Yoshimi Hatsukade

Measurement of metallic contaminants in food with a high-Tc SQUID

We have proposed and demonstrated a high-Tc SQUID system for detecting metallic contaminants in foodstuffs. There is a demand for the development of systems for detecting not only magnetic materials but also non-magnetic materials such as Cu and aluminium in foodstuffs to ensure food safety. The system consists of a SQUID magnetometer, an excitation coil and a permanent magnet. For a non-magnetic sample, an AC magnetic field is applied during detection to induce an eddy current in the sample. For a magnetizable sample, a strong magnetic field is applied to the sample prior to the detection attempt. We were able to detect a stainless steel ball with a diameter of 0.1 mm and a Cu ball less than 1 mm in diameter, for example.

A food contaminant detection system based on high-Tc SQUIDs

We have designed and constructed a computer controlled food contaminant detection system for practical use, based on high-Tc SQUID detectors. The system, which features waterproof stainless steel construction, is acceptable under the HACCP (Hazard Analysis and Critical Control Point) programme guidelines. The outer dimensions of the system are 1500 mm length × 477 mm width × 1445 mm height, and it can accept objects up to 200 mm wide × 80 mm high. An automatic liquid nitrogen filling system was installed in the standard model. This system employed a double-layered permeable metallic shield with a thickness of 1 mm as a magnetically shielded box. The distribution of the magnetic field in the box was simulated by FEM; the gap between each shield layer was optimized before fabrication. A shielding factor of 732 in the Z-component was achieved. This value is high enough to safely operate the system in a non-laboratory environment, i.e., a factory. During testing, we successfully detected a steel contaminant as small as 0.3 mm in diameter at a distance of 75 mm.

A high-Tc SQUID micro-detector with a high performance magnetic shield for contaminant detection in industrial products

A high-Tc superconducting quantum interference device (SQUID) system for the detection of magnetic foreign matter in industrial products was developed. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. Metallic particles with outer dimensions less than 100 µm cannot be detected by conventional x-ray imaging. Therefore we developed a detection system based on a high-Tc SQUID microscope with a high performance magnetic shield. The use of SQUID microscopes with a 0.5 mm thick vacuum window was proposed. This design enables the SQUID to approach the object to be measured as close as 1 mm and enhances the sensitivity. A new magnetic shield with sleeves was carefully designed and built. As a result, we could successfully measure small particles sized 100 µm. This detection level was hard to achieve using a conventional x-ray detection method.

High Tc SQUID Detection System for Metallic Contaminant in Lithium Ion Battery

A highly sensitive detection system for magnetic contaminants using a High-Tc superconducting quantum interference device (SQUID) was developed. Finding ultra-small metallic contaminants is a big issue for manufacturers producing commercial products such as lithium ion batteries. When the contamination does occur, the manufacturer of the product suffers a great loss to recall the tainted products. The outer dimension of metallic particles less than 100 microns can not be detected by X-ray imaging, which is commonly used as the inspection method. In most cases, the matrix of industrial products is magnetized and the magnetic signal from the matrix is large enough to mask the signal from contaminants. We developed a detection system based on a high-Tc SQUID gradiometer. A specially designed low noise planar gradiometer for the system was developed. The flux white noise level of the SQUID gradiometer was 8-16 muphi0/Hz1/2 at 1 kHz. Use of the gradiometer and horizontal magnetization could solve problem above. We tested the performances of the system and found that small iron particles as small as 50 mum times 50 mum on the electrode of the lithium ion battery could be clearly detect. This detection level is difficult to achieve using other methods.

Eddy-Current-Based SQUID-NDE for Detection of Surface Flaws on Copper Tubes

An eddy-current-based SQUID-NDE system has been developed to detect shallow surface flaws of less than 50 mum in depth on heat-exchanger copper tubes using an HTS-SQUID gradiometer and an Helmholtz-coil-type inducer. In this study, detectable flaw sizes on the tubes were investigated by experiments and simulation. Copper tube specimens with flaws of various sizes were inspected by the system with an excitation field of 5.6 muT at 3 kHz. A magnetic anomaly due to the shallowest flaw of 10 mum depth, 100 mum width and 15 mm length was successfully detected. The experimental results showed that the magnetic signal amplitude due to a flaw was proportional to the effective flaw size given by the product of flaw depth, width and length. A numerical simulation was carried out to calculate the magnetic signal from a flaw on a copper tube to determine the dependence on the flaw size. It is concluded that a flaw with a volume of 106 mum3 should be detectable by improving the system parameters.

Development of Metallic Contaminant Detection System Using Eight-Channel High-

In this paper, a roll-to-roll eight-channel (8-ch) high-Tc superconducting quantum interference device (SQUID) detection system for magnetic contaminants in a lithium-ion (Li-ion) battery anode sheet was developed. Finding ultra-small metallic foreign matter is an important issue for a manufacturer because metallic contaminants carry the risk of an internal short. When contamination occurs, the manufacturer of the product suffers a great loss from recalling the tainted product. Metallic particles with outer dimensions smaller than 100 μm cannot be detected using a conventional X-ray imaging system. Therefore, a highly sensitive detection system for small foreign matter is required. We have already developed a detection system based on a single-channel SQUID gradiometer and horizontal magnetization. For practical use, the detection width of the system should be increased to at least 65 mm by employing multiple sensors. In this paper, we present an 8-ch high-Tc SQUID roll-to-roll system for inspecting a Li-ion battery anode with a width of 65 mm. A special microscopic type of a cryostat was developed upon which eight SQUID gradiometers were mounted. As a result, small iron particles of φ35 μm on a real Li-ion battery anode with a width of 70 mm were successfully detected. This system is practical for the detection of contaminants in a Li-ion battery anode sheet.

T_{c}

In our study, we constructed a ultra-low field (ULF) nuclear magnetic resonance (NMR)/magnetic resonance imaging (MRI) system employing a high-temperature superconductor (HTS)-rf-SQUID and room-temperature coils. In the system, we employed a pulsed polarizing field <i>B</i>_p perpendicular to a measurement field <i>B</i>_m; a high-speed switching circuit with an optical FET was used to switch off <i>B</i>_p of approximately 30 mT. When a field gradient d<i>Bz</i>/d<i>z</i> of approximately 10 nT/cm was applied to a sample, which was designed to contain water in two compartments, a ¹H-NMR spectrum with two peaks was observed. The frequency difference between the two peaks roughly corresponded to the distance between each center of the water in the two parts. We measured the ¹H -NMR signals for water and mineral oil and found a clear difference in their signal amplitudes owing to their different molecular compositions. The longitudinal relaxation times T₁ of water and the oil were also estimated by changing the polarizing time of <i>B</i>_p. From these results, it was confirmed that ¹H- and T₁-weighted contrast imaging could be realized by using this system.

SQUIDs

There is a possibility that individuals ingest contaminants that have been accidentally mixed with food because processed foods have become very common. Therefore a detection method of small contaminants in food and pharmaceuticals is required. High-T c SQUID detection systems for metallic contaminants in foods and drugs have been developed for safety purposes. We developed two systems; one large system is for meat blocks and the other small system is for powdered drugs or packaged foods. Both systems consist of SQUID magnetometers, a permanent magnet for magnetization and a belt conveyor. All samples were magnetized before measurements and detected by high Tc SQUIDs. As a result, we successfully detected small syringe needles with a length of 2 mm in a meat block and a stainless steel ball as small as 0.3 mm in diameter.

Liquid-State Nuclear Magnetic Resonance Measurements for Imaging Using HTS-rf-SQUID in Ultra-Low Field

We introduce a method to improve the detection sensitivity for the magnetization M of superparamagnetic nanoparticles (MNP). The M response of MNP to an applied magnetic field H (M-H characteristics) could be divided into a linear region and a saturation region, which are separated at a transition point H(k). When applying an excitation magnetic field (H(ac)) with a frequency ω0 and an additional dc bias field H(dc) = H(k), the second harmonic of M reaches the maximum due to the nonlinearity of the M-H characteristics. It is stronger than any other harmonics and responsible for small H(ac) without a threshold. The second harmonic selected as the readout criterion for M response of MNP is systematically analyzed and experimentally proven.

High- T c SQUID Metal Detection System for Food and Pharmaceutical Contaminants

A simple flip-chip configuration of YBa2Cu3O7−x (YBCO) square and cross-shaped films overlapping on a directly coupled multi-pickup-loop HTS dc-SQUID magnetometer was tested to enhance the robustness of the HTS SQUID magnetometer in an ac magnetic field. The YBCO films were expected to work as a superconducting shield to prevent flux vortices from entering and moving in the device. With the shields, most of the SQUIDs characteristics such as critical current Ic, modulation voltage Vpp, magnetic flux noise S1/2, effective area Aeff, and magnetic field noise SB1/2 were enhanced. The robustness of the magnetometer in an applied ac magnetic field was successfully enhanced by the coverage with the shields, particularly the cross-shaped shield. It is inferred that the cross-shaped shield reduced flux trapping and jumping in the SQUID ring and at the edges of the pickup loops.