Electroactive phases of poly(vinylidene fluoride) : determination, processing and applications

Investigations in the development of lead-free piezoelectric ceramics have recently claimed comparable properties to the lead-based ferroelectric perovskites, represented by Pb(Zr,Ti)O3, or PZT In this work, the scientific and technical impact of these materials is contrasted with the various families of “soft” and “hard” PZTs On the scientific front, the intrinsic nature of the dielectric and piezoelectric properties are presented in relation to their respective Curie temperatures (T
 C) and the existence of a morphotropic phase boundary (MPB) Analogous to PZT, enhanced properties are noted for MPB compositions in the (Na,Bi)TiO3-BaTiO3 and ternary system with (K,Bi)TiO3, but offer properties significantly lower The consequences of a ferroelectric to antiferroelectric transition well below T
 C further limits their usefulness Though comparable with respect to T
 C, the high levels of piezoelectricity reported in the (K,Na)NbO3 family are the result of enhanced polarizability associated with the orthorhombic-tetragonal polymorphic phase transition being compositionally shifted downward As expected, the properties are strongly temperature dependent, while degradation occurs through the thermal cycling between the two distinct ferroelectric domain states Extrinsic contributions arising from domains and domain wall mobility were determined using high field strain and polarization measurements The concept of “soft” and “hard” lead-free piezoelectrics were discussed in relation to donor and acceptor modified PZTs, respectively Technologically, the lead-free materials are discussed in relation to general applications, including sensors, actuators and ultrasound transducers

Lead-free piezoelectric ceramics: Alternatives for PZT?

The elastic and ultimate properties of compact bone tissue

A detailed review of the literature on ultrasonic propagation properties of mammalian tissues and organs has revealed 144 papers containing compilable data. Over 1300 lines of parametric data are listed, including the tissue, species, age, specimen preparation, anatomical structure, pathology, temperature, measurement method, frequency, velocity, attenuation, acoustic impedance, and density.

Comprehensive compilation of empirical ultrasonic properties of mammalian tissues

http://antonirogalski.com/wp-content/uploads/2011/12/Infrared-detectors-Status-and-trends.pdf

Infrared detectors: status and trends

Changes in the net dipole moment of certain materials form the basis for a broad range of IR detectors.

/pdf/pyroelectricity-from-ancient-curiosity-to-modern-imaging-1386buacs9.pdf

Pyroelectricity: From Ancient Curiosity to Modern Imaging Tool

A new method for measuring the spatial distribution of combined polarization and space charges in poled polymer electrets has been developed. The technique, called the laser‐intensity‐modulation method (LIMM), is based upon measurement of the pyroelectric current generated by the electret when it is heated with a laser beam which is intensity‐modulated at frequencies varying from 200 to 2500 Hz. A special analytical technique is used to transform the current‐frequency measurements to spatial distributions. The method gives high resolution and is very stable with respect to measurement errors. The technique can be easily implemented in a laboratory with conventional equipment. The advantages and limitations of LIMM are illustrated by means of calculations based upon simulated data. Experimental results on a number of laboratory and commercially poled samples are presented.

Laser‐intensity‐modulation method: A technique for determination of spatial distributions of polarization and space charge in polymer electrets

The piezoelectric effect was first observed in polyvinylidene fluoride polymer (PVDF) in 1969, and the pyroelectric effect was found several years later. A number of additional ferroelectric polymers have been discovered since that time including the copolymer PVDF with trifluoroethylene (P(VDF-TrFE)), and the odd-numbered nylons. A large number of applications of piezoelectricity and pyroelectricity have been developed. The magnitudes of the effects in polymers are much lower than those of ferroelectric ceramics (an exception is the piezoelectric effect in porous polymers). However, other factors make these very desirable materials for applications. The polymers have low permittivities, low acoustic impedances and low thermal conductivities. They are available in large area sheets, flexible, and relatively low in cost. Major applications include microphones and loudspeakers, ultrasonic devices, SAW transducers, actuators, single-element infrared detectors and many others. This review will describe some of the lesser-known applications of these materials in the areas of tactile devices, energy conversion, porous polymers, property measurement, pyroelectric infrared sensors, shock sensors and space science.

Review of some lesser-known applications of piezoelectric and pyroelectric polymers

INVESTIGATIONS have recently been made into the generation of electric potentials in bone subjected to mechanical stress1–5. Shamos, Lavine and Shamos5 and Fukada and Yasuda3 have suggested that the potentials are the result of a piezoelectric effect in the collagen of the bone. Fukada and Yasuda have also found a piezoelectric effect in the collagen of the Achilles tendons of a horse and a cow4. Other workers1,2 have suggested that the electric potentials in bone may be generated either by the bending of mucopolysaccharide molecules such as hyaluronic acid or by stress at the interface between collagen and hydroxyapatite. The polar crystal structure of the collagen molecule means that it could exhibit a pyroelectric effect as well as piezoelectricity. We have therefore investigated the existence and magnitude of the pyroelectric effect, and tried to find the origin of the electric potentials in stressed bone.

Sidney B. Lang

Papers

Pyroelectricity: From Ancient Curiosity to Modern Imaging Tool

Laser‐intensity‐modulation method: A technique for determination of spatial distributions of polarization and space charge in polymer electrets

Review of some lesser-known applications of piezoelectric and pyroelectric polymers

Pyroelectric Effect in Bone and Tendon

Sourcebook of pyroelectricity