We designed and fabricated microscale lens arrays on a flexible substrate. The flexibility of the substrate allows for wide field of view imaging as well as optical focus scanning. Fresnel zone plates (FZPs), which are compact and lightweight, are used as microlenses for focusing. The arrangement of FZPs on flexible substrate can be reconfigured to maximize FOV. Tunable focus can also be achieved by stretching the FZPs laterally. In addition, the lightweight microlenses can be actuated to scan the focus axially. The lenses have a wide range of applications including displays, contact lenses, microscopy, surveillance and optical communications.
The diameter of the microlenses ranges from 100 to 500 µm. The thickness of the lenses is 100 µm. Unlike refractive and reflective lenses, the focusing capability of FZPs is achieved via diffraction. FZPs consist of alternating black and white zones to modulate the phase of the incident light. The light diffracted from edge of the regions to achieve multiple focus. Most of the energy is diffracted into the first focus. The dark regions are made of silicon nanowires which are highly absorbent for visible spectrum. Standard processes, including wet and dry etching, are used to etch silicon substrate and form nanowires. The white zones are designed for both reflective and transmissive lenses. The lenses are implemented on PDMS as flexible substrate. The silicon nanowires are embedded into PDMS so that the shape of individual lens as well as the arrangement of the array can be reconfigured. In this article, we report our design, fabrication process and experiments.
Optical detection and imaging have wide applications in biomedicine and biological and chemical analyses. With
continuing miniaturization effort to realize integrated microsystems, micro-scale optical components become more and
more important. For any optical system, lenses are critical elements. In this paper, I will present our work on liquid
microlenses. I will first introduce a few types of microlenses and microlens arrays, including tunable liquid microlenses
actuated by temperature-, pH- and infrared light-responsive hydrogels. Then, I will discuss about potential applications
of these lenses in medical instruments. I will describe miniaturized cameras capable of multiple viewpoints, and
prototype flexible endoscopes implementing infrared-light responsive liquid microlenses at their distal ends.
Lab on a chip has found many applications in biological and chemical analysis, including pathogen detections. Because
these labs on chips involve handling of fluids at the microscale, surface tension profoundly affects the behavior and
performance of these systems. Through careful engineering, controlled liquid-liquid or liquid-gas interfaces at the
microscale can be formed and used in many interesting applications. In this talk, I will present our work on applying
such interfaces to microsensing. These interfaces are created at hydrophobic-hydrophilic boundaries formed within
microfluidic channels and pinned by surface tension. We have designed and fabricated a few microsensing techniques
including chemical and biological sensing using dissolvable micromembranes in microchannels, chemical and biological
sensing at liquid crystals interfacing either air or aqueous solutions, and collection of gaseous samples and aerosols
through air-liquid microfludic interfaces. I will next introduce on-chip microlenses and microlens arrays for optical
detection, including smart and adaptive liquid microlenses actuated by stimuli-responsive hydrogels, and liquid
microlenses in situ formed within microfluidic channels via pneumatic control of droplets.
We report an in situ formed tunable liquid microlense array and its applications for enhancing dynamic lab-on-a-chip performance. The de-ionized water microlenses are intrinsically formed via liquid-air interfaces of liquid droplets at T-shaped junctions of octadecyltrichlorosilane(OTS) treated polymerized isobornyl acrylate(poly(IBA)) microchannels., and can be separately tuned in focal lengths by pneumatic manipulation. Via the tunable microlenses, excitation light is dynamically focused onto the fluorescent fluidic sample, thus the fluorescence emission signal for detection is amplified. We have further shown the potential for surface reaction study at microfluidic interfaces by the microlense array.
We present a microfluidic chemical/biological sensor based on dissolvable membranes incorporating gold
nanoparticles. The presence of the target analyte in a fluidic sample being assayed dissolves the membrane,
causing the change in its optical absorption. To enhance the contrast between the membrane and the fluidic sample,
the membranes are chemically treated to exhibit strong absorption at certain wavelengths. Here, we use
N,N'-cystaminebisacrylamide (CBA) cross-linked poly(acrylamide) (PAAm) membranes dissolved by a sample
solution containing dithioerythritol (DTT) to demonstrate this approach. The dissolvable membrane incorporates
gold nanoparticles to exhibit strong absorption at 572nm.
We report on the on-chip integration of a valve and pump for acquiring microfluidic samples and moving them through
micro-channels. The valve employs temperature-sensitive hydrogels which are controlled by micro-heaters. The pump
is a nickel rotor actuated magnetically by an external rotating magnet. The valve is fabricated as a series of hydrogel
rings spaced within microfluidic channels. The expanded state of the hydrogel cylinders at low temperatures blocks
liquid flow. Upon application of heat, the hydrogels contract in volume allowing liquid to flow through them. The
pump brings about a recirculating movement of the liquid within the microchannel due to the rotation of the nickel rotor.
The device is fabricated by combining liquid phase photopolymerization of structural polymers and temperature
responsive hydrogels, with nickel electroplating. The valve has a response time of ~45 s and the pump generates a flow
rate of ~1 μL/min.
Current silicon on-chip inductor have the problems of low quality factors (Q), low self-resonant frequencies, poor electromagnetic isolation and lack of a good radio-frequency (RF) ground plane. To address these issues, we present a new method to fabricate an on-chip copper spiral inductor. The basic structure of the inductor consists of a spiral polysilicon coil suspended over a cavity etched into the silicon substrate. Copper (Cu) is electrolessly deposited onto the polysilicon spiral in order to obtain high conductivity. The formation of the suspended coil is realized by first creating a silicon oxide block embedded in the silicon substrate, then fabricating on the oxide the coil by polysilicon surface micromachining, and in the end removing the embedded oxide by hydrofluoric acid (HF). The benefit of using a suspended spiral structure is two-folded: first, the electrical and magnetic coupling between the inductor and the substrate is reduced dramatically, thus decreasing the substrate loss, and second, by reducing the parasitic capacitance between the inductor and the substrate, the self- resonance of the inductor at an undesirably low frequency can be avoided. The metallized bottom and side-walls of the cavity under the inductor serve both as an electromagnetic shield for isolation and as an RF ground plane. Initial experimental results show that the maximum Q-factor can be as high as 26 for a 2.14 nH inductor. The self-resonant frequency is measured to be 10.3 GHz.
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