Neelakanta, P.S. "Smart Materials" The Electrical Engineering Handbook Ed. Richard C. Dorf Boca raton crc Press llc. 2000
Neelakanta, P.S. “Smart Materials” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000
58 Smart materials 58.2 Smart/Intelligent Structures 58.3 Objective-Based Classification of Smart/Intelligent Materials Smart Structural materials Smart Thermal Materials Smart 8.4 Material Properties Conducive for Smart Material Piezoelectric Effect. Magnetostrictive Effect. Electroplastic Effect - Memory Effects. Electrorheology Property.Nonlinear Electro-optic Properties.Nonlinear Electromagnetic Properties 8.5 State-of-the-Art Smart Materials Piezoelectric Smart Materials Magnetostrictive Smart Materials. Electroplastic Smart Materials. Shape-Memory Smart Materials. Electrorheological Smart Fluids.Electro-optic Smart Materials. Electroacoustic Smart Materials. Electromagnetic Smart Materials. Pyrosensitive Smart Materials 58.6 Smart Sensors gnetostriction-Based Sensors. Shape-Memory Effects-Based Sensors. Electromagnetics-Based Sensors Electroacoustic Smart Sensors 58.7 Examples of Smart/Intelligent Systems Structural Engineering Applications. Electromagnetic Applications P.S. Neelakanta 58.8 High-Tech Application Potentials Florida Atlantic University 58.9 Conclusions 58.1 Introduction Smart materials are a class of materials and/or composite media having inherent intelligence together with self-adaptive capabilities to external stimuli, Also known as intelligent materials, they constitute a few subsets of the material family that"manifest their own functions intelligently depending on environmental changes I Rogers and Rogers, 1992] Classically, such intelligent material systems have been conceived in the development of mechanical structures that contain their own sensors, actuators and self-assessing computational feasibilities in order to modify their structural (elastic) behavior via feedback control capabilities. The relevant concepts have stemmed from intel ligent forms of natural (material) systems, namely, living organisms; hence, in modern concepts smart or c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 58 Smart Materials 58.1 Introduction 58.2 Smart/Intelligent Structures 58.3 Objective-Based Classification of Smart/Intelligent Materials Smart Structural Materials • Smart Thermal Materials • Smart Acoustical Materials • Smart Electromagnetic Materials • Pyrosensitive Smart Materials 58.4 Material Properties Conducive for Smart Material Applications Piezoelectric Effect • Magnetostrictive Effect • Electroplastic Effect • Shape-Memory Effects • Electrorheological Property • Nonlinear Electro-optic Properties • Nonlinear Electroacoustic Properties • Pyrosensitive Properties • Nonlinear Electromagnetic Properties 58.5 State-of-the-Art Smart Materials Piezoelectric Smart Materials • Magnetostrictive Smart Materials • Electroplastic Smart Materials • Shape-Memory Smart Materials • Electrorheological Smart Fluids • Electro-optic Smart Materials • Electroacoustic Smart Materials • Electromagnetic Smart Materials • Pyrosensitive Smart Materials 58.6 Smart Sensors Fiber-Optic-Based Sensors • Piezoelectric-Based Sensors • Magnetostriction-Based Sensors • Shape-Memory Effects-Based Sensors • Electromagnetics-Based Sensors • Electroacoustic Smart Sensors 58.7 Examples of Smart/Intelligent Systems Structural Engineering Applications • Electromagnetic Applications 58.8 High-Tech Application Potentials 58.9 Conclusions 58.1 Introduction Smart materials are a class of materials and/or composite media having inherent intelligence together with self-adaptive capabilities to external stimuli. Also known as intelligent materials, they constitute a few subsets of the material family that “manifest their own functions intelligently depending on environmental changes” [Rogers and Rogers, 1992]. Classically, such intelligent material systems have been conceived in the development of mechanical structures that contain their own sensors, actuators and self-assessing computational feasibilities in order to modify their structural (elastic) behavior via feedback control capabilities. The relevant concepts have stemmed from intelligent forms of natural (material) systems, namely, living organisms; hence, in modern concepts smart or P. S. Neelakanta Florida Atlantic University
E IGURE 58.1 Set of structures (Adapted from B. K. Wada, J. L. Fanson, and E. Crawley, "Adaptive structures, "J. Intell Mat. Syst. Struct, 1, 1990.) intelligent materials and systems are conceived as those that mimic the life functions of sensing, actuation, control, and intelligence. The inherent intelligence and self-adaptable control of artificial smart materials terms of the constituent processing, microstructural characteristics, and defects to permit the self-conditionings to adapt in a controlled manner to various types of stimuli. The dividing line between smart materials and the D-called intelligent structures is not, however, distinct. In simple terms, intelligent material systems are constructed of smart materials with a dedicated, discrete set of integrated actuators, sensors, and so on, and nart materials contain largely a built-in or embedded set of distributed sensors. In general, the term smart materials usually connotes the structural constituent in which the discrete functions of sensing, actuation, signal processing and control are tangibly integrated. Intelligent structures, as an extension, are constructed with mart materials to respond to the environment around them in a predetermined, desired manner Intelligent or smart materials that manifest their own functions intelligently vis-a-vis the changes in the Irroundings are capable of performing, in general( Chong et al., 1990) Primary functions specifying the adaptive roles of the sensor, the effector and processor capabilities Macroscopic functions that enclave the extensive or global aspects of the intelligence inherent in the Built-in social utility aspects with an instilled human-like intelligence with hyper-performance capabilities 58.2 Smart/Intelligent Structures The framework of intelligent structures as a subset in the gamut of conventional material-based syster illustrated in Fig. 58. 1. This general classification of material structures refer to [Chong et al, 1990] Sensory structures, which possess sensors that enable the determination or monitoring of system states characteristics"[Chong et al., 1990] Adaptive structures, which possess actuators that facilitate the alteration of system-states or character istics in a controlled manner Adaptive systems, which contain actuators, but no sensors Referring to Fig 58.1, the intersection of sensory versus adaptive structures depicts the controlled structures with a feedback architecture. That is, the active structure has an integrated controlled unit with sensors and/or ctuators that have structural as well as control functionality. Hence, the logical subset that defines an intelligent structure is a highly integrated unit(with controlled logic, electronics, etc. )that provides the cognitive element of a distributed or a hierarchic controlled structure c 2000 by CRC Press LLC
© 2000 by CRC Press LLC intelligent materials and systems are conceived as those that mimic the life functions of sensing, actuation, control, and intelligence. The inherent intelligence and self-adaptable control of artificial smart materials should be programmable in terms of the constituent processing, microstructural characteristics, and defects to permit the self-conditionings to adapt in a controlled manner to various types of stimuli. The dividing line between smart materials and the so-called intelligent structures is not, however, distinct. In simple terms, intelligent material systems are constructed of smart materials with a dedicated, discrete set of integrated actuators, sensors, and so on, and smart materials contain largely a built-in or embedded set of distributed sensors. In general, the term smart materials usually connotes the structural constituent in which the discrete functions of sensing, actuation, signal processing and control are tangibly integrated. Intelligent structures, as an extension, are constructed with smart materials to respond to the environment around them in a predetermined, desired manner. Intelligent or smart materials that manifest their own functions intelligently vis-à-vis the changes in their surroundings are capable of performing, in general (Chong et al., 1990): • Primary functions specifying the adaptive roles of the sensor, the effector and processor capabilities (including the memory functions) • Macroscopic functions that enclave the extensive or global aspects of the intelligence inherent in the materials • Built-in social utility aspects with an instilled human-like intelligence with hyper-performance capabilities 58.2 Smart/Intelligent Structures The framework of intelligent structures as a subset in the gamut of conventional material-based systems is illustrated in Fig. 58.1. This general classification of material structures refer to [Chong et al., 1990]: • Sensory structures, “which possess sensors that enable the determination or monitoring of system states or characteristics” [Chong et al., 1990] • Adaptive structures, which possess actuators that facilitate the alteration of system-states or characteristics in a controlled manner • Sensory systems, which may contain sensors, but no actuators • Adaptive systems, which contain actuators, but no sensors Referring to Fig. 58.1, the intersection of sensory versus adaptive structures depicts the controlled structures with a feedback architecture. That is, the active structure has an integrated controlled unit with sensors and/or actuators that have structural as well as control functionality. Hence, the logical subset that defines an intelligent structure is a highly integrated unit (with controlled logic, electronics, etc.) that provides the cognitive element of a distributed or a hierarchic controlled structure. FIGURE 58.1 Set of structures. (Adapted from B. K. Wada, J. L. Fanson, and E.F. Crawley, “Adaptive structures,” J. Intell. Mat. Syst. Struct., 1, 1990.)
58.3 Objective-Based Classification of Smart/Intelligent Materials Smart Structural materials Itelligent structural engineering materials are the classical versions of smart systems in which the mechanical (elastic) properties of a structure can be modified adaptively by means of an imbedded distribution of smart material(s), and an associated (integral)set of sensors and actuators together with an external control syster to facilitate adaptive changes in the elastic behavior of structures so that motion, vibration, strength, stiffness, redistribution of load path in response to damage, etc. are controlled Smart Thermal materials A smart thermal material, in response to environmental demands, can self-adaptively influence its thermal states(temperature or such thermal properties as conductivity, diffusivity, absorptivity), by means of an integrated conglomeration of thermal sensors, heaters, or actuators with an associated control system Smart Acoustical materials Smart acoustical materials can be classified as those that have self-adaptive characteristics on theiracousticalbehavior such as transmission, reflection, and absorption of acoustical energy) by means of sensors that assess the acoustical states(intensity, frequency, response, etc. ),along with a set of actuators(dampers, exciters)with an associated control system. Again, the self-adaptive behavior of these materials is in response to ambient acoustical changes Smart electromagnetic materials Smart Magnetic shielding materials As warranted by the surroundings, the self-adaptive shielding effectiveness to magnetic fields at low frequencies (power frequencies such as 60 or 50 Hz) can be achieved by means of an integrated set of magnetic field sensors and actuators(magnetic biasing, current elements, etc. )plus a control system arrangement[Neelakanta and High-Frequency Smart Shielding Materials Corresponding to radio and higher frequency environments, the shielding requirement warrants curtailing both electric and magnetic fields. Hence, the relevant self-adaptive intelligent shielding system would consist of an array of distributed electromagnetic sensors with appropriate elements(actuators )and a control system Smart Radar- Absorbing materials Absorption of microwave/millimeter wave energy at radar frequency is useful in radar stealth applications. Adap- tively controllable smart radar-absorbing materials(smart RAMs) can be synthesized with integrated distrib uNion of electromagnetic detectors(sensors)with appropriate actuators and control system [Neelakanta et al., 1992] Smart Optical Surface Materials Smart optical surface materials can be envisioned as those in which the surface optical properties(hue, intensity, etc. )can be adaptively controlled by means of an intelligent sensor/actuator combinational control system. Pyrosensitive Smart Materials Electromagnetic active surfaces constituted by pyrosensitive inclusions have been successfully developed to manage the electromagnetic reflection and/or absorption characteristics from the active surface by means of thermal actu ation of the pyrosensitive nodes imbedded in the medium[Neelakanta et al., 1992]. With the inclusion of a feedback systems, smart operation in adaptively manipulating the active surface characteristics can be achieved. 58.4 Material Properties Conducive for Smart Material applications Certain specific characteristics of materials make them suitable for smart material applications. These properties are:
© 2000 by CRC Press LLC 58.3 Objective-Based Classification of Smart/Intelligent Materials Smart Structural Materials Intelligent structural engineering materials are the classical versions of smart systems in which the mechanical (elastic) properties of a structure can be modified adaptively by means of an imbedded distribution of smart material(s), and an associated (integral) set of sensors and actuators together with an external control system to facilitate adaptive changes in the elastic behavior of structures so that motion, vibration, strength, stiffness, redistribution of load path in response to damage, etc. are controlled. Smart Thermal Materials A smart thermal material, in response to environmental demands, can self-adaptively influence its thermal states (temperature or such thermal properties as conductivity, diffusivity, absorptivity), by means of an integrated conglomeration of thermal sensors, heaters, or actuators with an associated control system. Smart Acoustical Materials Smart acoustical materials can be classified as those that have self-adaptive characteristics on their acoustical behavior (such as transmission,reflection, and absorption of acoustical energy) by means of sensors that assess the acoustical states (intensity, frequency, response, etc.), along with a set of actuators (dampers, exciters) with an associated control system. Again, the self-adaptive behavior of these materials is in response to ambient acoustical changes. Smart Electromagnetic Materials Smart Magnetic Shielding Materials As warranted by the surroundings, the self-adaptive shielding effectiveness to magnetic fields at low frequencies (power frequencies such as 60 or 50 Hz) can be achieved by means of an integrated set of magnetic field sensors and actuators (magnetic biasing, current elements, etc.) plus a control system arrangement [Neelakanta and Subramaniam, 1992]. High-Frequency Smart Shielding Materials Corresponding to radio and higher frequency environments, the shielding requirement warrants curtailing both electric and magnetic fields. Hence, the relevant self-adaptive intelligent shielding system would consist of an array of distributed electromagnetic sensors with appropriate elements (actuators) and a control system. Smart Radar-Absorbing Materials Absorption of microwave/millimeter wave energy at radar frequency is useful in radar stealth applications. Adaptively controllable smart radar-absorbing materials (smart RAMs) can be synthesized with integrated distribution of electromagnetic detectors (sensors) with appropriate actuators and control system [Neelakanta et al., 1992]. Smart Optical Surface Materials Smart optical surface materials can be envisioned as those in which the surface optical properties (hue, intensity, etc.) can be adaptively controlled by means of an intelligent sensor/actuator combinational control system. Pyrosensitive Smart Materials Electromagnetic active surfaces constituted by pyrosensitive inclusions have been successfully developed to manage the electromagnetic reflection and/or absorption characteristics from the active surface by means of thermal actuation of the pyrosensitive nodes imbedded in the medium [Neelakanta et al., 1992].With the inclusion of a feedback systems, smart operation in adaptively manipulating the active surface characteristics can be achieved. 58.4 Material Properties Conducive for Smart Material Applications Certain specific characteristics of materials make them suitable for smart material applications. These properties are:
1. Piezoelectric effect 3. Electroplastic effect 5. Electrorheological properties 6. Nonlinear electro-optic properties 7. Nonlinear electroacoustic properties 8. Nonlinear electromagnetic properties 9. Pyrosensitive properti iezoelectric effect Piezoelectric property of a material refers to the ability to induce opposite charges at two faces (correspondingly, to exhibit a voltage difference between the faces)of the material as a result of the strain due to mechanical force(either tension or compression) applied across the surfaces. This process is also reversible in the sense that a mechanical strain would be experienced in the material when subjected to opposite electric charging at the two faces by means of an applied potential. In the event of such an applied voltage being alternating, the material specimen will experience vibrations likewise, an applied vibration on the specimen would induce an alternating potential change between the two faces. The most commonly known materials that exhibit piezoelectric properties are natural materials like quartz and a number of crystalline and polycrystalline compounds The strain versus the electric phenomenon perceived in piezoelectric materials is dictated by a coefficient that has components referred to a set of orthogonal coordinate axes(which are correlated to standard crystal lographic axes). For example, denoting the piezoelectric coefficient(ratio between piezoelectric strain compo- nent to applied electric field component at a constant mechanical stress or vice versa) as dmm, the subscript n (1 to 3)refers to the three euclidian orthogonal axes, and m= l to 6 specifies the mechanical stress-strain components. The unit for dmm is meter/volt which is the same as coulomb/newton energy impressed on the material. Being a reversible process, a relevant inverse ratio is also applicable Magnetostrictive Effect Magnetostrictive effect refers to the structural strain experienced in a material subjected to a polarizing magnetic flux. A static strain of Al/l is produced by a dc polarizing magnetic flux density B, such that Al/l CB,, where C is a material constant expressed in(meter/weber )taking the units for B, as weber/meter The magnetic stress constant(A)in(newton/weber)is given by A=2CB Y, where Y, refers to the Youngs modulus of a linearly strained free bar. The coefficient(A)could be both positive or negative. For examp nickel contracts with increasing B, whereas magnetic alloys such as 45 Permalloy(45% Ni 55% Fe), Alfer (13%AL, 87%Fe)exhibit positive magnetostrictive coefficient [Reed, 1988 Electroplastic Effect The electroplastic effect(EPE)refers to the plastic deformation of metals with the application of high-density electric current with an enhanced deformation rate(that persists in addition to that caused by the side effects of the current such as joule-heating and the magnetic pinch effect). The plastic strain rate resulting from a current pulse is given by Eye=a F exp(Bn) where E, is the strain rate occurring during the current pulse, Ea is the strain rate in the absence of the current pulse, J is the current density and a and B are material constants Typically the EPe has been observed in zinc, niobium, titanium, etc Shape-Memory Effects The mechanism by which a plastically deformed object in the low-temperature martensitic condition reg its original shape when the external stress is removed and heat is applied is referred to as the shape-m c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 1. Piezoelectric effect 2. Magnetostrictive effect 3. Electroplastic effect 4. Shape-memory effects 5. Electrorheological properties 6. Nonlinear electro-optic properties 7. Nonlinear electroacoustic properties 8. Nonlinear electromagnetic properties 9. Pyrosensitive properties Piezoelectric Effect Piezoelectric property of a material refers to the ability to induce opposite charges at two faces (correspondingly, to exhibit a voltage difference between the faces) of the material as a result of the strain due to mechanical force (either tension or compression) applied across the surfaces. This process is also reversible in the sense that a mechanical strain would be experienced in the material when subjected to opposite electric charging at the two faces by means of an applied potential. In the event of such an applied voltage being alternating, the material specimen will experience vibrations. Likewise, an applied vibration on the specimen would induce an alternating potential change between the two faces. The most commonly known materials that exhibit piezoelectric properties are natural materials like quartz and a number of crystalline and polycrystalline compounds. The strain versus the electric phenomenon perceived in piezoelectric materials is dictated by a coefficient that has components referred to a set of orthogonal coordinate axes (which are correlated to standard crystallographic axes). For example, denoting the piezoelectric coefficient (ratio between piezoelectric strain component to applied electric field component at a constant mechanical stress or vice versa) as dmn, the subscript n (1 to 3) refers to the three euclidian orthogonal axes, and m = 1 to 6 specifies the mechanical stress-strain components. The unit for dmn is meter/volt which is the same as coulomb/newton. In the piezoelectric phenomenon, there is an electromechanical synergism expressed as a coupling factor K defined by K2 , which quantifies the ratio of mechanical energy converted into electric charges to the mechanical energy impressed on the material. Being a reversible process, a relevant inverse ratio is also applicable. Magnetostrictive Effect Magnetostrictive effect refers to the structural strain experienced in a material subjected to a polarizing magnetic flux. A static strain of Dl/l is produced by a dc polarizing magnetic flux density Bo such that Dl/l = CBo 2 , where C is a material constant expressed in (meter4 /weber2 ) taking the units for Bo as weber/meter2 . The magnetic stress constant (L) in (newton/weber) is given by L = 2CBoYo where Yo refers to the Young’s modulus of a linearly strained free bar. The coefficient (L) could be both positive or negative. For example, nickel contracts with increasing Bo, whereas magnetic alloys such as 45 Permalloy (45% Ni + 55% Fe), Alfer (13% Al, 87% Fe) exhibit positive magnetostrictive coefficient [Reed, 1988]. Electroplastic Effect The electroplastic effect (EPE) refers to the plastic deformation of metals with the application of high-density electric current with an enhanced deformation rate (that persists in addition to that caused by the side effects of the current such as joule-heating and the magnetic pinch effect). The plastic strain rate resulting from a current pulse is given by eI /eA = a J2 exp(bJ) where eI is the strain rate occurring during the current pulse, eA is the strain rate in the absence of the current pulse, J is the current density and a and b are material constants. Typically the EPE has been observed in zinc, niobium, titanium, etc. Shape-Memory Effects The mechanism by which a plastically deformed object in the low-temperature martensitic condition regains its original shape when the external stress is removed and heat is applied is referred to as the shape-memory