Detection of a thin sheet magnetic anomaly by squid-gradiometer systems: possibility of hydrofracture azimuth determination

A study of the signal physics of magnetic anomaly detection was carried out by superconducting gradiometer and magnetometer loop systems with SQUID sensors for possible application to the LASL geothermal energy program. In particular, the crack produced by hydrofracture of a deep HDR geothermal borehole would be filled with a magnetic material such as ferrofluid. When polarized by the earth's field, this material would produce a localized crack magnetic anomaly which is characteristic of the azimuth of the vertical crack with respect to magnetic north. Signatures of the anomaly would be determined by taking rotation data before and after filling the crack with magnetic material. A mathematical description was found for these signatures. To test the theory and the feasibility of the idea, the deep borehole vertical cracks were simulated by using panels to define sheets 1.5 mm thick, 1.2 m wide, and 2.5 m high. When filled with ferrofluid of suitable magnetic permeability, the local anomaly develops. Signatures were measured with a horizontal axial gradiometer rotated about a vertical axis. Good agreement was found between theory and experiment for aximuths in the east and west quadrants but only fair agreement in the north and south quadrants

Revision of the statistical mechanics of phonons to include phonon line widths

Zubarev in 1960 obtained the smeared Bose-Einstein (B-E) function in order to take into account the fact that the eigenenergy associated with a fixed phonon wave vector q and fixed polarization index j is not precisely defined but instead, is smeared by phonon-phonon and phonon-electron interactions. The ratio GAMMA(qj)/..omega..(qj) is often quite small, i.e., of the order of 0.01 or less, where GAMMA is the phonon linewidth and h-bar ..omega.. is the eigenenergy. However, in strongly anharmonic crystals GAMMA/..omega.. may be as large as 0.3 at certain points of the Brillouin zone. In such dramatic cases one would suspect that such phonon linewidths would have some observable effect on the thermodynamic properties. The purpose of this work is to derive the expression for the average free energy per mode for a crystal having large phonon linewidths and to test the properties of the thermodynamic functions derivable from the average free energy per mode. (WHK

Analysis of the macroscopic equations for second sound in solids

The microscopic theories of second sound in solids can be expressed in macroscopic form when the normal and resistive process phonon relaxation times tau/sub N/(..omega..,T) and tau/sub R/(..omega..T) have been averaged appropriately over all ..omega..'s. Thus, for a given temperature T, tau/sub N/(T) and tau/sub R/(T) can be regarded as fixed parameters. The macroscopic equations for the heat current in three dimensions can be expressed in one dimension. A method for solving this expression in closed form is presented. (GHT

Superconductor imaging surface magnetometry: Principles and applications

We present in this paper the principles of superconductor imaging surface magnetometry. This new method should permit MEG and other weak field measurements without the necessity of an expensive magnetically shielded room. We report results showing signal to noise rejection ratios of 1/333,000 with simple apparatus. The goal of 1/1,000,000, seldom achieved by second order gradiometers, should be readily attainable in improved imaging magnetometers. 3 refs., 2 figs

Experiments on superconductor imaging surface magnetometry

The recent development of a new concept in magnetometry has led to experiments to evaluate the performance of such systems. The superconductor imaging surface magnetometer employs superconducting plates and shells to deflect magnetic noise and to image nearby dipole sources while the SQUID pick-up coils are located in areas where the noise has been greatly reduced. The experiments herein reported confirm the principles of imaging magnetometry for detecting nearby dipole sources. 2 refs., 2 figs., 1 tab

THE PHONON-ELECTRON INTERACTION IN Pb-Bi ALLOYS

Le coefficient de diffusion phonon-électron (C) est déduit des mesures de conductivité thermique entre 0,5 K et 10 K, et de résistivité électrique à 4,2 K. Une relation est établie entre les variations de C avec la concentration des alliages et les changements du nombre de porteurs libres.The phonon-electron scattering coefficient (C) is deduced from measurements of the thermal conductivity between 0.5 K and 10 K, and of the electrical resistivity at 4.2 K. The variation in C with alloy content is related to changes in the number of free carriers

Principles of superconductor imaging surface gradiometry

Magnetic sources in the vicinity of superconducting surfaces produce images in such a way that a single pick-up coil parallel to the surface acts as a first order gradiometer. The principles will be described, together with specific discussions of the imaging by planar and spherical surfaces. The fact that these surfaces also deflect noise due to remote sources make this concept particularly appealing as a method for detecting extremely weak sources in a hostile environment. Possible applications to neuromagnetometry, corrosion detection and non-destructive evaluation will be discussed. 2 refs., 2 figs

OBSERVATION OF LONG N-S INTERFACES DURING NORMAL ZONE PROPAGATION

Dans des mesures de la vitesse de destruction par le courant de la supra-conductivité, nous avons trouvé des interfaces N-S mobiles ayant une longueur exceptionnellement grande. Ceci semble en contradiction avec les travaux de nombreux auteurs qui supposent une longueur nulle. La theorie de l'état critique fournit une base possible d'interprétation.In measurements of the velocity of destruction of superconductivity by current, we find the length of the propagating N-S interfaces to be exceptionally long. This is in contrast with the works of many authors who assume zero lengths. Critical state theory provides the basis for possible interpretations

Use of superconducting plates and shells to deflect magnetic noise fields: Application to MEG (magnetoencephalography)

Insertion of a superconducting plate or shell in a magnetic field causes a surface current distribution which opposes the applied field. Resultant fields near plate edges are higher while those near centers are much lower than applied fields. We make use of these principles in MEG by placing suitably oriented gradiometers at points where noise fields are smallest. Signals from nearby brain wave sources are enhanced because the net signal is a combination of that from the sources and that from its image. The principles of noise deflection and source imaging are applied to new concepts of gradiometry. 4 refs., 2 figs