Measurement and Evaluation of the Defect Size in Soft Magnetic Composites Using Magnetic Field Inspections

This article presents a method for detecting defects and assessing their size in soft magnetic composites (SMCs) based on magnetograms obtained from a magnetic field camera and a numerical analysis of the magnetic field around them. For the purpose of the experiment, toroidal samples of a metal–polymer composite were made, in which holes and gaps simulating defects were prepared. The magnetic camera allowed for registering the magnetic flux density image near the surface of the samples. As a result, magnetograms with information about the location and geometry of defects were obtained. A numerical analysis was used to investigate the influence of various factors, such as defect depth, its size and material permeability. Theoretical changes in magnetic field over defects stay in good agreement with measurements, which is a strong indication that surface field magnetograms can be useful in a quality assessment of the considered composites. The effectiveness and usefulness of the method in detecting surface and shallow subsurface defects in SMC materials was confirmed. The influence of a possible tangent component of the exciting field was demonstrated and discussed.

Towards Tracking of Deep Brain Stimulation Electrodes Using an Integrated Magnetometer

This paper presents a tracking system using magnetometers, possibly integrable in a deep brain stimulation (DBS) electrode. DBS is a treatment for movement disorders where the position of the implant is of prime importance. Positioning challenges during the surgery could be addressed thanks to a magnetic tracking. The system proposed in this paper, complementary to existing procedures, has been designed to bridge preoperative clinical imaging with DBS surgery, allowing the surgeon to increase his/her control on the implantation trajectory. Here the magnetic source required for tracking consists of three coils, and is experimentally mapped. This mapping has been performed with an in-house three-dimensional magnetic camera. The system demonstrates how magnetometers integrated directly at the tip of a DBS electrode, might improve treatment by monitoring the position during and after the surgery. The three-dimensional operation without line of sight has been demonstrated using a reference obtained with magnetic resonance imaging (MRI) of a simplified brain model. We observed experimentally a mean absolute error of 1.35 mm and an Euclidean error of 3.07 mm. Several areas of improvement to target errors below 1 mm are also discussed.

Flaw Classification Algorithm for Heat Exchanger Tubes Using a Bobbin-Type Magnetic Camera

This paper presents an algorithm that estimates the presence, location, shape, and depth of flaws using a bobbin-type magnetic camera consisting of bobbin probes and a bobbin-type integrated giant magnetoresistance (GMR) sensor array (BIGiS). The presence of the flaws is determined by the lobe path of the Lissajous curves obtained from bobbin coil with respect to the applied frequency. The location of the flaw, i.e., whether it is an inner diameter (ID) or outer diameter (OD) flaw, can be determined from the rotational direction of the lobe with respect to the frequency change. The shape of the flaw is then determined from the area of the lobe and the BIGiS image. At this stage, multi-site damage can be determined from the BIGiS image. The effectiveness of the flaw classification algorithm was evaluated using various types of artificial flaws introduced into small-bore tube test specimens made of austenitic stainless steel.

Real-Time Eddy Current Imaging and Flaw Detection Under Tube Support Plate by Cylinder-Type Magnetic Camera

In this study, a novel method is proposed to detect flaws directly under tube support plate (TSP) of heat exchanger tube using a cylinder-type magnetic camera (CMC). The CMC measures and images magnetic flux density changes occurring around a defect by applying a time-varying magnetic field to a metallic object through magnetic sensors which are arrayed in a matrix. If there is a flaw directly under the TSP, the magnetic flux density is concentrated in the TSP due to its higher permeability. Accordingly, flaws directly under the TSP are difficult to be detected. In order to solve this problem, the principle that the magnetic flux density distribution around the TSP is uniform in the circumferential direction is used. When the magnetic flux density signals obtained at the position where the TSP is placed are set as reference signals and the signals obtained by rotating the sensor probe in the circumferential direction are compared with the reference signals, it is possible to detect the flaw signals from which the TSP signals are removed. If the flaw is formed in the circumferential direction, the flaw can be detected by moving the sensor probe in the axial direction and comparing the signals with the reference signals. The proposed method to detect flaws directly under the TSP was verified using an artificially flawed heat exchanger tube (HXT) test specimen made of titanium alloy.

Magnetic Camera and its Applications in Aging Aircraft, Express Train and Pipelines for Green Technology

Operation of the corresponding large machine is not allowed during the regular NDT period. Therefore, reducing the test period and extending the test frequency, i.e., lowering the machine stoppage time due to an inspection is a very important technique for efficient energy usage. For this reason, IT-based real-time non-destructive testing (IT-NDT) technology has been being developed. This presentation reports on a magnetic camera, which is one IT-NDT technology, including the up-to-date experiences.