Detector field of view

When equation 12 is vaUd, the detector is said to be a background-limited infrared photodetector (BLIP). When this is the case, attempts often are made to improve D by cold shielding which reduces ( ). The ideal D is shown in Figure 3 as a function of wavelength with background photon flux as a parameter. The line of termination in the lower left corner represents TN values for a 180° (27T) detector field of view, 300 K ambient background... 

Because the performance of infrared detectors is limited by noise, it is important to be able to specify a signal-to-noise ratio in response to incident radiant power. An area-independent figure of merit is D ( dee-star ) defined as the rms signal-to-noise ratio in a 1 Hz bandwidth per unit rms incident radiant power per square root of detector area. D can be defined in response to a monochromatic radiation source or in response to a black body source. In the former case it is known as the spectral D, symbolized by D (A,/1) where A is the source wavelength, / is the modulation frequency, and 1 represents the 1 Hz bandwidth. Similarly, the black body D is symbolized by D (T,/, 1), where T is the temperature of the reference black body, usually 500 K. Unless otherwise stated, it is assumed that the detector field of view is hemispherical (2n ster). The units of D are cm Hz /watt. The relationship between Df measured at the wavelength of peak response and Z) (500 K) for an ideal photon detector is illustrated in Fig. 2.14. For an ideal thermal detector, Df D T) at all wavelengths and temperatures. 

D double star O Specific detectivity per an angle 6, independent on the detector field of view (FOV). The unit is cm Hz sterad AV D = D sin0... 

Other limitation for the spatial resolution can be found in the detector. A limited number of pixels in the camera array can be a reason for pure resolution in the case of a big field of view. For example, if field of view should be 10 by 10 nun with camera division 512x512 pixels the pixel size will be approximately 20 microns. To improve the relation of the field of view and the spatial resolution a mega-pixel sensor can be used. One more limitation for the spatial resolution is in mechanical movement (rotation) of the object, camera and source. In the case of a mechanical movement all displacements and rotations should be done with accuracy better than the spatial resolution in any tested place of the object. In the case of big-size assemblies and PCB s it is difficult to avoid vibrations, axle play and object non-planarity during testing. 

Fig. 3. Ideal photon detector sensitivity as a function of cutoff wavelength. Lower background flux generates less photon-induced noise giving higher sensitivity. The sensitivity limit for the condition of 300 K background temperature and hemispherical (27T) field of view is shown.

Fig. 9. Spectral sensitivity of detectors where the detector temperatures in K are in parentheses, and the dashed line represents the theoretical limit at 300 K for a 180° field of view, (a) Detectors from near uv to short wavelength infrared (b) lead salt family of detectors and platinum siUcide (c) detectors used for detection in the mid- and long wavelength infrared. The Hg CdTe, InSb, and PbSnTe operate intrinsically, the doped siUcon is photoconductive, and the GaAs/AlGaAs is a stmctured supedattice and (d) extrinsic germanium detectors showing the six most popular dopants.

Fig. 3.15 Left External view of the MIMOS II sensor head (SH) with pyramid structure and contact ring assembly In front of the Instrument detector system. The diameter of the one Euro coin is 23 mm the outer diameter of the contact-ring is 30 mm, the inner diameter is 16 mm defining the field of view of the Instrument. Right. Mimos II SH (without contact plate assembly) with dust cover taken off to show the SH Interior. At the front, the end of the cylindrical collimator (with 4.5 mm diameter bore hole) Is surrounded by the four SI-PIN detectors that detect the radiation re-emltted by the sample. The metal case of the upper detector is opened to show its associated electronics. The electronics for all four detectors Is the same. The Mossbauer drive is inside (in the center) of this arrangement (see also Fig. 3.16), and the reference channel is located on the back side In the metal box shown In the photograph...

Another source of variability, which can have still different characteristics, is comprised of the interaction of any of the above factors with a nonlinearity anywhere in the system. These nonlinearities could consist of nonlinearity in the detector, in the spectrometer s electronics, optical effects such as changes in the field of view, and so on. Many of these nonlinearities are likely to be idiosyncratic to the cause, and would have to be characterized individually and also analyzed on a case-by-case basis. 

The flame detector is an optical device that responds to the radiant energy that is given off by a flame. When a flame or explosion occurs within the field of view of the detector, the resulting electromagnetic radiation travels toward the detector at... 

The IR/UV flame detectors are used to sense fires. Flame detectors that use only IR or UV can experience false alarms. The IR/UV detector is designed to recognize a different type of flame signature from the detectors while rejecting common false sources. When the conditions of any one of the several fire conditions are met the detector indicates a fire. IR/UV flame detectors generally have a cone of vision from 60 to 120-degree solid cone field of view. 

Sensing Volume. The sensing volume of a sensor is the volume where the air is actually monitored. The sensing volume is the reaction chamber of a flame photometric detector or a chemiluminescence device, the field of view of an open-path sensor, or the White cell of a reduced-pressure optical system. The residence time of the sample within the sensing volume ultimately limits the temporal resolution of most chemical sensors. 

A variety of factors can contribute to intensity in chemical images. Analytical microscope images can exhibit significant shading across the field of view. The shading might be caused by nonuniform illumination, nonuniform camera (detector)... 

Detector elements 11 are formed on a ceramic substrate 1. Each detector element includes a photosensitive zone 9, an output terminal 4 and a common terminal S. The detector elements are arranged in an array protruding from a common metal line 3, which is connected to a terminal pad 6. The terminal electrodes and the common metal line are formed on a comb-like patterned photo-conductive layer 2. An aperture plate 7 of silicon or ZnS having apertures 8 formed therein by an anisotropic etching method is prepared. The purpose of the aperture plate is to restrict the field of view of the photosensitive zones. An auxiliary electrode 30 is formed on the aperture plate. When the aperture plate is assembled with the substrate using an adhesive, the auxiliary electrode is pressed against the common metal line and the common terminal, which together reduce the electrical resistance. 

A shield comprising apertures corresponding to detector elements are attached to an HgCdTe detector layer in JP-A-61147118 to determine the field of view of the detector elements. 

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