Seiichiro Ariyoshi

Imaging of Magnetic Nanoparticles Using Second-Harmonic Signals

Magnetic nanoparticle imaging (MPI) utilizes the non-linear magnetization response M for the detection of superparamagnetic iron oxide magnetic nanoparticles (MNPs). When an external ac magnetic field is applied to the MNPs, some harmonic responses such as second, third, and higher ones arise. We propose and demonstrate that the use of the second-harmonic response is the most effective technique to enhance the signal. The advantage of using the second-harmonic response is that the response can be measured even in a small ac field. A 2-D MPI system using this technique was realized and its performance was evaluated. The MPI system has no mechanical parts but instead magnetically scans an MNP phantom by changing the dc bias field in two directions. The cosine component of the signal is detected by a lock-in-amplifier and differentiated in one direction. The image of the phantom is then reconstructed using the d(cosθ)/dz data. As a result, the position of the phantom may be identified down to the iron content of 9 μg.

Development of Metallic Contaminant Detection System Using RF High-Tc SQUID With Cu Pickup Coil

We developed a metallic contaminant detector using a high-Tc rf-SQUID with a Cu pickup coil for industrial products. For manufacturers producing industrial products, problems arising from metallic contaminants are critical issues. A detection system using a SQUID is a powerful tool for sensitive inspections. However, since the detection width is dependent on the size of the SQUID, multiple sensors are required for practical use. However, such devices are costly and complicated. This is the reason as to why the SQUID system has not been widely used in the field. Therefore, we have recently proposed a new detection system using Faradays law of electromagnetic induction. The detection section consists of a pair of permanent magnets surrounded by copper wound pickup coils. The output of the pickup coil is remotely connected to a copper wound input coil. The input coil couples magnetically with a SQUID. In this case, the width of the pickup coil can be widened as to be as large as 27 mm in diameter. As compared with 1-ch SQUID direct detection, the width of the new method is three times larger. In this paper, we describe the performance of the system with a conveyor, which uses an LC resonant circuit. By applying the LC resonance, the amplitude increased and the signal to noise ratio (SNR) was improved by a factor of two.

Evaluation of YBa2Cu3O7-δ-based microwave kinetic inductance detectors with rewound spiral resonators

We propose a YBCO-based microwave kinetic inductance detector with rewound strip structure (spiral-MKID) suitable for imaging applications. The superconducting rewound strip acts as a microwave resonator and broadband antenna. A 25-pixel MKID array with a width of 10 ?m and slightly varying length of each of the resonators was fabricated on a 10×10 mm2-MgO substrate. Microwave resonance characteristics of the array were evaluated by measuring one of the scattering-matrix elements, S21, using a vector network analyser. The 25 resonance dips were clearly observed around 5 GHz; the frequency spacing between adjacent pixels was 13 MHz, with a standard deviation of 5 MHz. Each resonance frequency was shifted by 170 MHz, owing to the temperature change from 11 K to 50 K. We showed that the YBCO-based spiral-MKIDs with 200 nm-thick films have loaded quality factors of 1,200 at 11 K and 700 at 50 K. We irradiated visible light to a single pixel on the array. The obtained noise equivalent power was on the order of 10?9 W/Hz1/2, while the response time was smaller than 30 ms at 13 K. The responsivity of the array at 70 K was six times larger than that at 13 K.

Ultra-Low Field SQUID-NMR using LN2 Cooled Cu Polarizing Field coil

We are developing an Ultra-Low Field (ULF) Magnetic Resonance Imaging (MRI) system using a High-Temperature Superconductor superconducting quantum interference device (HTS rf-SQUID) for food inspection. The advantages of the ULF-NMR (Nuclear Magnetic Resonance) / MRI as compared with a conventional high field MRI are that they are compact and of low cost. In this study, we developed a ULF SQUID-NMR system using a polarizing coil to measure fat of which relaxation time T1 is shorter. The handmade polarizing coil was cooled by liquid nitrogen to reduce the resistance and accordingly increase the allowable current. The measured decay time of the polarizing field was 40 ms. The measurement system consisted of the liquid nitrogen cooled polarizing coil, a SQUID, a Cu wound flux transformer, a measurement field coil for the field of 47 μT, and an AC pulse coil for a 90°pulse field. The NMR measurements were performed in a magnetically shielded room to reduce the environmental magnetic field. The size of the sample was 35 mm × L80 mm. After applying a polarizing field and a 90°pulse, an NMR signal was detected by the SQUID through the flux transformer. As a result, the NMR spectra of fat samples were obtained at 2.0 kHz corresponding to the measurement field Bm of 47 μT. The T1 relaxation time of the mineral oil measured in Bm was 45 ms. These results suggested that the ULF-NMR/MRI system has potential for food inspection.

Development of three channel SQUIDs contaminant detector for food inspection

Mixture of metallic contaminants to food is serious problems not only for consumers but manufactures. To ensure the food safety, finding small metallic contaminants is important. A metal contaminant may come from a machine in the process of food and it contaminates food. Finding small metallic contaminants is important for food safety. Food manufactures are installing inspection systems such as eddy current detectors and X-ray imaging. The eddy current metal detector is widely used in a food factory. However, the sensitivity (threshold level) is not stable and is highly influenced by the conductivity of the material. The X-ray imaging is a useful technique and is getting popular in food factories and other industries. However, the lower detection limit for practical X-ray usage is in the order of 1 mm. Moreover, X-ray radiation sometimes causes ionization of the food, which may often change a taste of the food.

Ultralow-Field High-Tc SQUID NMR/MRI System With a 77-K Cooled Copper Flux Transformer

We propose a high-Tc superconducting quantum interference device ultralow-field magnetic resonance imaging (ULF MRI) system for food inspection. Although the ULF MRI is compact and low cost, compared with a conventional high-field MRI, the detected signal is extremely weak. Thus, a nuclear magnetic resonance (NMR) system was constructed and optimized before realizing the MRI system. The purpose of the study is to improve the signal-to-noise ratio (SNR) of the NMR signal. A copperwound flux transformer cooled at 77 K by liquid nitrogen and LC resonance were employed and tested to improve the SNR. As a result, the measured SNR was approximately equal to 236 with LC resonance, improving by a factor of 7.8.