Thermometry is essential in laboratory and industry settings. We propose a noninvasive temperature measurement method based on the superparamagnetic properties of nickel-plated films.When the nickel(Ni) film is uniformly heated from 100K to 300K, we observe that the polarization angle of the reflected polarized light decreases correspondingly. Compared with optical temperature measurement, this method introduces magnetic physical quantity, which increases the penetration of temperature measurement. Compared with magnetic temperature measurement, this method introduces optical physical quantity, which greatly increases the amount of information contained in the measurement channel. On this basis,we introduce the characteristic matrix of membrane system, and the improved the Mean Field(MF) theory which can interpret superparamagnetism. Our experiment has demonstrated that the above theoretical model is feasible from low temperature to normal temperature. The thin film sensor element provides the necessary temperature information for cryogenic wind tunnel design and hypersonic vehicle surface model design in real time

Spatial resolution is a key metric for characterizing magnetic particle imaging (MPI), and magnetic relaxation is a critical factor affecting the spatial resolution. This study investigates the point spread functions (PSFs) of MPI and analyzes the potential of breaking through the spatial resolution limit, which equals the full width at half maximum (FWHM) of the Langevin function derivative. In this work, different PSFs of MPI were built based on the magnitude and real and imaginary parts of complex susceptibility. The imaging performance was evaluated using the FWHM and a self-defined convergence parameter. The results show that image reconstruction can achieve a narrower PSF based on the imaginary part of complex susceptibility, and the heavy-tailed distribution of the derivative of the Langevin curve can be optimized. This suggests that there is scope to improve the spatial resolution and image contrast of MPI.

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The article has studied the mechanism of magnetic nanoparticles (MNPs) affecting magnetic field uniformity. The spatial distribution of MNPs in liquid was simulated based on Monte Carlo method. Combined with the induced field of the single MNP, the magnetic field distribution of magnetofluid was obtained. In the simulation, magnetic field uniformity was described by a statistical distribution. As the chemical shift (CS) and full width at half maximum (FWHM) of magnetic resonance (MR) spectrum can reflect the uniformity of magnetic field, the simulation was verified by spectrum experiment. Simulation and experimental results proved that the CS and FWHM of the MR spectrum are basically positively correlated with the concentration of MNPs and negatively correlated with the temperature. The research results can explain how MNPs play a role in MR by affecting the uniform magnetic field, which is of great significance for improving the temperature measurement accuracy of magnetic nanothermometers and the spatial resolution of magnetic particle imaging.