Extras din document Notiuni teoretice: Efectul piezoelectric a fost descoperit in anul de catre fratii Pierre si Jacque Curie si pus in evidenta prin aparitia unei diferente de potential electric la capetele unui dielectric sau feroelectric, atunci cand asupra lui actioneaza o forta de compresie mecanica. Diferenta de potential se datoreaza polarizarii electrice a materialului piezoelectric sub actiunea deformatoare a solicitarii mecanice externe. Polarizarea electrica consta in aparitia unor sarcini electrice pe suprafata materialelor piezoelectrice supuse actiunii fortelor de compresie sau de intindere. Piezoelectricitatea este caracterizata printr-o relatie directa intre cauza si efect.
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History[ edit ] Discovery and early research[ edit ] The pyroelectric effect , by which a material generates an electric potential in response to a temperature change, was studied by Carl Linnaeus and Franz Aepinus in the midth century.
The first demonstration of the direct piezoelectric effect was in by the brothers Pierre Curie and Jacques Curie. Quartz and Rochelle salt exhibited the most piezoelectricity. A piezoelectric disk generates a voltage when deformed change in shape is greatly exaggerated. The Curies, however, did not predict the converse piezoelectric effect. The converse effect was mathematically deduced from fundamental thermodynamic principles by Gabriel Lippmann in For the next few decades, piezoelectricity remained something of a laboratory curiosity, though it was a vital tool in the discovery of polonium and radium by Pierre and Marie Curie in More work was done to explore and define the crystal structures that exhibited piezoelectricity.
World War I and post-war[ edit ] The first practical application for piezoelectric devices was sonar , first developed during World War I. In France in , Paul Langevin and his coworkers developed an ultrasonic submarine detector. By emitting a high-frequency pulse from the transducer, and measuring the amount of time it takes to hear an echo from the sound waves bouncing off an object, one can calculate the distance to that object.
The use of piezoelectricity in sonar, and the success of that project, created intense development interest in piezoelectric devices. Over the next few decades, new piezoelectric materials and new applications for those materials were explored and developed. Piezoelectric devices found homes in many fields. Ceramic phonograph cartridges simplified player design, were cheap and accurate, and made record players cheaper to maintain and easier to build. The development of the ultrasonic transducer allowed for easy measurement of viscosity and elasticity in fluids and solids, resulting in huge advances in materials research.
Ultrasonic time-domain reflectometers which send an ultrasonic pulse through a material and measure reflections from discontinuities could find flaws inside cast metal and stone objects, improving structural safety. World War II and post-war[ edit ] During World War II , independent research groups in the United States , Russia , and Japan discovered a new class of synthetic materials, called ferroelectrics , which exhibited piezoelectric constants many times higher than natural materials.
This led to intense research to develop barium titanate and later lead zirconate titanate materials with specific properties for particular applications.
One significant example of the use of piezoelectric crystals was developed by Bell Telephone Laboratories. Lack, working in radio telephony in the engineering department, developed the "AT cut" crystal, a crystal that operated through a wide range of temperatures. This development allowed Allied air forces to engage in coordinated mass attacks through the use of aviation radio.
Development of piezoelectric devices and materials in the United States was kept within the companies doing the development, mostly due to the wartime beginnings of the field, and in the interests of securing profitable patents. New materials were the first to be developed—quartz crystals were the first commercially exploited piezoelectric material, but scientists searched for higher-performance materials.
In contrast, Japanese manufacturers shared their information, quickly overcoming technical and manufacturing challenges and creating new markets. In Japan, a temperature stable crystal cut was developed by Issac Koga. Japanese efforts in materials research created piezoceramic materials competitive to the United States materials but free of expensive patent restrictions.
Major Japanese piezoelectric developments included new designs of piezoceramic filters for radios and televisions, piezo buzzers and audio transducers that can connect directly to electronic circuits, and the piezoelectric igniter , which generates sparks for small engine ignition systems and gas-grill lighters, by compressing a ceramic disc. Ultrasonic transducers that transmit sound waves through air had existed for quite some time but first saw major commercial use in early television remote controls.
These transducers now are mounted on several car models as an echolocation device, helping the driver determine the distance from the car to any objects that may be in its path. Mechanism[ edit ] Piezoelectric plate used to convert audio signal to sound waves The nature of the piezoelectric effect is closely related to the occurrence of electric dipole moments in solids.
The latter may either be induced for ions on crystal lattice sites with asymmetric charge surroundings as in BaTiO3 and PZTs or may directly be carried by molecular groups as in cane sugar. Dipoles near each other tend to be aligned in regions called Weiss domains. The domains are usually randomly oriented, but can be aligned using the process of poling not the same as magnetic poling , a process by which a strong electric field is applied across the material, usually at elevated temperatures.
Not all piezoelectric materials can be poled. This might either be caused by a reconfiguration of the dipole-inducing surrounding or by re-orientation of molecular dipole moments under the influence of the external stress. Piezoelectricity may then manifest in a variation of the polarization strength, its direction or both, with the details depending on: 1.
The change in P appears as a variation of surface charge density upon the crystal faces, i. Linear piezoelectricity is the combined effect of The linear electrical behavior of the material: D.
Squeeze certain crystals such as quartz and you can make electricity flow through them. The reverse is usually true as well: if you pass electricity through the same crystals, they "squeeze themselves" by vibrating back and forth. In practice, the crystal becomes a kind of tiny battery with a positive charge on one face and a negative charge on the opposite face; current flows if we connect the two faces together to make a circuit. In the reverse piezoelectric effect, a crystal becomes mechanically stressed deformed in shape when a voltage is applied across its opposite faces. What causes piezoelectricity? Think of a crystal and you probably picture balls atoms mounted on bars the bonds that hold them together , a bit like a climbing frame. So a lump of iron is just as much of a crystal as a piece of quartz.
Gokazahn Behind the sound wave the crystal stays deformed in the equilibrium position for the high electric field. Thus the current gain of this transistor is one for piezoelectroc ns switching, but it still has voltage gain. The driver must withstand the doubled voltage returned to it. Descoperirea efectului piezoelectric a fost precedata si chiar favorizata de efectul piroelectric, cunoscut nca din secolul alXVIIlea, la cristalul de turmalina.
History[ edit ] Discovery and early research[ edit ] The pyroelectric effect , by which a material generates an electric potential in response to a temperature change, was studied by Carl Linnaeus and Franz Aepinus in the midth century. The first demonstration of the direct piezoelectric effect was in by the brothers Pierre Curie and Jacques Curie. Quartz and Rochelle salt exhibited the most piezoelectricity. A piezoelectric disk generates a voltage when deformed change in shape is greatly exaggerated.