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Superconducting quantum interference device instruments and applications
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Image of FIG. 1.
FIG. 1.

Resistance of mercury (a) (after Ref. 2) and vs (b) absolute temperature.

Image of FIG. 2.
FIG. 2.

(Color online) Meissner effect in a superconducting ring cooled in an externally applied magnetic field.

Image of FIG. 3.
FIG. 3.

(Color online) Flux quantization.

Image of FIG. 4.
FIG. 4.

(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.

Image of FIG. 5.
FIG. 5.

(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.

Image of FIG. 6.
FIG. 6.

(Color online) Dual junction (dc) SQUID loop. The capacitor represents the self-capacitance of the junction.

Image of FIG. 7.
FIG. 7.

(a) bias point for Josephson junction; (b) voltage vs externally applied flux at constant bias current.

Image of FIG. 8.
FIG. 8.

The phase space for (a) type-I and (b) type-II superconductors.

Image of FIG. 9.
FIG. 9.

(Color online) Flux transformer for coupling external flux (two turn “detection coils”). Not to scale.

Image of FIG. 10.
FIG. 10.

(Color online) (a) Schematic of fractional turn SQUID sensor; (b) fabricated device. The pads are for coupling in the bias and feedback currents.

Image of FIG. 11.
FIG. 11.

(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.

Image of FIG. 12.
FIG. 12.

Triangle pattern showing detected output (rf) voltage vs flux coupled into the SQUID.

Image of FIG. 13.
FIG. 13.

(Color online) Block diagram of a typical dc SQUID. The detection coil (connected to the input coil) is omitted for clarity.

Image of FIG. 14.
FIG. 14.

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 .

Image of FIG. 15.
FIG. 15.

(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 ).

Image of FIG. 16.
FIG. 16.

(Color online) External feedback circuit. Note that the internal feedback circuitry (shown in Fig. 13) is not used.

Image of FIG. 17.
FIG. 17.

(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.

Image of FIG. 18.
FIG. 18.

(Color online) Schematic diagram of typical SQUID input circuit.

Image of FIG. 19.
FIG. 19.

(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.

Image of FIG. 20.
FIG. 20.

Response of gradient coils relative to magnetometer response ( suppressed).

Image of FIG. 21.
FIG. 21.

(Color online) Sensitivity/ vs coil diameter for different detection coil designs. , ; base diameter; lead length (from SQUID sensor to detection coil) .

Image of FIG. 22.
FIG. 22.

(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).

Image of FIG. 23.
FIG. 23.

(Color online) First order gradiometer with three noise cancellation channels.

Image of FIG. 24.
FIG. 24.

(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.

Image of FIG. 25.
FIG. 25.

Typical design of a fiber glass Dewar used for biomagnetic measurements (superinsulation not shown).

Image of FIG. 26.
FIG. 26.

(Color online) Different methods of achieving close Dewar tail spacing. Thermal shielding is omitted for clarity.

Image of FIG. 27.
FIG. 27.

CryoSQUID components (Ref. 53).

Image of FIG. 28.
FIG. 28.

rms field noise spectra in various environments as a function of frequency (after Ref. 59).

Image of FIG. 29.
FIG. 29.

Commercial magnetically shielded room showing first layer of mu-metal shielding and rigid aluminum frame.

Image of FIG. 30.
FIG. 30.

(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).

Image of FIG. 31.
FIG. 31.

(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)].

Image of FIG. 32.
FIG. 32.

Beam current meter.

Image of FIG. 33.
FIG. 33.

(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).

Image of FIG. 34.
FIG. 34.

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.

Image of FIG. 35.
FIG. 35.

(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.

Image of FIG. 36.
FIG. 36.

Calculated resistivity as a function of frequency.

Image of FIG. 37.
FIG. 37.

Calculated 2D inversion map and resultant geologic interpretation. Horizontal span . After Ref. 100.

Image of FIG. 38.
FIG. 38.

(Color online) Tensor made from discrete magnetometers.

Image of FIG. 39.
FIG. 39.

(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.

Image of FIG. 40.
FIG. 40.

(Color online) Block diagram of controlled source electromagnetic system.

Image of FIG. 41.
FIG. 41.

(Color online) interval data from Ref. 104 for (a) copper sphere and (b) artillery shell.

Image of FIG. 42.
FIG. 42.

(Color online) Magnetic microscope image of Martian meteorite ALH84001, after Ref. 110.

Image of FIG. 43.
FIG. 43.

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.

Image of FIG. 44.
FIG. 44.

(Color online) Scan of 1, 3, 5, and holes in a steel plate.

Image of FIG. 45.
FIG. 45.

X-ray of vector set (, , and ) of detection coils (-diam).

Image of FIG. 46.
FIG. 46.

(Color online) Sheet inducer.

Image of FIG. 47.
FIG. 47.

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).

Image of FIG. 48.
FIG. 48.

(Color online) On-axis magnetization of strain sensor.

Image of FIG. 49.
FIG. 49.

(Color online) Effect of intervening materials.

Image of FIG. 50.
FIG. 50.

(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.

Image of FIG. 51.
FIG. 51.

(Color online) Magnetic field map generated by current flow and its deconvolved current map.

Image of FIG. 52.
FIG. 52.

(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 .

Image of FIG. 53.
FIG. 53.

(Color online) SSM scan of the ink in the region around George Washington’s right eye on a one dollar bill.

Image of FIG. 54.
FIG. 54.

(Color online) Sensitivity and spatial resolution of a number of SQUID microscopes.

Image of FIG. 55.
FIG. 55.

(Color online) (a) Binding reaction between antibody and antigen in magnetoimmunoassay; (b) schematic diagram of magnetoimmunoassay measurement.

Image of FIG. 56.
FIG. 56.

Magnetocardiogram of fetus ( gestation).

Image of FIG. 57.
FIG. 57.

Typical amplitudes and frequency ranges for various biomagnetic signals (based on a tail gap).

Image of FIG. 58.
FIG. 58.

(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 .

Image of FIG. 59.
FIG. 59.

(Color online) Field contour map generation.

Image of FIG. 60.
FIG. 60.

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 .

Image of FIG. 61.
FIG. 61.

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 .

Image of FIG. 62.
FIG. 62.

Whole head neuromagnetometer (coil-in-vacuum construction).

Image of FIG. 63.
FIG. 63.

(Color online) MCG biomagnetometer components (gantry and electronics not shown).

Image of FIG. 64.
FIG. 64.

(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 .

Image of FIG. 65.
FIG. 65.

(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 .

Image of FIG. 66.
FIG. 66.

(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).

Image of FIG. 67.
FIG. 67.

(Color online) Magnetopneumography measurement system.


Generic image for table
Generic image for table
Table I.

Properties of superconducting materials (parts of this table were taken from Refs. 7 and 15).

Generic image for table
Table II.

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.

Generic image for table
Table III.

Typical sensitivities of SQUID instruments.

Generic image for table
Table IV.

Areas in which SQUID magnetometers are being used in medical research.


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Scitation: Superconducting quantum interference device instruments and applications