东莞思威特电子压电陶瓷的典型应用.doc

东莞思威特电子压电陶瓷的典型应用一、压电声响器Piezoelectric ceramic sounder1、发声元件的结构The structure sounding element罗宾逊和迪得逊对健康人的耳朵进行测验的结果，发现耳朵对3千赫左右的频率最为敏感。因此，压电陶瓷发声元件的谐振频率设计在3000Hz左右。 一般采用如图2.25所示结构，其外形尺寸为直径10-50毫米，总厚度0.4-0.5毫米.在压电陶瓷发生元件上施加交变电压时,发声元件挠曲振动，振动基波的谐振频率可由下式给出:Robinson and Dixon tested the healthy humans ears, they had found that the most sensitive frequency is 3KHz to humans ear. So, the resonant frequency of piezoelectric ceramic sounder is 3KHz in design. Generally, using the structure as shown in Fig.2.25, the diameter size is in 10-50 mm, the total thickness is in 0.4-0.5 mm. The sounder element will produce flexural vibration when the piezoelectric ceramic element input AC voltage. The resonant frequency of fundamental vibration wave is shown the formula. C-振动片固定方式常数(波节固定时为0.467,周边固定时为0.233);t-厚度; r-半径;Y0-杨氏模量;0-金属振动片和压电陶瓷片的合成密度。 因此，当材料一定时，压电陶瓷发声元件的频率与其总厚度成正比，与其半径平方成反比。如图2.26所示.C-The fixed mode constant of vibrator(Wave node fixed mode equal to 0.467, Circum node fixed mode equal to 0.233);t- thickness; r- radii; Y0-Young modulus; 0- Metal disk and piezoelectric ceramic disk of combining density So, the frequency of piezoelectric ceramic sounder and the total thickness are direct proportion, and the quadratic radius is inversely proportion when the material is given. As shown in Fig.2.26.压电陶瓷发声元件的谐振频率随复合振动片直径的增加成指数曲线下降。 发声元件中的压电陶瓷片的大小主要根据对阻抗的要求确定。图2.28是压电陶瓷片的直径d与金属振动片的直径D的比值与谐振阻抗的关系。The resonant frequency of piezoelectric sounder and the diameter compound vibration plate decreases with the exponential curve. The piezoelectric ceramic size of sounder is confirmed which is based on the required impedance. The ration of piezoelectric ceramic diameter d and metal diameter D, it and the resonant impedance relation is shown in the Fig.2.28.由图可知，对于基波振动来说，d/D的比值越趋近于1，谐振电阻越小，即要获得较低的阻抗值必须使压电陶瓷片的直径接近于金属振动片的直径，其比值小于0.7。It can be seen from the figure, for fundamental wave vibration, d / D ratio is approach 1, the resonance resistance is getting smaller, the piezoelectric ceramic plate diameter need close to the metal diaphragm diameter if we need to obtain the low impedance value, the ratio is less than 0.7.2、发声元件对材料的要求Requirements of sounder element materials1)、金属材料的选择：振动片用材料应具有良好的导电性，而且容易加工的金属弹性材料，表2.7列出金属材料的特性。 制作发声元件振动所用的金属材料，其杨氏模量应大而线膨胀系数应尽量接近PZT等压电陶瓷材料的线膨胀系数。表2.7中所列的钛、不锈钢、磷青铜和黄铜均较合适，其中以钛最为理想，但是价格太昂贵；因此，常用的金属材料是黄铜和不锈钢二种。由于黄铜的杨氏模量比不锈钢的小，由式（2.25）可知,这就是为什么当两者尺寸相同时,用不锈钢振动片的谐振频率比用黄铜振动片的频率要高的原因。1), Metal materials selection: The materials of vibration should have good electrical conductivity, and easy to processing elastic metal materials, Table 2.7 lists metal material characteristics. Making a sound element using in plate vibrator, the youngs modulus and linear expansion coefficient should be possible close to the piezoelectric ceramic material. Listed in table 2.7 titanium, stainless steel, phosphor bronze and brass are more appropriate, Titanium is the most ideal, but the price is too expensive; So , the brass and stainless steel are used commonly. Because the Youngs modulus of brass is less than the stainless steel, as the formula (2.25) shows,This is why when the same size, the resonant frequency of stainless steel vibrator is higher than using the brass.表2.7几种金属材料的性能2)、对压电陶瓷的材料要求：当发声元件的频率一定时，总希望发声元件的输出声压越高越好，而输出声压的高低取决于驱动复合振动片的力的大小，这一驱动力可由下式决定：F = CE 33TKp V (2.26) CE-弹性劲度常数；33 T -自由相对介电常数；Kp-平面机电偶合系数；V-驱动电压; 其中的CE，33T 和Kp为材料的特性参数，因此，要获得较高的声压，必须选择具有较高弹性劲度常数，按高自由相对介电常数和较高平面机电耦合系数的压电陶瓷。通常选用Kp60%， 33T3500的压电陶瓷材料。2), The requirements of piezoelectric ceramic material: when the frequency of sound element is constant, Hoping sound element output sound pressure level the higher the better, and the output sound pressure depends on the driving force of composite vibrator, the driving force is determined by formula (2.26): 压电陶瓷发声元件的规格和主要性能：压电陶瓷发声元件根据其不同用途有不同的电极结构，图2.29中示出两种不同的形式。其中A型为最常见的形式，用他激电路驱动，能发出动物的模拟声。D型带有反馈电极，可采用自激电路，使电路简单化，能发出大的声音。The type A is the most common form, using external drive circuit, can produce simulate animals sound. The type D there is feedback electrode, using self- drive circuit, the circuit is simple, can make a loud sound.3、压电声响器的结构和性能The structure and properties 1）压电陶瓷发声元件的固定方式有三种The Piezoelectric sound element was fixed, there is three modes.波节圆固定，压电陶瓷发声元件处于自由振动的状态，阻抗最小。周边固定，被固定的部分略有振动，故阻抗最大，频率较低。中心固定，阻抗较小，频率最低。波节直径d和金属片直径D关系如下式：d=0.55DFixed in the nodal circle, the piezoelectric ceramic sound element in free vibration state, the impedance is minimal.Fixed in the surround, the fixed part can vibrate a little part, so the impedance is highest, the frequency is lower.Fixed in the center, the impedance is smaller, the frequency is the lowest.The relation of nodal diameter d and metal plate diameter D relation as follows formula: d = 0.55D. 2)声共鸣器的设计Acoustic resonator design 为了使压电陶瓷发声元件所产生的声音有足够大的音响,须经声学放大。由于压电陶瓷发声元件本身的机械Qm值较高，具有尖锐的频响特性，因此需要利用共鸣效应加以改善。利用共鸣原理进行声学放大有三种形式：音箱、反射板和共鸣器，其中音箱的特点是音色圆润。反射板的特点是可得到大的声压，而共鸣器则结构简单，设计方便，最为常用。图2.30示出不同固定方式的共鸣器结构。共鸣器设计关键是选择适当的空腔和放音孔。共鸣器的空腔是声顺元件，管状放音孔是声质量元件，适当地加以组合可以达到良好的声音共鸣效果。对周边固定和波节圆固定的发声元件共鸣器的共鸣频率可用亥姆霍兹公式表示：In order to make the piezoelectric sound element generated the large enough sound, need to acoustic amplification. Because the mechanical Qm value of piezoelectric sound element is higher, with sharp frequency response characteristic, Therefore need to use a resonance effect to try to improve. Using the principle of resonance acoustic amplifier there is three kinds of forms: loudspeaker box, reflection plate and acoustical resonator chamber, the characteristic of loudspeaker box can produce mellow sound. The characteristic of reflection plate produce high sound pressure level, the structure of acoustic resonator chamber is simple, convenient design, the most commonly used. Fig.2.30 shows the different fixed mode acoustic resonator structure.式中： MA-声质量； V-声速； l-放音孔长度； d1-放音孔直径； h-空腔高度； CA-声顺； K-常数。 一般以共鸣器的共鸣器频率略低于发声元件的谐振频率为宜。共鸣器空腔高度与声压有如图2.31所示的关系，设计时需要全面考虑，以取得最佳共鸣效果。4、驱动电路Driving circuit1）自激振荡驱动方式：利用压电陶瓷发声元件自身的谐振频率激励发声。压电陶瓷发声元件在谐振点附近具有较低的阻抗，因此声压的大小由输入电流的大小来决定，属于电流驱动型，主要用于要求大声压的地方。这种方式以正弦波驱动最为有效。Self- driving mode: Using the resonant frequency excitation of piezoelectric ceramics sound element produce sound. Piezoelectric sound element has a lower impedance in a near resonant frequency point, So the sound pressure level depend on the input current, which belongs to a current driving type, it mainly used to need loud sound pressure level . The most effective driving method is that used sine wave.2）他激振荡驱动方式：利用外加讯号频率激励发声。如用多谐振荡器、间歇振荡器等振荡电路来驱动。采用这种方式发出的声压较低，适用于发出具有各种音色的音响。在这种方式中，压电陶瓷发声元件一般工作在谐振点以外的频率，因此，输入阻抗较大，输入电流较小，属于电压驱动型。另外，为了提高声压，常采用矩形波驱动。External drive mode: Using a external signal frequency excitation produce sound. For example , multivibrator, blocking oscillator etc. circuit to drive. Using this kind of means of a sound pressure level is lower, apply to produce various tone sound. In this way , the working frequency of the piezoelectric ceramic sound element is not in the resonant frequency point, therefore, So the input impedance is larger, the input current is smaller, belongs to a voltage driving type. In addition, order to improve output the sound pressure level, using a rectangular wave drive.5、压电声响器的应用Application of piezoelectric ceramic buzzer汽车关开门等提示或者报警; 家用电器报警; IT数码产品提示声或者报警; 仪器仪表触摸提示声;边防哨所、矿工井下电话、电铃; 模拟声玩具；设备音响提示，烟雾报警等。Auto close open the door prompt sound or alarm; white goods alarm; IT products prompt sound or alarm; instrumentation touch beep；border post, bell miner, telephone, analog sound toys；equipment audio prompts, smoke alarm.二、 压电陶瓷点火器Piezoelectric ceramic ignition一种将机械力转换为电火花而点引燃烧物的装置。它利用压电陶瓷元件受机械力作用发生弹性形变而产生的高压输出，然后通过高压火花放电，点燃易燃气体。图1.1为点火器用圆柱体压电陶瓷元件。如下图，是家用压电陶瓷点火器原理。转动凸轮开关1利用凸轮凸出部分的作用力推动冲击块3，并压缩冲击块后的弹簧2，当凸轮转到一定位置时，凸轮凸出部分脱离冲击块，在弹簧力的作用下，冲击块给压电陶瓷元件4一个冲击力。使压电陶瓷元件两端产生高压，从中间电极6引出，并在压电点火器的间隙处形成电火花点燃气体。Piezoelectric ceramic ignition is a device which can convert mechanical force to electric spark to light the burning material. Main principle is: the piezoelectric ceramic component produces the elastic deformation due to mechanical force, meanwhile it produces high voltage output and causes spark discharge so that this phenomenon light flammable gas. Figure 1.1 is showing the piezoelectric ceramic component applied in ignition cylinder device三、压电陶瓷变压器Piezoelectric ceramic transformer如图1.5所示，这种长方形的陶瓷变压器，左半部分上下两面敷设银电极，沿厚度方向进行极化。当加上交变电场时，瓷片产生机械振动，这一部分称为驱动部分。右半部分的端面敷设银电极，并沿长度方向极化，这部分将机械能转换成电能，称为发电部分。陶瓷变压器的结构有单层和多层。Fig.1.5, It is a kind of rectangle ceramic transformer, There are silver electrode on the left part of the two sides up