Pyroelectric definition

When the film is short-circuited and heated to high temperatures at which the molecules attain a sufficiently high mobility, a current is observed in the external circuit. This phenomenon is called pyroelectric effect, thermally stimulated current, or, when the film has been polarized by a static field prior to measurement, depolarization current. The conventional definition of pyroelectricity is the temperature dependence of spontaneous polarization Ps, and the pyroelectric constant is defined as dPJdd (6 = temperature). In this review, however, the term will be used in a broader definition than usual. The pyroelectric current results from the motion of true charge and/or polarization charge in the film. Since the piezoelectricity of a polymer film is in some cases caused by these charges, the relation between piezoelectricity and pyroelectricity is an important clue to the origin of piezoelectricity. 

The ideal route would be one in which the pyroelectric detector material is laid down in thin film form by a route compatible with the production of the silicon ROIC. There are obvious parallels with the development of FeRAMS (see Section 5.7.5) and the substantial effort now devoted to their development will have a positive impact on the manufacture of pyroelectric arrays. Challenges he in the requirement to process the deposited films at temperatures not too high for the underlying integrated circuit, and the need to engineer the temperature diffusion characteristics within the element and its surroundings so as to optimise image definition. 

The difference between the two definitions rests with the fact that a pyroelectric crystal must possess an overall (observable) permanent electric dipole. Thus a pyroelectric crystal is built from unit cells, each of which must contain an overall electric dipole, (Figure 4.11b). The pyroelectric effect will only be observed, however, if all of these dipoles are aligned throughout the crystal, (Figure 4.11c). [Note that a ferroelectric crystal is defined in a similar way. The difference between a pyroelectric crystal and a ferroelectric crystal lies in the fact that the direction of each overall electric dipole in a ferroelectric crystal can be altered by an external electric field.]... 

It is very common to confuse the definition of optical sensor resolution with other optical system features. Different optical sensors are conceived to detect spatial differences in electromagnetic energy, as, for example, digital cameras (CCD and CMOS), tube detectors (vidicon and plumbicon), and pyroelectric and microbolometer detectors. Such optical sensors are able to resolve differences in the variations of the electromagnetic field. This ability depends... 

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 ... 

The first definitive theory of pyroelectricity, with which rrrajority of later irrves-tigators agreed, was formrrlated by William Thorrrson (Lord Kelvin) in 1878 and... 

A polar material, whose electric dipoles can reverse direction as a consequence of an external electric field, is by definition a ferroelectric material. These materials form a subgroup of pyroelectric materials. 

Pyroelectric sensors Pyroelectric Thermal flow sensors Definition... 

This leads us to the definition of a generalized pyroelectric coefficient dD a f. , ... 

---