The SQUID sensors used by our pioneering method:

We use sensor equipment modular cryogenic probes which can incorporate up to four SQUID sensors for measuring different magnetic field components.

The sensors provide stable performance in high noise environments, operating reliably in the presence of strong ambient d/c signals and signals from the Earth's magnetic field. All sensors have an ultimate stable field-conditions dc-SQUID sensitivity of better than 20 fT/√Hz.

SQUID

To allow uninterrupted operation between liquid helium top-ups, the system includes two optimised fibreglass dewars with a helium hold time of at least one week. There is an optional feature that incorporates a conventional electric receiver, allowing magnetic and electrical signal recording to proceed simultaneously.

Our long-base Gradiometer

The Gradiometer system is a variation of the standard system. It uses two SQUID stations working as a gradiometer to achieve greater receiver sensitivity.

The magnetometer stations can be up to 1000m distant from each other. The Gradiometer significantly reduces the background telluric noise up to 100 times and allows the highest quality of magnetic telemetry reception.

SQUID Technical Specifications

  • Miniature low-noise fiberglass cryostat
    - weight: 1.5 kg, length 600 mm, diameter 110 mm
    - liquid helium capacity: 2 litres
    - approximate helium hold time (without probe): 40 hours

  • Detachable dc SQUID detector module
    - SQUID sensor (sensitivity 20 fT/?Hz)
    - 2 Nb superconducting shield and Nb screw terminals
    - axial (Z) sensing loops of 14 mm diameter
    - heater to remove trapped flux

  • Low boil off cryogenic probe
    - SQUID matching transformer circuit
    - flexible 0.6 m cable with sealed 7-pin Fisher connector
    - 0.3 l/day additional helium loss

  • SQUID electronics
    - 110 dB dynamic range
    - RFI protection, and IP65 oil and water proof sealing
    - 0.8 nV/?Hz input noise
    - USB/RS232 digital control
    - 12-bit D/A converters for adjustment of SQUID parameters
    - 1W (12V) total power consumption with attached SQUID electronics

  • Vibration proofed low noise SQUID station container
    SQUID control software package
    - based on the visual programming language Agilent VEE Pro
    - compatible with operation systems including WinXP and WinNT
    - intuitive user friendly interface
    - data flow display
    - real time digital filtering and spectrum analysis
    - control of SQUID sensor with automatic adjustment capability
    - gradiometric analysis of the incoming data
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