Juhun Lim

Two-Axis Electrostatic Gimbaled Mirror Scanner With Self-Aligned Tilted Stationary Combs

We demonstrate an electrostatic two-axis gimbaled mirror scanner with tilted stationary combs (TSCs). We fabricate the scanner using self-aligned micro-assembly to realize angular offsets between stationary and movable comb electrodes. The TSCs enabled quasi-static operation by generating sufficient scanning angles for the slow axis, whereas in-plane comb electrodes provided torsional oscillation at resonance for the fast axis. The proposed self-alignment method can enhance side stability by minimizing lateral shifts of the electrodes during the micro-assembly. We experimentally verify the fabricated mirror scanner in terms of scanning frequencies and scanning angles for finger-vein authentication. The resonant frequencies and optical-scan angles were 263 Hz and 8.5°, respectively, for the slow axis, and 1959 Hz and 24.6°, respectively, for the fast axis. We obtain high-resolution finger-vein images in transmission mode using the mirror scanner and a near infrared laser, which will possibly improve live finger identification by employing the laser Doppler technique.

Ex vivo characterization of age-associated impedance changes of single vascular endothelial cells using micro electrical impedance spectroscopy with a cell trap

We aimed to characterize aging of single vascular endothelial cells, which are indicators of senescence, using micro electrical impedance spectroscopy (μEIS) for the first time. The proposed μEIS was equipped with two barriers under the membrane actuator near the sensing electrodes, increasing its cell-trapping capability and minimizing the interference between the target cell and subsequent cells. The cell-trapping capability in μEIS with barriers was considerably improved (90%) with a capture time of 5 s or less, compared to μEIS without barriers (30%). Cells were extracted from transgenic zebrafish to minimize an initial discrepancy originating from genetic differences. In order to estimate useful parameters, cytoplasm resistance and membrane capacitance were estimated by fitting an electrical equivalent circuit to the data of ex vivo sensor output. The estimated cytoplasm resistance and membrane capacitance in the younger vascular endothelial cells were 20.16 ± 0.79 kΩ and 17.46 ± 0.76 pF, respectively, whereas those in the older cells were 17.81 ± 0.98 kΩ and 20.08 ± 1.38 pF, respectively. Discrimination of each group with different aging showed statistical significance in terms of cytoplasm resistance (p < 0.001) and membrane capacitance (p < 0.001). Considering both of the sensor and cellular level, the optimal frequency was determined as 1 MHz at which the electrical impedance of each group was clearly discriminated (p < 0.001).

Imaging of the Finger Vein and Blood Flow for Anti-Spoofing Authentication Using a Laser and a MEMS Scanner

A new authentication method employing a laser and a scanner is proposed to improve image contrast of the finger vein and to extract blood flow pattern for liveness detection. A micromirror reflects a laser beam and performs a uniform raster scan. Transmissive vein images were obtained, and compared with those of an LED. Blood flow patterns were also obtained based on speckle images in perfusion and occlusion. Curvature ratios of the finger vein and blood flow intensities were found to be nearly constant, regardless of the vein size, which validated the high repeatability of this scheme for identity authentication with anti-spoofing.

An electrostatic two-axis gimbaled mirror scanner with tilted stationary vertical combs fabricated by self-aligned micro-assembly

An electrostatic two-axis gimbaled mirror scanner was demonstrated using tilted stationary vertical combs and self-aligned micro-assembly. Side stability was enhanced and the optical scan angles were 6.8/15.4 degrees on the slow/fast axes, respectively.

A finger-vein imaging and liveness detection for identity authentication using 2-axis MEMS scanner

A novel finger-vein imaging system based on a laser and scanner is proposed to improve identity authentication. Imaging of vein pattern using enhanced-resolution speckle-based blood flow for liveness detection is experimentally demonstrated.