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The spatial distribution of the polarization and space charge in thermally poled poly (vinylidene fluoride) is studied using the laser intensity modulation method. Injected space charge, localized near the electrode polymer interface, tends to prevent the formation of uniform polarization in the polymer bulk. The actual amount of charge existing in the poled specimen is determined using hysteresis measurements and thermally stimulated discharge current (TSDC) measurements. By using the peak cleaning technique and by measuring the pyroelectric current during the cooling of the specimen, the contribution of depolarization current and space charge detrapping to the TSDC measurement is considered. From hysteresis measurements a relaxation process was observed around 65°C which was related to the dipolar relaxation in the crystalline phase known as the αc relaxation. A significant increase of the TSDC at temperatures higher than 130°C was observed meaning that the dipolar charge and the space charge are very stable up to high temperature. In this temperature range, the pyroelectric current is significant. Two relaxation processes were identified for a polarizing temperature lower than 120°C. One is centred around the polarizing temperature and is related to space charge release. The second is related to dipole relaxation in the crystalline phase. The position of the last peak is determined by interaction between the dipoles and the internal electric field, resulting from the charge stored in the sample. We propose to call this as the αcρ interaction. The higher temperature of the dipolar peak was identified as 86°C with an activation energy of 0.52±0.04 eV.

Recently, a laser intensity modulation method (LIMM) has been developed to determine spatial distributions of both polarization and space charge in the bulk of polymeric insulators. Polarization arising from field-induced orientation of dipoles and trapped space charges provides pyroelectric current when a metal-polymer-metal sandwich is heated with a laser beam that is intensity modulated in an appropriate range of frequencies. Present work provides an improved analytical technique to transform the pyroelectric current-frequency data into a spatial distribution of polarization and space charges. Some experimental results with a polar polymer and the associated spatial distribution of polarization are presented in support of the mathematical model.

The spatial distribution of charges injected by monoenergetic electrons in Teflon FEP has been determined by two different techniques - the laser-induced pressure pulse (LIPP) technique and the laser-intensity modulation method (LIMM). A new numerical deconvolution technique for the LIMM is used. A comparison of the results provided by the two techniques shows good agreement.

Piezoelectric resonator arrays for tunable acoustic waveguides and metamaterials J. Appl. Phys. 112, 064902 (2012) Focused high frequency needle transducer for ultrasonic imaging and trapping Appl. Phys. Lett. 101, 024105 (2012) A rigid, monolithic but still scannable cavity ring-down spectroscopy cell Rev. Sci. Instrum. 83, 043115 (2012) Acoustic resonator based on periodically poled transducers: Concept and analysisThe mechanical and electrical properties of transducers are modeled by finite-difference representations of the relevant physical equations, and the numerical problems are discussed. The theory is applied to ͑a͒ a ceramic transducer of dimensions 1 cmϫ1 cmϫ200 m, ͑b͒ a polymer P of the same dimensions, and ͑c͒ a 1-3 composite transducer consisting of transverse rods of ceramic embedded in a matrix of polymer. The results for the ceramic agree with the one-dimensional model, viz.:voltage of order 4-5 V and no resonance below 10 MHz. For the polymer, the resonant frequency of 3.9 MHz is close to the 4 MHz predicted by the one-dimensional theory. For the composite, introduction of the ceramic has an immediate effect on s 11 , s 12 and s 13 , whereas it has little effect on d 31 unless the density of the ceramic in the mix is 30% or higher.