20 Dec New method for magnetic nanoparticle thermometry
Researchers from the Institute for Electrical Measurement Technology and Fundamentals of Electrical Engineering at the Technical University of Braunschweig study on their last paper a new and improved method for magnetic nanoparticle thermometry allowing high-frequency measurements and eliminating the influence of Brownian relaxation.
Magnetic nanoparticle thermometry independent of Brownian relaxation
- Jing Zhong, Meinhard Schilling and Frank Ludwig
Journal of Physics D: Applied Physics, Volume 51, Number 1
An improved method of magnetic nanoparticle (MNP) thermometry is proposed. The phase lag ϕ of the fundamental ƒ0 harmonic is measured to eliminate the influence of Brownian relaxation on the ratio of 3ƒ0 to ƒ0 harmonic amplitudes applying a phenomenological model, thus allowing measurements in high-frequency ac magnetic fields. The model is verified by simulations of the Fokker–Planck equation. An MNP spectrometer is calibrated for the measurements of the phase lag ϕ and the amplitudes of 3ƒ0 and ƒ0 harmonics. Calibration curves of the harmonic ratio and tanϕ are measured by varying the frequency (from 10 Hz to 1840 Hz) of ac magnetic fields with different amplitudes (from 3.60 mT to 4.00 mT) at a known temperature. A phenomenological model is employed to fit the calibration curves. Afterwards, the improved method is proposed to iteratively compensate the measured harmonic ratio with tanϕ, and consequently calculate temperature applying the static Langevin function. Experimental results on SHP-25 MNPs show that the proposed method significantly improves the systematic error to 2 K at maximum with a relative accuracy of about 0.63%. This demonstrates the feasibility of the proposed method for MNP thermometry with SHP-25 MNPs even if the MNP signal is affected by Brownian relaxation.