Radiant input signals

Fig. 3.4 Examples of multiple step signal conversion from input signals to output signals a) all steps of energy conversion are non-radiant (which means that they are matter-based), b) one conversion step makes use of the radiant energy domain...

A sensor is typically a device that transforms signals from the mechanical, thermal, radiant, chemical, or magnetic domain to the electrical domain. A single sensor may be based on crosseffects between different signal domains to achieve the signal transformation to the electrical domain to be read by a human or an electronic instrument. These cross-effects are shown in Table 1, where the input signal domains are on the left-hand side, and the output signal domains are at the top (Meijer 2008). 

The basic function of a detector is to convert radiant input to an output signal of some convenient type. For our purposes, that output is always electrical - either a current or a voltage. The responsivity TL is the ratio between the output signal and the radiant input (see Figure 1.6). 

Typical detectivity values as a function of wavelength for PbS photoconductive and various photovoltaic detectors. is a figure of merit defined as A /NEP, where A is the detector area and NEP is the noise-equivalent power, the rms radiant power in watts of a sinusoidally modulated input incident on the detector that gives rise to an rms signal equal to the rms dark noise in a 1-Hz bandwidth. Data from Hughes Aircraft Company. 

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