Patent ID: 8624584

Claim:
A device for detecting a magnetic field response or changes in a magnetic response of at least one magnetic particle in a carrier fluid, said detection comprising measuring said magnetic particles characteristic rotation period, and said measurement involving measurement of a Brownian relaxation in said carrier fluid under influence of an external pulsed magnetic field, said device comprising means for generating said pulsed magnetic field, at least two substantially identical detection coils connected in gradiometer coupling to detection electronics for measuring differential induced voltage which is dependent on the frequency dependent susceptibility or the magnetization change, wherein the differential induced voltage is Δ ⁢ ⁢ V = ⁢ N ⁢ ⅆ ⅆ t ⁢ ( Φ 1 - Φ 2 ) = ⁢ μ 0 ⁢ NA ⁢ ⁢ α ⁢ ⅆ ⅆ t ⁢ ( H + M - H ) = ⁢ μ 0 ⁢ NA ⁢ ⁢ α ⁢ ⅆ ⅆ t ⁢ M wherein N is a number of turns in two identical detection coils, A is the cross sectional area in the detection coils, H the magnetic field produced by an excitation coil, α a magnetic coupling factor and M is a magnetization of the particle system.