Noninvasive measuring method for rapid temperature variation under DC excitation magnetic field

A noninvasive method for measuring rapid temperature variation of a measured object under a DC excitation magnetic field, comprising steps of:

• (1) positioning ferromagnetic particles at an area of said measured object;
• (2) applying said DC excitation magnetic field to said area, thereby enabling said ferromagnetic particles to reach saturation magnetization state;
• (3) obtaining steady temperature T1 of said measured object at room temperature, and calculating initial spontaneous magnetization M1 of said ferromagnetic particles according to said steady temperature T1;
• (4) detecting amplitude A of a magnetization variation signal of said ferromagnetic particles after temperature of said measured object varies, and calculating temperature-after-variation T2 according to said amplitude A of said magnetization variation signal;
• and
• (5) calculating temperature variation ΔT=T2−T1 according to said temperature-after-variation T2 and said steady temperature T1.
• wherein in said step (4), said calculating temperature-after-variation T2 is performed by:
• calculating said temperature-after-variation T2 according to a relationship between said temperature-after-variation T2 and said amplitude A of said magnetization variation signal:
• wherein α is proportional coefficient of magnetization variation ΔB to spontaneous magnetization variation ΔM, β is amplification factor of a test circuit, N is turns of an inductance coil, S is inner area of the inductance coil, Δt is duration of temperature changing process, M(T=0) is spontaneous magnetization of the ferromagnetic particles at absolute zero temperature, s is a parameter of thermal demagnetization curve of a ferromagnetic material, Tc is Curie temperature of the ferromagnetic particles, M(T=0) and Tc are determined for a defined ferromagnetic particle material, and M1 is the initial spontaneous magnetization of the ferromagnetic particles at temperature T1.