Metallic contaminant detection system using multi-channel high Tc SQUIDs

https://doi.org/10.1016/j.jmmm.2012.02.072Get rights and content

Abstract

We have developed the magnetic metallic contaminant detectors using multiple high Tc SQUID gradiometers for industrial products. Finding ultra-small metallic contaminants is a big issue for manufacturers producing commercial products. The quality of industrial products such as lithium ion batteries can deteriorate by the inclusion of tiny metallic contaminants. When the contamination does occur, the manufacturer of the product suffers a great loss to recall the tainted products. Metallic particles with outer dimension less than 50 μm cannot be detected by a conventional X-ray imaging. Therefore a high sensitive detection system for small foreign matters is required. However, in most of the cases, the matrix of an active material coated sheet electrode is magnetized and the magnetic signal from the matrix is large enough to mask the signal from contaminants. Thus we have developed a detection system based on a SQUID gradiometer and a horizontal magnetization to date. For practical use, we should increase the detection width of the system by employing multiple sensors. We successfully realized an eight-channel high-Tc SQUID gradiometer system for inspection of sheet electrodes of a lithium ion battery with width of at least 60 to 70 mm. Eight planar SQUID gradiometers were mounted with a separation of 9.0 mm. As a result, small iron particles of less than 50 μm were successfully measured. This result suggests that the system is a promising tool for the detection of contaminants in a lithium ion battery.

Introduction

Finding ultra-small metallic contaminants is an important issue for manufacturers producing commercial products such as lithium-ion batteries. Manufacturers of faulty products suffer significant financial losses when they have to recall their products. Although the industry requirement is to find metallic particles that have a diameter of 50 μm, particles smaller than 100 μm cannot be detected by X-ray imaging, which is commonly used as the inspection method. Therefore, a highly sensitive detection system for small contaminants is required. Some SQUID detection systems for detecting contaminants in food have been developed [1], [2], [3], [4]. One of these systems is commonly available now [5]. However, in most cases, the matrix of industrial products is magnetized, and the magnetic signal from the matrix is sometimes sufficiently large to mask the signals from the contaminants. Thus, we have proposed the use of a planar gradiometer and horizontal magnetization of the sample prior to measurement. This combination reduces the large signal from the matrix and clarifies the signal from the metallic contaminants [6], [7], [8]. For practical use, it is important to increase the detection width of the system by employing multiple sensors with a wide sensing area. We describe a detection system based on eight-channel high-Tc SQUID gradiometers.

Section snippets

Principle

The principle of the detection system is shown in Fig. 1. The magnet horizontally magnetizes the metallic contaminant and the matrix of the test object. The SQUID gradiometer detects these remanent magnetic fluxes. If they are magnetized vertically, since the matrix such as a lithium ion battery electrode is magnetized, a signal from the contaminant is hidden by that from the matrix and cannot be seen [6]. However, it is expected that the magnetic poles appear at both ends of the matrix and the

Conclusion

A multi-channel high-Tc SQUID contaminant detection system for industrial products, with width of more than 70 mm was developed. An iron ball with a diameter of 50 μm was successfully measured by a single-channel SQUID gradiometer when the ball was placed at a distance of 3 mm from the gradiometer. We also demonstrated that the eight-channel system can detect a 95 μm square iron ball in the range of 72 mm with S/N ratio of more than 10. The success of the eight-channel system proposed in this paper

References (11)

  • T. Nagaishi et al.

    IEEE Transactions on Applied Superconductivity

    (2007)
  • S. Tanaka et al.

    Superconductor Science and Technology

    (2006)
  • H.J. Krause et al.

    IEEE Transactions on Applied Superconductivity

    (2005)
  • M. Bick et al.

    Superconductor Science and Technology

    (2005)
  • S. Tanaka et al.

    Superconductor Science and Technology

    (2007)
There are more references available in the full text version of this article.

Cited by (0)

View full text