Visualization of Lubrication Conditions Using the Electrical Impedance Method Considering Surface Roughness

Kosugi, Daichi; Aikawa, Fumiaki; Iwase, Shunsuke; Maruyama, Taisuke; Momozono, Satoshi

doi:10.3390/lubricants14060221

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Visualization of Lubrication Conditions Using the Electrical Impedance Method Considering Surface Roughness

by

Daichi Kosugi

¹,

Fumiaki Aikawa

^1,2,

Shunsuke Iwase

¹,

Taisuke Maruyama

^1,*

and

Satoshi Momozono

²

¹

NSK Ltd., 1-5-50 Kugenuma-shinmei, Fujisawa 251-8501, Japan

²

NSK Tribology Collaborative Research Cluster, Institute of Science Tokyo, 4259, Nagatsuta, Midori, Yokohama 226-8501, Japan

^*

Author to whom correspondence should be addressed.

Lubricants 2026, 14(6), 221; https://doi.org/10.3390/lubricants14060221

Submission received: 27 February 2026 / Revised: 23 March 2026 / Accepted: 27 April 2026 / Published: 29 May 2026

(This article belongs to the Special Issue Mechanical Tribology and Surface Technology, 2nd Edition)

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Abstract

In this study, we developed an improved electrical impedance method for measuring oil film thickness with a correction for surface roughness effects. Statistical analysis of the oil film thickness distribution revealed that rough surfaces exhibit higher capacitance values than those predicted by the ideal parallel-plate model, despite having the same mean film thickness. Consequently, a corresponding roughness correction formula was derived. The accuracy of the method was verified in ball-on-disk type apparatus using balls with a rough surface. The corrected oil film thickness agreed more closely with the Hamrock–Dowson equation and with optical interferometry measurements than did the uncorrected result. These outcomes confirm that oil film thickness can be estimated considering surface roughness. The technique is therefore expected to facilitate the optimization of lubrication conditions and enable more reliable bearing-life prediction.

Keywords: electrical impedance method; condition monitoring; oil film thickness; surface roughness; electric field analysis; elastohydrodynamic lubrication

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MDPI and ACS Style

Kosugi, D.; Aikawa, F.; Iwase, S.; Maruyama, T.; Momozono, S. Visualization of Lubrication Conditions Using the Electrical Impedance Method Considering Surface Roughness. Lubricants 2026, 14, 221. https://doi.org/10.3390/lubricants14060221

AMA Style

Kosugi D, Aikawa F, Iwase S, Maruyama T, Momozono S. Visualization of Lubrication Conditions Using the Electrical Impedance Method Considering Surface Roughness. Lubricants. 2026; 14(6):221. https://doi.org/10.3390/lubricants14060221

Chicago/Turabian Style

Kosugi, Daichi, Fumiaki Aikawa, Shunsuke Iwase, Taisuke Maruyama, and Satoshi Momozono. 2026. "Visualization of Lubrication Conditions Using the Electrical Impedance Method Considering Surface Roughness" Lubricants 14, no. 6: 221. https://doi.org/10.3390/lubricants14060221

APA Style

Kosugi, D., Aikawa, F., Iwase, S., Maruyama, T., & Momozono, S. (2026). Visualization of Lubrication Conditions Using the Electrical Impedance Method Considering Surface Roughness. Lubricants, 14(6), 221. https://doi.org/10.3390/lubricants14060221

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

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Visualization of Lubrication Conditions Using the Electrical Impedance Method Considering Surface Roughness

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