JPH0136315B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flat transducer using a piezoelectric thin plate. Useful for audio microphones or speakers. More specifically, a flat thin plate of piezoelectric material with electrodes on both principal surfaces is deformed in a curved manner, and in order to keep the curved state stable, it is fitted into a frame whose size is no larger than the curved and reduced outer circumference. The present invention relates to an ultra-thin piezoelectric ceramic transducer that has a simple structure that only includes electrical input/output terminals that are electrically connected to electrodes.

Recently, advances have been made in the technology for miniaturizing radios, tape recorders, etc. and making them battery-powered for long periods of time, and thin, pocketable types have become popular. This trend is largely due to advances in circuit integration technology, which has supported the spread of pocketable calculators. Calculators were also equipped with small sounding devices developed for wristwatch alarms, and input and output of calculations began to utilize not only displays for the eyes but also audio signals for the ears.

Nowadays, battery-powered watches, calculators, radios,
There is a trend for electronic micro devices such as tape recorders to include a display, a sounding body, and/or a microphone. In this case, with the advent of liquid crystal displays, displays have become smaller, flat, and have less power, but there is no sounding device that completely satisfies the requirements for small size, thinness, and low power.
Therefore, the need for the development of flat-plate speakers has increased rapidly, and it has become a technological issue of the times.

As mentioned earlier, the sounding body required for electronic micro devices must be small, flat, and low power. Piezoelectric buzzers are excellent in that they are small, flat, and low power, but they are resonators for signals with a fixed frequency, and cannot cover the desired acoustic band and cannot be used as a speaker for audio signals with a wide frequency band. It was very difficult for me to pronounce these words.

Furthermore, the present inventor had previously proposed a speaker using a transparent piezoelectric material, but the problem still remained that the generated sound was small.

The purpose of the present invention is to ensure practically sufficient audio,
The object of the present invention is to provide a transducer with clear reception.

In general, simply applying an AC signal to a flat plate will result in
Although the bending mode cannot be excited, a bimorph structure can easily excite the bending mode. but,
A bimorph has a structure in which two flat plates are glued together, and the in-plane expansion and contraction of one plate is restrained by the other plate through the bonded surface, resulting in bending motion. Therefore, stress is constantly generated on the bonded surfaces during bending motion, and this stress can be said to be the driving force behind the bending motion.

As is clear from the above-mentioned principle of bending motion in a bimorph vibrator, the piezoelectric plate can no longer deform freely, but can only deform while being constrained by the bonded surfaces. For this reason, the conversion efficiency for converting electrical input into mechanical vibration is half that of a case where free deformation is possible.

On the other hand, Japanese Patent Publication No. 49-44658 discloses a transducer in which a piezoelectric ceramic plate is held in a curved surface by a metal frame, but this requires a special structure that allows the metal frame to be twisted. The scope of use was limited.

However, in the present invention, the piezoelectric thin film is fitted into a holding plate made of a resin material and is provided with a curved surface, so it is difficult to convert the in-plane expansion and contraction of the piezoelectric body into bending motion in a form close to free deformation. Therefore, we can provide a vibrator that can

According to the present invention, the piezoelectric flat plate is curved in advance, and the peripheral portion of the plate is held so that the curved state can be maintained stably. Both main surfaces of the piezoelectric plate are in a free state, so when a voltage is applied to the electrodes, it expands and contracts almost freely, but since the size of the peripheral part of the plate is held unchanged, bending movement occurs. When the plate stretches, the curvature increases and the radius of curvature becomes smaller; when the plate contracts, the radius of curvature becomes smaller; and when the plate contracts, the radius of curvature becomes larger. At this time, the difference in the radius of curvature on both sides becomes larger as the curvature becomes larger, and as the plate thickness becomes thicker. When an electric signal is applied and bending vibration occurs, the energy conversion efficiency decreases depending on the difference in the amount of change in the radius of curvature on both sides of the plate. The thinner the piezoelectric body is, the higher the conversion efficiency is, and the smaller the vibration amplitude is, the higher the conversion efficiency is, approaching the conversion efficiency during free deformation.

What has been described above is the principle of the operating mechanism of the piezoelectric ceramic transducer of the present invention as a speaker, and it has been found that the thinner the plate, the higher the electrical-mechanical energy conversion efficiency. By the way, in the case of a speaker, since vibration is applied to the air, the acoustic output is determined by the vibration area and amplitude, and mechanical impedance such as the stiffness of the diaphragm does not matter much.

On the other hand, in the case of a microphone, it is necessary to play the role of converting the sound pressure created by air vibration into an electrical signal.
The mechanical impedance of the diaphragm must be low enough to respond sufficiently to air vibrations. If the transducer operates in bending mode, the diaphragm must be as thin as possible and easy to bend. Since the thinner the transducer of the present invention is, the higher the conversion efficiency is, it is also advantageous when used as a microphone.

Furthermore, the tons duzer of the present invention has the characteristic that it can be used with high efficiency in practical use. When using a transducer as a speaker or microphone, the transducer must be held in some way.

A bending mode vibrator is generally held at its periphery. Conventional bimorph types usually have a thin metal plate attached to the neutral plane for reinforcement, while unimorph types usually have a piezoelectric plate attached to the metal diaphragm. To hold these bimorph oscillators, the periphery of the metal plate is fixed to a frame, etc., using the so-called "peripheral fixation" method (first method).
Figure). Although the peripheral support method (Fig. 2) is more efficient in holding the bending mode vibrator,
In practice, it is difficult to hold using the peripheral support method, so
Since the metal plate is made larger than the piezoelectric plate and its periphery is fixed, the energy conversion efficiency is even lower than the theoretical value.

On the other hand, in the tons duuser of the present invention, the piezoelectric vibrator is held in a curved state in a slightly smaller frame, so as shown in FIG. One of the major features is that it has a structure that makes it easy to obtain conversion efficiency close to the value.

Further, in the present invention, the piezoelectric vibrator is held in a curved manner by a holding plate made of a resin material, and by utilizing the vibration of the holding plate itself, a highly efficient, broadband transducer is obtained.

FIGS. 4a and 4b are a schematic plan view and a cross-sectional view of a transducer according to an embodiment of the present invention, respectively.

A piezoelectric disk made of Pb(ZrTi)O ₃ -based transparent piezoelectric ceramic with a diameter of 20 mm and a thickness of 0.2 mm is prepared. Transparent electrodes 72 are coated on both main surfaces of the transparent piezoelectric ceramic disk 71, and polarization treatment is performed using these electrodes by applying a high DC voltage. Prepare a polycarbonate transparent plate 75 with a square size of 150 mm on a side and a thickness of 1.5 mm, make a hole with a diameter of 26.95 mm in the center of each plate, fit the transparent ceramic disc 71 into the hole 74, and set the radius of curvature. Maintain the curved surface so that R is 200 to 150 mm.

Transparent films 76 and 77 are coated along the diagonal lines on both the front and back surfaces of the polycarbonate square plate in place of lead wires, and terminals 78 and 77 are coated, respectively.
79 is connected. This transparent lead wire 76,
Silver paste 73 is applied to the end of hole 74 of 77 to electrically connect it to electrode 72 of transparent piezoelectric plate 71 . When an audio signal was applied to the terminals 78 and 79, the tone ducer thus completed could emit a rich sound volume as a speaker.

The feature of this embodiment is that a transparent flat plate speaker was realized, and another feature is the function of the diaphragm of the sounding section. That is, since the polycarbonate holding plate 75 holds the diaphragm 71 in a curved state, the area around the hole 74 is distorted by a considerable compressive force. Therefore, when the diaphragm 71 vibrates and undergoes a curved deformation, the holding plate 75 also vibrates as a reaction, and sound is also emitted from the surface of the holding plate. This is a feature of this embodiment; the diaphragm 71 generates high-frequency sound, and the holding plate 75 generates low-frequency sound. In terms of speaker functions,
The diaphragm 71 portion functions as a tweeter, and the holding plate 75 portion functions as a woofer. As a result, the frequency response of the output is broadband, starting from 50Hz
It was confirmed that the frequency exceeds 10KHz. This is a good result that could not be achieved with flat speakers.

FIG. 5 is a schematic perspective view of a transducer as yet another embodiment of the present invention.

The same transparent ceramic plate as in the example shown in Figure 4 was
A rectangular plate 91 with a size of 40 mm and a thickness of 0.2 mm is formed, coated with a transparent electrode, and polarized to form a piezoelectric plate. This is curved into a curved surface with a radius of curvature of R = 200 to 150 mm. It is held by fitting into a polycarbonate plate 95 of 70 mm and 1.5 mm thick. Prepared separately,
A box 96 made of polycarbonate and having a size of 100 mm x 70 mm x 15 mm is covered with the above-mentioned 95 with a lid and fixed. This box can accommodate audio equipment such as a radio and tape recorder, and when the output is applied to the transparent electrode through the contacts and the metal frame 97, the vibrator 91 operates as a speaker, but the box 96 Because it acted as a resonance box, a fairly large volume was obtained.

The transducer of the present invention has been explained above using examples. 1. It can be used as both a transmitter and a receiver, 2. It can be configured to be ultra-thin, 3. It has a simple structure, and 4. It is electrically /In addition to basic features such as high acoustic conversion efficiency, the transparent transducer and wideband transducer were also explained using examples.

As described in detail above, the present invention provides an excellent transducer using a piezoelectric thin film fitted with a frame of a predetermined holding jig and provided with a curved surface, and is widely used in small electronic devices for generating sound. It can be applied as a body or receiver, and has great industrial benefits.

[Brief explanation of drawings]

1 and 2 are model diagrams for explaining a conventional transducer, FIG. 3 is a model diagram for explaining a transducer of the present invention, and FIGS. 4 and 5 are model diagrams for explaining the transducer of the present invention, respectively. FIG. 2 is a schematic explanatory diagram of a transducer according to an embodiment of the present invention. Explanation of symbols, 71...Piezoelectric ceramic vibrator,
72...Transparent electrode, 73...Silver paste, 74...
... Hole, 75 ... Holding plate, 76, 77 ... Transparent lead wire, 78, 79 ... Terminal.

Claims (1)

[Claims] 1. A transducer comprising at least a piezoelectric thin film, electrodes formed on both main surfaces of the thin film, a frame holding the periphery of the thin film, and electric signal applying means for applying an electric signal to the electrodes. In,
A piezoelectric ceramic transducer characterized in that the frame is made of a plate-shaped resin material held so as to be able to vibrate, and the piezoelectric thin film is fitted into the frame to maintain the thin film in a curved surface.