Tatsuoki Nagaishi

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.

Four‐channel YBa2Cu3O7−y dc SQUID magnetometer for biomagnetic measurements

A four‐channel YBa2Cu3O7−y thin film dc SQUID magnetometer was fabricated. Biomagnetic measurements were performed by using the four‐channel system at 77 K in a magnetically shielded room. We have successfully measured four‐channel magnetocardiac signals clearly in real‐time mode. The best magnetic field resolution of the four SQUIDs was 370 fT/Hz1/2 at 10 Hz and 200 fT/Hz1/2 in the white noise region.

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.

YBa2Cu3O7-x Thin Film Prepared by Laser Ablation

High critical current density YBa2Cu3O7-x thin films on (100)SrTiO3 were successfully prepared by laser ablation. The zero resistance transition temperature (Tc(R=0)) was 90.5 K and the critical current density (Jc) at 77.3 K was 8.0×106 A/cm2 under a zero magnetic field. Jc degraded to 1.7×104 A/cm2 in a magnetic field of 8 T parallel to the c-axis of the film, and to 4.0×105 A/cm2 in a magnetic field of 8 T perpendicular to the c-axis of the film. The characteristics of the film, mis-oriented crystallites and stacking faults, were revealed by transmission electron microscopy (TEM).

First Practical High Tc SQUID System for the Detection of Magnetic Contaminants in Commercial Products

The first practical High Tc SQUID system for the detection of magnetic contaminants in commercial products was developed. The system consists of three SQUIDs cooled by liquid nitrogen, a permalloy magnetic shield, a conveyer, and a magnetization unit. The SQUIDs are driven by modulated FLL circuits, which are controlled by a microchip computer operated by a PC through a USB interface. A LabView-based operating software was developed for SQUID tuning, data acquisition, and identification of the presence of contaminants. The developed system can inspect objects having cross sectional areas of up to 200 mm in width and 80 mm in height. The system performance was evaluated using stainless steel balls. The system could detect a stainless steel ball having diameter as small as 0.3 mm. The sensitivity of the system is practically preferable to that of metal detectors. Moreover, the SQUID system could detect stainless steel fragments down to several hundred microns that could not be detected by an X-ray detector on an actual factory line. Two systems have already been installed in food processing plants and have been functioning reliably and successfully detecting magnetic contaminants for over half a year.

HTS scanning SQUID microscope

A HTS scanning SQUID microscope has been developed. Two CCD cameras are installed, one for monitoring sample surface and another for checking distance between the sample and a SQUID probe. A heater to remove flux trappings in a SQUID chip is also equipped. A needle was used for a flux guide to get high spatial resolution. Spatial resolution depends on conditions of measurements. It needs some standard to evaluate spatial resolution of the scanning SQUID microscope.

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

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.

High Tc SQUID system for transient electromagnetic geophysical exploration

Transient electromagnetic (TEM) method using high temperature SQUID (HTS SQUID) for geophysical exploration has been developed. In terms of high sensitivity, wide bandwidth and its easy handling, HTS SQUIDs are anticipated for use with the coolant of the liquid nitrogen. The development was focused on high magnetic field sensitivity and high slew rate for better resolution and deeper depth of exploration. A highly sensitive large direct couple SQUID is made with step-edge junctions on a 20 mm by 20 mm substrate. The effective area is 0.52 mm/sup 2/ and the typical magnetic field noise is 50-100 fT/Hz/sup 1/2/. The flux locked loop circuit is a direct-readout type for the purpose of high frequency response up to 100 kHz and has low amplifier noise of 0.5 nV/Hz/sup 1/2/. The system achieved noise level of 200 fT/Hz/sup 1/2/ under the magnetic field environment and the slew rate of 7.3 mT/sec. We conducted field trials at several sites in Japan with the successful operation of the system. It was confirmed that the system has up to two orders improved sensitivity than the conventional system which enables the exploration of deeper regions. The reconstructed resistivity profile by 1-D inversion of the SQUID data agrees well with the results of the drilling survey.

PROPERTIES OF YBA2CU3O7-Y LARGE WASHER SQUID

For practical purposes of SQUIDs, the magnetic field sensitivity should be enhanced. Since the flux capture area of SQUIDs is proportional to the product of the hole size and the outer dimension of the washer, higher magnetic field sensitivity is expected when the hole sizes or the washer sizes are enlarged. We have fabricated YBa2Cu3O7-y SQUIDs with large washers (11 mm×11 mm) and investigated these properties. As a result the magnetic field sensitivity was improved by a focussing effect and was 0.34 pT/Hz1/2 at a white noise level.

High Tc SQUID Based Metallic Contaminant Detection System for Beverage or Ground Meat

A computer controlled contaminant detection system based on high-Tc Superconducting Quantum Interference Device (SQUID) for a beverage or ground meat has been designed and constructed. There is a strong demand for detection of metallic contaminants in ground meat or juice with pulp because a strainer cannot be applied to such a pulpy liquid. Two identical SQUIDs were employed so that they can keep the sensitivity over the full width of the tube. As a result, we could successfully measure small iron particles in the order of hundreds of microns. This detection level is hard to achieve by a conventional X-ray detection or eddy current methods. We believe that this system is the first practical SQUID based metallic contaminant detector for a beverage.