Theoretical Modelling on the Magnetization by Electric Field Through Product Property.

Multilayer composites of piezoelectric and magnetostrictive materials can be designed to exhibit the magnetoelectric (ME) effect. This ME effect can be realised as an electric polarisation induced by a magnetic field (called MEH effect) or a magnetization by an electric field (called MEE effect). Theoretical modelling of the MEE effect for 2-2 connectivity composites has been developed for three different boundary conditions for perfect coupling at the interface. The calculated MEE coefficients using material properties of piezoelectric lead zirconate titanate (PZT) and magnetostrictive Terfenol-D are a few orders of magnitude larger than those of single phase ME materials and the calculated values are compared with experimental results in the literature. Keywords: magnetoelectric, multiferroic, piezoelectric, magnetostrictive, piezomagnetic, laminated composites, modelling

Strong electron emissions induced and extracted by pyroelectric crystals

A high voltage pulse generated by changing the temperature of a pyroelectric crystal was used to induce strong electron emissions from a ferroelectric cathode. The effects of the extracting voltage provided by an external power source or by another pyroelectric crystal on the electron emission property were investigated. As for a normal ferroelectric cathode, both the electron emission current and the total emitted electrons were found to increase with the increasing extracting voltage. However, the final voltage on the cathode after electron emission was also found to depend on the extracting voltage at the anode. The electron emission was also found to depend not only on the pulse generation and the ferroelectric cathode as reported previously, but also on the capacitance of the anode. These phenomena were explained by a surface-plasma-assisted electron emission mechanism

Pyroelectric effect enhancement through product property under open circuit condition

An analytical model for the pyroelectric (PY) effect under open circuit condition and 2-2 connectivity laminates of various pairs of PY and nonpyroelectric (NP)/elastic materials has been developed. It is evident from our analysis that there indeed is a substantial dissimilarity between the PY coefficients and figure of merit for efficiency for various PY-NP pairs under short circuit and open circuit conditions. We believe this implies that there should be a greater distinction made between the PY coefficients under these two electrical conditions than previously thought. The indicators for various PY-NP material pairs that can be utilized to determine their PY coefficient enhancement potential under open circuit condition have been identified. The investigated PY materials are lead zirconate titanate (PZT-5H and PZT-5A), barium titanate, lithium tantalate, lithium niobate, and polyvinylidene fluoride (PVDF), while the NP materials are stainless steel, polytetrafluoroethylene (PTFE or Teflon), chlorinated polyvinyl chloride thermoplastic (CPVC), aluminum, zinc, and Invar 36. Extraordinarily large PY coefficient of 97×10-4 C m-2 K-1 at minimum thickness ratio Rmin is expected for PZT-5H-CPVC pair while PVDF-CPVC could show increase in the secondary PY coefficient of up to 350%. In addition, where the figure of merit for efficiency is concerned, for the same volume of the composite PZT-5A-PTFE pair it reaches 24, a 24-fold increase in efficiency at Rmin. Our analysis techniques should provide a methodological way for appraising the potentials of particular PY material and its 2-2 laminates for applications under open circuit condition such as PY X-ray generation, electron accelerator, and nuclear fusion

Accurate measurement of the piezoelectric coefficient of thin films by eliminating the substrate bending effect using spatial scanning laser vibrometry

One of the major difficulties in measuring the piezoelectric coefficient d(33,f) for thin films is the elimination of the contribution from substrate bending. We show by theoretical analysis and experimental measurements that by bonding thin film piezoelectric samples to a substantial holder, the substrate bending can be minimized to a negligible level. Once the substrate bending can be effectively eliminated, single-beam laser scanning vibrometry can be used to measure the precise strain distribution of a piezoelectric thin film under converse actuation. A significant strain increase toward the inside edge of the top electrode (assuming a fully covered bottom electrode) and a corresponding strain peak in the opposite direction just outside the electrode edge were observed. These peaks were found to increase with the increasing Poisson's ratio and transverse piezoelectric coefficient of the piezoelectric thin film. This is due to the non-continuity of the electric field at the edge of the top electrode, which leads to the concentration of shear stress and electric field in the vicinity of the electrode edge. The measured d(33,f) was found to depend not only on the material properties such as the electromechanical coefficients of the piezoelectric thin films and elastic coefficients of the thin film and the substrate, but also on the geometry factors such as the thickness of the piezoelectric films, the dimensions of the electrode, and also the thickness of the substrate

Feasibility of an electrostatic energy harvesting device for CFCs aircraft

A novel energy harvesting concept is proposed for treating local electrostatic energy produced on flying composite aircrafts. This work focuses on the feasibility research on collecting static charges with capacitive collectors. The existing energy harvesting system and the electrification of the typical carbon fibre composites (CFCs) aircraft has been reviewed. The detailed model experiments were then designed to characterize different configurations for electrostatic energy harvesting on aeroplane. In the lab, the static charge was produced by a corona discharging device, and a capacitor or a metal sheet was put in the electric field to collect the charges under four different configurations. After that, the rest results for these configurations were analysed, which is followed by the discussion about the results application on the aircraft. This work has proved that it is feasible to collect the local static electricity on flying aircraft, and it could provide a new direction of energy harvesting system in aviation field

Aerogel/epoxy thermal coatings for carbon fibre reinforced plastic substrates

The present work studies an aerogel/epoxy composite that was dip coated onto a carbon fibre substrate by adding the aerogel at the 1 h and the 1.5 mark of the epoxy cure. Both coatings show decrease in thermal conductivity values (39% and 47% respectively) when compared to a pure epoxy coating. The coatings’ reflectance spectra also provided further evidence for the existence of the nano-pores within the aerogel particles. The aerogel coating was modelled using material properties from literature and solved using finite element methods. The model, which validated using experimental data, was then used to predict the coating’s performance in cyclic thermal loads. Additionally, coatings on a single surface- top and bottom; were also modelled and compared with the double coating system wherein it was seen that the double coating system had the lowest rate of temperature change and fluctuations at steady-state in contrast to the bottom coating which, showed the fastest drop in temperature as well as the highest fluctuations at steady state conditions. The performance of the top coating was in the middle

Non-isothermal cure kinetics of aerogel/epoxy composites using differential scanning calorimetry

The present work determines the non-isothermal cure parameters of aerogel/epoxy samples along with the effect of a wetting agent. The cure parameters were calculated using Kissinger and isoconversional methods after which the reaction was modeled with the Sestak–Berggren equation. It is seen that the composites had higher activation energy and frequency factor values compared to the pure resin, and similarities in cure parameters between the aerogel/epoxy composites with and without the wetting agent were seen. Hence, the former’s use is advocated due to its positive influence on the resin–aerogel interface without sacrificing the cure parameters

In-situ tuning of catalytic activity by thermoelectric effect for ethylene oxidation

Thermoelectric material BiCuSeO used as a support and promoter for catalytic ethylene oxidation is reported here. The catalytic activity on the continuous and non-continuous catalyst Pt supported on BiCuSeO was observed to be promoted in-situ by a thermoelectric Seebeck voltage generated by the temperature gradient across the material. It is also shown this thermoelectric promotion of catalysis enabled the thermoelectric material BiCuSeO itself to be highly catalytic active for ethylene oxidation. A good linear relationship between the logarithm of the reaction rate and the thermoelectric Seebeck voltage was observed. This thermoelectric promotion of catalysis is attributed to the change of work function of the catalyst surface, accompanied by a charge transfer from the bulk to the surface due to the thermoelectric effect

Effect of extrusion and compression moulding on the thermal properties of nylon-6/silica aerogel composites

The article presents the effect of a lower extrusion speed and compression moulding processes on the thermal properties of polyamide 6 (PA-6)/aerogel composite. Scanning electron and optical microscope images showed that although most of the aerogel was destroyed during extrusion at 65 r/min, extrusion at 5 r/min showed a better retention of the aerogel structure. However, when subjected to moulding in a compression press, both composites extruded at different speeds suffered significant damage. Nevertheless, the extruded samples did show a lower thermal conductivity compared to the virgin polymer. Further, it was observed that the sample extruded at 5 r/min had a lower damage coefficient value with an overall loss of around 33% to the aerogel structure when compared to the material extruded at 65 r/min, which endured a structural loss of 41% to the aerogel in it

Morphological, optical and thermal characterisation of aerogel-epoxy composites for enhanced thermal insulation

The present work explores the possibility of introducing aerogel at different stages of the epoxy resin cure to identify the most effective method that ensures minimal destruction of the aerogel particles. The aerogel particles are added at 0.5 h, 1 h and 1.5 h after the resin and the hardener are mixed together. Additionally, the effect of a wetting agent that improves the interface between the aerogel and the resin is also investigated. The different materials are characterised using optical images and ESEM-EDX to determine the most effective processing route. Additional data are also provided by determining the different material’s optical transmittance and reflective characteristics. From the experimental results, it is observed that the addition of aerogel at the 1-h mark proves to be the most efficient route to follow. In addition, the wetting agent displays a negligible effect on the samples in the study; hence, its usage is advocated due to its influence on the interface strength. Therefore, the aerogel/epoxy/wetting agent sample with the aerogel added at the 1 h mark looks promising. A 13.3% decrease in thermal conductivity when compared with the pure resin/hardener sample along with the damage coefficient value of 0.183 demonstrates the material’s potential for thermal insulation applications