A multifrequency eletromagnetic applicator with an integrated AC magnetometer for magnetic hyperthermia experiments

Abstract

In the present paper, a lab-made electromagnetic applicator for magnetic hyperthermia experiments is described, fabricated and tested. The proposed device is able to measure the specific absorption rate (SAR) of nanoparticle samples at different magnetic field intensities and frequencies. Based on a variable parallel LCC resonant circuit fed by a linear power amplifier, the electromagnetic applicator is optimized to generate a controllable and homogeneous AC magnetic field in a 3.5 cm3 cylindrical volume, in a wide frequency range of 149–1030 kHz with high field intensities (up to 35 kA m−1 at low frequencies and up to 22 kA m−1 at high frequencies). In addition, a lab-made AC magnetometer is integrated in the electromagnetic applicator. The AC magnetometer is fully compensated to provide accurate measurements of the dynamic hysteresis cycle for nanoparticle powders or dispersions. From these dynamic hysteresis loops the SAR of the nanoparticle samples can be directly obtained. To show the capabilities of the proposed set-up, the AC hysteresis loops of two different magnetite nanoparticle samples with different sizes have been measured for various field intensities and frequencies. To our knowledge, no other work reports an electromagnetic applicator system with integrated AC magnetometer providing such characteristics in terms of frequency and intensity.

An induction heating device using planar coil with high amplitude alternating magnetic fields for magnetic hyperthermia

“…Lacroix et al [12], Ivkov et al [5] and Garaio et al [13] employed solenoid coil in their hyperthermia applicator with a diameter of 11 mm, 36 mm and 15 mm, respectively. Similarly, a solenoid coil of 60 mm height, 50 mm diameter and 25 turns was described by Cano et al [14] and the maximum magnetic flux intensity reached 150 Gs.…”

Harmonic phases of the nanoparticle magnetization: An intrinsic temperature probe

“…17 consists in the measurement of the dynamic magnetization versus applied magnetic field. 19,20 This method permits precise and quick SAR measurements, allowing multi-parametric study for different frequencies, field intensities, and as a function of temperature. 21,22 Using the fundamentals and advantages of this last technique, we propose here an accurate, simple, and fast method for monitoring and controlling the temperature of magnetic nanoparticles during magnetic hyperthermia.…”

“…In order to obtain the spectrum of the MNP sample magnetization, first the AC hysteresis loops or dynamic magnetization, M(t), were measured by the lab-made AC magnetometer descried in an earlier work. 20 Afterward, the Fast Fourier Transform (FFT) of the M(t) signal was performed in order to obtain the complex harmonics M n with their corresponding magnitudes jM n j and phases u n (see Eq.…”

“…21,22,26 This thermal dependence is the direct result of the variation with temperature of the phase between magnetization M and applied magnetic field H. Hence, one can deduce that the harmonic phases of magnetization signal must vary with temperature as well. Therefore, the harmonic spectrum of the magnetization of water dispersed maghemite sample was measured when varying temperature from 30 to 50 C at different field frequencies (75, 302, 676, and 1030 kHz) and intensities (5,10,20, and 25 kA m À1 ). Figure 2 shows the so obtained results at 10 and 20 kA m À1 field intensities and for different field frequencies.…”

“…This error can be induced by the power amplifier that feeds our particular resonant circuit and generates the magnetic field. 20 At high field intensities, the amplifier works near its own saturation and tends to add harmonics to the output signal. Hence, high order harmonics appear in the applied magnetic field, H(t), and although their magnitude is very small, they can add errors to the measurements.…”