Contrast sensitivity functions (CSFs) were determined electrophysiologically with the steady-state visual evoked potential (VEP). Psychophysical CSFs obtained by the method of increasing contrasts were also measured concurrently with the VEP trials. The VEP contrast thresholds were obtained using a rapid recording technique in which the contrast of a counterphase sinewave modulated at a temporal frequency of 7.5 Hz was swept from 0.5% to 40% over a period of 22 s in 39 equal logarithmic steps. For this pattern reversal stimulus, the amplitude and phase of the second harmonic response as a function of contrast were measured using a discrete Fourier transform (DFT). Contrast sensitivities at five spatial frequencies ranging from 0.5 to 14.9 cpd were measured. The VEP contrast thresholds were determined by a linear extrapolation to zero amplitude. The contrast threshold obtained by the two methods correlated at 0.816 for 14 subjects. For all five spatial frequencies there were no significant differences between the contrast sensitivities derived from the two methods.
Scanning mirrors can deflect, reflect, and pattern the laser beam. Traditional laser galvanometers rely on deflection motors and mirrors, which are bulky and costly. Micro‐electro‐mechanical systems (MEMS) micromirrors have small size and high integration, but they require long preparation cycles and sophisticated equipment and expensive materials. Polymer scanners prepared by 3D printing technology have the advantages of low cost and rapid preparation, but their reliability needs further study. In this study, a single‐axis electromagnetic scanner was proposed and tested for reliability. The mechanical structure of the scanning mirror is prepared by fused deposition modeling (FDM) using acrylonitrile butadiene styrene (ABS) as material, the radial magnetic field is provided by neodymium magnet set, and laser patterned copper foil serves as the drive coil. The prepared scanner achieved an optical scan angle of 45.2° at a resonant state of 276 Hz. The effect of temperature and humidity on the device reliability is investigated experimentally. Temperature has a significant influence on the resonance frequency and scanning angle of ABS‐based scanner. In addition, the change of relative humidity has less effect on the scanner. The five scanners tested were still working properly after 240 h (more than 2 × 108 cycles) of testing without failures and less than 1.5% frequency drift has been observed.
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