(a) Layout of our bare SQUID design. The SQUID terminals are labeled and and the contact pads for the feedback coil and . (b) Equivalent electric circuit diagram of the bare SQUID. is the shunt resistance in parallel with the Josephson junctions and is the inductance of the device.
(a) Layout of our multiloop SQUID design. and are the SQUID terminals and and the contact pads of the integrated feedback coil. (b) Expanded view of the center of the multiloop SQUID. The Josephson junctions are labeled , the shunt resistances , and the SQUID upper contacts , respectively. The dark and light regions represent the two superconducting layers forming each spoke, which are separated by an insulating layer in crossover regions. (c) Equivalent circuit diagram of the multiloop SQUID. represents the shunt resistance in parallel with the and is the inductance of each individual spoke (fractional turn). The inductance of the device is inversely proportional to the number of spokes.
Detailed cross-sectional schematic of the SQUID microscope Dewar. Top: Cryostat. (A) G-10 fiberglass Dewar casing, (B) liquid reservoir, (C) liquid reservoir. Middle: Positioning mechanism. (D) Rotary vacuum feed-through, (E) G-10 rod, (F) lead screw, (G) slider, (H) slider posts, (I) brass connection, (J) Kevlar tread, and (K) lever arm. Bottom: SQUID Dewar tail. (L) Aluminum flexure bearing support structure, (M) aluminum thermal radiation shield, (N) cryopump, (O) copper L-shaped bracket, (P) copper cold finger, (Q) flexible copper braids, (R) micrometer positioning screws, (S) brass bellows, (T) G-10 cone, (U) sapphire rod, and (V) thick sapphire window.
Photograph of the entire system including a nonmagnetic scanning stage and SQUID Dewar wooden support structure. The SQUID microscope system is housed inside a three-layer -metal magnetically shielded room.
Comparative magnetic field maps of a thin section of a basalt pillow recorded using (a) a hand-wound nine-turns diameter pick-up coil inductively coupled to a commercial SQUID sensor. (b) Bare SQUID design with an effective diameter of . (c) Optical picture of the imaged area. (d) Line scans through both magnetic field images at identical locations as indicated by arrows in (a) and (b). The dashed line corresponds to image (a) and the solid line to image (b).
Schematic of spring-loaded mechanism mounted on the top of the scanning stage. (A) Tail of the SQUID microscope, (B) sample holder, (C) support frame, (D) rubber bands, (E) geological thin section (sample), and (F) Plexiglas pedestal attached to base of the scanning stage.
(a) Relative height between the scanning stage platform and the vacuum window of the SQUID microscope during a line scan. The steps in the curve result from the thickness of the sapphire window and a thin layer of epoxy used to glue the sapphire window to the backing window. (b) Vertical displacement of the sample holder while pressed against the window by the spring-loading mechanism during a line scan. From these measurements, we estimated a tilt of between the sample surface and the sapphire window.
(a) Superposition of the magnetic field map from the sample and the magnetic field generated by wires across the sample used for registration purposes. (b) Optical picture of the sample. The dashed line shows the position of the wire. This registration technique allows us to correlate magnetic features with features in the optical image (arrows).
Photograph of the experimental setup to record the magnetocardiogram on the surface of an isolated rabbit heart. (A) Tail of the SQUID microscope, (B) isolated rabbit heart, (C) tissue bath, and (D) registration wires.
(Color) (a) Optical image of a Langendorff perfused rabbit heart indicating the imaging areas used to record transmembrane potentials (blue square) and magnetic fields (red square) associated with action currents. (b) Time trace of the transmembrane potential and the magnetic field recorded from the same location on the surface of the heart. (c) Image of the transmembrane potential distribution after stimulation. The two wave fronts from opposite sides are about to collide. (d) Magnetic field image composed of time traces after the stimulus from the area indicated by a white dashed square in (c).
Flux noise and field sensitivity of all our SQUID sensor configurations. and are the magnetic flux and field noise per unit bandwidth at the specified frequency.
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