Improved direct-coupled dc SQUID read-out electronics with automatic bias voltage tuning

Drung, D.; Bechstein, S.; Franke, Karl-Heinz Pd Dr.-Ing. habil.; Scheiner, M.; Schurig, T.

doi:10.1109/77.919485

Cited by 40 publications

(28 citation statements)

References 5 publications

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“…Optically pumped alkali atom magnetometers [1] have recently reached sensitivities below one femtotesla in a 1 Hz bandwidth [2,3], comparable or better than those of the most sensitive low temperature superconducting quantum interference devices (SQUIDs) [4]. These ultra-high sensitivities have been achieved by operating at low magnetic fields and high alkali density, in a regime where spin-exchange collisions do not broaden the magnetic resonance [5,6].…”

Section: Introductionmentioning

confidence: 99%

Femtotesla atomic magnetometry in a microfabricated vapor cell

Griffith¹,

Knappe²,

Kitching³

2010

Opt. Express

155

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Abstract:We describe an optically pumped 87 Rb magnetometer with 5 fT/Hz 1/2 sensitivity when operated in the spin-exchange relaxation free (SERF) regime. The magnetometer uses a microfabricated vapor cell consisting of a cavity etched in a 1 mm thick silicon wafer with anodically bonded Pyrex windows. The measurement volume of the magnetometer is 1 mm 3 , defined by the overlap region of a circularly polarized pump laser and a linearly polarized probe laser, both operated near 795 nm. Sensitivity limitations unique to the use of microfabricated cells are discussed.

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Section: Introductionmentioning

confidence: 99%

Femtotesla atomic magnetometry in a microfabricated vapor cell

Griffith¹,

Knappe²,

Kitching³

2010

Opt. Express

155

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“…Large-area bipolar audio transistors, which are commonly used for direct SQUID readout, have a very good low-frequency noise performance but exhibit a strong increase in current noise and signal distortion above about 1 MHz due to their high capacitances [3]. To overcome this problem, we have developed a composite preamplifier consisting of a slow dc amplifier in parallel with a fast ac amplifier (see Fig.…”

Section: High-speed Squid Readout Electronicsmentioning

confidence: 99%

“…The dc amplifier was built using low-noise bipolar audio transistors [3], whereas the rf amplifier was realized with a junction field-effect transistor (JFET) input stage in order to minimize current noise. The connection between SQUID and readout electronics may be done via coaxial lines as well as via twisted pairs; however, best high-frequency performance is obtained using coaxial lines.…”

Section: High-speed Squid Readout Electronicsmentioning

confidence: 99%

“…The maximum slew rate of the feedback flux, another important system parameter, is correspondingly limited to ( is the flux quantum). For our various SQUID applications, we have developed a low-noise wideband SQUID readout electronics which is highly flexible and convenient to use [3], [4]. Its maximum FLL bandwidth of about 6 MHz is a factor of three below the theoretical limit but high enough for almost all SQUID applications.…”

Section: Introductionmentioning

confidence: 99%

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dc SQUID Readout Electronics With Up to 100 MHz Closed-Loop Bandwidth

Drung

Assmann

Beyer

et al. 2005

IEEE Trans. Appl. Supercond.

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High-speed readout electronics for sensors based on dc superconducting quantum interference devices (SQUIDs) are presented. The SQUID sensor involves a series array of 16 dc SQUIDs and an intermediate transformer to enhance its current sensitivity. By using a highly gradiometric design and 5 m linewidth for the SQUID array, the device can be cooled down in fields of up to 85 T and be operated magnetically unshielded. A special feedback coil design minimizes the parasitic coupling between feedback and input coil. The SQUID sensor is directly connected to the room temperature electronics. A composite preamplifier is used consisting of a slow dc amplifier in parallel with a fast ac amplifier. A virtual 50 input resistance with negligible excess noise is realized by active shunting. Two types of high-speed readout electronics were developed. The first was designed for optimum dc performance, high flexibility, and user-friendliness. It is fully computer controlled. The white voltage and current noise levels are 0.3 nV Hz and 3 pA Hz, respectively, resulting in an overall system noise level of 0.4 8 0 Hz or a coupled energy sensitivity around 500 (8 0 is the flux quantum and is Planck's constant). The maximum flux-locked loop (FLL) and open-loop bandwidths are about 20 MHz and 50 MHz, respectively. The second readout electronics is an ultra-high-speed prototype which was designed for maximum speed at the expense of dc performance. A very low intrinsic signal delay of 1.7 ns and a high open-loop bandwidth of 300 MHz were measured. Using a novel FLL scheme, a very high signal bandwidth of 130 MHz was achieved with 0.8 m distance between SQUID and electronics.

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“…Therefore the noise spectrum (b) indicates the intrinsic noise of the SQUID sensor. The data of (d) is cited from [5] to indicate the intrinsic noise of their SQUID sensors. evoked dipole in the subject's brain by an extension of a radar theory -MUSIC (multiple signal classification approach).…”

Section: Neuromagnetic Squid Measurementmentioning

confidence: 99%