Search results for "ACOUSTIC"
showing 10 items of 1590 documents
Size dependence of magnetic domain patterns in exchange-biased Permalloy/NiO microstructures
2002
The magnetic domain structure in Permalloy (Ni81Fe19) micropatterns (10?100??m) on NiO has been investigated by means of soft x-ray photoemission electron microscopy. The exchange anisotropy between the Ni81Fe19 patterns and the NiO layer results in the formation of complex domain structures which markedly differ from the simple Landau?Lifshitz configurations. The domain structures reflect the competition between the exchange anisotropy and the dipole?dipole interaction in a weakly coupled system. The observed domain structures change with the feature size, as the domain patterns lose complexity in the smaller structures.
Reference-Plane Invariant Method for Measuring Electromagnetic Parameters of Materials
2010
This paper presents a simple and effective wideband method for the determination of material properties, such as the complex index of refraction and the complex permittivity and permeability. The method is explicit (non-iterative) and reference-plane invariant: it uses a certain combination of scattering parameters in conjunction with group-velocity data. This technique can be used to characterize both dielectric and magnetic materials. The proposed method is verified experimentally within a frequency range between 2 to 18 GHz on polytetrafluoroethylene and polyvinylchloride samples. A comprehensive error and stability analysis reveals that, similar to other methods based on transmission/re…
Can be GPR technique useful for strength characterization of concrete?
2010
The possibility of material characterization through the GPR measurements, taking into account the integration with the ultrasonic technique, has been studied and possible relationships between the permittivity of materials and their bulk density are discussed. We present here two different approaches. The first one describes an attempt to correlate the mechanical strength of concrete (as well the ultrasonic velocity) with the permittivity of the material. A series of samples of concrete, characterized by different material properties, were used for georadar and ultrasonic measures, seeking correlations among experimental data. The second approach illustrates the comparison between GPR and …
Electrical transport in carbon black-epoxy resin composites at different temperatures
2013
Citation: J. Appl. Phys. 114, 033707 (2013); doi: 10.1063/1.4815870 (Received 3 May 2013; accepted 27 June 2013; published online 17 July 2013) Results of broadband electric/dielectric properties of different surface area—carbon black/epoxy resin composites above the percolation threshold are reported in a wide temperature range (25–500 K). At higher temperatures (above 400 K), the electrical conductivity of composites is governed by electrical transport in polymer matrix and current carriers tunneling from carbon black clusters to polymer matrix. The activation energy of such processes decreases when the carrier concentration increases, i.e., with the increase of carbon black concentration…
Optically assisted trapping with high-permittivity dielectric rings: Towards optical aerosol filtration
2016
Controlling the transport, trapping, and filtering of nanoparticles is important for many applications. By virtue of their weak response to gravity and their thermal motion, various physical mechanisms can be exploited for such operations on nanoparticles. However, the manipulation based on optical forces is potentially most appealing since it constitutes a highly deterministic approach. Plasmonic nanostructures have been suggested for this purpose, but they possess the disadvantages of locally generating heat and trapping the nanoparticles directly on surface. Here, we propose the use of dielectric rings made of high permittivity materials for trapping nanoparticles. Thanks to their abilit…
Thermal and conductivity dependence of GaAs based acoustic biosensors
2016
GaAs BAW sensors using shear acoustic waves were developed for biological detection and quantification. The sensor consists of a 50–350µm thick membrane where thickness shear acoustic waves were produced with a lateral field excitation (LFE). The LFE electrode arrangement is located on one side of the membrane. The other side is dedicated for proteins or cells capture through a bio-functionalized interface formed on the GaAs surface. Sensitivity of this type of sensor had been evaluated by modeling to 0.1ng.Hz−1. Detection needs to be done in liquid environment with complex biological analytes such as blood or plasma. These analytes can inevitably induce temperature and surface charge varia…
GPR multi-component data analysis
2007
In order to test the capabilities of ground-penetrating radar (GPR) detection, models were reproduced in a laboratory using both plastic and metal cylinders as well as sheets to represent anomalies buried in a plastic tank containing sand. These models, which represent pipes and dipping layers in a homogeneous medium (i.e., sand), were used to detect the object’s position and study its polarization properties based on the different dielectric contrasts between the object and the surrounding medium. We paid particular attention to the choice of medium through which the wavefield propagated, to be sure of its isotropy and homogeneity, in order for the velocity to be the same for every path tr…
Influence of the suspension of continued treatment with flurazepam and amobarbital on two discrimination learning schedules.
1977
The authors have studied the effect of the suspension of chronic treatment with flurazepam and amobarbital on the operant behavior of rats that for the first time were in the presence of two fixed-interval discrimination schedules. With the sound discrimination schedule, the responses emitted by the treated animals had characteristics similar to those of control animals. With the temporal discrimination schedule, though it is not possible to distinguish between learning rates, modifications in the intensity of the effect (increases in lever pressing) indicate that, considering the doses, the action of flurazepam is slight and that of amobarbital clear and statistically significant.
Compositional dependence of element-specific magnetic moments in Ni2MnGa films
2009
Element-specific magnetic moments were investigated for epitaxial Ni2Mn1+xGa1−x and (Ni2MnGa)1−x(Co2FeSi)x Heusler films using x-ray absorption spectroscopy and x-ray circular magnetic dichroism in transmission. The epitaxial films of the Ni2MnGa-derived compositions were prepared by dc-sputtering on Al2O3 substrates at 773 K. X-ray diffraction confirms a (1 1 0) oriented growth. An increase in the Mn concentration reduces the magnetic spin moment of both Mn and Ni. An increase in the content of Co2FeSi in the Ni2MnGa compound leads to an increase in the Mn and Ni spin moments and to a decrease in Tm for 5% Co2FeSi and finally to a suppression of the phase transition for 20% Co2FeSi. The or…
Dielectric barrier discharge at the triglycine sulfate crystal surface: the role of the electric field of the domain structure
2014
Dielectric barrier discharges (DBD) at the triglycine sulfate crystal surface, generated in air under controlled gas pressure, have been investigated. Electrical characterization of these DBD discharges, produced at temperatures below as well as above the ferroelectric phase transition, are presented. The influence of the electric field of the domain structure on these DBD discharges are discussed in the frame of a model which takes into account the dynamics of the domain structure of the ferroelectric barrier under the action of an external voltage.