The study of magnetic field sensor of high temperature superconducting ceramics

Ceramic high-temperature superconducting (HTSC) material consists of numerous granules, and Josephson transitions are formed between the borders. The nonlinear magnetic susceptibility of the Josephson medium is the core basis of magnetosensitive sensors. The magnetic sensitivity of weak magnetic fields (≤ 1 nT) magnet-modulation sensor (MMS) based on HTSC ceramic material of the composition (Bi-2223) is studied. Magnetosensitive elements in the form of cylindrical rods were prepared from the prepared powder of Bi-2223 HTSC material according to well-known ceramic technology. The rods had a length ∼ 18 - 20 mm, diameter ∼ 4 mm, the density of the critical current ≤ 10 A / cm², the critical temperature of ∼ 103 K. Two coils were tightly wound at 16 mm of its length: the exciting one, consisting of two identical counter switched sections of 200 turns each, and on top of it - a signal one that contains 400 turns. MMS magnetosensitivity was defined as S_U = dU/dB₀, where U is the magnitude of the signal on the 2nd and 4th harmonics, B₀ is the measured DC magnetic field. The measurements were performed at temperature 77 K, similar to the method described in our previous studies. A similar behavior of the MMS was observed at the 2nd harmonic at B₀ ≥ ± 1000 μT. The resolution on magnetic field, magnetic flux and the dynamic range of the measurements evaluation gave values of ∼ 0.2 nT, ∼ 1 ϕ₀ (the magnetic flux quantum) and ≥ 120 dB, respectively. Thus, the studied MMS has the characteristics that are not practically inferior to the characteristics of the MMS based on Y-123. Moreover, it has a number of benefits: Bi-2223 ceramic HTSC material is resistant to degradation and cheaper than Y-123 ceramic HTSC. With a further selection of properties of Bi-2223 HTSC material, shapes and sizes of rods, modes and other settings, there are possible improvements of the characteristics of MMS more than 1 - 2 times, thus they will be in demand in medical diagnostics (magnetocardiography, measurement of blood flow velocity), noninvasive monitoring of implanted items (stimulants, artificial heart machines, etc.), and in other applications for detection of ultraweak magnetic fields ≤ 1 _pT. (author)