Numerical Study on Electromagnetisms and Material Characteristics of Magnetic Flux Shield for Eddy-Current Type Proximity Sensor

Koichi KOIBUCHI  Koichiro SAWA  Takashi HONMA  Takumi HAYASHI  Kuniyoshi UEDA  Hiroshi SASAKI  

IEICE TRANSACTIONS on Electronics   Vol.E90-C   No.7   pp.1497-1503
Publication Date: 2007/07/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e90-c.7.1497
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Development of Electromechanical Devices (Selected Papers from ICEC2006))
Category: Signal Transmission & Sensing
proximity sensor,  eddy-current loss,  magnetic circuit,   numerical analysis,  plastic magnetic material,  

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Eddy-current type proximity sensor is a non-contact type sensing device to detect the approach of a conductor by increase of coil resistance due to eddy-current loss. This paper proposes to add the cap-shaped magnetic flux shield at the top of the ferrite core for the actual sensor. In conventional proximity sensors, main magnetic flux path passes through the air between the target conductor and ferrite core. Proposed sensor, in contrast, has closed magnetic circuit geometry. It means that main magnetic flux path is almost completed by the core and the shield. Therefore, it is predicted that flux does not reach the target conductor and it causes debasement of sensing property. However, it is shown that the calculated results by FEM and measured results of sensing property of the proposed sensor is enhanced compared with the actual sensor. This paper quantitatively accounts the electromagnetisms of the proposed sensor from sensing property, flux distributions and eddy-current loss in each part of the sensor body. Moreover, material characteristics for the proposed shield, such as relative permeability and conductivity, are found.