Wavelet packet based channel equalization

Recently, considerable amount of attention is being given to the field of wavelets and wavelet packets. It has found numerous applications in signal representation, image compression and applied mathematics. In this paper, we present a channel equalization method based on wavelet packets. The proposed equalizer structure is based on the fact that for sufficiently narrowband sequences, a non-ideal channel can be modelled as an attenuation and delay. If the data sequence is used to modulate a set of narrowband wavelet packets, then no equalization is required at the receiver end. The equalization problem reduces to that of determining the delay introduced by the channel for each of the wavelet packets. A minimum square variance algorithm for adaptively choosing the delay has been proposed. This algorithm has been shown to perform as desired analytically in a simple delay channel case. Simulations have been used to study its performance in the non-ideal channel’s case and the results corroborate theoretical predictions.     

Microchemomechanical Systems

The development of microchemomechanical systems (MCMS) as an analogy to microelectromechanical systems (MEMS) is reviewed, with the distinction that the mechanical actuation of microscale structures is effected by chemical cues as opposed to electricity. The intellectual motivation to pursue MCMS, or the creation of integrated chemical‐stimuli‐responsive devices, is that such structures are widely observed in nature. From a practical standpoint, since chemicals can readily diffuse and produce changes over large distances, this approach is especially attractive in enabling wireless and autonomous devices at small size scales.     

Voltage-gated ion transport through semiconducting conical nanopores formed by metal nanoparticle-assisted plasma etching

Nanopores with conical geometries have been found to rectify ionic current in electrolytes. While nanopores in semiconducting membranes are known to modulate ionic transport through gated modification of pore surface charge, the fabrication of conical nanopores in silicon (Si) has proven challenging. Here, we report the discovery that gold (Au) nanoparticle (NP)-assisted plasma etching results in the formation of conical etch profiles in Si. These conical profiles result due to enhanced Si etch rates in the vicinity of the Au NPs. We show that this process provides a convenient and versatile means to fabricate conical nanopores in Si membranes and crystals with variable pore-diameters and cone-angles. We investigated ionic transport through these pores and observed that rectification ratios could be enhanced by a factor of over 100 by voltage gating alone, and that these pores could function as ionic switches with high on-off ratios of approximately 260. Further, we demonstrate voltage gated control over protein transport, which is of importance in lab-on-a-chip devices and biomolecular separations.     

Photolithographically patterned smart hydrogel based bilayer actuators

We describe the fabrication of photopatterned actuators, composed of stimuli-responsive hydrogel bilayers made from N-isopropyl-acrylamide (NIPAm), acrylic acid (AAc), and poly-ethylene oxide diacrylate (PEODA). The hydrogels were deposited by spin coating and casting and were patterned by non-contact photolithography. We investigated the swelling behavior of the individual photopatterned hydrogels in aqueous solutions of varying pH and ionic strength (IS). By combining materials with optimal swelling responses, bilayer structures were triggered via changes in pH and IS to actuate into three dimensional (3D) structures. We also used these hydrogel bilayers as hinges to actuate integrated structures composed of rigid polymeric SU-8 panels, patterned to resemble the shape of a Venus Flytrap. This system provides a straightforward way to design and fabricate actuator hinges composed entirely of polymers.