Spectral Drop Analysis and 3‐D Liquid Drop Fingerprint

Abstract

Fiber drop analysis reveals the variation regularity of the light signal passing through the liquid drop during the drop growth. The coupled light signal reflects mechanical and optical properties of the tested liquids, but it is not only dependent on the profile and volume of the drop, but it is also dependent on the liquid absorption. Thus, spectral drop analysis is introduced into the drop analyzer to study the liquid composition by studying the absorption spectrum of the multi‐wavelength light signal passing through the liquid. A three‐dimensional (3‐D) liquid drop fingerprint (LDF) can be obtained by merging the light intensity signal from the fiber drop sensor, the drop volume signal from the capacitive drop sensor or CCD image processing, and the absorption spectrum signal from the fast Fourier transform (FFT) infrared spectrum analyzer. The 3‐D LDF covers a more extensive range of physical and chemical properties of liquids, and it enhances the capability of drop analysis for fine discrimination among different liquids. The principle of fiber‐capacitive‐image‐spectral (FCIS) drop analysis is introduced in this paper. The processing of the light intensity signal and the design of transmission optical paths are discussed. The relative spectral curve of the liquid is developed.

Keywords:

• Spectral drop analysis
• Absorption
• Spectrum
• Transmission optical path
• 3‐D Liquid drop fingerprint

Acknowledgments

The authors would like to express their thanks to the Ministry of Science and Technology of China (MOST) and the National Science and Technology Bureau of Singapore (NSTB) because the project is supported by the NSTB‐MOST Joint Research Program (Number: 003/101/04).