discontinuously in the length direction on the vibration tip side, and the oscillator This is a vibrator with a long protrusion formed in the length direction.

First, in a cantilevered piezoelectric bimorph resonator, the length of the resonator is 1
The fundamental resonant frequency fo and its higher-order resonant frequency fn determined by o and its thickness are obtained, and if the thickness of the vibrator is constant, the lower limit frequency of reproduction is determined by the effective length l of the vibrator, that is, the relationship between the vibrator and the diaphragm. It is uniquely determined by the connection point distance, and it is difficult to lower the frequency below that distance.

This is true regardless of the shape of the vibrator.

Here, as a means of simply lowering the lowest resonant frequency fo in such a cantilevered vibrator, it is self-evident that the total length of the vibrator is lengthened and a connection point with the diaphragm is provided inside the vibrator, or It is possible to add additional mass, but in either case, only a reduction in fo is obtained, and the reproduction output in the low range is too low to be of practical use.

Therefore, in this invention, first, by making the width of the vibrating tip side of the cantilever vibrator wider than the fixed side, a resonant frequency f2 in the width direction is set between the fundamental resonant frequency fo and its higher-order resonant frequency f1. This is to flatten the reproduction frequency characteristics.

That is, as shown in FIG. 1, a semicircular piezoelectric plate 2 is attached to a metal plate 1 having a rectangular shape protruding from a semicircular circumferential part, and the rectangular part is fixed to, for example, a diaphragm frame 3. The other end, which is wider than this, is the vibrating tip.

Furthermore, the coupling point between the diaphragm 4 and the vibrator is an auxiliary vibrating part 5 that is provided protruding from the straight line portion on the vibrating tip side.

In other words, the width dimension of the vibrator is the length l toward the vibrating tip side.

Since the auxiliary vibration section 5 is narrowed discontinuously in the direction, the vibration node position is not moved to the connection point with the diaphragm 4, and the reproduction frequency characteristics are further improved as shown schematically in the diagram of FIG. As shown in the figure, the surface is significantly flattened.

The effect of this frequency flattening is the main vibration part width w1 of the vibrator.
This is obtained by discontinuously narrowing the auxiliary vibrating part width w2 relative to the width, and the dimension ratio of w1/w2 is preferably % or less.

Therefore, it is clear that the shape of the main vibration part may be any shape.

The lowest resonant frequency f in the vibrator having the structure described above and having frequency characteristics with excellent flatness.

As mentioned above, even if the length lo of the vibrator is increased in order to lower the oscillator, the resulting frequency characteristic in the low range will have a low output as shown by the broken line in FIG. 2, which is not practical.

Therefore, as shown in FIG. 3, the present invention makes the longitudinal dimension of the vibrator partially protrude longer than the connection point with the diaphragm, that is, the black point of the auxiliary vibrating section 5 here. In this embodiment, protrusions 6 and 7 are provided.

By providing such protrusions 6 and 7 on the vibrating tip side of the vibrator, the total length 1o' of the vibrator is lower than the fundamental resonance frequency fo determined by the effective length 1o of the main vibrating part.
It is possible to generate a resonance frequency fo' determined by , and expand the reproduction band to a lower frequency range.

In addition, coupled with the fact that the vibrator has a shape that has a wider vibrating tip than the fixed side as described above, there is no drop in output in the bass range, and the lower limit frequency is expanded from fo to fo' as shown in the chart in Figure 4. flat frequency characteristics can be obtained.

Furthermore, the protrusion lengths of the protrusion 6 provided on the vibrating tip side and the other protrusion 7 are set in a relationship with the protrusion 7 of lc/', which is shorter than the protrusion 6 of lo', which is the total length of the vibrator. Accordingly, 1
Since the resonance point fd/ determined by "o" occurs between <fo' and fo" as shown by the broken line in FIG. 4, the flatness of the frequency characteristic is further improved.

The vibrator having the configuration described below can expand the reproducing ability in the low range without causing a decrease in the output, and can obtain a flat output characteristic.

This expansion of the reproducing ability in the low range is achieved by partially providing the vibrating tip with a protrusion that is longer than the connection point with the diaphragm.

Therefore, the present invention is not limited to the above-mentioned example in which the protrusions are provided at two locations, but it is also possible to provide a large number of protrusions such as four locations as shown in FIG.

Furthermore, either symmetrical or asymmetrical with respect to the center axis of the vibrator is effective.

The effect is the same even if the basic shape of the vibrator is rectangular, trapezoidal, circular, etc., and the same effect can be obtained even if the piezoelectric plate is bonded to both the front and back surfaces of the metal plate.

Furthermore, in addition to forming the above-mentioned protruding part integrally with the metal plate of the main vibrating part, it is also possible to bond that part to another elastic body with a different thickness, or to attach a piezoelectric plate to the protruding part as well. The shape, etc. of the protrusion may be selected so that the resonant frequency obtained by the protrusion becomes a desired value.

Examples according to the present invention will be shown below to clarify its effects.

A phosphor bronze plate with a thickness of 0.1 mm is used as the metal plate, the main vibration part is a semicircle with a diameter of 25 m7IL, the fixed part is 10 mm in width,
Rectangular shape with a length of 2 mm, the connection point with the diaphragm is on the auxiliary vibration part with a width of 2 mm and a length of 1.5 mm, and a width of 3 mm at the vibrating tip.
Two protrusions are provided, and the length of one is equal to the total length of the vibrator 1o.
' was set to 20 mm, and the other was set to full length l♂ of 17 mm.

On one side of the metal plate formed in this way, a thickness of 0.1 mm,
A semicircular piezoelectric plate made of zircon-lead titanate porcelain having a diameter of 25 mm was adhered to produce a piezoelectric bimorph vibrator according to the present invention shown in FIG. 3.

Then, the fixing part of this vibrator was adhesively fixed to the diaphragm support frame of the speaker, and the diameter was 28 mm and the thickness was 50 μm.
The polyimide film was formed into a cone shape, and the center point of the diaphragm was connected to the auxiliary vibration part, and the peripheral edge of the diaphragm was glued to the support frame via roll edges to create a piezoelectric speaker.

For comparison, a piezoelectric speaker of the same size was assembled using the vibrator shown in FIG. 1, in which two protrusions were removed from the vibrator.

A sine wave voltage with an effective amount of 1 cm was applied to these two types of piezoelectric speakers, and the sound pressure at 10 CrrL on the axis was measured.

As a result, as shown in the graph of FIG. 6, when the vibrator according to the present invention is used, a new resonance point f
Due to the effects of o' and f d', the playback band is approximately 30
It can be seen that the frequency has been expanded to near 0 Hz.

On the other hand, in the case of the vibrator for comparison, fo is approximately 6
50H2, and the lower limit of reproduction and its output characteristics are superior to those of the conventional rectangular vibrator, but there is a significant difference when compared with the vibrator provided with the protrusion according to the present invention.

As is clear from the above embodiments, the piezoelectric speaker using the piezoelectric vibrator configured according to the present invention has significantly improved lower limit frequency of the reproduction band, its output, and frequency characteristics, and has improved both audio reproduction ability and clarity. This is an extremely practical speaker.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the basic form of a piezoelectric vibrator and a piezoelectric speaker according to the present invention, FIG. 2 is a graph schematically showing the frequency characteristics of the piezoelectric speaker in FIG. 1, and FIGS.
The figure is an explanatory diagram of a piezoelectric vibrator and piezoelectric speaker according to the present invention, FIG. 4 is a graph schematically showing the frequency characteristics of the piezoelectric speaker in FIG. 3, and FIG. 6 is a frequency characteristic of the piezoelectric speaker according to the present invention in an embodiment. This is a graph showing. In the figure, 1...metal plate, 2...piezoelectric plate,
3... diaphragm frame, 4... diaphragm, 5... auxiliary vibration part, 6.7... protrusion part.

Claims (1)

[Scope of Claims] 1 One end of the piezoelectric bimorph vibrator is a fixed side, a connection point with a diaphragm is provided at the other end of the vibrating tip side, and the vibrating tip portion partially protrudes longer than the connecting point. Piezoelectric bimorph vibrator. 2. The piezoelectric bimorph vibrator according to claim 1, wherein the width on the vibrating tip side is wider than the width on the fixed side. 3 The connection point with the diaphragm is placed on an auxiliary vibration part that protrudes discontinuously in the length direction from the main vibration part, and the width of the auxiliary vibration part is not more than % of the width of the main vibration part.Claim 2 The piezoelectric bimorph resonator described in .