Fabrication and characterization of PDMS microlenses based on elastomeric molding technology

On-Demand Dynamic Terahertz Polarization Manipulation Based on Pneumatically Actuated Metamaterial

In this paper, a new tuning strategy is proposed by incorporating a pneumatically actuated metamaterial to achieve on-demand polarization manipulation at THz frequencies. Through controlling the actuation pressure, the device function can be flexibly switched among three types of polarization conversion capabilities within the same operation frequency band, from 1.3 THz to 1.5 THz, in which the mutual conversion between linear polarization and circular polarization, such as a quarter-wave plate, and handedness inversion between circular polarizations as a helicity inverter as well as a helicity keeper, have been successfully achieved between the incidence and reflection. Moreover, the intrinsic tuning mechanism for the polarization manipulation is also discussed.

A microfluidically controlled concave-convex membrane lens using an addressing operation system

Electrical control toolkits for microlens arrays are available to some extent, but for applications in environments with strong electromagnetic fields, radiation, or deep water, non-electrical actuation and control strategies are more appropriate. An integrated digital microfluidic zoom actuating unit with a logic addressing unit for a built-in membrane lens array, e.g., a flexible bionic compound eye, is developed and studied in this article. A concave-convex membrane fluidic microvalve, which is the component element of the logic gate, actuator, and microlens, is proposed to replace the traditional solenoid valve. The functions of pressure regulation and decoding can be obtained by incorporating microvalves into fluidic networks according to equivalent circuit designs. The zoom actuating unit contains a pressure regulator to adjust the focal length of lenses with three levels, and the logic addressing unit contains a decoder to choose a typical lens from a hexagonal lens array. The microfluidic chip control system is connected flexibly to the actuating part, a membrane lens array. It is shown from a simulation and experimental demonstration that the designed and fabricated system, which is composed of a whole microfluidic zoom unit, addressing technology, and a microlens array, works well. Because these components are constructed in the same fabrication process and operate with the same work media and driving source, the system can be made highly compatible and lightweight for applications such as human-machine interfaces and soft robots.

Simple yet universal fabrication strategy for a focused photoacoustic transmitter

Aiming to address existing technical challenges and explore a simple yet effective and universal solution for making a polydimethylsiloxane (PDMS)-based focused photoacoustic transmitter, a novel fabrication strategy is proposed. Different from the traditional technical route based on direct photoacoustic layer coating on a rigid concave substrate, it works by utilizing an elastomeric molding process, through which the originally flat photoacoustic conversion layer, consisting of PDMS-candle soot nanoparticles/PDMS-PDMS composite, is transformed into a concave contour with controllable radius of curvature and finally merged into a soft PDMS substrate. For proof-of-concept demonstration, two types of focused photoacoustic transmitters (6.3 mm and 8 mm focal lengths) operating at 5.3 MHz with -6  dB bandwidth of 134% are successfully fabricated, showing both distinct acoustic focusing capability and high energy conversion efficiency. Moreover, different from conventional focused counterparts, acoustic signals with nearly symmetric bi-polar waveform can be obtained at the focuses, facilitating ultrasound cavitation-based applications.

2D to 3D convertible terahertz chiral metamaterial with integrated pneumatic actuator

Aiming to achieve real 3D chiral metamaterial structure, a new strategy is proposed. During which a 2D to 3D conversion mechanism based on integrated pneumatic actuator is used to provide a relatively simple yet effective process solution. With this concept, only the lithography-based planar process is required, and a symmetric tuning capability over the shape of the 3D chiral metamaterial as well as its chirality both can be achieved through controlling the applied pressure. At the same time, the resultant optical activity and circular dichroism associated with this tunable 3D chiral metamaterial are also studied and exciting characteristics demonstrating enantiomeric symmetry have been successfully obtained as well.

Two distinct mechanisms upon absorption of volatile organic compounds into siloxane polymers

The response of polysiloxane materials to volatile organic compounds (VOCs) including benzene, toluene, ethylbenzene, and toluene (BTEX), as well as cyclohexane, acetone, methanol and isopropanol is studied using thin film large-angle refractometry. Refractive index and thickness changes are measured to quantify the diffusion rate and partition coefficients associated with the absorption and desorption of VOC vapours into polydimethylsiloxane (PDMS) and polydiphenylsiloxane (PDPS) - PDMS copolymer films. Absorption of volatile solvent vapours into siloxane polymers is found to follow two distinct mechanisms with different absorption rates. These mechanisms are also associated with different excess volumes of mixing and may be accompanied by a polymer restructuring step.

Patterned paper as a low-cost, flexible substrate for rapid prototyping of PDMS microdevices via "liquid molding"

This report describes the use of patterned paper as a low-cost, flexible substrate for rapidly prototyping PDMS microdevices via "liquid molding". The entire fabrication process consists simply of three steps: (1) fabrication of patterned paper in NC membrane by direct wax printing (or modified wax printing that we call "transfer wax printing"); (2) formation of liquid mold on wax-patterned NC membrane; (3) PDMS molding and curing on wax-patterned NC membrane anchored with liquid micropatterns. All these procedures can be finished within only 1.5 h without the use of a photomask, photoresist, UV lamp, etc. Through the use of wax-patterned NC membrane coupled with a liquid mold as a template, different PDMS microdevices such as microwells and microchannels have been fabricated to demonstrate the usefulness of the method for PDMS microfabrication. The height of microwells and microchannels can also be tailored flexibly by adjusting the liquid filling volume. This method for prototyping PDMS microdevices has some favorable merits including simple operation procedures, fast concept-to-device time, and low cost, indicating its potential for simple PDMS microdevice fabrication and applications.