Man Geun Kim

Dynamic Characterization of Human Breast Cancer Cells Using a Piezoresistive Microcantilever

In this paper, frequency response (dynamic compression and recovery) is suggested as a new physical marker to differentiate between breast cancer cells (MCF7) and normal cells (MCF10A). A single cell is placed on the laminated piezoelectric actuator and a piezoresistive microcantilever is placed on the upper surface of the cell at a specified preload displacement (or an equivalent force). The piezoelectric actuator excites the single cell in a sinusoidal fashion and its dynamic deformation is then evaluated from the displacement converted by measuring the voltage output through a piezoresistor in the microcantilever. The microcantilever has a flat contact surface with no sharp tip, making it possible to measure the overall properties of the cell rather than the local properties. These results indicate that the MCF7 cells are more deformable in quasi-static conditions compared with MCF10A cells, consistent with known characteristics. Under conditions of high frequency of over 50 Hz at a 1 μm preload displacement, 1 Hz at a 2 μm preload displacement, and all frequency ranges tested at a 3 μm preload displacement, MCF7 cells showed smaller deformation than MCF10A cells. MCF7 cells have higher absorption than MCF10A cells such that MCF7 cells appear to have higher deformability according to increasing frequency. Moreover, larger preload and higher frequencies are shown to enhance the differences in cell deformability between the MCF7 cells and MCF10A cells, which can be used as a physical marker for differentiating between MCF10A cells and MCF7 cells, even for high-speed screening devices.

Micromachined ultrasonic transducer using piezoelectric PVDF film to measure the mechanical properties of bio cells

We proposed a new method to measure the frequency-dependent attenuation of bio cells using piezoelectric ultrasonic transducer. The polyvinylidene fluoride (PVDF) polymer was employed as piezoelectric material to take an advantage of its low acoustic impedance (2.7 Mrayl) so that the transmission of acoustic power will be improved by impedance matching with that of liquid medium. The thickness of PVDF film is 110 µm and the resonance frequency of the 1st thickness mode is 8.7 MHz. In order to characterize the fabricated ultrasonic transducer, a transducer and an acoustic wave reflector were positioned face to face. The output voltage for reflected transmitted ultrasonic wave was measured with impulse method and was transformed into the Round Trip Insertion Loss (RTIL) where the dominant frequency ranges from 5 MHz to 9 MHz.

A micromirror scanner with vertical combs tilted by assembly process

We have developed a simple assembly technology to realize the tilted vertical combs for electrostatic micromirror scanners. The in-plane vertical comb electrodes are easily transformed into out-of-plane tilted comb by asymmetrical pushing down the levers of the spring that is attached to the micro mirror. The fabricated mirror scanner showed the optical scan angle of up to 1.3deg at 60 V and the resonant frequency of 3.15 kHz.

A micromachined 4-port optical switch with no propagation length difference for add drop modules

We demonstrate a micromachined 4-port optical switch with 4 moving micromirrors. It features no propagation length difference and requires no collimators or planar lightwave circuits for low insertion loss. The optical performances were evaluated using 8 optical fibers (4 input-output pairs) of thermally expanded core (TEC) fibers.

A beam reconfigurable antenna using MEMS switches

A beam reconfigurable antenna based on folded dipole structure has been presented. The antenna can switch beams without the input impedance variation. The front-to-back ratio is measured as approximately 7dB. To implement the antenna, a bi-stable leaf spring MEMS switch is considered.

Glass Reflowed Microlens Array and its Optical Characteristics

We have demonstrated glass microlens array fabricated by thermal reflow process to take advantage of durable lens material and simple process. The microlens was designed using ray tracing, and was realized by controlling the diameter and height of cylindrical glass pattern. The glass pattern (Diameter x Height = 250 x 28 um) was formed by etching a glass plate with HF solution for 4 min (E/R: ~7 um). Then the glass pattern was reflowed at 850degC that is above the glass transition temperature (Tg = 820degC), in the furnace to form a spherical shape. The profile of microlens was measured using a confocal microscopy and the diameter of the spherical shape is larger than 80 percent of the mask pattern size. The fabricated microlens was evaluated in terms of focal length (~600 um) and beam waist (~12 um) using an IR source (lambda=1550 nm).

A Discrete Positioning Microactuator: Linearity Modeling and VOA Application

In this paper, we propose a discrete microactuator that can produce a desirable nonlinear displacement of the digital input. To develop a design algorithm with an arbitrary displacement function, we used curved comb electrodes that were electrically separated for each digital input. The algorithm was used to linearize the variable optical attenuator with a constant increment of 0.5 dB and an attenuation range of 32.6 dB. The experimental linearity was considerably improved down to 4.2% with an insertion loss of 1.1 dB

A MEMS scanner with four orthogonally arranged rotators actuated by electromagnetic force

A torsional optical microscanner was demonstrated with four orthogonally arranged rotators, which offer a unique advantage to amplify a scanning angle through torque arms. The four rotators to oscillate the micromirror were operated by an interaction between input current through the microcoil and external magnetic field. For the fabricated optical scanner with the mirror area of 1.2×1.2mm2, the optical scanning angle was experimentally measured as large as 16° at 54mA and the resonant frequency was 8.55 kHz for the x-axis rotation, respectively.

Laser Doppler Vibrometer Using a 45°-angled Optical Fiber for In-plane Dynamic Measurement of MEMS Actuators

A FOLDV (fiber optic laser doppler vibrometer) using a 45deg-angled optical fiber with a self-aligned micro lens can be used to measure the in-plane dynamic motion of microstructure that does not allow optical access in sidewall direction. This system features a good immunity to external disturbance and easy alignment of optical components during system assembly. The performance of the proposed fiber-based vibrometer is evaluated in terms of signal stability, and compared with other type of LDV.

A discrete positioning microactuator: linearity modeling and VOA application

We proposed a discrete microactuator enabling a desirable nonlinear displacement with respect to digital input. Curved comb electrodes were employed to linearize the attenuation of a variable optical attenuator (VOA) with a constant step of 0.5 dB. The experimental insertion loss (IL) was 1.1 dB and attenuation range was 32.6 dB with 4.2% in linearity.