Resistance of mercury (a) (after Ref. 2) and vs (b) absolute temperature.
(Color online) Meissner effect in a superconducting ring cooled in an externally applied magnetic field.
(Color online) Flux quantization.
(Color online) (a) Quantum mechanical wave function of a superconducting current penetrating a normal region, showing the attenuation of the wave function as it penetrates an insulating layer. (b) Quantum mechanical wave function penetrating a thin normal region separating two superconducting regions. (c) Current vs voltage curve of a shunted Josephson tunnel junction measured across the junction. In an ideal Josephson junction, the transition from resistive to superconducting behavior would be a sharp vertical transition, rather than the real-world curved transition shown.
(Color online) Different types of Josephson junctions: (a) point contact, (b) microbridge, also known as a Dayem bridge, (c) thin-film tunnel junction (the barrier can either be an insulating (SIS) or normal metal (SNS) material, (d) bicrystal, (e) step edge grain boundary, (f) step edge superconductor-normal-superconductor, and (g) ramp edge superconductor-normal-superconductor with a barrier. After Ref. 18.
(Color online) Dual junction (dc) SQUID loop. The capacitor represents the self-capacitance of the junction.
(a) bias point for Josephson junction; (b) voltage vs externally applied flux at constant bias current.
The phase space for (a) type-I and (b) type-II superconductors.
(Color online) Flux transformer for coupling external flux (two turn “detection coils”). Not to scale.
(Color online) (a) Schematic of fractional turn SQUID sensor; (b) fabricated device. The pads are for coupling in the bias and feedback currents.
(Color online) Block diagram of SQUID input and electronics for locked-loop operation of a rf SQUID. The input circuitry from the experiment (e.g., a detection coil which would be connected to the input coil) is omitted for clarity. PSD refers to phase sensitive detection, JJ means Josephson junction, and ref means reference.
Triangle pattern showing detected output (rf) voltage vs flux coupled into the SQUID.
(Color online) Block diagram of a typical dc SQUID. The detection coil (connected to the input coil) is omitted for clarity.
Energy sensitivity vs frequency for a number of different SQUID devices: (a) is a LTS rf SQUID operated at a bias frequency of ; (b) is a dc biased LTS dc SQUID with amorphous silicon barriers; (c) is (b) using ac biasing; (d) is a dc biased LTS dc SQUID with barriers; and (e) is an ac biased HTS dc SQUID utilizing a ramp edge junction [Fig. 5(g)]. Devices (a)–(d) were operated at ; device (e) was at .
(Color online) ac biasing. The modulation oscillator is used to chop the dc bias current at a frequency typically twice that of the modulation frequency (here ).
(Color online) External feedback circuit. Note that the internal feedback circuitry (shown in Fig. 13) is not used.
(Color online) ac susceptibility system using external feedback. The external feedback signal is generated (in parallel to the internal feedback in this example) to the magnet power supply and then attenuated before being fed into the input circuit. The capacitive circuit element generates the quadrature signal.
(Color online) Schematic diagram of typical SQUID input circuit.
(a) Magnetometer; (b) first derivative axial gradiometer; (c) first derivative planar gradiometer; (d) second derivative axial gradiometer; (e) second derivative asymmetric axial gradiometer; (f) first derivative radial gradiometer.
Response of gradient coils relative to magnetometer response ( suppressed).
(Color online) Sensitivity/ vs coil diameter for different detection coil designs. , ; base diameter; lead length (from SQUID sensor to detection coil) .
(Color online) HTS patterned tape on flexible substrate (upper). HTS tape bent into axial gradiometer configuration. The flux is transported and inductively coupled to a 90° oriented HTS SQUID magnetometer (lower).
(Color online) First order gradiometer with three noise cancellation channels.
(Color online) (a) Left ordinate: first order gradiometer low frequency drift; right ordinate: reference magnetometer. (b) Left ordinate: gradiometer (heavier line) and reference magnetometer (lighter line) attenuated by (dc shifted by ); right ordinate: difference between gradiometer and attenuated reference magnetometer.
Typical design of a fiber glass Dewar used for biomagnetic measurements (superinsulation not shown).
(Color online) Different methods of achieving close Dewar tail spacing. Thermal shielding is omitted for clarity.
CryoSQUID components (Ref. 53).
rms field noise spectra in various environments as a function of frequency (after Ref. 59).
Commercial magnetically shielded room showing first layer of mu-metal shielding and rigid aluminum frame.
(Color online) Shielding factors for various shielded rooms. The trailing number refers to the number of mu-metal layers. The dashed line is the shielding factor for an aluminum eddy current room (Ref. 62).
(Color online) Field sensitivities and bandwidths typical of various applications. The dashed lines indicate the sensitivity of commercially available SQUIDs [lower line LTS, Fig. 14(d); upper line HTS, Fig. 14(e)].
Beam current meter.
(Color online) (a) ac and dc current, (b) magnetic field, (c) dc voltage, (d) dc resistance, (e) ac resistance/inductance bridge, and (f) ac mutual inductance (susceptibility bridge).
Magnetic susceptibility measurement apparatus (liquid helium Dewar not shown): (a) ac susceptibility; (b) signal and excitation coil details; (c) second derivative oscillating magnetometer for dc measurements with external dc field coils.
(Color online) Variable temperature susceptometer (various electrical leads omitted for clarity). The trace on the right shows the response of the detection coil(s) as a function of sample position height.
Calculated resistivity as a function of frequency.
Calculated 2D inversion map and resultant geologic interpretation. Horizontal span . After Ref. 100.
(Color online) Tensor made from discrete magnetometers.
(Color online) Output of HTS planar gradiometer flying over a commercial vehicle (arbitrary units). The gradiometer was inside a tail mounted stinger on a Cessna Caravan airplane.
(Color online) Block diagram of controlled source electromagnetic system.
(Color online) interval data from Ref. 104 for (a) copper sphere and (b) artillery shell.
(Color online) Magnetic microscope image of Martian meteorite ALH84001, after Ref. 110.
Measurement configurations for SQUID NDE: (a) intrinsic currents, (b) remnant magnetization, (c) flaw-induced perturbations in applied currents, (d) Johnson noise or corrosion activity in conductors, (e) eddy currents induced by an applied ac magnetic field, (f) hysteretic magnetization by application of stress or an applied field, and (g) diamagnetic and/or paramagnetic materials in an applied field.
(Color online) Scan of 1, 3, 5, and holes in a steel plate.
X-ray of vector set (, , and ) of detection coils (-diam).
(Color online) Sheet inducer.
Side view of Tristan NLD-510 Dewar in MS-830 showing customer constructed sample translation stage and measurements of 304 stainless steel as a function of percent of failure (Ref. 111).
(Color online) On-axis magnetization of strain sensor.
(Color online) Effect of intervening materials.
(Color online) Magnetic field maps of a room temperature embedded strain sensor under a -thick concrete overcoating. (a) Bare sensor showing dipole characteristics; (b) sensor under concrete; (c) bare concrete. Image (d) is a digital subtraction of B and C showing that it is possible to image objects deep underneath magnetically complex coverings. The scans cover a area.
(Color online) Magnetic field map generated by current flow and its deconvolved current map.
(Color online) Magnetic image of data on a hard disk. Measurements were made at a vertical stand-off of . The bit spacing is and the intertrack spacing is .
(Color online) SSM scan of the ink in the region around George Washington’s right eye on a one dollar bill.
(Color online) Sensitivity and spatial resolution of a number of SQUID microscopes.
(Color online) (a) Binding reaction between antibody and antigen in magnetoimmunoassay; (b) schematic diagram of magnetoimmunoassay measurement.
Magnetocardiogram of fetus ( gestation).
Typical amplitudes and frequency ranges for various biomagnetic signals (based on a tail gap).
(Color online) Magnetic field generated by a current dipole. For a sphere, the dipole is located at midpoint of the maxima and minima at a .
(Color online) Field contour map generation.
Neuromagnetic patterns generated by the interictal spike complex in a patient with a partial epileptic seizure disorder. The individual patterns are measured at intervals of approximately .
Minimum detectable current dipole for a first derivative, six turn, gradiometer with a coil diameter of (Ref. 123) as a function of off-axis position and depth .
Whole head neuromagnetometer (coil-in-vacuum construction).
(Color online) MCG biomagnetometer components (gantry and electronics not shown).
(Color online) Peripheral nerve signals generated by an electrical shock at the median nerve (the brighter trace is ; the others are and ). The forearm location is shown by the outlined box. The first (vertical) peak is the stimulus artifact. The next peak is the detected peripheral nerve as it travels up along the forearm. The distance between the two (expanded) sensor locations is . The peak of the detected signal between the upper and lower expanded time display has shifted by .
(Color online) Shift in BER [in cycles/min (CPM)] before and after chemically induced occlusion of a mesenteric (intestinal) artery. The BER frequency varies as a function of position within the GI tract. The gastric BER is typically , the small intestine BER is , and the duodenum BER is .
(Color online) (a) Ferritometer® components. Typical patient movement is vertically. The combination of a second order detection coil and a first order magnetizing coil gives excellent near field sensitivity while rejecting distant sources. (b) Installed system showing ultrasound scanner (to left of gantry) and plastic calibration phantom (on bed).
(Color online) Magnetopneumography measurement system.
Properties of superconducting materials (parts of this table were taken from Refs. 7 and 15).
Relative attenuation along the axis of ideal semi-infinite cylinder (Ref. 68). is the distance measured from the open end of the can and is the diameter of the can.
Typical sensitivities of SQUID instruments.
Areas in which SQUID magnetometers are being used in medical research.
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