Staff members at Los Alamos National Laboratory (LANL) produced a summary of the structural health monitoring literature in 1995. This presentation will summarize the outcome of an updated review covering the years 1996 2001. The updated review follows the LANL statistical pattern recognition paradigm for SHM, which addresses four topics: 1. Operational Evaluation; 2. Data Acquisition and Cleansing; 3. Feature Extraction; and 4. Statistical Modeling for Feature Discrimination. The literature has been reviewed based on how a particular study addresses these four topics. A significant observation from this review is that although there are many more SHM studies being reported, the investigators, in general, have not yet fully embraced the well-developed tools from statistical pattern recognition. As such, the discrimination procedures employed are often lacking the appropriate rigor necessary for this technology to evolve beyond demonstration problems carried out in laboratory setting.

A review of structural health monitoring literature 1996-2001

Fundamentals, processes and applications of high-permittivity polymer–matrix composites

Current research on the blends of natural and synthetic polymers as new biomaterials: Review

A ceramic-powder polymer composite, making use of a relaxor ferroelectric polymer that has a high room-temperature dielectric constant as the matrix, is developed. The experimental data show that the dielectric constant of the composites with Pb(Mg1/3Nb2/3)O3–PbTiO3 powders can reach more than 250 with weak temperature dependence. In addition, the composites under a proper preparation procedure exhibit a high breakdown field strength (>120 MV/m), leading to a maximum energy storage density of more than 15 J/cm3. Experimental results also indicate that the high electron irradiation does not have much effect on the dielectric behavior of Pb(Mg1/3Nb2/3)O3–PbTiO3 powders, possibly due to the relaxor nature of the ceramic.

High-dielectric-constant ceramic-powder polymer composites

Ordinary differential equations of the first order linear differential equations complex numbers and linear algebra simultaneous linear differential equations numerical methods the descriptive theory of nonlinear differential equations mechanical systems and electric circuits Fourier series Fourier integrals and Fourier transforms the Laplace transformation partial differential equations Bessel functions and Legendre polynomials applications and further properties of matrices vector analysis the calculus of variations analytic functions of a complex variable infinite series in the complex plane the theory of residues conformal mapping.

Advanced Engineering Mathematics. By C. R. Wylie. Pp. xiv, 813. 1966. (McGraw-Hill.)

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

Reconstituted collagen membranes (thickness 20-40 microns used in periodontal guided tissue regeneration, were prepared by solubilization of bovine serosa and bovine tendon using an alkaline treatment and by solubilization of bovine serosa in acetic acid. Dielectric properties of these materials were determined in the frequency range of 10 -5 -10 6 Hz (poling temperature = 313 K, poling time = 3 h, E = 10 7 V/m), using a General Radio Bridge system (high frequencies) and a discharge current technique (low frequencies). The true pyroelectric coefficient p(T) was determined for these materials by a direct method over an appropriate temperature range. Their magnitude appear to be in the range of 10 -4 to 10 -5 C/m 2 K -l , which is considerably higher than that of the ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymer vinylidene fluoride-trifluorethylene (VDF-TrFE).

Dielectric and pyroelectric characterization of anionic and native collagen

The variation in the polarization distribution through the thickness of a polymer electret is determined by heating each electrode of the sample with a laser beam which is modulated at various frequencies between 0.1 and 100 kHz. The periodic heating induces temperature waves which are attenuated exponentially as a function of both depth in the sample and frequency of modulation. The resulting “thermal probe” heats regions having different polarizations and produces an AC pyroelectric current. A linear least-squares analysis of the experimental current-frequency data gives the polarization distribution.

A technique for determining the polarization distribution in thin polymer electrets using periodic heating

Composites, made of lead zirconate titanate (PZT) ceramic powder and castor oil-based polyurethane (PU), were prepared in the film form. The films were obtained in the thickness range 100–300 μm using up to 50/50 vol.% of ceramic. Another composite (PZT/C/PU) was obtained by adding a small amount (1.0 vol.%) of graphite (C) to the PZT/PU composite. By increasing the conductivity of PU-containing graphite, polarization of PZT could be carried out with better efficiency. A comparison of piezo- and pyroelectric activities and spatial distribution of polarization between graphite doped and undoped composites reveal the advantages of using semiconductor filler. These composites were used as sensors to detect acoustic emission (AE). The detection was made using two simulated sources of AE, i.e., ball bearing drop and pencil lead break. PZT/C/PU composite was able to detect both flexural and extensional components of wave vibration.

Characterization and application of PZT/PU and graphite doped PZT/PU composite

The piezo- and the pyroelectric properties of poled polyvinylidene fluoride (PVDF) and its copolymers arise primarily from the ferroelectric orientation of the C-F dipoles rather than trapped space...

D. K. Das-Gupta

Papers

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

Dielectric and pyroelectric characterization of anionic and native collagen

A technique for determining the polarization distribution in thin polymer electrets using periodic heating

Characterization and application of PZT/PU and graphite doped PZT/PU composite

Pyroelectricity in polymers