Single-fiber emission

Netravali, A.N., Topoleski, L.T.T., Sachse, W.H. and Phoenix, S.L. (1989c). An acoustic emission technique for measuring fiber fragment length distributions in single fiber composite test. Composites Sci. Technol. 35, 13-29. 

The field emission cathode is made of PAN carbon fibers bundle encapsulated into the glass capillary. The diameter of the single fiber is 7 pm (the bundle contains about 300 fibers). 

Passive optodes shown in Figure 17-34 are used for Raman or fluorescence spectrometry. 1 vo types of monofiber optode have been described [166], as shown in Figure 17-34a. They require the use of a pierced mirror and suitable optics to separate the source laser and fluorescence emission beams at the fiber-measuring instrument junction. With a single fiber the observation of fluorescence is divided into four zones in order to calculate the effective optical path (/,). For a fiber with radius rg and numerical aperture A and observation in a medium with refractive index n , this path was evaluated by Deaton [191] as... 

AN Netravali, W Sachse. Some remarks on acoustic emission measurements and the single-fiber-composite test. Polymer Composites 12 370-373, 1991. 

FIGURE 13. (a) The photon emission for a glass fiber/epoxy composite where the fibers debond inside the epoxy matrix, yielding visible photons detected with a photomultiplier. The arrow indicates where the entire sample failed, (b) The same type of data from debonding occurring in a single fiber specimen. Again, the arrow indicates when the entire sample fractured. 

J. T. Dickinson, A. Jahan-Latibari, and L. C. Jensen, Fracto-emission from single fibers of Kevlar-49, J. Mater. Sci. 20, 1835 (1985). 

Sachse, W., Netravali, A.N. and Baker, A.R., An enhanced, acoustic emission-based, single fiber-composite test, J. Nondestruct. Eval., 11(3/4) (1992). 

In the second half of the 1990s, mainly Park et al. from Korea published several papers on BF-reinforced composites. They tested polycarbonate (PC)" and epoxy resin (EP) based polymer composites with the methods of single fiber fragmentation and acoustic emission. It was found that in the case of PC matrix composite (when aminosilane was used as a treating agent), the number of acoustic events correlated well with the value of the interfacial shear strength determined from the fragmentation tests. 

The wavelength of fluorescence emission is different from its excitation wavelength, and a single fiber is sufficient for transport of both excitation and emission radiation. A single fiber is also used to measure fluorescence quenching, which occurs when a compound that absorbs in the same spectral region as the emission is present. In the future it may be possible to make time-resolved fluorescence measurements. However, fluorescent lifetimes are between 1 and 10 nanoseconds, and such measurements would require complex and costly apparatus. 

Ruorescence is better adapted to analysis by optical sensors than absorption. Only a single fiber is used because the wavelength of emission is different from that of excitation. Furthermore, fluorescence is a sensitive technique that can detect voy low concentrations. It has the furtlKT advantage of having a signal that is linear as a function of low concentrations. 

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