Seunghwan Moon

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.

A gimbal-less two-axis electrostatic scanner with tilted stationary vertical combs and serially connected springs via a microassembly process

We propose a gimbal-less two-axis electrostatic microelectromechanical system (MEMS) scanner with tilted stationary vertical combs (TSVCs) fabricated via a microassembly process. The gimbal-less two-axis scanner has the advantage of being of a compact size and also does not need any additional fabrication sequence for electrical isolation. The TSVCs and coupled springs (T-shaped springs and folded springs) allow the mirror scanner to rotate around two axes with a large scanning angle. The fabrication steps for the proposed scanner can be remarkably reduced by employing a microassembly process, as there is no need to conduct a multistep etching process for height offset between two vertical combs. It was found that the width of the folded spring and the T-shaped spring dominated the resonant frequency of the fast axis and the slow axis, respectively. By modeling the capacitance change of TSVCs with respect to the rotational angle (θ), the effective tilted angle (ETA), as a new design criterion, was introduced to determine an adequate operation range. The optical scanning angle of the fabricated scanner was up to 7.8° at 90 V for the slow axis in quasistatic mode and up to 17.3° at 100 V for the fast axis in resonant mode at 2.84 kHz. The fabricated scanner can be used for various endoscopic optical applications.

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.

Contact resistance of micromachined electrical switches incorporating a chevron-type bi-stable spring

Micromachined electrical switches with bi-stable springs, which can stay at one of the two stable states without consuming energy, are proposed. Cascaded bent beams are incorporated as thermoelastic microactuators and are characterized through a coupled electro-thermo-mechanical analysis using ANSYS. For improved electrical switch performance, the contact resistances should be kept as low as possible. Therefore, the shape of the contact head needs to be optimized, though to date there have been few studies pertaining to the contact heads of electrical switches reported, except for a flat contact shape. In this paper, the effects of contact angle on the electrical resistance are investigated for contact angles of 30°, 45°, and 60°. It is subsequently observed that the contact resistance decreases with the contact angle due to a greater normal contact force; the minimum contact resistance is 0.22 Ω at a contact angle of 60°. The contact resistance shows negligible change during repeated ON/OFF switching operations.

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.

In-plane microneedle chip fabricated by crystalline wet etching of (110) silicon wafer

In this research, simple crystalline wet etching of (110) silicon is employed to fabricate an in-plane silicon microneedle chip, which is composed of microneedle tips, microchannels and reservoir. The required penetration forces to insert the fabricated microneedles into the skin of chicken breast flesh without failure were 70 mN (500 µm in displacement) and 250 mN (2 mm in displacement) for a single tip and five tips, respectively.

Gimbal-Less Two-Axis Electromagnetic Microscanner with Twist Mechanism

We present an electromagnetically driven microscanner based on a gimbal-less twist mechanism. In contrast to conventional microscanners using a gimbal-less leverage mechanism, our device utilizes a gimbal-less twist mechanism to increase the scan angle in optical applications requiring a large scanning mirror. The proposed gimbal-less scanner with twist mechanism increases the scan angle by 1.55 and 1.97 times for the slow and fast axes, respectively, under the same force; 3.64 and 1.97 times for the slow and fast axes, respectively, under the same maximum stress, compared to the gimbal-less leverage mechanism. The scanner with a 3-mm-diameter mirror and a current path composed of a single-turn coil was fabricated, and it showed the maximum scan angle of 5° (quasi-static) and 22° (resonant) for the slow and fast axes, respectively. The experimentally estimated crosstalk was as small as 0.47% and 0.97% for the fast and slow axes affected by the other axes, respectively, which was determined using a newly employed methodology based on fast Fourier transform.

Feasibility study of the OCT probe using MEMS optical scanner array for high speed inspection

We developed a microscanner-based optical coherence tomography probe for the 3-dimensional inspection of display panels, which will be extended to arrayed scanners to enhance inspection speed. The scanning range and beam diameter were 13.1 mm and 84.5 μm, respectively.

Two-axis quasistatic gimbal-less microscanner with concentrically tilted stationary comb electrodes

Two-axis quasistatic gimbal-less microscanners were fabricated through the microassembly of a glass lid and stationary comb electrodes. The total optical scan angles were enlarged to 5.2° and 5.8° for horizontal and vertical scan axes, respectively.

An electromagnetic two-axis micro scanner with dual radial magnetic fields

An electromagnetic scanner with dual radial magnetic fields was developed to enlarge torque in both horizontal and vertical scans. Scan angles were 50.55° and 9.06° for horizontal and vertical scans, respectively, for single current path.