Magnetometer is a sensor for detection magnetic signals. To achieve a high-sensitivity in sensing weak magnetic signals, MagQu utilizes high temperature superconductor (HTS) dc superconducting quantum interference devices (SQUIDs) for high-sensitivity magnetometer.
A dc SQUID is a very sensitive magnetometer used to measure extremely weak magnetic fields, it consists of two Josephson junctions connected in parallel on a closed superconducting loop. The output voltage cross Josephson junctions varies with magnetic flux through the loop formed with Josephson junctions in parallel.
The SQUID operation is based on the dc Josephson Effect. In the absence of any external magnetic field, the input current I0 is divided into the two branches equally. If an external magnetic field is applied to the superconducting loop, an induced current, Id, is generated. The induced current is in the same direction as I0 in one of the branches, and is opposite to I0 in the other branch; the total current becomes I0/2 + Id in one branch and I0/2 - Ids in the other. When the current of any one branch exceeds the critical current of the Josephson junction, a voltage is appearing across the junction.
HTS SQUIDs are sensitive enough to measure fields as low as 1 pT (1×10−12 T). Thus, SQUID is usually useful to probing ultra-weak magnetic signal, and shows impacts to such applications as bio-magnetic detections (e.g. magnetocardiography), non-destructive evaluation, geophysical investigation,low-field nuclei magnetic resonance, and magnetically labeled biomolecule assays.
