Decay length evanescent

Conventional evanescent sensing works exceedingly well for relatively small biomolecules such as proteins and DNA molecules whose size is much smaller than the decay length. However, it becomes less sensitive when detecting biospecies, such as cells, with dimensions over 1 pm. In Chap. 15, deep-probe waveguide sensors are developed to overcome this limitation, which have a decay length comparable to the size of the biospecies of interest. 

The effective sampling depth or penetration depth (dp) is representative of the characteristic decay length and represents the distance at which the intensity of the evanescent field has decayed to 1/e with respect to the maximum (at the interface), as defined by ... 

A. The electromagnetic field decays evanescently into the adjacent media, with a decay length of several hundreds of nanometers. 

Example 3.13 Determine the approximate and the exact values of the evanescent decay length for water, assuming that the wavelength is 100 microns, Vp = 200 mis and Vwater = 1480 m/s. 

Solution Approximate evanescent decay length is S approx (A/2n) = 15.92 microns. Exact evanescent decay length Ss exact - (A/2tr)[l - (Vp/V/r) ]" = 16.06 microns. 

Solution The viscous decay length is 250 nm, which is much smaller than the evanescent decay length 16 microns, from Example 3.55). The value of is 1.3 x 10 kg/m ... 

Figure 4.9 Response of 5.6-MHz FPW device coated with S00-/m-thick agar gel upon immersion in 0.1 M NaCl, showing gravimetric detection of ions that diffuse to within an evanescent decay length of the sensor membrane. (Dam provided by Amy Wang and Ben Cosieiio, U.C. Berkeley and Berkeley Microlnsiruments, Inc., respectively.)...

Figure 8.11 Decay lengths of an evanescent wave as a function ofy at t 650 nm. The range of the decay length is changed from 153 to 205 nm.

The calculated exponential decay lengths were 160, 150, 120 and 105nm for the A1 thin film and the A1/C20 LB films with monolayer, three and five layers, respectively. The experimental results were slightly larger than the calculated ones. It was thought that the difference was caused by the large size of the probe tip. The results showed that evanescent fields on the Al thin films and the A1/C20 thin films could be detected by means of our measuring system. 

This field is known as an evanescent wave and has a decay length or penetration depth on the order of the wavelength of the incident light. 

The attenuated, refracted wave, is referred to as an evanescent wave and decays with the characteristic length scale ... 

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