|Our models SQE-DC-100k and SQE-DC-400k are ac-flux modulated dc SQUID
readout circuits with a modulation frequency of 100 kHz and 400 kHz, respectively.
Other modulation frequencies are available on request. The electronics
features a very-low-noise preamplifier with a noise temperature of less
than 10 K ( typically 6 K for a source impedance of 20 ohms ). Due
to the ac-flux modulation, drift and low-frequency excess noise due to
temperature fluctuations are supressed. The SQUID readout measures
only 94 mm by 57 mm by 35 mm. As it is small and light, it can be
placed close to the SQUID.
This SQUID readout is ideally suited for measurements at lower signal
frequencies, such as noise thermometry, gravity-wave or geophysical experiments,
or biomagnetic measurements.
The SQUID readout circuits are controlled by our control box SQC-1,
which can be placed several meters away from the readout. This control
box is used to set the bias current of the SQUID, the flux-modulation amplitude,
the phase shift between modulation and internal lock-in reference, and
the feedback resistor. The actual parameters are displayed on a illuminated
LCD display and can be changed manually, or by a personal computer via
the serial port. A personal computer, however, is not required to
operate the SQUID readout. The internal microcontroller of the control
box can be switched off when performing extremely sensitive measurements.
The parameters for 20 different SQUIDs can be stored internally, and can
be recalled when the same device is being used the next time. The
box can either be battery operated (at any dc voltage between 18 and 24
volts) or supplied from a mains-operated power supply. The current
consumption is about 200 mA (display on), or 100 mA (display off).
The SQUID readout is supplied with power from the control box. The
SQUID readout can also be supplied with a built-in rechargable battery
allowing for a measuring time of 4 to 8 hours (in a larger box, see the
picture of our SQE-DC-BR-400k).