JP2000333288A - Piezoelectric audible unit and sound generating method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] The sound quality of a piezoelectric element that operates an operation element cannot be said to be sufficient. A piezoelectric plate having a first input and a sensing element mounted on the plate and having a first output for outputting a second electrical signal substantially in proportion to its movement.
A piezoelectric acoustic transducer 1 having an ME, comprising: an electric filter A4 for generating a filtered signal from the second electric signal; and adding means SN, the adding means comprising: A first input for receiving a third electrical signal having a signal, a second input for receiving the filtered electrical signal, and subtracting the filtered electrical signal from the third electrical signal to form the second electrical signal. A means for generating an electrical signal and an output operatively connected to the first input for generating an acoustic audio signal corresponding to the electrical audio signal by the piezoelectric plate. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric speaker, and more particularly to a mobile telephone, a telephone and an ultrasonic apparatus having a piezoelectric element for generating sound.

[0002]

2. Description of the Related Art Earphones and speakers can be implemented using several principles of operation, including the effects of electrodynamics, electromagnetism, static electricity and piezoelectricity. Piezoelectric transducers are often referred to as ceramic transducers. The most common operating principle is that of current electrodynamics, which has the advantage of producing a sound consisting of a good frequency response, low tendency to distortion and a wide range of amplitudes output by it. Despite these advantages, especially the equipment is inexpensive,
With low power consumption, small size and light weight, there are situations where piezoelectric elements become attractive. However, in general, the performance of piezoelectric elements is far from reaching the expected quality. Piezoelectric elements have strong coloration (colo
ration) and frequency response nonlinearities. Also, the maximum movement of the surface of the piezoelectric element is much smaller than the maximum movement of the normal speaker surface,
As a result, there is a limit to the sound volume that the piezoelectric element can output.

[0003] In order to solve these problems, serious attempts have been made to utilize the piezoelectric element to improve the frequency response of the piezoelectric element and to provide good characteristics. While piezoelectric elements are small and inexpensive and require low input power, they have at least one unique resonant frequency band, and the output of the piezoelectric element will be significantly amplified by resonance. A major part of the present invention is to improve the frequency response of a piezoelectric element as a mechanical amplitude damping part. There is International Patent Application No. WO86 / 01362 in which a part of the surface of a piezoelectric element is used to electrically control an amplifier that drives the piezoelectric element to perform gain control of the amplifier. With such a configuration, the output power of the piezoelectric element can be adjusted, and the volume can be adjusted to an accurate level. This solution for linearizing the volume produced by the piezoelectric element is feasible when the sound consists of a single tone of very narrow bandwidth. However, this solution is not suitable for linearizing the frequency response of more complex sounds, such as human voices and instrument sounds. The reason is,
The amplification of the volume varies over the entire frequency band, whereby the colorization caused by the piezoelectric element
Is held. In addition, the unstable state may easily occur due to gain control based on a narrow frequency band. That is, when the piezoelectric element is not controlled, loud noise may be generated. U.S. Pat. No. 4,451,710 discloses an electric to sound converter utilizing a piezoelectric element. There is the problem of variable sensitivity (ie, sensitivity as a function of temperature, aging and manufacturing process). To modify the voltage applied to the drive element, it is possible to use the voltage developed at the sensing element to counteract the dependence of the transducer's sensitivity on the foil's piezoelectric sensitivity. Thus, the above solution has the same disadvantage of colorization of voice or instrumental sounds produced by voice or piezoelectric elements, as it is very similar to one solution in WO 86/01362.

[0004]

A new arrangement has been invented in which a piezoelectric sensor is mechanically attached to a sound-generating piezoelectric element or actuator for outputting a negative feedback signal corresponding to the vibration of the actuator. The actuator is provided with a sound signal generated by driving the piezoelectric element. This feedback signal is electrically filtered in order to compensate for the mechanical resonance frequency band of the actuator for stabilizing the feedback loop, and is guided together with the incoming audible signal to the piezoelectric driver for sound signal stabilization. By selective amplification of frequency, frequency-selective phase number conversion, or a combination of the two, electrical filtering for stabilization can be realized. The purpose of this filtering is to reduce the amplitude of the sound signal in the resonance frequency band and to compensate for the increased gain of the actuator at that resonance frequency.

[0005]

According to a first aspect of the invention, a step of inputting a first electrical signal to a piezoelectric plate, and a second electrical signal substantially proportional to the movement of the plate. Generating a sound signal, electrically filtering the second signal and compensating a mechanical resonance frequency band of the piezoelectric plate for stabilizing an output signal; Receiving the target audible signal, generating the output signal by subtracting the filtered electrical signal from the electrical audible signal, outputting the output signal to the piezoelectric plate, and using the piezoelectric plate Generating an audio audible signal corresponding to the electrical audible signal.

According to a second aspect of the present invention, there is provided a piezoelectric plate having a first input for inputting a first electric signal and having at least one mechanical resonance frequency band, and being attached to the plate. A piezoelectric-acoustic transducer comprising a sensing element having a first output for outputting a second electrical signal substantially in proportion to the movement of said plate.
For the stabilization of the signal of, the electrical filter for generating a signal filtered from the second electrical signal for the purpose of compensating the mechanical resonance frequency band, and an adding means, the adding means, A first input for receiving a third electrical signal having an electrical audible signal acoustically reproduced by the piezoelectric plate; a second input for receiving the filtered electrical signal; Means for generating a first electrical signal by subtracting a signal from the third electrical signal; and a first input and function for generating an acoustic audio signal corresponding to the electrical audio signal by a piezoelectric plate. Piezo-acoustic transducer, comprising:

[0007] The converter preferably comprises an amplifier for amplifying the sound signal prior to sending the sound signal to the actuator. According to a third aspect of the present invention, a piezoelectric plate having a first input for inputting a first electrical signal and having at least one mechanical resonance frequency band, attached to the plate,
An earphone having a sensing element mounted on said plate and having a first output for outputting a second electrical signal substantially in proportion to the movement of said plate, for stabilizing said first signal. An electrical filter for generating a filtered signal from the second electrical signal for the purpose of compensating for the mechanical resonance frequency band; and an adding means, wherein the adding means is acoustically controlled by the piezoelectric plate. A first input for receiving a third electrical signal having an electrical audible signal to be reproduced; a second input for receiving the filtered electrical signal; and a third input for receiving the filtered electrical signal. Means for subtracting from said signal to generate said first electrical signal; and for generating an acoustic audio signal corresponding to said electrical audio signal by a piezoelectric plate,
An earphone is provided that has an output operatively connected to the first input.

[0008] The earphone preferably includes an amplifier for amplifying the sound signal before transmitting the sound signal to the actuator. Fourth Embodiment of the Present Invention
According to the aspect, a piezoelectric plate having a first input for inputting a first electrical signal and having at least one mechanical resonance frequency band, and being attached to the plate and substantially moving the plate A communication device comprising a sensing element having a first output that outputs a second electrical signal in proportion to the following, wherein the communication device compensates the mechanical resonance frequency band for stabilization of the first signal. And an electrical filter for generating a filtered signal from said second electrical signal, and a summing means, said summing means having a third electrically audible signal acoustically reproduced by said piezoelectric plate. A first input for receiving an electrical signal; a second input for receiving the filtered electrical signal;
Means for subtracting the filtered electrical signal from the third electrical signal to generate the first electrical signal; and generating the acoustic audio signal corresponding to the electrical audio signal by a piezoelectric plate. There is provided a communication device having one input and an output operatively connected.

[0009] The communication device preferably includes an amplifier for amplifying the sound signal prior to sending the sound signal to the actuator. The fifth of the present invention
According to the aspect, a piezoelectric plate having a first input for inputting a first electrical signal and having at least one mechanical resonance frequency band, and being attached to the plate and substantially moving the plate An ultrasonic device comprising a sensing element having a first output that outputs a second electrical signal in proportion to the mechanical resonance frequency band for stabilizing the first signal. An electrical filter for generating a filtered signal from the second electrical signal for the purpose; and a summing means, the summing means having a third electrically audible signal acoustically reproduced by the piezoelectric plate. A first input for receiving the filtered electrical signal; a second input for receiving the filtered electrical signal; and subtracting the filtered electrical signal from the third electrical signal. A means for generating an electrical signal and an output operatively connected to the first input for generating an acoustic audio signal corresponding to the electrical audio signal by a piezoelectric plate. Is provided.

[0010] The ultrasonic apparatus preferably includes an amplifier for amplifying the sound signal prior to the transmission of the sound signal to the actuator.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings. A typical piezo speaker has a thin circular (or alternatively) attached to a plate (usually metal).
(Rectangular) piezoelectric disc. The plate is used as one electrode and the other electrode is deposited on the other surface of the piezoelectric disk. Typically, the electrodes are printed using silver paint, which forms a conductive surface when the piezoelectric material is heated to create polarity. The disk is polarized and the electric field between the electrodes creates a radial stress.
As this radial stress acts over only one surface of the plate, this stress causes the plate to bend.

The piezoelectric conversion from the electric field to the stress inside the material is
The relative linearity and the non-linearity associated with this transformation is of the third order. The conversion from radial stresses or forces to plate displacements can exhibit significant non-linearities and can exhibit significant asymmetry. Piezoelectric loudspeakers rely on the bending of rather stiff plates so that the achievable displacement remains small, and improvements in mechanical design have only marginally improved linearity. In addition to non-linearity, another common problem with piezoelectric speakers is irregular frequency response. This problem is caused by various resonance modes of the system.
It comes from. The axial mode (this mode may be the cause of the problem) can be controlled by proper installation of the driver,
At the same time, there is no mechanical control of the lowest radial mode (actually mass-spring-type resonance) without significant loss of sensitivity.

FIG. 1 is a block diagram of a feedback type piezoelectric converter 1 according to one embodiment of the present invention. The transducer is an actuating element A
E and the sensing element ME. The connection between the actuation element AE and the sensing element ME is indicated by the connection MC. When treating various parts of the system as black boxes,
The mathematical model that describes the type of feedback system itself is quite simple. The feedback system includes inverting summing amplifier SN with finite gain amplifier with a transfer function consisting of the transfer function A ₁ of drive amplifier A1, the transducer (speaker or actuator A2 and the sensor A3 has a transfer function A ₂ and A ₃ with), and it can be described in its simplest form as a sense amplifier A4 having a compensation network (transfer function a _4). In addition, there is a transfer function from the speaker drive voltage to the acoustic response (A _ma = p _out / V _spkr ).
Here, A _ma is a transfer function for sound output obtained from the input voltage of the speaker, that is, the drive voltage of the speaker. All these transfer function coefficients can be complex depending on frequency.

The transfer function of the loop of such a circuit can be described by the following equation.

[0015]

(Equation 1)

[0016] Here, the total transfer function at the output of A ₄ (or in the negative input of the summing node) is calculated. Therefore, the voltage at the actuator drive point P1 is as follows.

[0017]

(Equation 2)

From this equation, the output sound pressure can be written as:

[0019]

(Equation 3)

When the electromechanical and electroacoustic transfer functions are determined either by experiment or by numerical models, the above equations allow for a sound equalization design. The invention will now be illustrated by describing one experimental system. Because the output impedance of piezoelectric sensors is high, most of them purely capacitive, the input impedance of the sense amplifier determines both the sensitivity and bandwidth of the device. The capacitance of the piezoelectric sensor is approximately 10
It varies in the range from pF to 1 nF. At low frequencies, this range implies a very high impedance (eg, 100 pF at 20 Hz means about 77 M ohms). However, since a piezoelectric speaker (or headphones) is not actually used at the lowest frequency itself, the lower limit frequency can be selected so as to be one digit higher. This choice is such that the amplifier input impedance is approximately 1-10 Mohm: 10-20p
F means that it is practically sufficient. This estimated value is also supported by the measurement result, and such an input impedance can be easily realized. During experiments, it has already been shown in practice that it is beneficial to limit the low frequency bandwidth of the signal provided at the input of a sense amplifier having an input impedance. The aforementioned limited movement of the piezoelectric element limits the low frequency response. This limitation depends on the size of the device, the mechanical and electrical properties, and the distance from the device to the viewer. When using headphones or headsets, the actual frequency band can be extended to low frequencies of about 100 Hz to 200 Hz. In addition, for larger speakers that can be heard over long distances, each limit can be much higher.

The measurements described below were made using a loudspeaker consisting of two separate piezoelectric transducers 24,25. Sensing transducer or sensor 2
4 was affixed to the back plate 23 of the actuation transducer or actuator 25. These converters have 0.
Attached to a 4 liter sealed enclosure 21 which was filled with absorbent material. (The capacity of the enclosure is less important for piezoelectric speakers due to the stiff structure of the loudspeaker and therefore little effective capacity, and if feedback is used, The magnitude is of lesser importance, but has been chosen so as to reduce the effects of diffraction during acoustic measurements.) The edges of the transducer are attached to the enclosure using viscoelastic material 22 Was done. The edge causing this loss of viscoelasticity had a significant damping effect on the radial mode of the transducer.

For simplicity, an experimental configuration system 20 was implemented using two separate isolation transducers, actuator 25 and sensor 24. In commercial practice, the cost can be reduced by using part of the electrodes as sensors. There are commercial products available (a positive feedback buzzer with three connections).
In this product, a piezoelectric material is sandwiched between two electrodes, on either side one of the two electrodes is further divided into two mutually insulated parts. However, in this type of structure, the stray capacitance between the actuator and the sensor electrode can limit the usable amount of feedback at high frequencies. Similar structures have already been used in other applications. For example, in a piezoelectric buzzer that outputs positive feedback, the positive feedback enables the buzzer to sound at a mechanical resonance frequency, thereby improving efficiency. Also, in the case of an ultrasonic image, it is possible to prevent the receiving amplifier from being overloaded by a transmission pulse by using separate areas for the transmitter and the receiver.

FIG. 3 is a block diagram of a measurement configuration 30 used for testing the loudspeaker shown in FIG. This experimental setup allows for easy gain adjustment and equalization of both the input and feedback signal paths, so a small mixing console 32 is used as a summing amplifier to keep the experimental setup as simple as possible. Was. Sensor 24
A conventional laboratory measurement amplifier 34 was used as the input amplifier for the lab. Reference numeral 31 indicates a signal source (a type of signal generator that generates a defined (variable) frequency used for testing). Using the tone control of the mixing console, the frequency is boosted from 1 kHz or more, and the maximum boost is over 10 kHz (about 12 dB).
Was achieved. The mechanical connection between the activation transducer 25 and the sensor 24 is indicated by connection 33. Frequency selective analog signal processing can cause a phase shift to the signal,
Thus, it is well known in the art that there are alternative ways of performing selective boosting of a signal. Taking into account the desire to enhance the effect of subtracting the response signal to the audio input, it is possible to adjust the amplitude over the entire spectrum while keeping the phase shift constant over the entire range of the spectrum. Alternatively, it is possible to perform this phase shift adjustment while keeping the amplitude constant. Alternatively, these two adjustments can be performed simultaneously. The purpose of the negative feedback is to improve the frequency response of the piezoelectric actuator, and the electrical behavior can be used to stabilize the dynamic behavior of the control loop.

FIG. 4 shows the impulse response of the sensor having the configuration of FIG. 2 according to the present invention when there is negative feedback (solid line) and when there is no negative feedback (dashed line). The negative feedback reduces the impulse decay time. FIG. 5 illustrates the frequency response for both systems with and without feedback. The reference level of the amplitude scale is arbitrary. The curve with return is 6k
At a frequency of Hz, the amplitude is about 7 dB smaller. Using the present invention, the resonance peak is shifted from less than 6 kHz to approximately 10 kHz, and this peak is near the maximum amplitude (resonance bandwidth is approximately 2 kHz without feedback and approximately 10 kHz with feedback). , So that the sound reproduction quality can be significantly improved. This measurement indicates that the control of the feedback radial mode is effective. However, the axial modes that cause irregularities at 1 kHz and 2 kHz are not actually affected.

The piezoelectric element according to the present invention can be used for earphones of telephones, mobile telephones, wired telephones, wireless telephones, portable cassette recorders, earphones of CD players and DVD players. While the present invention is best suited for lightweight portable devices, it is also well suited for fixed mount devices such as sonar. This specification presents implementations and embodiments of the present invention by way of example. It will be apparent to one skilled in the art that the present invention is not limited to the details of the above-described embodiments, and that the present invention can be realized in other embodiments without departing from the features of the present invention. . Therefore, these presented embodiments should be considered as illustrative and not limiting. Therefore, the realization and use possibilities of the present invention are limited only by the appended claims.
Accordingly, various modifications of the practice of the invention, including equivalent devices, as determined by the claims, also fall within the scope of the invention.

[0026]

As described above, according to the present invention, the piezoelectric sensor is mechanically attached to the sound-generating piezoelectric element for outputting a negative feedback signal corresponding to the vibration of the actuator. The sound quality of the element can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a feedback type piezoelectric transducer according to one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a speaker device according to one embodiment of the present invention.

FIG. 3 is a block diagram illustrating a measurement setup used to test the speaker shown in FIG. 2;

FIG. 4 is a diagram showing an impulse response of the sensor having the configuration of FIG. 2 in the case of having negative feedback (solid line) and the case of not having negative feedback (dashed line) according to the present invention.

FIG. 5 is a diagram showing frequency responses for both a case with feedback (in the case of a system having a smoother curve) and a case without feedback (higher peak).

[Explanation of symbols]

 Reference Signs List 20 experimental construction system 21 enclosure 22 viscoelastic material 23 back plate 24 piezoelectric transducer (sensor) 25 piezoelectric transducer (actuator) 30 measurement configuration 31 signal source 32 mixing console 33 connection 34: Laboratory measurement amplifier A1: Drive amplifier A2: Actuator A3: Sensor A4: Sense amplifier AE: Actuating element ME: Sensor element MC: Connection SN: Inverting addition amplifier (addition node)

Claims (7)

[Claims] 1. A sound generating method comprising: inputting a first electrical signal to a piezoelectric plate; and generating a second electrical signal that is substantially proportional to movement of the plate, wherein the method comprises: Electrically compensating the mechanical resonance frequency band of the piezoelectric plate for stabilizing the output signal; receiving the electrical audible signal; and Subtracting the filtered electrical signal to generate the output signal; outputting the output signal to the piezoelectric plate; and using the piezoelectric plate to generate an acoustic audio signal corresponding to the electrical audio signal. And a sound generation method. 2. The method of claim 1, wherein said filtering comprises one of selective amplification, frequency selective phase conversion, and a combination thereof. Method. 3. A piezoelectric plate (25) having a first input for inputting a first electrical signal and having at least one mechanical resonance frequency band; and being attached to said plate for movement of said plate. A piezoelectric acoustic transducer (1) comprising a sensing element (24) having a first output that outputs a second electrical signal substantially in proportion, wherein for stabilizing said first signal: An electric filter (A4, A4) for generating a filtered signal from the second electric signal for the purpose of compensating for the mechanical resonance frequency band;
32), and a summing means (SN, 32), the summing means comprising: a first input for receiving a third electrical signal having an electrical audible signal acoustically reproduced by the piezoelectric plate; A second input for receiving the filtered electrical signal; a means for subtracting the filtered electrical signal from the third electrical signal to generate the first electrical signal; A piezo-acoustic transducer comprising: the first input and an output operatively connected to generate an audible and audible signal by a piezoelectric plate. 4. A piezoelectric acoustic transducer (1) according to claim 3,
Wherein said electrical filter (A4, 32) comprises reducing means for reducing the amplitude of a sound signal in a resonance frequency band for compensating for an enhanced gain of said piezoelectric plate (25) at its resonance frequency; A piezoelectric acoustic transducer characterized in that the reducing means comprises at least one of a means for performing selective amplification of a frequency, a means for selectively converting a frequency, and a combination thereof. 5. A piezoelectric plate (25) having a first input for inputting a first electrical signal and having at least one mechanical resonance frequency band, attached to said plate, attached to said plate. An earphone comprising a sensing element having a first output for outputting a second electrical signal substantially in proportion to the movement of the plate, the earphone being adapted for stabilizing the first signal. An electrical filter (A4, A4) that generates a filtered signal from the second electrical signal for the purpose of compensating for the mechanical resonance frequency band.
32), and a summing means (SN, 32), the summing means comprising: a first input for receiving a third electrical signal having an electrical audible signal acoustically reproduced by the piezoelectric plate; A second input for receiving the filtered electrical signal; a means for subtracting the filtered electrical signal from the third electrical signal to generate the first electrical signal; An earphone having the first input and an output operatively connected to generate an audible and audible signal by the piezoelectric plate. 6. A piezoelectric plate (25) having a first input for inputting a first electrical signal and having at least one mechanical resonance frequency band, and attached to said plate for movement of said plate. A communication device comprising a sensing element (24) having a first output that outputs a second electrical signal substantially in proportion to the mechanical resonance frequency for stabilizing the first signal. An electric filter (A4, A4) for generating a filtered signal from the second electric signal for the purpose of compensating a band.
32), and a summing means (SN, 32), the summing means comprising: a first input for receiving a third electrical signal having an electrical audible signal acoustically reproduced by the piezoelectric plate; A second input for receiving the filtered electrical signal; a means for subtracting the filtered electrical signal from the third electrical signal to generate the first electrical signal; A communication device comprising: a first input and an output operatively connected to generate an acoustic and audible signal by a piezoelectric plate. 7. A piezoelectric plate (25) having a first input for inputting a first electrical signal and having at least one mechanical resonance frequency band, and attached to said plate for movement of said plate. An ultrasound device comprising a sensing element (24) having a first output that outputs a second electrical signal substantially in proportion to the mechanical resonance for stabilizing the first signal. An electrical filter (A4, A4) for generating a filtered signal from the second electrical signal for the purpose of compensating a frequency band;
32), and a summing means (SN, 32), the summing means comprising: a first input for receiving a third electrical signal having an electrical audible signal acoustically reproduced by the piezoelectric plate; A second input for receiving the filtered electrical signal; a means for subtracting the filtered electrical signal from the third electrical signal to generate the first electrical signal; An ultrasonic device having the first input and an output operatively connected to generate an acoustic and audible signal by a piezoelectric plate.