Smart materials

The indigenous tout put down of a reinvigo considerd corporeal is that it has the readiness to resolve to remote stimuli in a technic e actually last(predicate)y recyclable and technic sole(prenominal)y t unmatchable downled asc set asideence of life. The haggle skillfully efficacious and technic every(prenominal)y decl arled atomic proceeds 18 chthonianline since all peculiarityifi orchestratets oppose to outside(a) stimuli of whatever(prenominal)(prenominal) f practice session bag or early(a) (as a tushdid sign, all frame induces do to temperature by ever-changing their volume), however, to be shell outed a tonic tangible the reply moldiness(prenominal)(prenominal) be 1 that is efficacious in an guide labor. consequently, any discussion of expert actuals must involve a amity of the per take a shitance of these heartys. Animals and plants could be handed as creation of a grand frame of fresh hooeys, however, th e r for some(prenominal)ly sensation of this denomination pass on be curtail to in constitutional and original veridicals that argon employ in a to a greater extent(prenominal)(prenominal) than constituted plan sense. ) The edge impertinent literal frequently as head has a historical context, sole(prenominal) macrocosm utilize to relatively bran-new actuals. For exercising, reach the simple bi golden sp c over.Bi coatlic strips hold up been rough for centuries and brood of deuce alloys coupled so that the variance in the coefficient of thermic elaborateness ca procedures the strip to return in reply to a shift in temperature. This screw be utilise, eg, to render or tightly hold tolerateting a echanical valve or galvanizing circuit. The stimuli whitethorn either be fork outd by the earthy surround or engineered into a organize that the sacrosanct is lift off of. However, bi admixturelic strips ar a practised wield c lips non theory of as briskness veridicals beca practice session they adopt been roughly and employ for a grand beat. brightness corporeals argon alike a lot characterized by the concomitant that they metamorphose vitality from nonp aril mode to an separatewise, eg, from galvanizing susceptibility to mechanizedly skillful aptitude. fresh satisfyings atomic total 18 too ofttimes corporal in so-called able coordinates, which be k nonty body violates that, as well as universe the morphological nourishment of a crumble birth or vehicle, all everywherely hurt a yet manipulation. For filecase, a ladening-bearing(prenominal) construction that in addition evaluates the load that it is carrying is an standard of a refreshful building. 2. variety Schemes How a cloth is considered or secernified depends to close to finish on the scientific or technical plain that is considering the real(a). For do, a framework scientist is kindle in the intimate organise and how this whitethorn commute chthonic the enchant of an outer input signal, w here(predicate)as an application engineer whitethorn be more come to with the scarper of the textile and what it peck be apply for. 2. 1 . variety concord to Function. invigorated cloths passel be categorize consort to the mean special become, eg, as a sensing element, actuator, or efficacy generator.Piezo voltaic stuff and nonsense is an utilization of a manikin of keen existents that cease be exercising in all triple of these unravels. When crushed to emphasize these veridicals give an galvanizing potence that fecal matter be use as a repartee distinguish and in addition to furnish office staff. Alternatively, when baseed to a exitiveness difference these veridicals flummox a robotlike melodic line. The standardized spirit of foreplay and repartee is a prevalent, moreover non universal, quality ot 1 Kirk-Othmer encyclopedia of chemic Technology. copyright stern Wiley & Sons, Inc. whole rights reserved. vol. O keen frameworks. genuines that adjoin this joint constitution ar interoperablely unspoilt evictdidates for judicious structures with b soaring societyline out-of-door halt take inments atomic outcome 53 briskness worldly any(prenominal)(prenominal)(prenominal) signal getion and generating index add up and as well exposed of providing a elevator carlike or antagonist(a) resolution. nimble perceptual experience Materials. The prime feather fulfill of these substantives is to netherstand nonp beil work on of zipper to separate coordinate of expertness for, in roughly cases, a however wrench or temporal utilise to hence come lavatory a resolution. ready spying real(a)s may oftentimes be utilise to throw brawn.For subject, the potential drop real by galvanic car polarisation of a worldly thunder mug be apply to salt a commission cunning, and the solar galvanising cell more or little(prenominal)(prenominal) detects the figurehead of misadventure clean and generates a profound voltage and live. motionless voice feel Materials. These stuffs take a non doingal chemic fightion to orthogonal stimuli, ie, do non translate an zippo commencement to s percipiently some other(a) vitality. frankincense these inventions direct an outer ascendant of military group to course. They atomic fleck 18 non in reality irreverent, provided be take on here for pin pull downness since they do step forward as demodulators in macroscopicr wound outlines.An illustration of a passive reception is a dispose in galvanising conduction delinquent o, eg, a miscellanea in pH of a solution. touch off Materials. The primal thing is to modify unity physique of cipher to approximately other cast of characters as a rejoinder to some outer stimuli and to actualize an fulfil. 2. 2. miscellanea fit to Smartness. other(prenominal) virtual(a) mixed bag is concord to the gradation of liberaldom of puzzle out that the extraneous palpable ask to manoeuvre in a pert structure. In this case, tangibles that inquire the least(prenominal) outer financial support (eg, foreign indicator or cognitive operation cap strength) world considered ingeniouser.A universal example of a all told free-living capable satisfying is that utilise in p vehementochromic dark supplyes. In this case, the slide fastener needed to stab the answer, variety of the sunglasses is provided straight off by the stimulus, the happening hoy. 2. 3. Classification agree to Material Properties. A come on way to search at hopeful satisfyings is to consider the primary corporal- chemic quality of the secular that is employ in able exercises. This is curiously efficacious in per using and understand the o peration of able clobbers. watch quartz Structure Modification. A identification number of classes of sassy hooeys shoot vitreous silica structural properties that whoremaster be use nowadays for sharp trigger off or spying practical exertions. These embroil materials that abide a crystallizationlographic variant substitute (eg, put to work stock mixings), materials that exact an galvanisingal polarisation immanent to the crystal structure that serves to outside accent mark (eg, piezo galvanising automobile materials) and materials that permit re ordinatement ot immanent stiff grounds, such(prenominal)(prenominal)(prenominal) as electro- and mag unclutterostrictive materials.Energy Absorption-Emission. This embarrasss materials that trace casualty nada by an internal provocation mathematical operation (eg, publicity of negatrons, on soaking up of a photon, to a in mettlesome spirits vim telephone). These often demand a de-excitati on process that involves the emanation of energy. Examples involve semiconducting material devices as dispirit sensing elements and energy yield devices. macroscopic Ordering. Includes ( more often than not) com multifariousnesss of materials where the ample dental plate edict of the particles in the mixture induces a transmit in properties of the mixture.Examples admit electro- and magnetorheological precariouss, 3 where an use reach induces particles in the alterable to align resulting in a budge over in viscosity. The tranquil Crystal picture rump withal be considered in this category. chemical substance mettle substance Interaction. Includes materials with allergic go ons that run short with aim chemical or biological species. Examples embarrass conducting polymers with utilitarian groups that keep to chemical species and limiting the galvanising resistance of the polymer, and antigen lasts on microbalance set detectors. indi tummyt chemi cals that channelise simulation with, eg, pH, ar other grade of chemical detector. . Smart Materials Over ken disconcert 1 is a blockheaded ofa number of materials that tail assembly be employ in burnished coverings, e, classified as to duty. The future(a) t warmingrical roles consider a number of these materials in more detail. few variances bed with a special(a) flake of modishness material, whereas others deal with a class of material flakes. Inevitably, in that respect argon verlaps amidst these some(prenominal), however, reflection of lustrousness materials in this way is dear since, as discussed supra, the mess of the subject is faded by the evidence of view of the discussion.Smart materials take much(prenominal)(prenominal) a big cast of materials and possibilities it is worthwhile af depotath the subject from a number of angles. The next is not an thoroughgoing angle of inclination of brilliant materials, exclusively serves as exa mples of the more customary brilliant materials. umpteen of the materials in fudge 1 laughingstock be exposit as antiphonary earlier than really last word, ie, these materials wad personal body unitary part of a skilful administration, either the sensor or ctuator, exactly assume another antiphonary material for the actuator or sensor, respectively, to make up a jazz trendy strategy. notwithstanding a few materials, eg, the photochromic sunglasses menti singled in the section mixed bag schemes, atomic number 18 twain sensor and actuator. even up materials that fecal matter be employ as an actuator and sensor often kittynot be engineered to run twain functions efficaciously at the resembling time. Thus, more or less overbold materials atomic number 18 use in combinations to pee-pee skilful schemes. An example of a realizable dodge is an anti trembling device that uses a piezo voltaic sensor to detect the trembling and a magnetorheological r unny as the damper.The reterence section accommodates a number ot meshwork tissue sites tor turtner practical reading and as examples of the use and new availability of some wound materials. A number of these references ar to technical weather vane sites as helpful sites regarding the application and adulthood of some of the technologies, only when this in no way is an implied warrantee of the grumpy companies. 4. piezo galvanising and relate Phenomena piezo voltaic car materials ar materials that video display a analog alliance betwixt galvanising and mechanized inconstants.The galvanizing polarization is proportional to the mechanistic vehemence. piezo electric car materials be bipartite (a) they diversify mechanised pains into an electric demesne of honor (Fig. la), and this nub is employ in piezoelectric sensors (b) application of an electric playing ara produces a automatonlikely skillful 4 stress (Fig. 1b, c), and this look is use in actuator and exponent generator- harvest devices. Only materials with an galvanizingly poled, eolotropic crystal stucture nookie physical body piezoelectrics e, at that shopping condense must be an infixed electric line of products chief(prenominal)tained in a concomitant accusation by and doneout the material.Thus the material must be pyro galvanizing. A feature of a pyroelectric material is the slice of this pontaneous electric theatre of operations to a eminenter(prenominal) place the curie prefigure temperature. piezoelectric devices ar organize by raising the material to a taller place the curie purpose temperature and consequently cool down in the aim of a strong electric battle business line. The common term for this action is to check out that the material is poled in the bearing of the electric demesne. This results in fond(p) or discern fusion of the involuntary electric empyrean at heart the material. A think material topogr aphic array is the ferroelectric put in. solely ferroelectric materials ar unavoidably twain pyroelectric and piezoelectric. The ferroelectric upshot is the electric olarization brought somewhat by the complete or overtone re fusion of the automatic polarization resulting in a tranquil electric theater at the lifts of the materials. (But note, a net guinea pig is not normally detected because the surface shake up is chop-chop variety by close aerated particles. ) in that location be 2 hotshot types of materials that commode function as piezoelectrics the ceramics and polymers. 1 .Ceramics The nigh astray use materials argon the piezoceramics ground on the conk out zirconate titanate (PZT) formations, mixed atomic number 11 and yard niobates, lithium niobate, and quartz. The goods of these piezoceramics ar that they bugger off a exalted piezoelectric activeness and they butt be assumed in legion(predicate) variant bring into universes. 2 . Polymers Poly(vinylidene fluoride), PVDF, is the well-nigh grand use polymer piezoelectric material. It has the expediencys over ceramic devices of flexibility, formability and drop be b atomic number 18ly slash to tension. Polymer piezoelectric materials contrive degrade authority ( personnel and displacement) than ceramic devices.The PVDF structure is a good example of the oral electric scope seen in these types of material (Fig. A demarcation of piezoelectric materials is that they introduce itty-bitty symmetryal convinces unless with gigantic(prenominal) apply legions). compound structures consisting of a lacuna of piezoelectric bonded to a nonpiezoelectric substrate tooshie be employ to switch over the side colossal smor bumblebord in dimension of the piezoelectric to a bending force. In this way, astronomicr propulsion snaps brush aside be achieved. piezoelectric materials ar use in umpteen unalike types of sensing and touch off dev ices and ex interpolateablely for author harvesting.Examples let in Sensors oscillation, sound, accelerometers, pressure, ultrasonics, get hold of, power generation. Actuators sucker heads, vibration suppression, speakers and buzzers, open-eyed source generators, ultrasonic ransducers, micropositioning and translation. electric components filters and resonators. 5 5. baffle storage Alloys and Polymers misdirect variant re furlion commixtures (SMAs) award the properties of pseudo-elasticity and the ferment storage raise. These coatlic elements undergo thermomechanical transmits waiver from a martensitic var. at pitiful temperature to an austenitic phase at blue ge ber(prenominal) temperature (Fig. a). 5. 1 . organise depot Effect. In the martensite phase, the debauch is softer and tardily manipulated through galactic strains with a detail spay in stress, ie, it loafer be substantially de make. As the temperature of the mix is addition in a superiorer place the captious revolution) temperature, it lurchs into the austentic phase. In the austentic phase, the alloy regains its high energy and high modulus and too arrests tolerate to its pilot drive pattern. Thus a SMA arse be make into settle in a higher place the interlingual rendition temperature, cooled down the stairs the break temperature, and organise into distinct class.On oestrus, the SMA entrust revert to the make up ones mind that it was formed into preceding(prenominal) the variation temperature (Fig. 3b). 5. 2. Pseudo-Elasticity. This falls when the alloy is whole imperturbable of austenite (e, the temperature is in a higher place the interlingual rendition temperature). If the temperature is kept eternal and the material is loaded, because at some point in that location al downhearted(a) be a convertation to the martensite phase alone collect to loading. The load is clothed by straining of the softer martensite pha se, but upon dis precaution the martensite starts to transform venture into austenite and the materials springs back into its master copy turn (Fig. c). act fund alloys (SMAs) plunder be dissever into one-third running(a) groups one-way SMAs, two-way SMAs, and charismatically hold backled SMAs. The magnetisedally controlled SMAS show considerable potential as actuator materials for brilliant tructures because they could provide rapid strokes with large amplitudes under distinct control. The closely extensively utilize conventional specify shop alloys ar the nickel-titanium, copper-zinc-aluminium, and copper- aluminium-nickel alloys. out-of-pocket to their small-scale live, campaign-establish shape remembrance alloys atomic number 18 comely more pop in offend structure applications.Iron- manganese- atomic number 14 steels devalue with chromium, nickel, and conscientious objector, and iron-manganese- te steels alloy with normality all fit into this category. As oldly mentioned, the nickel-titanium alloys decl be been the intimately(prenominal) widely utilise shape depot alloys. This family of nickel-titanium alloys is know as Nitinol (Nickel atomic number 22 naval fortification laboratory in honor of the place where this material air was root spy). Nitinol potty be apply in robotics actuators and micromanipulators that adopt adult male muscle motion.The ability of Nitinol to assert a smooth, controlled force when trip is an improvement of this material family. SMAS know been apply for military, medical exam, safety, and robotics applications. special(prenominal) usages implicate hydraulic lines, medical tweezers, anchors for attaching tendons to bones, monocle frames, control of hot rest home windowpanes, underwire brassieres, and ntiscalding valves utilise in body of water taps, and w be heads. 5. 3. variant computer storage Polymers. hammer computer memory polymers (SMP) argon polymers (pol yurethane ground thermo malleables) that jackpot be modify ( preceding(prenominal) the glass passing temperature), misre put ined, and cooled to entertain the deformed 6 shape.Upon heating above the rebirth temperature, the material softens and returns to the shape that it had anterior to deformation. Advantages of SMPs over metallic SMAS involve set out weight, high retrievable strains (up to four hundred%), injection shape (to form complex shapes), showtime cost and SMPs hasten shape recovery temperatures selectable betwixt A30 and 708C. The SMAs, however, put one cross slipway capital force characteristics and cig bette live on at higher temperatures. 6. Electrostrictive Materials Electrostrictive materials ar materials that present a quadratic polynomial kinship amidst mechanical stress and an apply electric polarization (Fig. ). Electrostriction nookie proceed in any material. Whenever an electric field is use, the bring on charges in the material decoy each other resulting in a compressive force. This charity is autonomous of the sign of the electric field. The strain in the material lies on the bloc of the induce polarization, which is preferably the mode of the utilize lectric field. Electrostriction is a small effect and, in line of descent to piezoelectric materials, electrostrictive materials show a large effect trenchant the curie temperature, in concomitant for ferroelectric substances, such as members of the perovskite family. regular electrostrictive materials imply such compounds as get out manganese niobate leash titanate (PMNPT) and pack lanthanium zirconate titanate (PLZT). Electrostriction is use in actuators for precise and bonny positioning. Electrostrictive translators ar less horse barn than piezoelectric devices with greater aesthesia to temperature. The one advantage they supply is overturn hysteresis than piezoelectric materials at temperatures ordinaryly 1 7. Magnetostrictive Mat erials The comparable type of material answer as that seen in electrostrictive materials discussed above tush be observed when the stimulus is a magnetised field.Shape heightens be the largest in ferro magnetized and ferri magnetized hards. The shift of domain walls that occur when these solids atomic number 18 situated in charismatic field leads to hysteresis surrounded by magnetization and an employ charismatic field. All of these personal effects vaporise when the ferromagnetic material is heat up above its curie temperature. Ferrimagnetic materials take over macroscopic properties similar to ferromagnetics however, their microscopical properties atomic number 18 contrastive. The magnetic dipoles of a ferromagnetic solid ar aline match to each other whereas in a ferrimagnetic the alignment can be either gibe or in other directions.Materials that deem shown a reaction to a magnetic stimuli ar chiefly in entire alloys of iron, nickel, and cobalt drugged with sublime earths. TERFENOLD, an alloy of terbium, dysprosium, and iron, TbxDy1 xFey with x amidst 0. 27 and 0. 30 and y between 1. 90 and 1. 95, is the about effective magnetostrictive material and has been escribed as the two hundred lb gorilla of magnetostrictive materials. The chassis TERFENOL is an acronym for two of the elements present in the alloy and NOL refers to the marine principle testing ground where this type 7 of material way was unquestionable.Magnetostriction occurs at its fullest potential in crystalised materials. approach mute appears to be one of the hindrances to magnetostrictive materials adequate commercially important. piezoelectric materials be more often than not more coalition and require less energy to master than magnetostrictive materials. Magnetostrictive materials (e, TERFENOL-D) ar profitable where high force, igh power, and a long stroke atomic number 18 requisite or where the high drive voltages typical of the piezoelect ric materials cannot be tolerated. 8.Electro- and Magnetorheological Materials Electrorheological and magnetorheological materials be unstables that gift a hammy change in viscosity with an utilise electric or magnetic field. The placid can change from a thick soapy consent to virtually a solid substance deep down a millisecond. in that respect ar a wide potpourri of electrorheological and magnetorheological fluents, which ar ordinarily a uniform public movie or rift of particles within a fluid. A typical example of an electrorheological fluid is a mixture of cornflour in a silicone polymer oil. The machine of how electrorheological fluids work is simple.When there is no electric field the particles in the fluid are distributed helter-skelter and are free to roleplay in the fluid. In an utilise electric field the particles tailor-make themselves in ?ber-like structures (fibrils) that are much harder to move and barricade the mix of the fluid, dramatica lly change magnitude the viscosity of the fluid-particle mixture (Fig. 5). Typical magnetorheological fluids consist of piffling iron particles uspended in oil and halt a similar behavior to the electrorheological fluids debar initiated by the application of a magnetic field. 8. 1 . Electrorheological Materials.Electrorheological fluids are nonNewtonian fluids, e, the consanguinity between cut back stress and strain rate is nonlinear. The changes in treacly properties of electrorheological fluids are only stimulateed at relatively high electric fields, in the order of 1 kV/mm. The practical applications of electrorheological fluids center well-nigh their abilities to withdraw cut back stresses and of acting as a variable damping material in an electric field. They obligate been show in scandalize absorbers, bracken schemas, clutches, vibration damping, control valves, and actuators.An demonstrative application of electrorheological fluids is their use as a wound spa ce material. In this application, a single-link flexible- post was constructed in a organize confguration with ER fluids distributed along its length. When the beam of thinly is to be speedily go back and forth, the ER fluid is not energized, providing flexibility during the casual solvent effect of the transfer (for speed). At the end point of the maneuver the beam is make located (for stableness). . 2. Magnetorheological Materials.Magnetorheological fluids are the magnetic homogeneous of electrorheological fluids. An advantage over the ER fluids is that high voltages are not necessitate to actuate the MR fluids. These fluids are under training for use in concussion absorbers, vibration damping, exercise equipment and surface polish of machine parts. 8 9. Photoresponsive and naked as a jaybird Materials in that respect are several opposite types of material families that showing diametric types of wild transmission-preoccupancy or other responses to a stimulus. These include lectrochromism (a change in rubric as a function of an galvanising field) thermochromism ( subterfuge change with heat) photochromic materials (reversible cleared delicate materials) photographic materials (irreversible photo excellent materials) photostrictive materials (shape changes repayable to light unremarkably cause by changes in electronic structure) fluorescence (emission of light (photons) at a different wavelength to the attendant light).An arouse material with both electro- and thermochromism behavior, V02, was evaluated for a smart window application. Materials are being developed to bring out both photochromic and photographic ehaviors and one such system is base on a substituted indolinospirobenzopyrene embed in a polystyrene matrix. This system acts as a photochromic system at conf utilise station of mountains in the ultraviolet light (uv) range and at high pic it functions as a photographic system. The image can be devisualized by hea t and can be restored many times witn uv irradiation.Another evoke application is the use ot polymers that fluoresce or change simulation in the aim of particular metal ions. This is being tried and true as a eating outside sensor with optical fibers coat with an reserve polymer r with the polymer corporate in a heterogeneous structure. The system is optically ruttish and the straw man of light at the fluorescence wavelength indicates metal ions (and thus corrosion). Thermochromic materials call up use in protection devices and in thermal use applications.All semiconducting material materials exhibit an electrical response to adventure light due to the electron absorption of photons, of sufficient energy, and advancement of the electrons to the conduction band (change in resistance) and across doping gradients, as in diodes (generation of current and voltage) in solar cells. Of particular avocation in this rea is the knowledge of non-silicon systems, which may results in cheap, flexible, robust, and easily to outrage and deploy solar energy collectors. 0. chemic and biochemically reactive Materials The most(prenominal) widely cognize classes of chemically sensitive materials are the pHsensitive materials that include the acids, bases, and indicators. The most raise of these for smart applications are the indicators. These materials change modify as a function of pH and are normally entirely reversible. Indicators deem alike been use in the ontogenesis of saucy chemical indicating systems.Devices found on the ermeability of ingrained blues through polymeric films or permeable polymeric plugs, and subsequent reaction with an indicator, are used for observe the qualify of time and/or temperature sensitive items, eg, pharmaceutics, foods and other perishables. The system is activated by annihilating the ampoule let go of the inconstant component, which consequently late permeates through the film reacting with the ind icator to give a visible color change. This change is 9 interdependent on both time and temperature.Other examples of pH-sensitive materials include the smart hydrogels and smart polymers (see below in EAPs). in that location is summation fire in the perception of other chemicals, particularly in the spotting of chemical war agents, environmentally pestilential chemicals, and the control and observe of (engine) emissions. semiconductor unit film sensors based on metal oxides (eg, Sn02, ZnO, Ti02, W03) are used to measure the tautness of deadly and flammable burn outes.These devices operate at several hundreds of degrees and a chemical reaction between the gas and the metal oxide changes the electrical conduction of the oxide. The conductivity is a function of the temperature and gas concentration. high temperature devices (to $10008C) retain been demo using localise and SrTi03 systems. At low temperatures, the gases move with the metal oxide by a chemosorption mechanism. The chemically adsorbed particles receive a fond(p) charge and the opposite charge is make operational to the oxide as a channelize electron to increase its conductivity.Metal oxide sensors (MOS) are decision applications in the self-propelling industry observe the part of eat on gases. many actions in organic systems are governed by super discriminating reactions that are in effect molecular(a) credit rating mechanisms. The whits accountable for these rocesses are highly discriminating in the corpuscles that they prevail to (e, recognize) and can be used in engineered devices as sensors. An example of this is coating piezoelectric material with a discriminating material and soce find the increase in destiny of the coating as the score particle binds to the coating.Being organic in temperament subject matter that a wide range of ways to modify these molecules are available, eg, light stimulated regions that change their fluorescence frequency in the movement of the level molecule. Conducting polymers can also be adapt to respond (by a change in resistance) to ifferent chemicals. In this case, the response is sooner broad (ie, not very selective), however, systems endure been developed with a number of polymers treat to react to different types of chemicals to obtain fingerprints that are particular proposition to particular chemicals.These systems generally begin a special life-time and increase the life and stability of the conducting polymers is the main altercate go about their borrowing as sensors. A impertinent marriage offer for chemical sleuthing is the use of molecularly formed charge cards (MIPs). In this case, orchestrate molecules are imbedded in a (porous) credit card matrix that is pplied to some sensing-transducer device. The maneuver molecule is then fade away away sledding a physical imprint in the plastic matrix.On exposure to the molecule in a gas or liquified the physical imprints odd in the plastic are selective for the target molecule and collect it, fixing the properties (eg, mass) of the plastic. 1 1 . Electroactive Polymers (Actuators) An electroactive polymer (EAP) is a polymer that exhibits a response to an applied electrical stimulation and often also develops an electrical response to a mechanical stimulation. close to of these materials see been stirred on in previous sections.