HIS article presents an overview and assessment of the technology leading to the development of intelligent structures. Intelligent structures are those which incorporate actuators and sensors that are highly integrated into the structure and have structural functionality, as well as highly integrated control logic, signal conditioning, and power amplification electronics. Such actuating, sensing, and signal processing elements are incorporated into a structure for the purpose of influencing its states or characteristics, be they mechanical, thermal, optical, chemical, electrical, or magnetic. For example, a mechanically intelligent structure is capable of altering both its mechanical states (its position or velocity) or its mechanical characteristics (its stiffness or damping). An optically intelligent structure could, for example, change color to match its background.17 Definition of Intelligent Structures Intelligent structures are a subset of a much larger field of research, as shown in Fig. I.123 Those structures which have actuators distributed throughout are defined as adaptive or, alternatively, actuated. Classical examples of such mechanically adaptive structures are conventional aircraft wings with articulated leading- and trailing-edge control surfaces and robotic systems with articulated manipulators and end effectors. More advanced examples currently in research include highly articulated adaptive space cranes. Structures which have sensors distributed throughout are a subset referred to as sensory. These structures have sensors which might detect displacements, strains or other mechanical states or properties, electromagnetic states or properties, temperature or heat flow, or the presence or accumulation of damage. Applications of this technology might include damage detection in long life structures, or embedded or conformal RF antennas within a structure. The overlap structures which contain both actuators and sensors (implicitly linked by closed-loop control) are referred to as controlled structures. Any structure whose properties or states can be influenced by the presence of a closed-loop control system is included in this category. A subset of controlled structures are active structures, distinguished from controlled structures by highly distributed actuators which have structural functionality and are part of the load bearing system.

Intelligent structures for aerospace - A technology overview and assessment

A portable therapeutic device and method of use generate longitudinally propagating ultrasound and shear waves generated by such longitudinally propagating ultrasound to provide effective healing of wounds. A transducer having an operative surface is disposed substantially adjacent to the wound to emit ultrasound to propagate in the direction of the wound to promote healing. Reflections of the ultrasound by bone tissue, by skin layers, or by internally disposed reflective media propagate toward the wound as longitudinal waves, with shear waves generated by the longitudinal waves for the healing of the wound. A focusing element is used for focusing the propagation of the ultrasound at a predetermined angle toward the wound. The operative surface of the transducer may be annularly shaped to encircle the wound to convey the ultrasound and/or reflected ultrasound thereto. A housing may be provided for positioning the transducer near a portion of the skin near the wound, and for indenting the skin to form a cavity, with the transducer disposed in the cavity to emit the ultrasound toward an internal surface of the wound. Fixture structures, such as adjustable straps, may extend about a portion of the body to position the transducer near the wound.

Ultrasonic treatment for wounds

In the last 25 years, piezoelectric ceramic-polymer composites have been conceptualized, prototyped, fabricated, and implemented in an array of applications encompassing medical imaging and military missions, among others. A detailed snapshot of the materials used, and a detailed account of the major innovative methods developed in making various piezoelectric ceramic-polymer composites are presented. The salient aspects of processing of such composites are summarized, and structure-processing-property relations are described using connectivity as the unifying central concept. Computer-aided design (CAD)-based fabrication methods, which result in composites whose structural complexity surpass that of composites obtained with traditional methods, are described to introduce the reader to novel concepts in processing of piezocomposites. A brief survey of some recent advances made in modeling of (0-3), (1-3), and (2-2) composites also is provided.

Piezoelectric composites for sensor and actuator applications

Ferroelectric composites are now an established alternative to conventional ferroelectric ceramic materials and to the more recently discovered ferroelectric polymers. These materials due to their unique blending of polymetric properties of mechanical flexibility, formability and low cost with high electro-active properties have been been suggested to be a viable alternative both in piezoelectric and pyroelectric transducer applications. This review is devoted to the piezoelectric and pyroelectric properties exhibited by these type of composites with a special reference to those made of ceramic particles embedded in a polymer matrix (i.e. 0-3 connectivity type composite). A review of models predicting the electro-active properties of 0-3 composites is presented together with a proposal for a new mixed connectivity cubes model to be applicable to the case of high ceramic loading and/or when the ceramic grain size incorporated in the polymer matrix is comparable to the thickness of the sample. A review of the experimental results of the piezo- and pyroelectric properties of various ferroelectric composite materials, reported by several workers, is also presented in this paper. Special reference is made to composites made from calcium modified lead titanate and poly(vinyldene fluoride-trifluorethylene) emphasizing their advantages in the poling process which is a critical phase in the process of obtaining successful electro-active 0-3 composite electrets.

Inorganic ceramic/polymer ferroelectric composite electrets

Smart materials, which exhibit piezoelectricity, find an eclectic range of applications in the industry. The direct piezoelectric effect has been widely used in sensor design, and the inverse piezoelectric effect has been applied in actuator design. Ever since 1954, PZT and BaTiO3 were widely used for sensor and actuator applications despite their toxicity, brittleness, inflexibility, etc. With the discovery of PVDF in 1969, followed by development of copolymers, a flexible, easy to process, nontoxic, high density alternate with high piezoelectric voltage coefficient was available. In the past 20 years, heterostructural materials like polymer ceramic composites, have received lot of attention, since these materials combine the excellent pyroelectric and piezoelectric properties of ceramics with the flexibility, processing facility, and strength of the polymers resulting in relatively high dielectric permittivity and breakdown strength, which are not attainable in a single phase piezoelectric material. The current review article is an attempt to provide a compendium of all the work carried out with reference to PVDF-PZT composites. The review article evaluates the effect of grain size, content and other factors under the purview of dielectric and piezoelectric properties while evaluating the sensitivity of the material for sensor application. POLYM. ENG. SCI., 55:1589–1616, 2015. © 2015 Society of Plastics Engineers

Dielectric and piezoelectric properties of PVDF/PZT composites: A review

In the conventional poling method, piezoelectric ceramics and composites are poled by applying a large dc voltage. Poling of composites having a polymer matrix with 0–3 connectivity is especially difficult because the electric field within the high-dielectricconstant grains is far smaller than in the low-dielectric-constant polymer matrix. Therefore, very large electric fields are required to pole these types of composites. However, large electric fields often cause dielectric breakdown of the samples. In this study for improved poling, the corona discharge technique was used to pole piezoelectric ceramics, fired PZT composites, and 0.5PbTiO3· 0.5BiFeO3 0–3 polymer composites. An experimental setup for corona poling is described. The dielectric and piezoelectric properties of materials poled by the corona discharge technique were comparable to those obtained with the conventional poling method.

Poling of Lead Zirconate Titanate Ceramics and Flexible Piezoelectric Composites by the Corona Discharge Technique

The woven replication process was used to fabricate lead zirconate titanate (PZT)/polymer composites with 1-3, 2-3, and 3-3 connectivities by starting with novoloid-derived carbon fiber, woven fabric, and nonwoven felt templates, respectively. Activated carbon-fiber template material was impregnated with PZT by soaking it in a solution containing stoichiometric amounts of dissolved lead, zirconium, titanium, and niobium ions. Heat treatment burned out the carbon, leaving a PZT replica with the same form as the template material. Replicas were sintered in a controlled atmosphere and back-filled with an epoxy polymer to form final composites. This method, which is believed to be adaptable for mass production, is capable of producing composites and extremely fine microstructures. Woven composite samples have fiber tow diameters of 200 to 250 {mu}m and spacings between tows of about 150 to 250 {mu}m. Average d{sub 33} = 90 pC/N, g{sub 33} = 211 mV {center dot} m/N, and d{sub h}g{sub h} hydrophone figure of merit of 2100 {times} 10{sup {minus}15} m{sup 2}/N values are reported for woven PZT/polymer composites.

Lead Zirconate Titanate Fiber/Polymer Composites Prepared by a Replication Process

In the conventional poling method, piezoelectric ceramics and composites are poled by applying a large D.C. voltage directly to the sample. The poling of composites having a polymer matrix with 0–3 connectivity is especially difficult because the electric field within the high dielectric constant grains is far smaller than in the low dielectric constant polymer matrix. Therefore, very large electric fields are required to align the piezoelectric grains. Unfortunately, such large electric fields often cause localized dielectric breakdown of the samples which effectively prevents further poling.

Corona poling of PZT ceramics and flexible piezoelectric composites

This papers on piezoelectric lead zirconate titanate (PZT) ceramic fiber/polymer composite were fabricated by a novel technique referred to as relic processing. Basically, this involved impregnating a woven carbon-fiber template material with PZT precursor by soaking the template in a PZT stock solution. Careful heat treatment pyrolized the carbon, resulting in a PZT ceramic relic that retained the fibrous template form. After sintering, the densified relic was backfilled with polymer to form a composite. Optimized relic processing consisted of soaking activated carbon-fiber fabric twice in an intermediate concentration (405-mg PZT/(1-g solution)) alkoxide PZT solution and sintering at 1285{degrees}C for 2 h. A series of piezoelectric composites encompassing a wide range of dielectric and piezoelectric properties was prepared by varying the PZT-fiber orientation and polymer-matrix material. In PZT/Eccogel polymer composites with PZT fibers orientated parallel to the electrodes, K = 75, d{sub 33} = 145 pC/N, d{sub h} = 45 {plus minus} 5 pC/N, and d{sub h}g{sub h} = 3150 {times} 10{sup {minus}15} m{sup 2}/N were measured. Furthermore, in composites with a number of PZT fibers arranged perpendicular to the electroded surfaces, K = 190, d{sub 33} = 250 pC/N, d{sub h} = 65 {plus minus} 2 pC/N, and d{sub h}g{submore » h} = 2600 {times} 10{sup {minus}15} m{sub 2}/N.« less

Piezoelectric Lead Zirconate Titanate Ceramic Fiber/Polymer Composites

A replication process was used to fabricate woven PZT/polymer composites. Fabric templates consisting of woven carbon fiber were impregnated with PZT by soaking it in a solution containing stoichiometric amounts of dissolved lead, zirconium, titanium and niobium. Heat treatment burned out the carbon, leaving a PZT replica with the same form as the initial carbon weave. To form composites, replicas were sintered in a controlled atmosphere and backfilled with epoxy polymer. The process was attempted with as-received activated and nonactivated carbon fabrics, as well as those fabrics pretreated with hydrogen peroxide. Average d/sub 33/=90 pC/N, g/sub 33/=211 mV-m/N, and d/sub h/g/sub h/ hydrophone figure of merit of 2100*10/sup -15/ m/sup 2//N are reported for woven PZT/polymer composites. >

http://ieeexplore.ieee.org/iel2/592/5203/00200199.pdf

David J. Waller

Papers

Poling of Lead Zirconate Titanate Ceramics and Flexible Piezoelectric Composites by the Corona Discharge Technique

Lead Zirconate Titanate Fiber/Polymer Composites Prepared by a Replication Process

Corona poling of PZT ceramics and flexible piezoelectric composites

Piezoelectric Lead Zirconate Titanate Ceramic Fiber/Polymer Composites

Woven PZT ceramic/polymer composites for transducer applications