Characterization techniques - Micromixers Fundamentals Design and Fabrication - page 294

CHAPTER

8

Characterization techniques

CHAPTER OUTLINE

8.1 Imaging Techniques ..................................................................................................................... 295
8.1.1 Two-dimensional optical microscopy............................................................................295
8.1.2 Two-dimensional fluorescence microscopy ...................................................................299
8.1.3 Confocal laser scanning microscopy ............................................................................301
8.1.4 Acquisition and processing of digital images ................................................................303
8.1.4.1 Image sensors .......................................................................................................303
8.1.4.2 Digital images ........................................................................................................305
8.2 Measurement Using Optical Microscopy ........................................................................................ 307
8.2.1 Measurement of velocity field .....................................................................................307
8.2.2 Measurement of concentration field.............................................................................310
8.3 Quantification Methods for Micromixers......................................................................................... 312
8.3.1 Direct statistical methods...........................................................................................312
8.3.2 Indirect methods .......................................................................................................316
References ......................................................................................................................................... 320

8.1 IMAGING TECHNIQUES
8.1.1 Two-dimensional optical microscopy
Optical microscopy is the key tool for characterizing micromixers. It offers a noninvasive means of
measurement in microscale. Together with digital cameras and digital image processing, a number of
measurements in micromixers can be carried out with optical microscopy. Optical microscopy works
with the electromagnetic spectrum that is visible to the human eye. A typical human eye responds to
wavelengths in air from 400 to 700 nm. The corresponding wavelengths in other media are reduced by
a factor of the refractive index. A human eye has the maximum sensitivity at about 555 nm, which is the
green region. Tabl e 8 .1 shows the approximate ranges of the different spectral colors of visible light.
Because light is an electromagnetic wave, the relation between the propagation speed c , the
wavelength l , and the frequency n is

c ¼ nl: (8.1)

Table 8.1 Spectral colors of visible light

Color Violet Blue Green Yellow Orange Red

Wave length (nm) 380-450 450-495 495-570 570-590 590-620 620-750