Device for measuring a quantity of a superparamagnetic material

Device for measuring a quantity of a non-linear magnetic material devoid of hysteresis, known as a superparamagnetic material, the device comprising:

• four coils (1-4) of electrical wire having identical or substantially identical respective geometries and electrical and electromagnetic properties, and the four coils being electrically connected in series so as to form a chain with two end terminals (A, B) of said chain, a central terminal (C) in said chain, and two secondary terminals (S1, S2) of said chain that are each located between the central terminal and one of the two end terminals,
• means (5) for injecting a direct current (IDC) into the chain of coils (1-4), connected to the two end terminals (A, B) of the chain of coils, and means for adjusting an intensity of the direct current;
• means (6) for injecting a first alternating current (ILF) having a first frequency (LF), connected to inject said first alternating current into the chain of coils (1-4) through the central terminal (C), and to recover said first alternating current through the two end terminals (A, B), so that the first alternating current flows with first intensities (I1) that are identical or substantially identical through said two end terminals without flowing via the secondary terminals (S1, S2);
• means (7) for injecting a second alternating current (IMF) having a second frequency (HF) that is different from the first frequency (LF), connected to inject said second alternating current into the chain of coils (1-4) via the two secondary terminals (S1, S2), and to recover said second alternating current through the central terminal (C) and the two end terminals (A, B) so that the second alternating current flows with second intensities (I2) that are identical or substantially identical via said two secondary terminals, and so that said second alternating current flows with third intensities (I3) that are identical or substantially identical in all of the coils but in opposite directions between two successive coils in the chain;
• and
• means (9) for detecting at least one voltage component that exists between the two secondary terminals (S1, S2) of the chain of coils (1-4), with a frequency of said voltage component, called mixing frequency, being a linear combination of the first frequency (LF) and the second frequency (HF), with linear combination coefficients that are fixed non-zero integers,
• so that when the quantity of superparamagnetic material is located in one (2) of the coils (1-4), known as the measuring coil, the detection means (9) output a measurement signal that is proportional to said quantity of superparamagnetic material.