Technology of thermally stimulated diagnostics of anisotropy and optical axes in crystals

For implementing the technology of thermally stimulated diagnostics of anisotropy and optical axes in crystals, the sample is thermostated at a temperature not exceeding the melting point, an electric field not exceeding the breakdown field is applied to the sample and polarization is produced for a time greater than the relaxation time at this temperature. After that, without switching off the electric field, the sample is cooled to the liquid nitrogen temperature, following which the field is switched off, the sample is linearly heated to a temperature above the polarization temperature and the resultant thermally stimulated depolarization (TSD) spectra taken along and perpendicular to the optical axis of the crystal are examined. When comparing the spectra the presence of anisotropy is detected and the direction of the optical axes is determined from the magnitude and presence of the TSD maxima.

Polarization Parameters and Scaling Matter—How Processing Environment and Shape Factor Influence Electroactive Nanocomposite Characteristics

Polymeric-ceramic smart nanocomposite piezoelectric and dielectric materials are of interest due to their superior mechanical flexibility and ability to leverage characteristics of constituent materials. A great deal of work has centered on development of processes for manufacturing 0–3 continuity composite piezoelectric materials that vary in scale ranging from bulk, thick and thin film to nanostructured films. Less is known about how material scaling effects the effectiveness of polarization and electromechanical properties. This study elucidates how polarization parameters: contact versus corona, temperature and electrical voltage field influence the piezoelectric and dielectric properties of samples as a function of their shape factor, i.e., bulk versus thick film. Bulk and thick film samples were prepared via sol gel/cast-mold and sol gel/spin coat deposition, for fabrication of bulk and thick films, respectively. It was found that corona polarization was more effective for both bulk and thick film processes and that polarization temperature produced higher normalized changes in samples. Although higher electric field voltages could be achieved with thicker samples, film samples responded the most to coupled increases in temperature and electrical voltage than bulk samples.

Technology for thermostimulated diagnostics of anisotropy and optical axes of crystals

To implement the technology of thermally stimulated diagnostics of anisotropy and optical axes of crystals, the sample is thermostated at a temperature not exceeding the melting point, an electric field not exceeding the breakdown field is applied to the sample, polarization is produced for a time greater than the relaxation time at this temperature. After that, without disconnecting the electric field, cooling to the temperature of liquid nitrogen is performed, then the field is switched off, the sample is linearly heated to a temperature above the polarization temperature and the obtained thermally stimulated depolarization (TSD) spectra taken along and perpendicular to the optical axis of the sixth order C6 crystal are examined. When comparing the obtained spectra, the presence of anisotropy is determined, and the exact direction of the optical axes is determined by the magnitude and presence of the TSD maxima.

Extracting parasite effects of electrical bioimpedance measurements

The objective of this work is to develop a technique for filtering parasitic effects from the impedance spectra (IS) measured in biological material phantoms. IS data are contaminated with unexpected capacitive and inductive effects from cable, input/output amplifiers capacitances, electrode polarization, temperature and contact pressure when collecting data. It is proposed a model which contains an RLC-network in series with the Cole model (RSC), then called RLC-Cole. It was built four circuits composed by resistors, capacitors and inductors. An impedance analyzer (HF2IS) was used to perform the measurements in the frequency range of 1 to 3000 kHz. Data were fitted into the model and comparisons to the nominal values were made. In order to validate the proposed model, a gelatin phantom and a chicken breast muscle impedance spectra were also collected and analyzed. After filtering, Cole fitting was performed. Results showed a maximum root-mean-square error of 1% for the circuits, 2.63% for the gelatin phantom, whereas 2.01% for the chicken breast. The RLC-Cole model could significantly remove parasitic effects out of a tissue impedance spectrum measured by a 4-point electrode probe. This may be highly important in EIS systems whose objective is to discriminate a normal tissue from a cancerous one.

Piezoelectric Energy Harvesting from Floor Using Wounded PVDF Films

Energy harvesters of PVDF can be used to power small electrical loads or wireless sensor systems. Simple technologies are sufficient for the fabrication of these harvesting modules. Critical process step is the polarization of the piezoelectric material. Main piezoelectric parameters depend strongly on the polarization material. Particularly, the electric field strength and the polarization temperature influence the remanent polarization of PVDF. Dielectric breakdowns of the film at higher temperatures prevent a sufficient polarization. At least, all modules were polarized at a field strength of 100 – 120 MV/m and a temperature of 90°C.Modules with dimensions of 165mm x 95mm x 1.5mm were used to power a commercial available “development kit for Energy Harvesting Wireless systems” (EnOcean ‘EDK 300’). The modules possess of 20 layers of PVDF. Each module was connected via a standard four diode full rectifier bridge with the development kit EDK 300. Positioned underneath a parquet floor (thickness=10mm), the modules converted mechanical energy of footsteps into electricity. Goal of these investigations were to find out configurations suited to generate a sufficient energy level to supply the operation of the EDK 300. Two capacitors in the development kit are used to start the operation of the kit (C1=470μF) and to store converted energy (C2=0.25F). Already a few steps onto one module were sufficient to charge C1 and to start the operation of the EDK 300. Following steps (>100) produced energy which was stored in C2.

Electronic Configuration of Tungsten in 4H-, 6H-, and 15R-SiC

A commonly observed unidentified photoluminescence center in SiC is UD-1. In this report, the UD-1 center is identified to be tungsten related. The identification is based on (i) a W-doping study, the confirmation of W in the samples was made using deep level transient spectroscopy (DLTS), (ii) the optical activation energy of the absorption of UD-1 in weakly n-type samples corresponds to the activation energy of the deep tungsten center observed using DLTS. The tungsten-related optical centers are reported in 4H-, 6H-, and 15R-SiC. Further, a crystal field model for a tungsten atom occupying a Si-site is suggested. This crystal field model is in agreement with the experimental data available: polarization, temperature dependence and magnetic field splitting.