The measurement of film thickness is an important aspect in tribology, which is the study of friction, wear, and lubrication. The thickness of the lubricant film plays a crucial role in determining the lubrication regime of a system, and in turn, affects the friction and wear behavior of the system. There are several methods that are used to measure the thickness of a lubricant film, depending on the application and the type of lubricant.
One of the most widely used methods for measuring film thickness is the optical interferometry method. This method uses the interference of light waves to measure the thickness of a thin film. A light source is shone onto the surface of the film, and the reflected light is analyzed to determine the thickness of the film. This method is highly precise and can be used to measure film thicknesses in the nanometer range. It can be used to measure the thickness of transparent and semi-transparent films.
Another commonly used method is the laser-based method, this method uses the laser to measure the film thickness by analyzing the laser’s reflection, diffraction, or absorption.
Another method is the mechanical method; this method uses a mechanical probe to measure the film thickness. The probe is lowered into the lubricant film, and the position of the probe is measured to determine the thickness of the film.
Finally, there is the electrical method; this method uses an electrical signal to measure the film thickness by analyzing the capacitance or the impedance of the lubricant film. This method is based on the dielectric properties of the lubricant and it can be used to measure the film thickness of both liquid and solid lubricants. This method is relatively simple, easy to use, and can be used in-situ and in real-time.
In conclusion, the film thickness can be measured by different methods such as optical interferometry, laser-based, mechanical and electrical method. The choice of the method depends on the lubricant, the range of the film thickness, and the accuracy required.
 Dwyer-Joyce, R.S., Drinkwater, B.W. and Donohoe, C.J., 2003. The measurement of lubricant–film thickness using ultrasound. Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 459(2032), pp.957-976.
This article was written by Mahdieh Mosayebias part of an ongoing series of scientific communications written and curated by BioTrib’s Early Stage Researchers.
Mahdieh is researching the Design of Self Lubricating Prothesis at ETH Zurich, Switzerland.