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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.

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 100 K to 300 K, 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 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

A new remote method for measuring temperature using magnetic nanoparticles (MNPs) is presented in this paper. The method involves exciting MNPs in a dual-frequency AC magnetic field, and using tunnel magnetoresistance to detect the mixing-frequency magnetization response signals. The effects of the excitation magnetic field amplitude and frequency on the temperature measurement were analyzed. Based on the relationship between the MNPs’ magnetization harmonic amplitudes and their temperature, two-harmonic and four-harmonic temperature measurement models were established. The estimated temperature was obtained by the optimized parameter estimation algorithm. The temperature error was found to be less than 0.02 K using the two-harmonic model and less than 0.015 K using the four-harmonic model.

The effect of the nonlinear time-drift gain in the power amplifier on the instability in a magnetic nanothermometer was studied to allow a very stable magnetic nanotermometer to be designed, which was then used to measure the temperature of a light-emitting diode pn-junction. Experiments showed that the system response fluctuated by less than 0.04% and the temperature measurement error was less than 0.1 K when real-time measurements were made at 1 s intervals. The temperature of a pn-junction of a light-emitting diode cooled using a heat sink or circulating water was measured successfully using the improved magnetic nanothermometer.

This study reports on a new approach for remote nanothermometry with short response time (milliseconds) aiming to operate in liquid media using AC susceptibility components of a suspended magnetic nanoparticle subjected to the Brownian relaxation mechanism. A simple, low cost, and accurate system was designed to measure AC susceptibility using an AC magnetic field at small amplitude (6 Oe) and frequency range (5 kHz) superimposed on a weak DC magnetic field (up to 30 Oe). A model based on the AC susceptibility of magnetic nanoparticles (30 nm average diameter) was constructed to describe the temperature measurement sensitivity of the dominated Brownian relaxation time. A new approach for remote nanothermometry was achieved with measured AC susceptibility by the designed system and the proposed model. Our experimental results show that our magnetonanothermometer allows temperature errors lower than 0.3 K with standard deviations lower than 0.1 K in the temperature range from 310 to 320 K.

We herein describe several practical improvements to the method of obtaining the size distribution of magnetic nanoparticles (MNPs) using the magnetization curves obtained from a water-based MNP sample. A vibration sample magnetometer (VSM) was used in place of a superconducting quantum interference device (SQUID), to reduce MNP agglomeration and sedimentation by means of vibration during the measurements. A signal preprocessing method using background rejection was applied to improve the measurement technique for lower concentrations of water-based MNPs, because of the significance of the diamagnetic effect of water in dilute solutions. We further present the results of detailed studies using singular value decomposition (SVD) and the Tikhonov-regulated SVD method to reconstruct the size distribution of the original sample. The experiments show that the controlled use of SVD produces consistent results. Artificial oscillation found using both SVD and the Tikhonov-SVD methods indicates that the characterization of MNP using a magnetization curve could be subject to an upper limit to its accuracy for measuring size distribution.