Filters narrow-band

Due to the rather stringent requirements placed on the monochromator, a double or triple monocln-omator is typically employed. Because the vibrational frequencies are only several hundred to several thousand cm and the linewidths are only tens of cm it is necessary to use a monochromator with reasonably high resolution. In addition to linewidth issues, it is necessary to suppress the very intense Rayleigh scattering. If a high resolution spectrum is not needed, however, then it is possible to use narrow-band interference filters to block the excitation line, and a low resolution monocln-omator to collect the spectrum. In fact, this is the approach taken with Fourier transfonn Raman spectrometers. 

Resilient but rigid foundations such as by providing spring mounts or rubber pads for machines on the floor or for components and devices mounted on the machine so that they are able to absorb the vibrations, caused by resonance and quasi resonance effects, due to filtered out narrow band ground movements. The stiffness of the foundation (coefficient of the restoring force, k) may be chosen such that it would make the natural frequency of the equipment... 

Another area of concern is the Q of the filter at self-resonance. If the Q is too high, or in other words, the damping factor is too low, the filter will actually generate noise in the form of narrow-band ringing. This can be dealt with during the design. 

If further resolution is necessary one-third octave filters can be used but the number of required measurements is most unwieldy. It may be necessary to record the noise onto tape loops for the repeated re-analysis that is necessary. One-third octave filters are commonly used for building acoustics, and narrow-band real-time analysis can be employed. This is the fastest of the methods and is the most suitable for transient noises. Narrow-band analysis uses a VDU to show the graphical results of the fast Fourier transform and can also display octave or one-third octave bar graphs. 

A Del Electronics, Model ESP-100A, electrostatic precipitator was used for sample collection. Cigarette smoke particles were found to give approx the same particle distribution pattern on the collection filter paper as the gunshot residue, and since the smoke stains the paper, this provided a v rapid technique for optimizing operation conditions. With a flow rate of 15cfm and a corona current of 125 uA, the residue collects primarily on a narrow band across the sample paper. Samples were collected on Whatman No 1541 filter paper which lined the inside of the sample collection tube. The presence of this paper allowed air to flow only thru the center of the tube, so particle collection was made upon the filter paper exclusively. The filter paper samples were pelletized prior to neutron activation analysis... 

Figure 13, Demonstrating that a narrow band pass filter will increase...

Monochromators. Replica gratings and narrow band-pass filters are used commonly, more so than quartz prisms. Computer control of the monochromator is available in some instruments, so that optimum intensity at the desired wavelength or maximum absorption by the examined substance can be obtained. 

The word monochromator is derived from the Latin language, mono meaning one and chromo meaning color. It is a device more sophisticated than an absorption filter that isolates the narrow band of wavelengths from visible and ultraviolet sources. 

Time-resolved approaches for multi-analyte immunoassays have been described recently. Simultaneous determination of LH, follicle stimulating hormone (FSH), hCG, and prolactin (PRL) in a multisite manual strip format has been reported. 88 Four microtiter wells are attached to a plastic strip, two-by-two and back-to-back, such that the wells can be read on a microtiter plate reader. In a quadruple-label format, the simultaneous quantitative determination of four analytes in dried blood spots can be done using europium, samarium, dysprosium, and terbium. 89 In this approach, thyroid-stimulating hormone, 17-a-hydroxyprogesterone, immunoreactive trypsin, and creatine kinase MM (CK-MM) isoenzyme are determined from dried blood samples spotted on filter paper in a microtiter well coated with a mixture of antibodies. Dissociative fluorescence enhancement of the four ions using cofluorescence-based enhancement solutions enables the time-resolved fluorescence of each ion to be measured through four narrow-band interference filters. 

Photometers are relatively simple devices that make use of a light source and one or more filters to present a narrow band of wavelengths to a sample and then to a photodetector. One, two, or even three wavelength analyses are possible with these devices. In addition, photometers are designed for location on-line, with samples generally plumbed into a sample cavity in the analyzer. 

Conventional wisdom leans towards a simple measurement system featuring one or two optical elements and with a simple constraction. In practice there are many forms of filter assemblies that can be used and these are not limited to the use of a single filter and implementations featuring multiple filters on a wheel are often implemented in multichannel analyzers. Such assemblies (Figure 6.6C) can be quite small (25mm diameter as illustrated) and can accommodate a relatively large number of filters. Other forms of filter assemblies include clusters or arrays (multiple wavelengths), correlation filters (customized to the analyte), continuously variable filters, such as the circular variable filter (CVF) and the linear variable filter (LVF), and tunable filters (both broad and narrow band). 

Optical effects due to refraction and total internal reflection have been observed in dye-loaded zeolite L crystals of 2.5 p,m length and 1.4 p-m diameter by means of an optical microscope equipped with polarizers, a narrow band, and cutoff filters [23]. An astonishing effect taking place in an Ox +-loaded crystal is seen in Fig. 15. Looking at the polarized red emission, a homogeneous intensity distri-... 

Fig. 11. Fundamental and harmonic imaging In the fundamental imaging mode (a), a narrow-band pulse of ultrasound (US) centered at a given frequency (e.g., 2.5 MHz) is emitted the sound reflected by the organs is used to create the image, (b) Microbubbles, because they are extremely compressible in comparison to organ tissue, not only reflect sound more efficiently than tissues but also emit harmonics. In the harmonic mode, the signal from the tissues is filtered out, leaving only the harmonics, resulting in specific imaging of the bubbles [37].

Luminescence Lidar (light Detection and Ranging) is an active instrument, which sends out coherent waves to the object concerned. A fraction of the transmitted energy is transformed by the objects and sends back to the sensor. lidar instriunents measure both the traveUng time interval between sensor/object/sensor as well as the difference between emitted and returning energy, providing information on the exact position of the objects and on the material the objects are made of. Spectral selectivity was achieved usually with the aid of narrow band interference filters. 

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