ISSN:0094-243X    

DOI:10.1063/1.31340

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The theory of rf SQUID opteration, including the effects of fluctuations, is discussed. The theory is in agreement with the large signal and small signal behavior of real devices under optimum conditions. The noise levels of many existing rf SQUID systems are substantially above those predicted on the basis of amplifier noise temperatures. All rf SQUIDs seem to exhibit excess noise of unknown origin at low input frequencies. The limitations of devices and future directions of development are considered.

ISSN:0094-243X    

DOI:10.1063/1.31327

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A simple theory of the tunnel junction dc SQUID shows that the energy resolution per Hz with respect to an input coil is of order 4kBT(&pgr;LC)1/2/&agr;2, where C is the capacitance of each junction and &agr; is the coupling coefficient between the input coil and the SQUID inductance L. The dc SQUID with junction areas of about 104&mgr;m2has a typical energy resolution per Hz of of 7×10−30JHz−1. If the junction area is reduced to 102&mgr;m2or 1 &mgr;m2, the energy resolution per Hz is expected to improve by one or two orders of magnitude respectively. Further improvement should result from lowering the operating temperature.

ISSN:0094-243X    

DOI:10.1063/1.31344

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We review the presnet status of weak links and dc and rf biased SQUIDs made with high temperature superconductros. A method for producing reliable, reproducible devices using Nb3Sn is outlined and comments are made on directions future work should take.

ISSN:0094-243X    

DOI:10.1063/1.31354

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

In a little over ten years, the sensitivity of low temperature transport experiments has increased from 10−9V to 10−15V. This increase in resolution, made possible by the development of SQUID voltmeters, has spawned several new avenues of research, such as the study of the interface resistance between superconducting and normal boundaries, and the study of transport effects in inhomogeneous superconductors near the percolation threshold. In addition, other research areas have become revitalized, as previously well established theories were found unable to withstand the scrutiny of ultra‐high resolution measurements. The study of thermoelectricity in pure metals has developed rapidly during the decade, and new experimental techniques have been devised with resolution comparable to the best resistivity measurements.

ISSN:0094-243X    

DOI:10.1063/1.31367

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A discussion of the techniques used for performing a variety of magnetic resonance experiments using a SQUID is presented. In particular, measuremtns of the nuclear magnetism of liquid3He in the temperature range 1.2 K to 2 mK in magnetic fields of 3.7 to 309 Oe using pulsed NMR, cw NMR, adiabatic fast passage, and static susceptibility using the same detection system will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.31383

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

SQUID magnetometers in conjunction with superconducting magnets and shields are now being used for susceptometrs that provide unique combinations of sensitivity, speed, resolution, accuracy, stability and convenience. They are being integrated into systems with automated data acquisition and closed cycle helium refrigerators. These systems promise to become increasingly important for measurements of the magnetic properties of materials.

ISSN:0094-243X    

DOI:10.1063/1.31384

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Several experiments applying SQUID instrumentation to the study of diverse fields in fundamental physics are reviewed. Included from gravitational physics research are the relativity gyroscope experiment, an equivalence principle experiment and work on second generation gravitational wave detectors. Experiments studying the properties of elementary particles at rest include the He3nuclear gyroscope, fractional electric charge detector and a magnetic monopole charge detector, where new preliminary measurements on the magnetic charge of the fractional electric charge candidates are presented. Measurements of 2e/h and h/meare included as significant contributions to the determination of the fundamental physical constants. In addition a brief description of ultra‐low magnetic field shields used in four of these experiments is given.

ISSN:0094-243X    

DOI:10.1063/1.31385

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Two 3‐axis SQUID magnetometers were used to perform simultaneous magnetotelluric measurements at two sites separated by 4.8 km near Hollister, California. The data obtained at earch site were analyzed by using a standard least‐squares method, and also using the two magnetic field measurements at the other site as a lock‐in reference. The apparent resistivities obtained from the conventional analysis were nearly always biased downward by noise picked up in the magnetic channels, at some frequencies by as much as two orders of magnitude. By comparison, the same data analyzed with the remote reference technique showed no such bias.

ISSN:0094-243X    

DOI:10.1063/1.31386

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The unprecedented sensitivity of superconductive magnetic gradiometers affords means of measuring fluctuating gradients of magnetic fields from eddy currents generated by ocean waves moving sea‐water across the earth’s magnetic field. Our aim is to tell wave spectra from measurements of fluctuating magnetic gradients over oceans. As a first step in development of requisite experimental and analytical techniques, we report measurements of fluctuating magnetic gradients from surface waves passing an oceanographic research tower located about one mile off Mission Beach near San Diego, California, in 18m of water.The measurements give experimentally‐determined frequency response functions for gradients that substantially confirm response functions claculated using Amphere’s law. Before making measurements over an open ocean from aircraft, however, we require, first of all, means of continually maintaining magnitudes of gradiometer imbalance less than 10−6m−1. Development of methods and techniques for suppressing noise from aircraft platforms at frequencies of ocean waves as well as radio frequencies, and for constructing cryostats suited to aircraft, are presently of secondary importance.

ISSN:0094-243X    

DOI:10.1063/1.31387

出版商:AIP    

年代:1978

数据来源: AIP