Band Detectors

Multi-band fire detector monitors monitor several wavelengths of predominate fire radiation frequencies by photocells. They compare these measurements to normal ambient frequencies through micro processing. Where these are found be above certain levels an alarm is indicated. False alarms may even be recognized  

These detectors have a very high sensitivity and very encouraging stability. The microprocessor has the capability to be programmed to recognize certain fire types. 

May be inadvertently mis-programmed. The detector is relatively new on the market and needs further industry experience for wide acceptance. 

Type of Detection Detector Type Speed Cost 

Location or taclBtf Hazard Fixed Detector Type Options Reference 

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Such effects principally cannot be observed in multi band detectors such as a UV diode array detector or a Fourier transform infrared (FTIR) detector because all wavelengths are measured under the same geometry. For all other types of detectors, in principle, it is not possible to totally remove these effects of the laminar flow. Experiments and theoretical calculations show (8) that these disturbances can only be diminished by lowering the concentration gradient per volume unit in the effluent, which means that larger column diameters are essential for multiple detection or that narrow-bore columns are unsuitable for detector combinations. Disregarding these limitations can lead to serious misinterpretations of GPC results of multiple detector measurements. Such effects are a justification for thick columns of 8-10 mm diameter. 

Note about infrared radiation (IR) filters In the bolometer just described, the optimum conductance to the heat sink is G 2 x 10-10 W/K. This means that an absorbed power of the order of 1(T10 W saturates the bolometer. Since the bolometer is a broad-band detector, it would receive, e.g., a power of the order of 10 7 W from a 30 K black body. Of course, optical filtering is needed to reduce the bandwidth of the impinging radiation. Filtering takes usually place in several steps a room temperature filter eliminates visible light an intermediate temperature filter (at about 77 K) rejects the micron wavelengths, whereas the submillimetre or millimetre filter is made up of a low-pass and an interference band-pass filter. 

A broad band detector array with homogeneous sensitivity is achieved in JP-A-60102530 by providing a thin single crystal film of Hgi.xCd,Te having a concentration gradient of the composition ratio x. 

Numerical simulations of this model were carried out to test expectations. The results are shown in Figs. 8 and 9. The figure 8 shows the amplitude of the detected signal at the third harmonic of the modulation frequency when the operating point corresponds to the second node, i.e., n = 2, and the Bo is selected for the detection of radiation in the vicinity of 400 GHz, which lies near the lower edge of the Terahertz band, where the device sensitivity to such radiation has been confirmed by our experiments, see Fig. 3, for example. As confirmed by the simulations, the 3 harmonic sensing concept yields indeed a narrow band detector, with sensitivity between roughly 200 and 800 GHz, as... 

The properties of MCT detectors depend on their composition, that is their Hg Cd ratio. Narrow-band MCT detectors are typically about 50-fold more sensitive than DTGS, but do not respond to radiation below 750cm . The cut-off can be extended to a lower wavenumber, but at the expense of sensitivity. Thus, midband MCT detectors have a cut-off of about 600cm , while their sensitivity is about half that of the narrow-band detector. Wide-band detectors cut off at -450 cm but are even less sensitive. Fortunately, few spectra of organic samples contain useful bands below 700cm , as a result, FT-IR microscopes are almost invariably equipped with narrow-band MCT detectors. 

We first consider the photodetector and invoke an operational equivalent of the detection process (Goldberger and Watson, 1965b Glauber, 1965 Mandel, 1966). We specialize to the case of fast, broad-band detectors giving a count whenever the photon wave packet is in the active volume of the photocounter. The probability density for a photon in state l / (f)> to be localized at the position r is equal to the square of the wavefunction detection probability can be expressed as the integral over the detecting volume. 

The FTIR spectrometer is connected to the external unit by an interface mirror which diverts the beam to the spot on the plate. The reflected beam is then collected by using another set of mirrors and directed to a mercury cadmium telluride (MCT) narrow-band detector. This instrument can be used even with the strong absorbing layers used in TLC. 

A Bruker Equinox 55 FTIR spectrometer, equipped with an Axiom Analytical Diamond ATR Probe (DMD-270) and an external MCT mid-band detector, was used to collect infimred spectra of the polymerization components in real time. Each spectrum was an average of 8 scans, and spectra were acquired at 3.17 min intervals at a spectral resolution of 8 cm. An interval as... 

Petroff, M. D. Stapelbroek, M. G. (1980). Blocked impurity band detectors, radiation hard high performance LWIR detectors. In Proceedings, IRIS Specialty Group on Infrared Detectors, Menlo Park, California. 

Szmulowicz and Marasz (1987) Blocked Impurity Band Detectors An Analytical Model Figures of Merit by F. Szmulowicz and F. L. Marasz, /. Appl. Phys, 62, 2533-2540. 

Woods et al. (2011) Characterization of the Optical Properties of an Infrared Blocked Impurity Band Detector by S. I. Woods, S. G. Kaplan, T. M. Jung, and A. C. Carter, Appl. Opt. 50(25), 4824-4833. Abstract accessed 30 January 2013 at http //www.opticsinfobase.org/ao/abstract.cfm uri=ao-50-24-4824. This paper provides insight into the mechanisms involved, and how to analyze the structure. 

Goyal et al. (2011 poster) Germanium Blocked Impurity Band Detectors by S. Goyal, J. Bandaru, J. W. Beeman, and E. E. Haller. Poster Accessed 14 November 2011 at www.sofia.usra.edu/det workshop/posters/.../3-16goyal poster.pdf. 

Spectral band Detector Impedance Dark Current Back-Bias Range Range of In-Band Irradiance... 

D. M. Watson, M. T. GuptiU, J. E. Huf nan, T. N. Krabach, S. N. Raines, S. Satyapal, Germanium blocked-impurity-band detector arrays Unpassivated devices with bulk substrates , J. Appl. Phys. TA (6), pp. 4199-4206, 15 September 1993. 

Stetson, S. B., Reynolds, D. B., Stapelbroek, M. G., and Stermer, R. L., 1986, "Design and Performance of Blocked-Impurity-Band Detector Focal Plane Arrays, in Proceedings of 30th Annual International Technical SPIE Symposium on Infrared Detectors, Sensors, and Focal Plane Arrays, August 1986, San Diego, CA. 

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