Showing papers by "Keiji Enpuku published in 2018"

Detection of Slit Defects on Backside of Steel Plate Using Low-Frequency Eddy-Current Testing

Abstract: The evaluation of opposite-side defects in thick ferromagnetic objects (for example, steel plates) is essential for safety maintenance. Eddy-current testing (ECT) can detect defects in metallic specimens; however, owing to the skin effect, its use is limited to the evaluation of surface or subsurface defects. Therefore, in this paper, we propose a non-contacting inspection system that consists of two excitation coils and a detection coil to detect slit defects on the backside of a steel plate using low-frequency ECT (LF-ECT). Using the proposed system, we examine whether LF-ECT mainly detects the leakage or the flux induced by the eddy current, and also examine which direction of the excitation currents in the two excitation coils is suitable for detecting slit defects. The results suggest that the method to drive the current in the same direction and to detect the imaginary part of the magnetic flux density, which corresponds to the flux induced by the eddy current, is suitable for detecting slit defects. Subsequently, we examine the detection limit of the height of the slit defect when the thickness of the steel plate is 10 mm and the width and length of the slit defect are constant, at 50 and 1 mm, respectively. The results demonstrate that the slit defect can be detected by using the proposed system when the height is greater than or equal to 4 mm. Therefore, the proposed system is a promising tool to detect critical defects on the backside of steel plates.

Wash-free detection of C-reactive protein based on third-harmonic signal measurement of magnetic markers

Abstract: We demonstrate wash-free detection of C-reactive proteins (CRPs) based on third-harmonic signal measurement of magnetic markers. In the method presented here, the CRP concentration can be detected from the decrease in the third-harmonic signal from the sample solution. The relationship between the detected signal and the CRP concentration can be modeled quantitatively using a logistic function. The quantities of CRP that were detected using the proposed method showed good correlation with those obtained using the conventional optical method with a washing process. We also demonstrate CRP detection in a hemolysis sample solution that is not optically transparent.

Magnetic fractionation and characterization of magnetic nanoparticles for magnetic particle imaging

Abstract: We performed magnetic fractionation and characterization of Resovist® magnetic nanoparticles (MNPs) for use in magnetic particle imaging (MPI). We showed that the core size of the fractionated MNPs can be controlled by adjusting the separation field. We also showed that particles with core size of approximately 27 nm are optimal for MPI applications. To obtain MNPs of an appropriate core size and a narrow size distribution, we performed combined positive and negative fractionation. In the obtained fractionated MNPs, the third harmonic magnetization, which is used as the MPI signal, was 2.75 times as large as that of the original sample.

Empirical expression for DC magnetization curve of immobilized magnetic nanoparticles for use in biomedical applications

Abstract: We studied the magnetization (M-H) curve of immobilized magnetic nanoparticles (MNPs) used for biomedical applications. First, we performed numerical simulation on the DC M-H curve over a wide range of MNPs parameters. Based on the simulation results, we obtained an empirical expression for DC M-H curve. The empirical expression was compared with the measured M-H curves of various MNP samples, and quantitative agreements were obtained between them. We can also estimate the basic parameters of MNP from the comparison. Therefore, the empirical expression is useful for analyzing the M-H curve of immobilized MNPs for specific biomedical applications.

Magnetometer based on transfer and modulation of magnetic flux using high-critical-temperature superconductor coils

Abstract: We developed a new type of magnetometer to measure low-frequency magnetic fields with an operational principle based on magnetic flux transfer and modulation. This magnetometer consists of three coils: pickup, input and readout coils. The pickup and input coils were made from high-critical-temperature superconductor (HTS) tape and were connected with very low connection resistance to form a closed loop. The magnetic flux that is collected by the pickup coil can be transferred to the input coil even at low frequencies below 1 Hz. The magnetic flux at the input coil is then detected by the readout coil using a readout scheme based on modulation of the mutual inductance M between the input and readout coils. To modulate M over time, a magnetic wire was inserted into the readout coil and a time-varying current was supplied to the wire. Using this time-varying M, the magnetic flux is converted into an amplitude-modulated voltage across the readout coil for measurements. A prototype magnetometer was fabricated for demonstration. This magnetometer can operate at low frequencies down to f = 0.5 Hz without responsivity degradation. The magnetic field noise levels were 8 and 60 pT/Hz1/2 at 50 and 1 Hz, respectively.

Improving Tip Position-Estimation Performance of Gastric Tube by Compensating Geomagnetic Field With Offset Coils

Abstract: Naso- or oro-gastric tubes are used for patients who have difficulty swallowing, to deliver nutrients or medicines to the stomach. To observe whether the tube is inserted into the stomach correctly, we have proposed a method that estimates the position of the permanent magnet attached to the tip of the tube using several magnetic sensors placed outside the patient’s body [1], [2]. The mean of the tip position estimation error is less than 10 mm when the distance between the sensor plane and the permanent magnet is 150 mm [2]. However, if the system is used on pregnant or fat patients, the system needs to perform accurately even for distances greater than 150 mm. To achieve the requirement mentioned above, the sensitivity of the magnetic sensors should be enhanced. Although high-sensitivity magnetoimpedance (MI) and magnetoresistance (MR) sensors can detect signals of the order of nT, the performance is only achieved in a magnetically shielded room due to the limitation of the measurement range and the existence of the geomagnetic field; this creates a problem for the system’s practical use in hospitals. Therefore, we propose a method to compensate the geomagnetic field using offset coils.