First results for a novel superconducting imaging-surface sensor array

A superconducting imaging-surface system was constructed using 12 coplanar thin-film SQUID magnetometers located parallel to and spaced 2 cm from a 25 cm diameter lead imaging-plane. Some measurements included two additional sensors on the back side of the superconducting imaging-plane to study the field symmetry for the system. Performance was measured in a shielded can and in the open laboratory environment. Data from this system has been used to: (1) understand the noise characteristics of the dewar-SQUID imaging plate arrangement, (2) to verify the imaging principle, (c) measure the background rejection factor of the imaging plane, and (4) compare superconducting materials for the imaging plane. A phantom source field was measured at the sensors as a function of phantom distance from the sensor array to verify the imaging theory. Both the shape and absolute values of the measured and predicted curves agree very well indicating the system is behaving as a gradiometer in accordance with theory. The output from SQUIDs located behind the imaging surface that sense background fields can be used for software or analog background cancellation. Fields arising from sources close to the imaging plane were shielded from the background sensors by more than a factor of 1000. Measurement of the symmetry of sensor sensitivity to uniform fields exactly followed theoretical predictions

First results for a superconducting imaging-surface sensor array for magnetoencephalography

Magnetoencephalography (MEG) follows from the initial fundamental work of Cohen in 1968 and development by several groups, most notably at MIT and at NYU, based on the development of the Superconducting QUantum Interference Device (SQUID) using the Josephson effect. The SQUID`s incredible sensitivity to magnetic fields permits the measurement of the very weak magnetic fields emitted from the human brain due to intracellular neuronal currents. Current growth in MEG is dominated by multiple sensor arrays covering much of the head. These new large devices have primarily been developed and made commercially available by several companies including BTI in the US, CTF in Canada, and Neuromag in Finland. Large projects are also in place in Japan. These systems contain more than 100 sensors spaced at various intervals over the head using various configurations of magnetometers and gradiometers. The different designs available on the market are driven by factors such as detection efficiency, cost, and application. They now present a completely novel whole-head SQUID array system using a superconducting imaging-surface gradiometer concept derived at Los Alamos. Preliminary tests have demonstrated higher performance, lower noise, and additional shielding of background fields while using simpler fabrication techniques than existing whole-head MEG systems, which should reduce production costs

Experimental validation of superconducting quantum interference device sensors for electromagnetic scattering in geologic structures

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This project has supported the collaborative development with Sandia National Laboratories (SNL) and the University of New Mexico (UNM) of two critical components for a hand-held low-field magnetic sensor based on superconducting quantum interference device (SQUID) sensor technology. The two components are a digital signal processing (DSP) algorithm for background noise rejection and a small hand-held dewar cooled by a cryocooler. A hand-held sensor has been designed and fabricated for detection of extremely weak magnetic fields in unshielded environments. The sensor is capable of measuring weak magnetic fields in unshielded environments and has multiple applications. We have chosen to pursue battlefield medicine as the highest probability near-term application because of stated needs of several agencies

SQUIDs as Detectors in a New Experiment to Measure the Neutron Electric Dipole Moment

A new experiment has been proposed at Los Alamos National Laboratory to measure the neutron electric dipole moment (EDM) to 4x10{sup {minus}28} ecm, a factor of 250 times better than the current experimental limit. Such a measure of the neutron EDM would challenge the theories of supersymmetry and time reversal violation as the origin of the observed cosmological asymmetry in the ratio of baryons to antibaryons. One possible design for this new experiment includes the use of LTC SQUIDs coupled to large ({approximately}100 cm{sup 2}) pick-up coils to measure the precession frequency of the spin-polarized {sup 3}He atoms that act as polarizer, spin analyzer, detector, and magnetometer for the ultra-cold neutrons used in the experiment. The method of directly measuring the {sup 3}He precession signal eliminates the need for very uniform magnetic fields (a major source of systematic error in these types of experiments). It is estimated that a flux of {approximately}2x10{sup {minus}16} Tm{sup 2} (0.1 F{sub 0}) will be coupled into the pick-up coils. To achieve the required signal-to-noise ratio one must have a flux resolution of d F{sub SQ}=2x10{sup {minus}6} F{sub 0}/{radical}Hz at 10 Hz. While this is close to the sensitivity available in commercial devices, the effects of coupling to such a large pick-up coil and flux noise from other sources in the experiment still need to be understood. To determine the feasibility of using SQUIDs in such an application we designed and built a superconducting test cell, which simulates major features of the proposed EDM experiment, and we developed a two-SQUID readout system that will reduce SQUID noise in the experiment. We present an overview of the EDM experiment with SQUIDs, estimations of required SQUID parameters and experimental considerations. We also present the measured performance of a single magnetometer in the test cell as well as the performance of the two SQUID readout techniqu

SQUIDs as detectors in a new experiment to measure the neutron electric dipole moment

A new experiment has been proposed at Los Alamos National Laboratory to measure the neutron electric dipole moment (EDM) to 4{times}10{sup {minus}28} ecm, a factor of 250 times better than the current experimental limit. Such a measure of the neutron EDM would challenge the theories of supersymmetry and time reversal violation as the origin of the observed cosmological asymmetry in the ratio of baryons to antibaryons. One possible design for this new experiment includes the use of LTC SQUIDs coupled to large ({approximately}100 cm{sup 2}) pick-up coils to measure the precision frequency of the spin-polarized {sup 3}He atoms that act as polarizer, spin analyzer, detector, and magnetometer for the ultra-cold neutrons used in the experiment. The method of directly measuring the {sup 3}He precession signal eliminates the need for very uniform magnetic fields (a major source of systematic error in these types of experiments). It is estimated that a flux of {approximately}2{times}10{sup {minus}16} Tm{sup 2} (0.1 {Phi}{sub 0}) will be coupled into the pick-up coils. To achieve the required signal-to-noise ratio one must have a flux resolution of d{Phi}{sub SQ} = 2{times}10{sup {minus}6}{Phi}{sub 0}/{radical}Hz at 10 Hz. While this is close to the sensitivity available in commercial devices, the effects of coupling to such a large pick-up coil and flux noise from other sources in the experiment still need to be understood. To determine the feasibility of using SQUIDs in such an application the authors designed and built a superconducting test cell, which simulates major features of the proposed EDM experiment, and they developed a two-SQUID readout system that will reduce SQUID noise in the experiment. They present an overview of the EDM experiment with SQUIDs, estimations of required SQUID parameters and experimental considerations. The authors also present the measured performance of a single magnetometer in the test cell as well as the performance of the two SQUID readout technique

First Results for a Novel Superconducting Imaging-Surface Sensor Array

A superconducting imaging-surface system was constructed using 12 coplanar thin-film SQUID magnetometers located parallel to and spaced 2 cm from a 25 cm diameter lead imaging-plane. Some measurements included two additional sensors on the ''back'' side of the superconducting imaging-plane to study the field symmetry for our system. Performance was measured in a shielded can and in the open laboratory environment. Data from this system has been used to: (a) understand the noise characteristics of the dewar-SQUID imaging plate arrangement, (b) to verify the imaging principle, (c) measure the background rejection factor of the imaging plane, and (d) compare superconducting materials for the imaging plane. A phantom source field was measured at the sensors as a function of phantom distance from the sensor array to verify the imaging theory. Both the shape and absolute value of the measured and predicted curves agree very well indicating the system is behaving as a gradiometer in accordance with theory. The output from SQUIDs located behind the imaging surface that sense background fields can be used for software or analog background cancellation. Fields arising from sources close to the imaging plane were shielded form the background sensors by more than a factor of 1000. Measurement of the symmetry of sensor sensitivity to uniform fields exactly followed theoretical predictions

First Results for a Superconducting Imaging-Surface Sensor Array for Magnetocardiography

The authors have completed fabrication and preliminary testing of a 12-channel SQUID array using the superconducting image-surface gradiometer concept. Sensor response to point dipole magnetic sources, and uniform fields used to simulate ambient magnetic fields followed predicted values to high precision. Edge effects were not observed for sources, within 5cm of the center of the imaging surface independent of whether the source is close or far from the surface. The superconducting imaging-surface also reduced uniform ambient fields at the SQUID sensors by approximately a factor of ten. Finally, a high degree of symmetry was observed between sides of the imaging surface for uniform fields. This symmetry, together with the very small sensitivity of sensors on the back side of the imaging surface to sources close to the front side provides an excellent circumstance for implementing either digital or analog background rejection. Their goal is to implement a higher density array with the superconducting imaging surface, together with background rejection, and utilize this system for MCG and other biomagnetic studies