Magnetomodulation sensor of a weak magnetic field based on HTS (Bi, Pb)2Sr2Ca2Cu3O x ceramics

We studied the possibility to develop the magnetomodulation sensor of weak magnetic field based on the HTS (Bi, Pb)2Sr2Ca2Cu3O x ceramics with the operational temperature ∼77 K and critical temperature ∼105 K. The sensors involved two coils (excitation and signal ones), which were closely wound on a cylindrical HTS ceramic core. The core length was 10 mm, and the core diameter was ∼2.5 mm. It was found that the magnetic sensitivity S U (S U = dU 2/dH , where U 2 is the second-harmonic signal) for such sensors depends on the excitation frequency in the range ∼1-50 kHz, and on the excitation current I ac. For the excitation current ∼25 mA and excitation frequency ∼50 kHz, the highest value of sensitivity S U ∼ 390 V/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 ∼0.5 nT in the absence of shielding from the terrestrial magnetic field and from the magnetic fields, which corresponded to industrial noise