Surface Plasmon Resonance (SPR) is a wave phenomenon occurring at a metal-dielectric interface. A SPR-based biosensor operates by monitoring changes in the refractive index close to the interface that are produced in response to the interaction between the analyte and the receptors immobilized on the metal’s surface. The performance of these sensors depends on many parameters, including channel geometry, material properties and parameters related to chemical interaction between the analyte and immobilized receptors. This paper presents an integrated model that predicts the sensitivity of an SPR-based sensing platform under the Kretschmann configuration. The model uses the analytical solution of the differential equations that describe the analyte-bioreceptor interaction to correlate changes in analyte concentration to changes in refractive index at the sensing surface. These results are then connected with COMSOL simulations that relate changes in refractive index to changes in the SPR reflectivity curves. The resultant relations are integrated and the model is evaluated under different scenarios. This model will aid in the optimization of assay parameters prior to experimentation for maximum sensitivity; saving both time and expensive chemical reagents during the experimental phase.
In this work we present a novel microfabrication process that is based on combined use of dielectrophoresis (DEP) to
attract particles or cells to electrodes and to follow this step by an electrodeposition of polypyrrole (PPy) to entrap the
particles or cells on electrode surface. This process can be used for mass-production of high surface area structures as
well as to the creation of functionally graded materials. DEP was employed to pull the microparticles toward the surface
of the electrodes and hold them in place while PPy was electrodeposited. Polystyrene microbeads with diameters ranging
from 1 to 10 microns were employed in this study. Experimental results demonstrated that PPy can entrap the particles
attracted to the electrode surface by the positive DEP. It was also demonstrated that hierarchical structures can be created
where smaller microbeads are attached to, caught and secured on the surface of larger microbeads entrapped on the
electrode surface. Furthermore, as DEP can be employed for manipulating of wide variety of polarizable materials, this
process can also entrap inorganic and biological microparticles in the fabricated structure. Applications of this work
include, but are not limited to, the development of biomedical, electrokinetic, and energy storage devices,
electrochemical sensors, and scaffolds.
Residual stress can affect the performance of thin-film micromachined structures and lead to curling in cantilevers as well as distortion in the frequency of resonant devices. As the origin of residual stress is dependent on the fabrication processes, a nondestructive method for characterization of residual stress independent of processes conditions is desirable for supporting the design of microcantilever-based microsystems. In this paper we present a nondestructive characterization of the residual stress within composite microcantilever beams providing valuable insights toward
predicting their deflection profile after mechanical releasing from the substrate. The approach relies on the assumption of a linear gradient stress and a quadratic deflection profile across a composite microcantilever.
Surface Plasmon Resonance (SPR) is a wave phenomenon occurring at an interface between a dielectric and a metal. SPR has applications in label-free biodetection systems, where advances in microfabrication techniques are fostering the development of SPR-based labs-on-a-chip. This work presents a numerical analysis for the excitation of SPR using Kretschmann's configuration. With a SiO2 prism, an Au metal layer, and water as the dielectric, the system is made to be compatible with a post-CMOS microfabrication process. The results obtained from both theory and software simulation show that for a light source at 633 nm, a 50 nm thick Au film is optimal, with the reflectivity falling to a minimum of ~2% at an angle of ~68.5°, due to maximum electromagnetic SPR coupling. Simulations with a Ti adhesion layer were
also performed, showing a negative effect by increasing to ~17% the minimum reflectivity when SPR is achieved, thus reducing the dynamic range of the signal captured by the system's photodetector. SPR biosensors work by monitoring changes on the refractive index close to the SPR interface, these changes were simulated showing that a change of ~10-4 RIU on the dielectric medium produces a ~0.01°change in the SPR angle. These results will facilitate the physical implementation of label-free biosensing platforms with a CMOS image sensor (CIS) photodetection stage.
This work reports the experimental validation of a novel one-dimensional microscanner. The composite cantilever
device implements thermoelastic resonant actuation using temperature gradients induced across two frequency-selective
directions as a strategy to increase operating speed and decrease damping. The device was fabricated using 0.35-μm
CMOS technology and aspect ratio dependent etch modulation. Resonance peaks were measured around 6.4 and 44.7
kHz at atmospheric-pressure conditions; the power sensitivities (2.8 and 1.6 °/W) of the device may compromise its
performance for low-power, large-angle applications. Ultimately, the device is suitable for applications requiring a
variation from low- to high-stability conditions with increasing operating speed.
KEYWORDS: Mirrors, Interfaces, Telecommunications, Microopto electromechanical systems, Systems modeling, Control systems, Actuators, Free space optics, Sensors, C++
To improve productivity and design space exploration in MOEMS design, new high levels specification and validation methodologies are required. These methodologies have to deal with systems heterogeneity. In this paper we present SystemC based cosimulation methodology for the global validation of MOEMS which is starting from a heterogenous specification where the different modules may be described at different abstraction levels or using different specification languages.
KEYWORDS: Mirrors, Single mode fibers, GRIN lenses, Collimators, Free space optics, Signal attenuation, Gaussian beams, Tolerancing, Fiber couplers, Refractive index
One of the main promising applications of micro-machining in All-Optical-Networks (AON) is represented by free-space electro-mechanical Optical Cross Connects (OXCs); free-space components show lower attenuation and lower cross-talk than concurrent technologies based on wave-guides. Although micromachined electro-mechanical OXCs have been recently introduced into the market, further commercialization of devices with increased input/output port-count will certainly require decreasing insertion losses by proper design techniques of both, the electromechanical devices and the system packaging. Among different proposed micromachined architectures, one suitable for small- to medium-size cross-connects id defined by a two-dimensional array of tw-state microreflectors where signal routing occurs in a single plane parallel to the substrate; in this architecture, signals come from and go into Single-Mode Fibers (SMF) collimated by GRIN lenses. This paper discusses different losses mechanisms in micromachined free- space mirror-based OXCs, including both fiber/mirror misalignments on insertion losses. A third section analyzes the effects of imperfect micro-mirrors on insertion losses including finite mirror-size, orientation error, reflectivity and scattering. Finally, conclusions on the required fiber-packaging accuracy and the scalability of micromachined free-space OXCs are presented.
One of the most promising applications of MOEMS in Optical Networks is represented by free-space electro-mechanical Optical Cross-Connects (OXCs); these components show lower attenuation and lower insertion losses than concurrent components based on waveguides. Although some commercial micromachined electro-mechanical OXCs have been recently announced in the market, further deployment of these devices will certainly require decreasing insertion losses by proper design techniques of both, the electromechanical devices and the system packaging. In this document, we study insertion losses in micromachined free-space OXCs and the related packaging challenges; we assume in our discussions Single Mode Fiber (SMF) Cross-Connects using mirrors as beam steering devices. We start with an introduction to micromachined OXCs architectures, actuation mechanisms and collimators. In section 2, we present a study of insertion losses in SMFs links; the coupled effect of lateral and angular fiber misalignments is discussed. In section 3, we discuss insertion losses in OXCs when quarter-pitch GRIN lenses are used as fiber collimators; both sections 2 and 3 are based on Gaussian beam optics. In section 4, we explore the application of Scalar Diffraction Theory to OXC design, this is for calculating insertion losses including diffraction at the mirror plane. Finally, conclusions on insertion losses and the required fiber positioning accuracy are given.
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