The everyday life of human beings is influenced by their current surrounding. Matters regarding Transportation, housing, clothing, communication, recreation, and food production play a big role in human culture and their environs. The earliest humans had access to only a very limited number of materials, those that occur naturally: stone, wood, clay, skins, and so on however with the improvement of technology man has evolved from the Stone Age to metal, plastics the composite ages. The turn of the 21stcentury nonethelessushered in the smart materials era. By deﬁnition, smart materials are materials that react relative to their environments in anopportunefashion. This paper is set to explain the concept the behaviour of materials in specific applications in respect to materials science and materials engineering. The discussion in this paper is about ‘Smart materials’ which for some time have been regarded as materials of the future however some like ‘Piezoelectric materials’ have become the breakthrough material in engineering. Piezoelectric materials are derived from the effect of piezoelectriceffect that naturally occur in crystals in nature and mechanically engineered on polymers to create new elements that have given rise to new and effective items in the daily lives of human beings
Key words: Smart material, materials science, materials engineering, piezoelectric materials, piezoelectric effect
Smart Material (Piezoelectric Materials)
William D. Callister, Jr’s book ‘Materials Science and Engineering’ seventh edition introductory phase starts with the photo of the different types of Coke beverage bottles. The image portrays a familiar piece that is fashioned from three unlike materials created the drinks container. Beverage storage containers have been made out of aluminum cans(metal), glass (ceramic), and plastic (polymer).This quickly shows the changes in the use of different materials in generating different designs and providing viable alternatives. This by definition therefor explains “materials science” which is explained as the understanding of the relationships between the structures as well as properties of materials (Schwartz, 2002, p.8). Since its early stages, materials science has experienced a progressive evolution.This is evident from the usage of inert structural materials to materials fashioned for a specific purpose, to adaptive materials.
Current material evolution has led to the creation of smart materials which are engineered to not just as specific function but stimuli recognition, discrimination as well as reaction capabilities. Consequently the introduction of new construction or creative material also influences its design and structure. Through imagery Callister shows evolution by use ofmetal cans, to that of glass in design of the beverage bottle, which is dissimilar to that of the plastic design. From this one can derive the definition of “materials engineering” which is defined as the structure property associations, designing or engineering the structure of a material to create a predetermined novel usable item (p.9). Currently the world is going through a material evolution progressively, a new age known as ‘smart materials era’.
According to Callister’s functional outlook, thebiggest part played by materials scientist is to create or manufacture novel materials, whilethe roles played by materials engineer is called upon to use the novel material to create innovative products or systems using existing materials, and to develop methods for processing materials. By definition Smart materials are materials created to respond and positively react to their immediate environments in a timely manner creating novel designs of already existing items (p.10). The unique nature of these smart materials that make them revolutionary include the ability to receive, transmit, as well as process a as referred to by a user.
From a definitive perspective, engineering or manufacturing materials are regarded as smart if at some point within their performance past they act flexible to a stimulus. Materials that officially have the tag of being ‘smart’ consist of piezoelectric materials, shape memory alloys, electrostrictive materials, ultraviolet-(UV) sensitive materials, thermo-responsive materials, pH-sensitive materials, electrorheological materials, smart polymers, smart gels (hydrogels), smart catalysts, and magnetorheological materials (Wang, & Kang, 1998). According to Callister these specific materials are also supposed to be responsive to the four components of the discipline of materials science. Samples of technical applications of smart material structures are structures such as composite materials embedded with, sound control, actuators, vibration control, microelectromechanical systems (MEMS), sensors, ﬁber optics, shape control, product health and curative monitoring equipment, intelligent processing, active and passive controls, self-repair (healing), artiﬁcial organs, novel indicating devices, designed magnets, damping, aero-elastic stability, and stress distributions appliances(p.26). Smart structures are similarly found in automobiles, aerospace systems, ﬁxed- androtary-wing aircrafts, marine vessels, as well as medical devices.
Currently the smart material includePiezoelectric, which are formed when subjective materials mostly organic crystal and some polymers subjected to an electric charge or a variation in voltage, will go through some mechanical alteration, and vice versa. These events are termed the direct and converse effects. Electrostrictive, these are materials that have similar properties as piezoelectric materialshowever, the mechanical change is relative to the square of the electric field. This characteristic will always produce displacements in the same direction.Magnetostrictive, this are materials that are fashioned when specific materials are subjected to a magnetic field, (direct and converse effects), the mechanical change of this materials consequently make these materialshighly suitable to be used as sensors andactuators.An example of a Magnetostrictive material is Terfenol-D.Shape Memory Alloys. As some materials are subjected to a thermalfield, they undergo phase transformation which will produce shape changes. It deforms to its ‘martensitic’ condition with low temperature, and regains its original shape in its ‘austenite’ condition when heated. An Example of a shape memory alloy is Nitinol TiNi.Optical Fibres, are fibres that use intensity waves, frequency or polarization of modulation to measure strain, temperature, electrical, magnetic fields, pressure and other measurable quantities. These materials can be used as sensors.
From the above examples of used or usable smart material have a high potential in being used for revolutionary applications.
Table 1: Smart Systems for Engineering Applications
|General Requirements and Expectations||Smart Technologies Prospects|
|High degree of reliability, efficiency and sustainability not only of the structure but also of the whole system.||New sensing materials and devices.|
|High security of the infrastructures particularly when subjected to extreme and unconventional conditions||New actuation materials and devices.|
|Full integration of all the functions of the system||New control devices and techniques.|
|Continuous health and integrity monitoring||Self-detection, self-diagnostic, self-corrective and self-controlled functions of smart materials/systems.|
|Damage detection and self-recovery.|
|Intelligent operational management system.|
For the purpose of forming a technical discussion for this paper Piezoelectric Materials are used as a sample of smart materials and are explained to show the evolution of engineering from a material perspective.
Piezoelectric materials are materials or substances that are a result from the chemical reaction called piezoelectric effect. A piezoelectric effect by definition and function is the action of applying weights on the faces of particular crystal cuts, for instance quartz plate, identifying electric charges on the crystal surfaces, as well suggesting that the extent of charge is subjectively proportional to the applied weight (Uchino, 2010). In the 1920s period French scientist Langevin employed this process on quartz crystalsand in turn invent the ﬁrst SONAR, in the following years to come many more other scientist tried to employ the same process on other crystal and other inorganic materials hence discovering new elements for instance polycrystalline, piezoelectric ceramic, barium titanate.
From Langevins experiment it is clear that the piezoelectric effect exists in a number of naturally occurring crystals suchas quartz, tourmaline as well as sodium potassium tartrate. For a crystal to display the piezoelectric effect result, it must not have a centre of equilibrium. When a stress in terms of weight is applied to a crystal with a centre of equilibrium, it will alterthe spacing between the positive as well as negative charge in each fundamental cell unit,hence resulting in a net polarization at the crystal surface. The resulting element or materialwas hence used by Langevin’s to invent the SONAR device.
Just as in organic materials such as crystals the piezoelectric effect can also be applied to various kinds of polymers. After polymerization of the vinylidene ﬂuoride monomer, CH2-CF2 new materials such as semi-crystalline polymer, polyvinylidene ﬂuoride (PVDF), after polymerization are created. These new forms of polymers for instance semi-crystallinewere found to be highly piezoelectric. The PVDF material is created inleaves form from the nonpolar α-phase ﬁlm derived from the polymer melting. The second and ﬁnal step involves of reorientation of the unstructuredset up dipoles associated with the stretched β-phase by applying a poling ﬁeld in the directionnormal to the plane of the ﬁlm. The resulting piezoelectric polyvinylidene ﬂuoride has orthotropic symmetry. A series of polyimides has been invented at NASA, Langley for use in piezoelectric submissions in the aerospace industry. These polyimides have suspended triﬂuoromethyl (—CF3) as well as cyano (—CN) polar clusters (Varadan et al. 2006, p.34). Whenever these polyimides are charged with a voltage of the order of 100 MV/m at high temperatures, the polar clusters transform to a high degree of alignment thus hence creating polymer ﬁlms with high piezoelectric and pyroelectric properties( p.36).
Applications of Piezoelectric Materials
After the new materials have been created through material science as shown above they are then designed or structured to fashion items of various needs of human applications. For instance, a well-known application of piezoelectric ceramics derived from crystals is their use in ink-on-demand printing appliances. Several commercially existing ink jet printers are built upon this technological breakthrough. In this set up the impulse ink jet is fashioned using a cylindrical transducer that is compactly bound to the outer surface of a cylindrical glass nozzle with a select of sizable diameter (Leo, 2007, p. 45). As an addition to this application many other industrious engineers have extended this application upon this technology by using a printer as a chemical delivery system for the application of doped polymers for organic light-emitting displays (p. 47). A group of engineers from Princeton University have used a colour ink jet printer founded upon piezoelectric technology with a resolution of 640 dots per line as well as simply replaced the inks with polymer solutions. This technique has also been applied to the manufacture of color ﬁlters for liquid-crystal displays (p. 50).
Another application of the use of piezoelectric polymer ﬁlm comprise of the work of a group of engineers at the Thiokol Company as well as an earlier expedition or experiment to monitor adhesive joints. The research illustrated that during the bonding process the polyvinylidene ﬂuoride piezoelectric77 ﬁlm sensors devices monitored the adhesive cure ultrasonically as well as qualitatively hence showing a resultof vital void content. The research similarly identified that that normal bond stresses amounted during cyclic piling of single lap joints or electrometric butt joints. The scholars at the facility revealed that this was a vital step toward service life forecasts. Nonetheless, more and better-explained monitoring systems are required. An interesting application of piezoelectric ceramics can be illustrated in the hundreds of vertical pinball machines popular in the Pachinko parlors of Japan (Leo, 2007, p. 55). The machineries are put together with moulds of piezoelectric disks that can be used to stand in both sensors as well as actuators.
Table 2: Applications of Piezoelectric Materials Utilizing the Converse Effect
|Welding||Welding rigid thermoplastics
Seam welding ﬁlm and fabric
Lap welding of high electrical conductivity and dissimilar materials
Seam welding sheets
|Machining||Prophylaxis teeth dental treatment
Vibration-assisted rotary machining of hard, brittle materials
Impact grinding with abrasive slurries
Vibration-assisted drilling, tapping, and turning
|Forming||Drawing thin-wall metal tubing of large diameter-to-wall ratios
Drawing small-diameter wire from difﬁcult to form metals
|Cutting||Vibration-assisted cutting of ﬁbrous and spongy materials|
|Cleavage||Cleaving crystals and laminated objects|
|Densiﬁcation||Compaction of powder|
Table 3: Applications of Polyvinylidene Fluoride Piezoelectric Film
|Diagnostics: Apnea monitor, blood pressure cuff, pulse counter, stethoscope, sleep disorder monitor, respiratory airﬂow, patient bed monitor
Ultrasound: near-ﬁeld imaging, prostrate, transdermal, transluminal, coronary arterial, breast, lithotripter, hydrophone calibration
Handicapped aides: switches, braille reader, hearing aid, speech intensiﬁcation
Implantables: pacemaker activity monitor, vascular graft monitor, micro power source
Instrumentation: intravenous drop counter, IV air bubble detector, laser switch/monitor
|Automotive||accelerometers, occupancy seat sensor, compartment switches, horn, fuel level, tire rotation, security, keyless entry, motion (theft) sensor|
|Consumer||Musical instruments: pick-up, drum trigger
Sports equipment: target location, reaction time, foul time, force, sweet spot
Toys/games: switches, proximity (air ranging, pyro), novelty speakers, target scoring
Audio: tweeter, balloon speaker, novelty speaker (visor, poster), microphone, speaker distortion feedback, electronic piano keys Appliance: washer imbalance, vacuum soil sensing, dishwasher
Computer input/output: keypads, digitizers, mouse, joystick, pen, ink jet droplet generator, ink jet droplet detector, toner and ink jet level, coin counting, disk drive shock sensing
|Industrial||Switches: solid state, snap action, cantilever beam, keypad, vandal proof
Robotics: tactical sensor, micro positioner, safety mats and switches, bumper impact
Security and energy management: glass break detection, ﬂoor/mat sensors, penetration detection, ﬂame detection
Flow/level: fan monitor, ﬂuidic oscillator, doppler ultrasound, solid-state ﬂuid level, laminar/ turbulent layer
In conclusion, in dealing with smart materials and structures, there is still a large amount of unknown data analysisfor instance what makes a material or structure smart and others not smart.Many material scientists have applied the piezoelectric effect on various promising materials for instance crystals and polymers but the results have not been promising. As of those which have had a positive piezoelectric effect their limits are boundless and their properties remain intriguing to many material scientists.In this sense it can be understood that the materials regarded to as Piezoelectric materials have given a new rise to novel products and the type of smart structures that one can design is only limited to an engineer’s skill, capabilities, and ability to innovate
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