Smart Materials Focus on Piezoelectric Materials - Term Paper Example

when Due Smart Materials – Focus on Piezoelectric Materials This research seeks to establish the functionality of piezoelectric materials which constitutes as part of a smart material. First there was a brief introduction into the world of smart or intelligent materials then consequentially there was delving into what the piezoelectric materials entail, and their general applications. Generally piezoelectric materials have various applications in hospitals, printing, automobile industries, and other general usage as polymers. Introduction Smart materials usually belong to a group of materials referred to as ‘functional’ materials. They can also be termed to be “intelligent” but smart is commonly used so as to market the material and its products consequently. In terms of the global perspective, the world has undergone two drastic material-based ages during the past centuries – composite and plastic ages. Concurrently, in the midst of this two noted ages, a new era has become dominant and recognizable [1-4]. This is the era of smart materials. In relation to early definitions, smart/functional materials are those materials that adversely respond to their environment within a shorter time. It is imperative to note that the definition of functional/smart materials has been diversified to materials capable of receiving, transmitting, or processing stimuli such as temperature, stress, strain, pH stimuli, magnetic and electric fields, different radiation types, hydrostatic pressure among other forms of stimuli [5]. They react to this by being capable of producing a useful outcome that may comprise a signal that the materials act upon [1]. The end result of this can be caused by a series of events integrated together, a chemical reaction, absorption of a proton, translation or rotation of molecular structure segments, initiation and shifting of crystallographic flaws or other localized conformations, modification of localized strain and stress fields, among others. The effects fabricated can be a disparity in colour, dissimilarity in the refraction indexes, imbalances in the disposition of stresses and strains, or variations in volume. For a material to be classified to be smart/functional, its action of receiving and afterwards responding to stimuli in order to produce a useful outcome must be reversible. Additionally, it should be asymmetrical in nature, and this relates majorly to piezoelectric materials. Other functional materials manifest similar traits. However, scientists have performed little research in tandem to this observation [1]. From a purist point of view, there are some materials that qualify to be formally called smart. This include the likes of thermo responsive materials, pH-sensitive materials, UV-sensitive materials, smart polymers, smart gels (hydrogels), smart catalysts, piezoelectric materials, electrostrictive materials, electro rheological materials, magneto rheological materials, , and shape-memory alloys and polymers. In this treatment of the subject, I thereby delve to focus on piezoelectric materials which serves as one of the functional materials. I will indulge in research to explore more on the material as well as its applications. Piezoelectric Materials There is always a large influence of materials on society. It was highly noted and obvious in the Stone Age, Bronze Age, and Iron Age. It is imperative to note that these eras came about as a result of the most advanced material notable in those periods. This owes to the fact that these materials were used to identify and limit the technological state at the moment. On the other hand, the influence of these materials is still present in the modern society. However, the same materials are nowadays less visible than they used to be. In order for the economy to exist and function more efficiently, the materials are embedded within high tech and complex systems. Among the ‘invisible’ materials that are widespread around us though unknown to most in the public are the piezoelectric materials. Most importantly is that the few areas where piezoelectric components are indispensable include likes of automotive electronics, medical technologies, industrial systems and mobile phones. As the Fig 1. illustrates below, there is the adoption of piezoelectricty to capture unborn babies images in the womb. This is possible through echoes prevalent. Fig 1. Echoscopy image of an unborn baby in the womb Another predominant area where piezoelectric material is in use is at the back of the car where parking sensors are located. Piezoelectric Effect and History of Piezoelectric Materials In 1880, Jacques and Pierre Curie discovered the piezoelectric effect. After a tentative research, they came to a conclusion that if quartz, topaz, tourmaline, cane sugar and Rochelle salt crystals were subjected to mechanical strain, they became electrically polarized and the degree of polarization was proportional to the applied strain. In addition, their research made them discover the tendency of these materials to deform given they are exposed to an electric field. As a result, the term ‘inverse’ piezoelectric effect came to being. This owes to the fact that there existed a converse to the Curie’s ideology of direct-pressure piezoelectric effect discovered by Gabriel Lippman in 1881 [7-8]. The piezoelectric effect is exhibited in a number of naturally occurring crystals which include: Topaz, quartz, tourmaline, and sodium potassium tartrate. In order to exhibit the piezoelectric effect, a crystal must not have a centre of symmetry. Given stress - either compressive or tensile - is applied to a crystal with a centre of symmetry, it will alter the spacing between the positive and negative poles in each elementary molecule, and consequentially resulting to a net polarization at the crystal surface. The outcome is estimated to be linear. The polarization is directly proportionate to the applied stress [1-6]. Thus, tensile and compressive forces will generate electric fields and voltages of opposite polarity. The outcome is also reciprocal; thus, when the crystal is exposed to an electric field, it undergoes an elastic strain varying its length based upon the field polarity. Fig 2. Monocrystalline with single polar axis Polycrystalline with random polar axis Fig 2. Above shows symmetrical and asymmetrical concepts using monocrystalline with single polar axis and polycrystalline with random polar axis. In the figure below, Fig 3, however, we have that the piezoelectric effect is produced when the polycrystalline is heated in presence of a strong electric field. As shown, clearly, heat allows the movement of molecules to be more with ease, and the electric field forces comprised in the dipoles to line up and face nearly the same direction. Fig 3. Random Dipole Polarization Surviving Polarity As previously mentioned, the ceramic-based materials play a critical role in the subject of piezoelectric. Piezoelectric ceramics constitute polycrystalline ferroelectric materials with a perovskite-crystal-type structure. The crystal structure is tetragonal/rhombohedra nearly resembling a cube in nature. Piezoelectric ceramics have the general formula of A2+B4+O2-3 where A represents a large divalent metal ion such as lead or barium and B represents one or more tetravalent metal ions such as titanium, zirconium, or manganese. The piezoceramics are considered to be masses of minute crystallites that change crystal forms given Curie temperature. Above the Curie temperature, the ceramic crystallites have a simple cubic symmetry. This form is Centro symmetric with positive and negative charge sites coinciding with no dipoles present. The material is considered to be paraelectric. Below the Curie temperature, the ceramic crystallites have a tetragonal symmetry; this form lacks a centre of symmetry with the positive and negative charge sites no longer coinciding, thus each unit cell has an electric dipole whose direction may be reversed and switched by the application of an electric field. The material is now considered to be ferroelectric. Fig. 4. Below shows a PZT elementary cell with a) representing the lattice in form of a cubic form above Curie temperature and b) representing a tetragonal lattice below Curie temperature respectively. Fig. 4 Crystal structure of a traditional piezoelectric ceramic (BaTiO3) at temperature above (a) and below (b) Curie point Much reference is made to piezo axes and their relation to the poling axis. Convention and the IEEE Standard on Piezoelectricity state that the poling axis be termed the “3” direction with the same positive/negative sense as the applied voltage field. The remainder of the coordinate system is analogous to a right-handed orthogonal system, mapping x-1, y-2, and z-3, as shown in Fig 5. Fig 5. Basic symbols and terminology in piezoelectricity. Applications for Piezoceramics The piezoelectric effect provides the go ahead to use these materials as both an actuator and sensor. When a material is strained, it would be possible to measure its voltage. When adopted as sensors, these materials can be used for damage detection in buildings they are incorporated in. Also, they can be used as actuators since they have straining tendencies when an electric voltage is applied across the poling axis. As a result, PZTs make good candidates for active control systems or valve actuation [4-7]. Additionally, piezoceramics are also used as structural dampers because of their ability to adversely manipulate electrical energy to mechanical energy and vice versa. Given a PZT is used for passive vibration suppression, the force from the vibration displaces the PZT and thus resulting in a voltage difference. This voltage, electrical energy, can then be dispersed through a resistive circuit. For example, the use of piezoelectric elements for passive electronic damping has already been proven to work effectively in commercial products such as the K2 ski. The K2 ski designers used a resistor and capacitor (RC) shunt circuit to scatter the vibration energy absorbed by piezoelectric devices incorporated into the skis. Applications for Piezoelectric Materials Rubber, copolymers and piezoceramic blends of PVDF have been lead up to be used as piezoelectric materials. The most prevalent copolymer in this sense, is one based on polymerization reactions of trifluoroethylene and vinylidene fluoride. Polyvinylidene fluoride together with its copolymers with trifluoroethylene have high hydrostatic-mode responses, low mechanical quality and their acoustic impedance is same as that of water. As a result, they are ideal for underwater hydrophone applications [9]. In NASA Langley, polyimides have been developed for use in piezoelectric applications. The groups contain cyano (-CN) and pendant trifluoromethyl (-CF3) polar groups. When these polyimides are exposed to applied voltages amounting to 100MV/m at temperatures which are elevated, the polar groups develop high degree orientation. As a result, polymer films with high piezoelectric and pyro electric properties are formed. Piezoelectric entities have been developed as smart tagged composites which form soft piezoelectric ceramics (PZT-5A) contained in unsaturated polyester polymer matrix. These are used for structural health monitoring [10]. Conductive metal-filled particles with polyimide films have been explored for many microelectronic applications. The use of graphite-filled polymers has proven as potential micro sensors and actuators. These Piezoelectric materials have been used in thousands of applications in a wide variety of products in the consumer world in areas such as; industrial, medical, aerospace and military fields. One of the industrial uses of piezoelectric ceramics and polymers is in ‘ink-on’ demand printing. Several commercially available ink-jet printers apply this technology. Another application of piezoelectric polymer film is based on the work of a group of researchers at the Thiokol Company and an earlier work to monitor adhesive joints. The study also indicated that the normal bond stresses were quantified during cyclic loading of single lap joints and electrometric butt joints. This research showed that it was a significant leap in service life prediction. Another interesting application of piezoelectric ceramics can be illustrated by vertical pinball machines which are popular in the Pachinko parlours of Japan. The machines are assembled with stacks of piezoelectric disks that can act as both sensors and actuators. When a ball falls on the stack, the force upon generates a piezoelectric voltage pulse causing a response from the actuator stack through a feedback control system. The stack expands, causing the ball to be thrown out of the hole and moving it up a spiral. Conclusion Conclusively, smart materials play an important role in our societal life and mainly in engineering. We live in an era whereby in order to survive, we have to apply the applications of smart materials. Of the many types of smart materials we have, each and every one of them plays a crucial role in the day to day life we live. It is thus important to respect and use the quality materials wisely to sustain growth in the expertise areas. Works Cited 1. Amato, Sci. News, 137(10), 152–155 (Mar. 10, 1990). 2. Port, Business Week, No. 3224, 48–55 (Mar, 10, 1990). 3. Committee on New Sensor Technologies, Materials and Applications, National Materials Advisory Board, Commission on Engineering and Technical Systems, National Research Council Report, Expanding the Vision of Sensor Materials, National Academy Press, Washington, DC, 1995, pp. 33– 45. 4. C. A. Rogers, Sci. Am., 273(3), 122–126 (Sept. 1995). 5. J. A. Harvey, Kirk-Othiner Encyclopedia of Chemical Technology, 4th ed., Supplement, Wiley, New York, 1998, pp. 502–504. 6. Chopra, in Proceedings of the Smart Structures and Materials 1996—Smart Structures and Integrated Systems Conference for the Society of Photo-Optical Instrumentation Engineers, Vol. 2717, San Diego, Feb. 26–29, 1996, pp. 20–26. 7. T. Thomas, Portland, OR, private communication, 1999. 8. Technical bulletins and notes, Sensor Technology Limited, Collingwood, Canada. 9. T. T. Wang, J. M. Herbert, and A. M. Glass (eds.), Applications of Ferroelectric Polymers, Blackle and Sons, Glasgow, 1988. 10. J. O. Simpson, http:hsti1arc.nasa.gov/randt/ I995/Section131.fm513.html Read More