Breakdown Patterns in Branly's Coheror

Vandembroucq, Damien; Boccara, Albert Claude; Roux, Stéphane

doi:10.1051/jp3:1997123

Cited by 16 publications

(24 citation statements)

References 5 publications

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“…In a (loosely or not) packed granular system, the metal (or conducting entity) occupies a finite volume in space, and hopping from a grain to a (nearest neighbor) grain is likely to occur through rather wide and often inhomogeneous insulating barriers with finite thickness distributed over a sort of percolating network. 2,14,15,39,40 In contrast, in the case of a doped material, hopping between two impurity sites goes through only a narrow size insulating homogeneous barrier.…”

Section: A)mentioning

confidence: 99%

Unusual thermoelectric behavior of packed crystalline granular metals

Ausloos

Pękała

Latuch

et al. 2004

Journal of Applied Physics

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Loosely packed granular materials are intensively studied nowadays. Electrical and thermal transport properties should reflect the granular structure, as well as intrinsic properties. We have compacted crystalline CaAl-based metallic grains and studied the electrical resistivity and the thermoelectric power as a function of temperature ͑T͒ from 15 to 300 K. Both properties show three regimes as a function of temperature. It should be pointed out: (i) The electrical resistivity continuously decreases between 15 and 235 K, (ii) with various dependencies, e.g., ӍT −3/4 at low T, while (iii) the thermoelectric power (TEP) is positive, (iv) shows a bump near 60 K, and (v) presents a rather unusual square root of temperature dependence at low temperature. It is argued that these three regimes indicate a competition between geometric and thermal processes-for which a theory seems to be missing in the case of TEP. The microchemical analysis results are also reported, indicating a complex microstructure inherent to the phase diagram peritectic intricacies of this binary alloy.

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Section: A)mentioning

confidence: 99%

Unusual thermoelectric behavior of packed crystalline granular metals

Ausloos

Pękała

Latuch

et al. 2004

Journal of Applied Physics

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“…Except some sporadic works in the 1960-70s [9,10], the electrical conduction in granular media prompts renewed interest only since recently. Some works revisited the action of nearby electromagnetic wave (Branly effect) [11,12], others focused on the effect of an electrical source directly imposed on the system [8,13,14]. Both perturbations lead to a transition from an insulating state to a conductive state of the granular medium.…”

Section: Introductionmentioning

confidence: 99%

“…Here, we also report the first experimental map showing the current distribution within a 2D granular medium. Note that direct infrared visualizations and numerical simulations of temperature distribution exist [13,21], as well as various 2D models of random resistor network [22]. This work is a first step towards more complex systems, some questions being still open, e.g., the stress dependence of the electrical resistance of a granular packing [23].…”

Section: Introductionmentioning

confidence: 99%

Some aspects of electrical conduction in granular systems of various dimensions

et al. 2007

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Abstract. We report on measurements of the electrical conductivity in both a 2D triangular lattice of metallic beads and in a chain of beads. The voltage/current characteristics are qualitatively similar in both experiments. At low applied current, the voltage is found to increase logarithmically in a good agreement with a model of widely distributed resistances in series. At high enough current, the voltage saturates due to the local welding of microcontacts between beads. The frequency dependence of the saturation voltage gives an estimate of the size of these welded microcontacts. The DC value of the saturation voltage (≃ 0.4 V per contact) gives an indirect measure of the number of welded contact carrying the current within the 2D lattice. Also, a new measurement technique provides a map of the current paths within the 2D lattice of beads. For an isotropic compression of the 2D granular medium, the current paths are localized in few discrete linear paths. This quasi-onedimensional nature of the electrical conductivity thus explains the similarity between the characteristics in the 1D and 2D systems.

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“…This indicates the presence of long-time memory effects even the packing density remains constant around a value ρ = 0.72 ± 0.02. Large electrical fluctuations should be associated with the breaking/creation of granular arches.Although many experiments have been performed for studying dynamical, mechanical and geometrical properties of the granular matter [1], only very few reports [2][3][4][5][6] can be found in the scientific literature for studying electrical properties of such systems.In 1890, Branly reported [2] that the electrical resistance of packed metallic grains is affected by an incident electromagnetic wave. Branly's coherer was the first reported antenna.…”

mentioning

confidence: 99%

“…Although many experiments have been performed for studying dynamical, mechanical and geometrical properties of the granular matter [1], only very few reports [2][3][4][5][6] can be found in the scientific literature for studying electrical properties of such systems.…”

mentioning

confidence: 99%

Giant electrical fluctuations in metallic disordered packings

Vandewalle

Dorbolo

2001

The European Physical Journal E

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We have experimentally studied granular arches through electrical measurements. The packing is composed of 2d metallic pentagons and is submitted to small taps. Large electrical fluctuations are observed and they are distributed along power laws. This indicates the presence of long-time memory effects even the packing density remains constant around a value ρ = 0.72 ± 0.02. Large electrical fluctuations should be associated with the breaking/creation of granular arches.Although many experiments have been performed for studying dynamical, mechanical and geometrical properties of the granular matter [1], only very few reports [2][3][4][5][6] can be found in the scientific literature for studying electrical properties of such systems.In 1890, Branly reported [2] that the electrical resistance of packed metallic grains is affected by an incident electromagnetic wave. Branly's coherer was the first reported antenna. He discovered also that a small vibration of the packing affects drastically the electrical resistance. Ammi et al.[3] measured a non-Hertzian behavior of the electrical conductivity when a packing is submitted to high uniaxial pressures. In an other experiment, Vandembrouck et al. [4] visualized the electrical paths in a packing of metallic beads for different current densities.More recently, our group has studied the electrical properties of a 2d packing made of metallic beads [5]. Electrical fluctuations have been studied when the packing is submitted to small taps, and they revealed Lévy statistics, i.e. a non-Gaussian behavior. The broad distribution of the electrical fluctuations has been interpreted to be due to breaking contacts in the packing. However, the spherical beads we used had the tendency to self-organize into ordered hexagonal configurations. As a consequence, a strong compaction of the packing has been observed [5] in our electrical measurements.In the present note, we report new electrical measurements of a packing made of identical pentagons instead of beads. Pentagons have been chosen because they have the property to resist more to compaction than beads. Our experiment has also been improved by the addition of a a e-mail: nvandewalle@ulg.ac.be Charge Coupled Device (CCD) camera which tracks the density ρ of the packing during the whole experiment.Our experimental setup is the following. We have considered a two-dimensional granular system composed of identical metallic (aluminium) pentagons which are 1 mm thick and 1 cm wide. The main part of our experimental setup is a tilted plane (40 × 60 cm 2 ) on which the pentagons are placed. Typically, the tilt angle is θ = 20 • . About 1000 pentagons are placed on that tilted plane. At the base of the packing, a constant current i is injected through two pentagons separated by a distance of 30 cm. The tension U between those pentagons is measured with the help of a microvoltmeter. In each series of measurements, the following procedure has been repeated a large number n of times: i) a wooden hammer driven by a computer hits the bottom of th...

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Breakdown Patterns in Branly's Coheror

Cited by 16 publications

References 5 publications

Unusual thermoelectric behavior of packed crystalline granular metals

Unusual thermoelectric behavior of packed crystalline granular metals

Some aspects of electrical conduction in granular systems of various dimensions

Giant electrical fluctuations in metallic disordered packings

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