Biomedical Engineering Reference
In-Depth Information
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FIGURE 17.20
Relative uniformity of bR photoreceptor
responses among all pixels in the 4
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array.
individual pixels. Uniformity is investigated by measuring the photoresponse of each pixel
under identical illumination conditions. Figure 17.20 shows the pixel-to-pixel uniformity of
responsivity within the bR photoreceptor array that is illuminated by a laser beam with a sin-
gle wavelength of 568 nm and power of 2.5 mW. It is found that uniformity of
photoresponsivity between pixels across the array is more than 71% of the average value,
465.25 mV/mW.
17.4.6
Array Performance Under Mechanical Bending
A bR photoreceptor array with a plastic substrate provides the advantage of mechanical
flexibility. However, bending may give rise to some additional problems. Deposition of a
thick bR film using EPS may produce cracks in its surface under excessive bending
conditions. Delamination between electrodes and loss of contact with the bR film are also
possible. A simple experiment is conducted to demonstrate the effect of mechanical bend-
ing on the signal. The photoreceptor array is wrapped around rigid tubes of different
diameters. It is found that the proposed array keeps good photoresponse characteristics
without any cracks and exfoliation, even at the bend radius of 10 mm.
17.5
Application—Motion Detection
17.5.1
Overview of Motion Detection
Motion detection plays an important role in many applications, including autonomous
robot navigation and remote sensing. Conventional hardware implementation employs
progressive-scanned CCD or CMOS sensors for image capture and standard computers to
process the image sequences. It is often difficult or costly to achieve real-time performance
using such a serial architecture because it involves transmitting and processing large
