DuraAct贴片换能器技术

制造

DuraAct贴片换能器的有源层构成一块压电板。这些压电板根据一种已获专利的方法被嵌入纤维增强塑料(GRP)中,然后被粘合起来形成一个复合体。层压过程通过注入法在真空中的压热器中完成,从而形成完全无泡的高质量层合板。

由于材料具有不同的热膨胀系数,因此选用压热器的固化温度曲线来得出压电陶瓷板的规定内在预载。GRP聚合物涂层还可用作电气绝缘和机械预载。这项专利技术能实现坚固耐用又可弯曲的换能器元件的大批量生产。

Design & Production

The active layer in DuraAct patch transducers consists of one or more piezoceramic plates with metallized surfaces for electrical contacting. These plates typically measure between 200 and 500 μm in thickness. They are embedded in fiber-reinforced plastic (GRP) using a patented process and bonded to form a composite. The bonding process is carried out in an autoclave in a vacuum by means of an injection process to produce completely bubble-free laminates of the highest quality.

The curing temperature profile of the autoclave is selected so that a defined mechanical preload of the piezoceramic plates will result due to the different thermal expansion coefficients of the materials involved. The polymer coating of the GRP also serves as electrical insulation. Robust, bendable transducer elements that can be manufactured in large batches are the result of this patented technology.

DuraAct patch transducers are solid body actuators without moving parts. This means that wear and failure proneness are minimal. The electrical connection is made via two contact points to which wires can be soldered, glued or clamped, depending on the application.

How Do DuraAct Patch Transducers Work?

The piezoceramic plates that are used in all-ceramic DuraAct patch transducers are structurally similar to a capacitor. The ceramic serves as a dielectric between the metallic surfaces of the ceramic, which form the electrodes. When an electric voltage is applied, an electric field is created with lines running through the ceramic perpendicular to the plates. This causes a staggered contraction of the ceramic at 90° to the field lines so that the actuator constricts evenly along the plane. This behavior is called the transverse piezoelectric (d31) effect.

In the DuraAct Power patch transducer the multi-layer piezo element draws on the longitudinal or d33 effect. The displacement occurs parallel to the electric field E and the polarization direction P of the piezo actuator. The piezoelectric charge coefficients d33 for the longitudinal displacement are considerably higher than for the transversal displacement, meaning that the possible displacements are greater than for all-ceramic transducers.

The occurrence of acoustic surface waves can be converted using DuraAct Shear patch transducers. The shearing motion of the patch transducer is produced by the orthogonal application of an electric field E to the direction of the polarization P. The shear deformation coefficients d15 are generally the largest of the piezoelectric coefficients. When controlled with nominal voltages, the piezo ceramics achieve d15 (GS) values of up to 2000 pm/V. The permissible control field strength is limited in order to prevent a reversal of the vertically oriented polarization.

The electric field strength of the DuraAct patch transducers determines the displacement of the ceramic, therefore, allowing the simple control of the modules. This deformation is transmitted effectively to the structural elements via an uncomplicated bonding. The force is transmitted across the entire surface of the actuator by thrust and not at discrete points as is the case with conventional actuators. Massive force transfer points are therefore unnecessary. Conversely, structural deformations are converted to an electrical charge by the transducer, making it possible to use the element as a sensor or power generator. Division of the sensor and actuator functionality is achieved using an isolated contacting of several layers.

The reaction to a change in the electrical field or a deformation is extremely fast. This allows oscillations to be generated into the kilohertz range or also measured. Depending on the active piezo element used and its dimensions, different actuators produce different values with respect to control voltage and contraction. The relationship between deformation and control voltage is not linear.

DuraAct Patch Transducer Performance Graph

The actuator characteristics of piezoceramic transducers are primarily described by means of two parameters: the blocking force FB and the free displacement S0. If the unimpeded (free) actuator is controlled with a voltage U, it reaches its maximum displacement S0. The force required to push the maximally displaced actuator back to its original length is called the blocking force FBI.

If both parameters are plotted on a graph and connected with a line, the result is the performance graph of the actuator. The connecting line is called the load line. The ratio of external force to displacement can be read from the graph. In most applications, the actuator works against an elastic structure such as when deforming a spring or bending a plate. If the actuator deforms a spring, for example, the characteristic curve of the spring is plotted on the performance graph with the stiffness cF. The intersection point of the load lines and the characteristic curve denotes the operating point. The actuator works most effectively when the operating point is in the middle of the load lines.

DuraAct促动器通常被粘合在衬底上,其在整个表面上传递收缩,而非几个连接点。在这种配置中,该DuraAct/衬底组合充当一个弯曲元促动器。弯曲元促动器可实现快速、高精度和可重复的变形,被广泛用于打印机、阀和纺织工业等多种应用。

DuraAct贴片换能器基于横向压电效应,施加电场时将产生收缩。弯曲元折曲并施加一个正交力,如图所示。

自由、未闭锁弯曲元的自由变形为W0。将变形减小至0所需的力称为弯曲元闭锁力FBW,其明显小于促动器闭锁力。穿过这两点的曲线为衬底厚度和弹性的弯曲元特性曲线 

这些曲线反映实际的变形和力,通过由不同材料制成的50毫米衬底样本和P-876.A15 DuraAct贴片换能器测量。

除了DuraAct的特性曲线,弯曲元特性是特定应用中对促动器性能进行有效估算的基础,因此PI在所有数据表中都加入了这些曲线。

弯曲元促动器的参数

DuraAct Patch Transducer Power Requirements

To estimate the electrical requirements necessary for the operation of an actuator, the capacitance of the transducer plays an important role. The capacitance values of DuraAct patch transducers are typically in the nanofarad range and in each case are provided on the datasheets.

Here, the capacitance C is dependent on the type, thickness and area of the piezo ceramic used. To estimate the average electrical output Pm, the control frequency as well as the capacitance of the transducer and the voltage swing are required.
 

Pm = C · f · Uh2

f: frequency, Uh: voltage swing
 

The maximum power requirement Pmax can be calculated by multiplying the average electrical output by pi (π):
 

Pmax = Pm ・ π

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DuraAct压电贴片换能器

灵活、高效、耐用
版本/日期
BRO07E R1 2019-06
版本/日期
BRO07D R1 2019-06
文件语言
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pdf - 1 MB