Constant radiation power

From Eq. (3), we see that the intensity of the monochromatic beam is determined only by the magnitude of the integrated reflection and the integral width Wj. Furthermore, it also follows from Eq. (3) that sharp focusing for constant radiation power gives more intense monochromatic beams. 

In case of constant radiation power P, the temperature T rises from its initial value to its stationary value (dT/dt = 0),... 

When an incident radiation power P is absorbed, the temperature TA initially increases with time at a rate drA/df = P/C (as in formula (15.5)) and approaches the limiting value Ta = Ts+P/G, with a time constant r = C/G. 

FIGURE 27.3 Thermal rejection requirements of automotive and fuel cell systems (Tjmib = 38°C). Solid lines are lines of constant radiator fan power. (Reproduced from Hasten, D.A. and Bosco, A.D., in W. Vielstich, H.A. Gasteiger, and A. Lamm (Eds.), Handbook of Fuel Cells Fundamentals, Technology and Applications, Vol. 4, J. Wiley Sons, Chichester, 2003. With permission.)... 

Fig. 1 Matching of current-voltage characteristics of solar cell and electrolyzer (a) at constant light power density 1, 2, 3 - characteristics of solar cell at Ng = 1,2, and 4 (at Sj = const) 4 - characteristic of electrolyzer (Ng = 1) o - maximum power point (MPP) dashed line shows the locus of maximum cell output power at the given radiation power density (b) at varying radiation power density 1 , 2, 3, -characteristics of solar cell dashed line - locus of MPP hatched area - variations of MPP in the most probable limits of variation of the light power density and temperature 4 - characteristic of electrolyzer.

The total power radiated from an ideal black body and the wavelength corresponding to maximum power are given here as a function of absolute temperature. Constants used in the calculation are taken from the table Fundamental Physical Constants in Section 1. The radiated power in a band X at may be calculated from ... 

Here is the detector quantum efficiency. P, is the total received signal radiation power, and kT is the thermal excitation energy (k is Boltzmann s constant and T is the detector temperature). For photovoltaic and photo-conductive detectors, the input SNR is generally one-half that given in (7.186) [7.5, 14]. 

P radiated power per unit volume 0 dielectric constant... 

The time or frequency response of the detector, characterized by its time constant r. Many detectors show a frequency response that can be described by the model of a capacitor, which is charged through a resistor R and discharged through R2 (Fig. 4.72a). When a very short light pulse falls onto the detector, its output pulse is smeared out. If the output is a current i(t) that is proportional to the incident radiation power P(0 (as, for example, in photomultipliers), the output capacitance C is charged by this current and shows a voltage rise and fall, determined by... 

For a simple estimate of the sensitivity and its dependence on the detector parameters, such as the heat capacitance and thermal losses, we shall consider the following model [4.99]. Assume that the fraction p of the incident radiation power P is absorbed by a thermal detector with heat capacity H, which is connected to a heat sink at constant temperature (Fig. 4.73a). When G is the thermal conductivity of the link between the detector and the heat sink, the temperature T of the detector under illumination can be obtained from... 

Note The problem is equivalent to the analogous case of charging a capacitor (C H) through a resistor R that discharges through R2 (R2 1/C) (the charging current i corresponds to the radiation power P). The ratio r = H/G H/G RiG) determines the time constant of the device (Fig. 4.73b). 

When the radiation incident on the crystal was horizontally (H) polarized (the E vector oscillating in the plane of k and L) and the angle a was constant, the pattern observed depended on the radiation power P, i.e. on the intensity of the electric field. At low power the transmitted beam was uniform over its transverse cross section, and its divergence was small. As the power was increased, the angular divergence 0 of the beam increased sharply and the beam took on a complex structure rings appeared in the plane of the screen, which was perpendicular to k. They increased in number as the... 

The points on the pattern where the field strength is 70% of the maximum are known as the half-power points, and the angular separation of these points is the beam width. The gain of the antenna is increased by narrowing the beam width to concentrate the radiated power in the desired directions, and the product of the gain and beam width tends to be constant... 

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