Electrets

An efficient, flexible and unvaryingly porous polymer composite membrane based nanogenerator (PPCNG) without any electrical poling treatment has been realised as wireless green energy source
to power up smart electronic gadgets. Owing to self-polarized piezo- and ferro-electretic phenomenon of in situ platinum nanoparticles (Pt-NPs) doped porous poly(vinylidenefluoride-co-hexafluoropropylene)–
membrane, a simple, inexpensive and scalable PPCNG fabrication is highlighted. The molecular orientations of the -CH2/-CF2 dipoles that cause self-polarization phenomenon has been realized by angular dependent near edge X-ray absorption fine structure spectroscopy. The square-like hysteresis loop with giant remnant polarization, Pr68 lC/cm2 and exceptionally high piezoelectric charge coefficient, d33 = 836 pC/N promises a best suited ferro- and piezo-electretic membrane. The PPCNG exhibits a high electrical throughput such as, ranging from 2.7V to 23V of open-circuit voltage (Voc) and 2.9 lA to 24.7 lA of short-circuit current (Isc) under 0.5 MPa to 4.3 MPa of imparted stress amplitude by periodic human finger motion. The harvested mechanical
and subsequent electrical energy by PPCNG is shown to transfer wirelessly via visible and infrared transmitter-receiver systems, where 17% and 49% of wireless power transfer efficiency, respectively, has been realized to power up several consumer electronics.

Organic field-effect transistors (OFETs) consist of a gate dielectric and an organic semiconductor film. The performance of organic electronic devices substantially depends on the dielectric properties of the insulating gate layer. Only a few key parameters, primarily the dielectric constant and the resulting device capacitance, have been regarded to be of central importance. Many insulating layers are however not simple dielectrics, an example are space charge gate electrets with internally trapped charges. Space charge gate electrets affect the electrical characteristics of diodes and transistors in a much more sophisticated manner, they are for example the key element in flash memories. We present impedance measurements of an organic metal-insulator-semiconductor (MIS) diode and corresponding measurements of a related organic field effect transistor. Both devices have a comparable design, with polyvinylalcohol as gate electret and the methanofullerene PCBM as organic semiconductor. Pronounced electret effects of charge injection and trapping are observed by impedance measurements of the MIS structure and these effects are found equally expressed in the electrical characteristics of the OFET configuration, reflecting first steps towards organic flash memories

The turbulent flow structures responsible for the fluctuating wall pressure in the turbulent boundary layer on a cylinder in axial flow (delta/a = 5.04, Re(sub theta) = 2870) have been investigated. Simultaneous measurements of the fluctuating wall pressure and turbulent streamwise velocities have been performed throughout a large volume of the boundary layer (y(sup +) = 14 to y/delta = 1.91, 0 less than or equal to x/delta less than or equal to 1.52, azimuthal angle phi = 0 deg, 20 deg, 40 deg) with a subminiature electret microphone (d(sup +) = 25.9) and hotwire velocity probe (1(sup +) = 18.5). Pressure-velocity cross-spectra and cross-correlation measurements indicate that two primary groups of pressure fluctuations exist in the cylindrical boundary layer: (1) small-scale, high-frequency disturbances concentrated close to the wall associated with the burst-sweep cycle; and (2) large-scale, low-frequency disturbances extending from the wall to the turbulent/potential-flow interface that are consistent with a large spanwise-oriented 'vortex' in close contact with and inclined to the wall.

Technology advances have enabled modification of the size and shape of the electronic components to the microscale, with commensurate scaling down of their power requirements to milliwatts and microwatt range. Consequently, many complex electronic systems and devices such as wearable medical and autonomous devices consume power in the range less than 200 μW, and wireless sensor networks in the range μW to 100 mW are operated on battery power. Due to the salient limitations of battery power, such as longevity of charge and where applicable, the requirement for periodic recharging, possibilities for utilization of autonomous energy sources is critical for operation of such devices. Ambient energy sources, such as vibrations (1 μW to 20 mW), motion (wide range in power outputs), temperature gradient (0.5–10 mW), radiofrequency waves (>180 μW/cm2), light (100 μW/cm2 to 100 mW/cm2), acoustics (0.003–0.11 μW/cm2), and many other, have the potential to directly power the electronic device. Ambient energy harvesting, when used separately or in conjunction with batteries, will enhance the longevity of equipment operations requiring portable or autonomous power supply. This paper reviews the state of the art in energy-harvesting techniques, power conversion, and characterization of mini- and microscale self-sustaining power generation systems in the range 600 μW to 5 W, specifically focusing on low-power system applications, for personal assistive and mobile technology devices.

The high dielectric constant of dipolar charge electrets makes these materials attractive as gate dielectric in organic field effect transistors (OFET). Additionally, dipole electrets may even provide functionalities to such devices, like permanently polarized gate dielectrics for nonvolatile memories as well as pyro- or piezoelectric OFETs. Organic thin film transistors in top-contact geometry with pentacene as semiconductor and double layers of a ferroelectric polymer electret poly(vinylidene-fluoride tetrafluoroethylene hexafluoropropylene) and the polymer poly(vinyl cinnamate) as gate dielectric are shown. The electret is a terpolymer of vinylidene fluoride, trifluoroethylene and hexafluoropropylene with a high dielectric constant ε=10 at 1 MHz. The transistors show large intrinsic field effect mobility's in the range of μi=1 cm2/Vs and a large ratio of on- to off-current of about 105. The use of strongly polar high-k polymer gate dielectrics seems promising for applications of organic field effect transistors as non-volatile memory elements and in organic sensor systems.

The Geophysical Institute of Israel (GII) started a new project of establishing a calibration infrasound dataset for the Eastern Mediterranean/Middle East region for improvement of monitoring capabilities of international network infrasound stations. The dataset is intended to characterize the infrasonic wave propagation in the region: travel times, spectra, amplitudes, dependence on source yield, and atmospheric conditions. To achieve these goals, a series of experimental surface shots will be conducted at Sayarim Military Range (SMR), located in southern Israel, Negev desert, including the main calibration explosion of 80 tons (TNT equivalent). During the explosions numerous portable co-located infrasound and seismic systems will be deployed at near-source (0.1‐1 km) (accelerometers), local (10‐350 km), and regional distances (500‐1500 km) in neighboring countries (during the main explosion). Tripartite arrays of low-frequency electret condenser microphones will be installed at cl...

Chemical treatment of cellular polypropylene (PP) films was carried out. Their charge storage properties were investigated using the open circuit thermally stimulated discharge (TSD) current spectra and charge TSD spectra. The charge storage thermal stability of the HF-treated samples is significantly improved, as shown by a very strong high temperature peak at about 176°C. The charge stability of treated films is improved further by appropriately prolonging HF treatment time at RT. It was found that the reaction rate of HF with the oxidized surface layer is obviously enhanced by light radiation or treating temperature. However, charge storage stability becomes worse even than the virginal film prolonging HF-treating time under light radiation. An in situ TSD charge spectrum contains combined information on the changes of the mean charge depth and the deposited charge value. The dynamic change of the mean charge depth during heating was investigated by the in situ TSD charge spectra.

... B.Penn, H.Abdelaem et al i Photogalvanic pulsator, CLEO '2002, Technical Digest, SPIE Proc., Vol.4803, p.261, (2002) 11 .N.Kukhtarev, T.Kukhtareva, M. Bayssie D.Frazier, B.Penn, H.Abdelaem et al Photo-induced Optical and Electrical Pulsations and Pattern Formation in ...