Magnetomodulation sensor of a weak magnetic field based on HTS (Bi,Pb)2Sr2Ca2Cu3Ox ceramics

We studied the possibility to develop the magnetomodulation sensor of weak magnetic field based on the HTS (Bi,Pb)2Sr2Ca2Cu3Ox ceramics with the operational temperature ∼77K and critical temperature ∼105K. The sensors involved two coils (excitation and signal ones), which were closely wound on a cylindrical HTS ceramic core. The core length was 10mm, and the core diameter was ∼2.5mm. It was found that the magnetic sensitivity SU (SU=dU2/dH0, where U2 is the second-harmonic signal) for such sensors depends on the excitation frequency in the range ∼1–50kHz, and on the excitation current Iac. For the excitation current ∼25mA and excitation frequency ∼50kHz, the highest value of sensitivity SU∼390V/T was attained. When estimating the weakest magnetic field, which was detected by the sensor fabricated, we made allowance for the noise characteristics and errors of measurement devices used. The weakest detected field was ∼0.5nT in the absence of shielding from the terrestrial magnetic field and from the magnetic fields, which corresponded to industrial noise.