Saekwang Nam

Polymer‐Waveguide‐Based Flexible Tactile Sensor Array for Dynamic Response

A polymer-waveguide-based transparent and flexible force sensor array is proposed, which satisfies the principal requirements for a tactile sensor working on curvilinear surfaces, such as thinfilm architecture (thickness < 150 μm), localized force sensing (ca. 0-3 N), multiple-point re cognition (27 points), bending robustness (10.8% degradation at R = 1.5 mm), and fast response (bandwidth > 16 Hz).

A thin film active-lens with translational control for dynamically programmable optical zoom

We demonstrate a thin film active-lens for rapidly and dynamically controllable optical zoom. The active-lens is composed of a convex hemispherical polydimethylsiloxane (PDMS) lens structure working as an aperture and a dielectric elastomer (DE) membrane actuator, which is a combination of a thin DE layer made with PDMS and a compliant electrode pattern using silver-nanowires. The active-lens is capable of dynamically changing focal point of the soft aperture as high as 18.4% through its translational movement in vertical direction responding to electrically induced bulged-up deformation of the DE membrane actuator. Under operation with various sinusoidal voltage signals, the movement responses are fairly consistent with those estimated from numerical simulation. The responses are not only fast, fairly reversible, and highly durable during continuous cyclic operations, but also large enough to impart dynamic focus tunability for optical zoom in microscopic imaging devices with a light-weight and ultra-slim configuration.

Structure modulated electrostatic deformable mirror for focus and geometry control

We suggest a way to electrostatically control deformed geometry of an electrostatic deformable mirror (EDM) based on geometric modulation of a basement. The EDM is composed of a metal coated elastomeric membrane (active mirror) and a polymeric basement with electrode (ground). When an electrical voltage is applied across the components, the active mirror deforms toward the stationary basement responding to electrostatic attraction force in an air gap. Since the differentiated gap distance can induce change in electrostatic force distribution between the active mirror and the basement, the EDMs are capable of controlling deformed geometry of the active mirror with different basement structures (concave, flat, and protrusive). The modulation of the deformed geometry leads to significant change in the range of the focal length of the EDMs. Even under dynamic operations, the EDM shows fairly consistent and large deformation enough to change focal length in a wide frequency range (1~175 Hz). The geometric modulation of the active mirror with dynamic focus tunability can allow the EDM to be an active mirror lens for optical zoom devices as well as an optical component controlling field of view.

An electro-active polymer based lens module for dynamically varying focal system

We demonstrate a polymer-based active-lens module allowing a dynamic focus controllable optical system with a wide tunable range. The active-lens module is composed of parallelized two active-lenses with a convex and a concave shaped hemispherical lens structure, respectively. Under operation with dynamic input voltage signals, each active-lens produces translational movement bi-directionally responding to a hybrid driving force that is a combination of an electro-active response of a thin dielectric elastomer membrane and an electro-static attraction force. Since the proposed active lens module widely modulates a gap-distance between lens-elements, an optical system based on the active-lens module provides widely-variable focusing for selective imaging of objects in arbitrary position.

Highly Flexible and Transparent Skin-like Tactile Sensor

This demonstration shows a highly flexible, transparent, and thin tactile sensor. The sensor detects touch forces at single or multiple points with fast response and high bendability in response to dynamic input force (0–3 N) without any electronic components on sensing areas. The sensor is also capable of sensing pressure on curvilinear soft surface such as human skin without significant performance degradation. The force sensor has potentials to be used in a number of applications for measuring dynamic contact forces on various surfaces.

Thin film display based on polymer waveguides

This paper reports thin, transparent, and soft displays based on polymer waveguides that are compliant with curvilinear interfaces. In order to prove a feasibility of optical waveguide for a flexible display, we suggest the waveguide fabricated by a multi-step lithography process using two photo-curable pre-polymers with different refractive index. The displays are composed of light sources, polymer waveguides, and scatter patterns. The light signal propagating through the waveguides forms images of the scatter patterns by deflecting the light signals to outer surface. The scatter patterns are configured to a seven-segment. The seven-segment design with a switching methodology of the light sources contributes to selectively representing all decimal numbers from 0 to 9 by combination of activated segments. For a large area display based on the proposed methodology, a single light source interconnected to multi-waveguide section is integrated with a QWERTY key pad design. The display shows high transparency and flexibility without visual distortion.

Electrically tunable binary phase Fresnel lens based on a dielectric elastomer actuator

We propose and demonstrate an all-solid-state tunable binary phase Fresnel lens with electrically controllable focal length. The lens is composed of a binary phase Fresnel zone plate, a circular acrylic frame, and a dielectric elastomer (DE) actuator which is made of a thin DE layer and two compliant electrodes using silver nanowires. Under electric potential, the actuator produces in-plane deformation in a radial direction that can compress the Fresnel zones. The electrically-induced deformation compresses the Fresnel zones to be contracted as high as 9.1% and changes the focal length, getting shorter from 20.0 cm to 14.5 cm. The measured change in the focal length of the fabricated lens is consistent with the result estimated from numerical simulation.

Initial Progress Toward a Surface Morphable Tactile Interface

We demonstrate an initial progress prototype toward a surface morphable tactile interface. The surface is composed of thin film type electro-active material (EAP) and its initial shape is maintained to be a flat membrane. Surface of the membrane is designed to be protrusive by electric field. The height of the protrusion and transition speed of the shape change would be controllable by amplitude and frequency of driving signals.