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Structures of Smart Transducers
Published in Kenji Uchino, FEM and Micromechatronics with ATILA Software, 2018
The bending deformation in a bimorph occurs because the two piezoelectric plates are bonded together, and each plate produces its own extension or contraction under the applied electric field. This effect is also employed in piezoelectric speakers. The induced voltage associated with the bending deformation of a bimorph has been used in accelerometers. This is a very popular and widely used structure mainly because it is easily fabricated (the two ceramic plates are just bonded with an appropriate resin), and the devices readily produce a large displacement. The drawbacks of this design include a low response speed (1 kHz) and low generative force because of the bending mode. A metallic sheet shim is occasionally used between the two piezoceramic plates to increase the reliability of the bimorph structure, as illustrated in Figure 3.15. When this type of shim is used, the structure will maintain its integrity even if the ceramic fractures. The bimorph is also generally tapered to increase the response frequency while maintaining optimum tip displacement. Anisotropic elastic shims, made from such materials as oriented carbon-fiber-reinforced plastics, have been used to enhance the displacement magnification rate by a factor of 1.5 as compared to the displacement of a similar device with an isotropic shim.14
Designing with Materials and Devices and Fabrication Processes
Published in Kenji Uchino, Ferroelectric Devices, 2018
Unimorph and bimorph devices are defined by the number of piezoelectric ceramic plates: only one ceramic plate is bonded onto an elastic shim, or two ceramic plates are bonded together, respectively. The bimorphs are mainly considered here. The bimorph causes bending deformation because two piezoelectric plates are bonded together and each plate produces extension or contraction under an electric field. This effect is employed for various speakers. The bimorph induces voltage for a bending deformation, which can be used for accelerometers. Since the fabrication process is simple (two ceramic plates are just bonded using a resin) and large magnification of the displacement is easily obtained, this structure has been widely used. However, the drawbacks include a low response speed (1 kHz) and low generative force due to the bending mode (tensile stress concentrates on the top of the piezoplate). A metallic sheet (called the shim) is occasionally sandwiched between the two piezoceramic plates to increase the reliability, that is, the structure is maintained even if the ceramic fractures (Figure 3.24). Also notice the tapering of the bimorph, which increases the response frequency by maintaining the tip displacement magnitude.
Advanced materials for green aviation
Published in Emily S. Nelson, Dhanireddy R. Reddy, Green Aviation: Reduction of Environmental Impact Through Aircraft Technology and Alternative Fuels, 2018
In piezoelectric materials, mechanical stress causes crystals to electrically polarize and vice versa. Application of electric current causes the piezoelectric material to deform, enabling the material to work as an actuator, shown in Figure 5.18. The most widely used piezoelectric material is lead zirconate titanate (PZT) ceramic, Pb(Ti, Zr)O3. The displacement of a single layer of piezoceramic is too small for large stroke driving. Therefore several piezoelectric pieces are stacked together to provide large stroke. Two of the most popular actuator designs are multilayers and bimorphs (Fig. 5.19). In a multilayer design, multiple thin piezoceramic sheets are stacked together. The multilayer design has the advantage of low driving voltage, quick response (10 ms), and high generative force (1000 N). However, the multilayer design has low displacement (on the order of 10 mm), which may not be suitable for some applications. In the bimorph design, multiple piezoelectric and elastic plates are bonded together to generate a large bending displacement of several hundred microns. The drawback of the bimorph design is relatively low response time (on the order of 1 ms) and small generative force (on the order of 1 N). Applications of piezoceramic materials for green aviation include noise reduction, vibration reduction, and active flow control to reduce emissions and improve aerodynamic performance.
Flexural vibration of a lithium niobate piezoelectric plate with a ferroelectric inversion layer
Published in Mechanics of Advanced Materials and Structures, 2020
Piezoelectric devices based on flexural deformation or modes are widely used. This article is concerned with the application of Lithium niobate plates with an inversion layer as bending transducers. It is well known that in a homogeneous piezoelectric plate extensional and shear strains can be directly produced by a uniform electric field which is usually generated by a voltage across the plate thickness. To produce bending in a plate, a standard practice is to use a composite plate of two piezoelectric ceramic layers (bimorph) with opposite thickness poling and hence piezoelectric constants of opposite signs. In a piezoelectric bimorph, under a uniform thickness electric field, the strains in the two layers produced by the electric field have opposite signs. One layer contracts while the other extends or vice versa, and thus bending is created. Bimorphs have interfaces which are usually the origin of the degradation of structural strength and the drop of device quality factor. In a lithium niobate plate with an inversion layer, the piezoelectric constants of the inversion layer have opposite signs to those of the regular layer. Therefore, a uniform electric field can produce bending in such a plate. At the same time, a lithium niobate plate with an inversion layer does not have a usual interface and is effectively one plate. This suggests that a lithium niobate plate with an inversion layer can be used as a simple and effective bending resonator or transducer. It has the potential to become one of the major means of producing bending in a plate by an electric field.
On geometrical configurations of vibration-driven piezoelectric energy harvesters for optimum energy transduction: A critical review
Published in Mechanics of Advanced Materials and Structures, 2023
Dauda Sh. Ibrahim, Yuxiang Feng, Xing Shen, Umer Sharif, Abdurrahman Ahmad Umar
Conventional rectangular cantilever beam bonded with piezoelectric layers has been the generic shape used to harness vibration energy from ambient sources [56–61]. The setup for the piezoelectric transducer on the rectangular beam could be either a unimorph [26, 62], that is the substrate covered with a piezoelectric patch on its lower or upper surface as shown in Figure 5(a) or a bimorph which has two surfaces layered with the smart material as depicted in Figure 5(b). The unimorph configuration can be designed in 31-mode or 33-mode depending on electrode arrangements with respect to the piezoelectric layer. In the 31-mode, the layered piezoelectric material is sandwiched between two electrodes, while in the 33-mode, the electrode is on top of the transducer with an inter-digital electrode pattern. On the other hand, the bimorph configuration is commonly designed to operate in the bending mode so as to have the top layer in tension and the bottom layer in compression or vice versa when the system vibrates, hence generating electric charge in accordance with the piezoelectric effect. The charge poling of the top and bottom layers can be made in the same direction or in the opposite direction, which is commonly known as parallel or series poling. The essence is to induce accumulated current in parallel poling or voltage in series poling from each layer [63]. It is obvious that the bimorph configuration has the advantage of producing higher output when implemented in an energy harvesting scenario. However, the unimorph configuration is more preferable for MEMS applications due to the lower cost incurred for production [64].
Vibration control techniques during turning process: a review
Published in Australian Journal of Mechanical Engineering, 2021
X. Ajay Vasanth, P. Sam Paul, G. Lawrance, A.S. Varadarajan
They belong to a group of materials when mechanically strained produces an electric charge and vice-versa allowing them to be used either as a sensor or an. Piezoelectric materials have been widely used in many structural dynamic applications as they are light in weight, robust, and available in a variety of forms ranging from thin rectangular complicated forms. The basic fundamental, modelling of these materials were looked upon in the early 1990s. Smits, Dalke, and Cooney (1991) formulated the constituent equations of piezoelectric bimorphs with the upper and lower elements having opposite polarisation, which caused bending when excited by an electric field. Their model was a result of their development of an integrated micro-robot with legs that were moved piezoelectrically and the model was derived using strain energy method. Smits later extended the study to a piezoelectric heterogeneous bimorph. The heterogeneous bimorph consists of a piezoelectric element bonded to the top of a non-piezoelectric element. This model was also derived using strain energy method to predict the free-end shape and deflection for an applied electric field with the structure subjected to given boundary condition (Smits and Choi, The Constituent Equations of Piezoelectric Heterogeneous Bimorphs 1991). The use of sensors and actuators in a feedback control loop is said to make smart structure. Bailey and Hubbard (Bailey and Hubbard 1985) designed an active vibration damper for a cantilever beam using distributed parameter actuator and distributed-parameter control theory. A piezoelectric polymer bonded to one side of cantilever beam was used as actuator and the control algorithm for the active damper was designed using Lyapunov’s second method for distributed parameter system and from the results they observed that vibrations were successfully controlled. The method on applying the piezo electric material to the machining process will vary to a great deal.