This paper reports a fully computer-controlled two-dimensional A4-size electromagnetic noise imaging system with 0.1 mm positioning resolution up over 1.5 GHz. This system can map the near field from printed-circuit boards, personal handy phones, RF transmission lines and so on using a newly developed planar coil array. The 0.1 mm positioning resolution has been realized by a motor-controlled positioning system, and two-dimensional magnetic field mapping is also possible simultaneously for the first time.
A highly sensitive probe to measure thin film permeability was developed based on the skin effect.A microstrip-line-type probe on a flexible polyimide substrate was fabricated and placed in contact with a magnetic thin film.The permeability was optimized by the Newton-Raphson method.The permeability of amorphous Co85Nb12Zr3 film (25 mm x 25 mm and 5 nm in thickness) was evaluated using a permeameter.The measured values were in rough agreement with theoretical values based on the Landau-Lifshitz-Gilbert equation and eddy current generation up to 7 GHz.The proposed method shows promise for the measurement of very thin film (less than 10 nm in thickness) because the contact surface between the flexible probe and thin film fits very well, resulting in improvement of the signal-to-noise ratio.
Hyperthermia using magnetic particles is a very promising cancer therapy. In previous studies, we developed a mixture of magnetic micro/nanoparticles with high heating efficiency for tumor treatment and considerable change in permeability around therapeutic temperature for monitoring its temperature and position during heating. In this study, we examined experimentally the effect of applied magnetic field on the heating and permeability properties of the proposed mixture by manipulating the amplitude and frequency (H = 1.8–7.1 kA/m, f = 500 kHz, and H = 4.8 kA/m, f = 200–1000 kHz). It was found that the specific absorption rate (SAR) of the mixture increased with the amplitude and frequency (SAR α H1.68×f). Its intensity of magnetization (μ0M) at 20°C changed linearly with the amplitude, whereas it remained almost unchanged with the frequency. The results obtained here may enable us to find the optimal conditions of the applied magnetic field and the amount of magnetic particles required to treat a tumor of a given size.
We have developed a jaw tracking system with wireless resonated markers. The system consists of two resonated markers, driving coil, 40 pickup coils, DA converter, and AD converters. The two resonated markers were composed of a coil with NiZn ferrite and tip condenser. We attached to one marker on the incisor and the other on the forehead. Position accuracy of within 1 mm was achieved when the fabricated jaw model was moved about 40 mm. This system is available for tracking of reasonable jaw movement of normal subjects without disturbing the physiology.
We propose a novel method based on an inverse problem to design a single channel radio frequency (RF) receive coil for magnetic resonance imaging (MRI) with an optimized signal-to-noise ratio (SNR) for imaging the rat kidney. We identified a dedicated curved-surface coil design for use on the rat body surface utilizing inverse problem analysis using direct current calculation and quantitatively evaluated the indicators of coil performance using alternating current calculation. The proposed coil achieved increased SNR and signal intensity responses that were respectively 1.05- and 2-fold higher than those of conventional surface coils. In the future, we will fabricate a prototype coil and perform the MRI of the rat kidney to diagnose kidney diseases.
We developed the fully automatic permeameter which is made of driving plates and shielded loop coil available in 1 MHz–3GHz. We clarified the sensitivity of the permeameter and the sensitivity can be explained by an uncertainty of network analyzer. We evaluate the permeability of striped CoNbZr films (50, 20, 10 μm wide). A reasonable relation between permeability spectrum and domain observations can be demonstrated.
