Separators pyroelectric

The following discussion separates pyroelectric materials into 3 groups intrinsic pyroelectrics which are operated well below Tc, dielectric bolometer materials which are operated close to Tc, but with an electrical bias applied and ferroelectric thin films. 

Sharp EJ and Gam LE (1982) Use of low frequency sinusoidal temperature waves to separate pyroelectric currents from non-pyroelectric currents. Journal of Applied Physics 53 8980-8987. 

Fig. 22. Relation between polarities of poling field and pyroelectric current of polarized films a dipole orientation, b ion separation, and c homocharge injection...

Most of the crystals in this group are noncentric and thus piezoelectric. In fact sucrose has been shown to emit light only for cleavage with a component perpendicular to its pyroelectric axis (9). The observation of lightning provides clear evidence for charge separation and thus good evidence for fracture. 

Pyroelectric Separator—The pyroelectric effect is used mainly for the separation of quartz from feldspar. The mixture is heated in the hopper feeder by means of steam. On passing to a cold rotating cylinder below, the material causes pyroelectric polarization to appear on the quartz. This mineral adheres to the cylinder, while the feldspar is not affected. 

The pyroelectric effect results from the electric charge separation resulting from the stress caused by the temperature change. A small potential difference, sometimes too small to measure, develops across... 

Pyroelectric detector A thermal detector based on the temperature-dependent potential that develops between electrodes separated by a pyroelectric material. 

An alternative to the resistive elements is the pyroelectric anemometer based on LiTa03 [34]. These devices provide wide rangeability and high reproducibility but, because they are fabricated separately, can only be used as hybrid elements [35]. While this is a drawback in some applications, the results of Yu et al established that it is possible to use even relatively large pyroelectric anemometers (active regions 3 mm x 3 mm) to monitor flows as low as 10 mm min , values that silicon-based devices generally cannot match. 

The pyroelectric effect that is normally observed in a crystal is, in fact, composed of two separate effects called the primary (or true) pyroelectric effect and the secondary pyroelectric effect. If a crystal is fixed so that its size is constant as the temperature changes, the primary effect is measured. Normally, though, a crystal is unconstrained. An additional pyroelectric effect will now be measured, the secondary pyroelectric effect, caused by strains in the crystal produced by the thermal change. In general, the secondary effect is much greater than the primary effect, but both are utilised in devices. 

A large number of pyroelectrics crystallize in the so-called layer perovskite phases. These phases are made of layers of perovskites separated by... 

Finally, temperature modulated thermally stimulated current analysis has been applied to study dielectric materials via the separation of reversible pyroelectric effects from nonreversing thermally stimulated discharges. 

The surface polarization can be measured by different means. The most straightforward one is based on the pyroelectric technique [15]. To measure P one has to deal only with one surface of a cell with uniform director alignment, either planar or homeotropic at both interfaces. The main idea is to use a spatially dependent temperature increment in order to separate the contributions to the pyroelectric response coming only from the surface under study and not from the opposite one. By definition, the pyroelectric coefficient is y = dPIdT where P is macroscopic polarization of a liquid crystal and T is temperature. If we are interested only in the polarization originated from the orientational order we can subtract the isotropic contribution to y and calculate P in the nematic or SmA phases by integrating the pyroelectric coefficient, starting from a certain temperature T, in the isotropic phase ... 

They show the properties of piezoelectricity and pyroelectricity. Piezoelectricity refers to the separation of electric chares on the surface of the crystal upon mechanical stress, Pyroelectricity is the recovery of electric charges when the crystal is heated or cooled. 

Perovskites have numerous applications in electronic ferro, ferri, piezo, and pyroelectric properties, in sensors for gas detection, as membranes for gas separation, and in catalysis [2-4]. In heterogeneous catalysis, several points are of... 

In this context, the possibility to tune tire piezo- and pyroelectricity of specific composites (Floss et al. 2000) by means of separate poling of the inorganic particles and of the polymer crystallites should also be mentioned. In addition, piezo-, pyro-, and ferroelectric polymers such as PVDF and its relevant copolymers may be optimized by controlling fire poling of the amorphous and of the crystalline phase, as well as of the interface between fiiem (Maxwell-Wagner interface polarization) separately (Rollik et al. 1999). Furthermore, it is possible to follow the examples of the classical electret transducers (witti polymeric space-charge electrets) or of the dielectric-elastomer transducers (sometimes also called electro-electrets) and to... 

RoUik D, Bauer S, Gerhard (-Multhaupt) R (1999) Separate contributions to the pyroelectricity in poly(vinylidene fluoride) fiom the amorphous and crystaHine phases, as well as from their interface. J Appl Phys 85 3282-3288... 

In IR array detectors using pyroelectric materials such as TOS mooocrystal or PbTiO ceramics, the detecting plate must be cut into the array of detector elements in order to reduce the cross-talk of response between adjacent elements, which is caused mainly by high thermal diffusion in the plate. On the other hand, since thin films of pyroelect polymers have low thermal diffusion, linear array detectors [23-25] using polymer film with an array of separated electrodes can have small cross-talk between adjacent elements without cutting the film. 

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