Mathematical model of bessel beamformer with automatic gain control for smart antenna array system in Rayleigh fading channel

This paper analyzes the mathematical model of a Bessel beamformer with automatic gain control (AGC) in a multipath scenario using a digital modulation technique and makes comparison with the one without AGC. The Bessel beamformer with AGC is designated here as the modified Bessel beamformer. The desired useful and interfering signals operate with the same carrier frequency and Doppler shifts but in different directions. Based on simulation results, this modified Bessel beamformer is shown to provide an optimum solution and to accommodate more users in real‐time base stations of mobile communication system when implemented on smart antenna array systems. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Video-Based Automatic Incident Detection for Smart Roads: The Outdoor Environmental Challenges Regarding False Alarms

Video-based automatic incident detection (AID) systems are increasingly being used in intelligent transportation systems (ITS). Video-based AID is a promising method of incident detection. However, the accuracy of video-based AID is heavily affected by environmental factors such as shadows, snow, rain, and glare. This paper presents a review of the different work done in the literature to detect outdoor environmental factors, namely, static shadows, snow, rain, and glare. Once these environmental conditions are detected, they can be compensated for, and hence, the accuracy of alarms detected by video-based AID systems will be enhanced. Based on the presented review, this paper will highlight potential research directions to address gaps that currently exist in detecting outdoor environmental conditions. This will lead to an overall enhancement in the reliability of video-based AID systems and, hence, pave the road for more usage of these systems in the future. Last, this paper suggests new contributions in the form of new suggested algorithmic ideas to detect environmental factors that affect AID systems accuracy.     

Visual Prosthesis

Electronic visual prostheses have demonstrated the ability to restore a rudimentary sense of vision to blind individuals. This review paper will highlight past and recent progress in this field as well as some technical challenges to further advancement. Retinal implants have now been tested in humans by four independent groups. Optic nerve and cortical implants have been also been evaluated in humans. The first implants have achieved remarkable results, including detection of motion and distinguishing objects from a set. To improve on these results, a number of research groups have performed simulations that predict up to 1000 individual pixels may be needed to restore significant functions such as face recognition and reading. In order to achieve a device that can stimulate the visual system in this many locations, issues of power consumption and electronic packaging must be resolved.     

A Comparison of Two and Three Dimensional Dipole Antennas for an Implantable Retinal Prosthesis

The feasibility is investigated using three dimensional folded dipole antennas as a data-telemetry implantable receiving antenna in a dual-unit retinal prosthesis to restore partial vision to the blind. Three dimensional designs are explored in an effort to enhance certain antenna characteristics such as bandwidth and maximum gain while reducing the planar footprint size in comparison to its two dimensional equivalent. The current vector alignment between the three dimensional layers are examined through folding and rotating the dipole arms with respect to each other to fully optimize the antenna's characteristics. The performance of the 2D and 3D antennas were compared in simulations and further examined by fabricating and characterizing the performance in a transmit/ receive system in air and inside eye phantoms. Results show that three-dimensional antennas can provide larger bandwidth while being physically smaller than the correspondent two-dimensional ones, thus providing larger channel capacity that could lead to a system with an increased number of stimulating electrodes.     

Effects of Boundary Conditions in Laminated Composite Plates Using Higher Order Shear Deformation Theory

This paper extends the applicability of a modified higher order shear deformation theory to accurately determine the in-plane and transverse shear stress distributions in an orthotropic laminated composite plate subjected to different boundary conditions. A simpler, two-dimensional, shear deformable, plate theory accompanied with an appropriate set of through-thickness variations, is used to accurately predict transverse shear stresses. A finite element code was developed based on a higher order shear deformation theory to study the effects of boundary conditions on the behavior of thin-to-thick anisotropic laminated composite plates. The code was verified against three dimensional elasticity results. The study also compared the stresses and deformation results of higher order theory with those obtained using commercial software such as LUSAS, ANSYS and ALGOR. The commercial software are heavily used by designers to design various components/products made of composites. Various combinations of fixed, clamped and simply supported boundary conditions were used to verify a large class of anticipated applications. Results obtained from software are in good agreement for some cases and significantly differ for others. It was found that LUSAS and ANSYS yield better results for transverse deflection and in-plane stresses. But for transverse shear stresses, it is highly dependent on boundary conditions.     

Perceptual thresholds and electrode impedance in three retinal prosthesis subjects.

Three test subjects blind from retinitis pigmentosa were implanted with retinal prostheses as part of a FDA-approved clinical trial. The implant consisted of an extraocular unit that contained electronics for wireless data, power, and generation of stimulus current, and an intraocular unit that consisted of 16 platinum stimulating electrodes arranged in a 4 x 4 pattern within a silicone rubber substrate. The array was held to the retina by a small tack. The stimulator was connected to the array by a multiwire cable and was controlled by a computer based external system that allowed precise control over each electrode. Perception thresholds and electrode impedance were obtained on each electrode from the subjects over several months of testing. The electrode distance from the retina was determined from optical coherence tomography imaging of the array and retina. Across all subjects, average thresholds ranged from 24-702 microA (1-ms pulse). The data show that proximity to the retina played a role in determining the threshold and impedance, but only for electrodes that were greater than 0.5 mm from the retina.     

Electrical stimulation in isolated rabbit retina.

Experiments were conducted to assess the effect of stimulating electrode parameters (size, position, and waveform shape) on electrically elicited ganglion cell action potentials from isolated rabbit retina. Thirty-eight isolated rabbit retinas were stimulated with bipolar stimulating electrodes (either 125 or 25 microm in diameter) positioned on either the ganglion or the photoreceptor side. Recording electrodes were placed between the optic disc and the stimulating electrodes. Cathodic-first, biphasic, current waveforms of varying pulse durations (0.1, 0.5, 1 ms) were used. For the four conditions tested (125-electrode and 25-microm electrode, ganglion cell, and photoreceptor positions) threshold currents ranged from 6.7 to 23.6 microA, depending on location and pulse duration. With 1-ms pulse duration, no statistically significant difference was seen between threshold currents when either size electrode was used to stimulate either the ganglion cell side or the photoreceptor side. For all groups, the threshold currents using the 1-ms pulse were lower than those using 0.1 ms, but the 0.1-ms pulses used less charge. These experiments provide a number of valuable insights into the relative effects of several stimulation parameters critical to the development of an implanted electronic retinal prosthesis.     

The dependence of spectral impedance on disc microelectrode radius

As microelectrodes gain widespread use for electrochemical sensing, biopotential recording, and neural stimulation, it becomes important to understand the dependence of electrochemical impedance on microelectrode size. It has been shown mathematically that a disc electrode, coplanar in an insulating substrate and exposed to a conducting media, exhibits an inhomogeneous current distribution when a potential step is applied. This distribution is known as the primary distribution, and its derivation also yielded an analytic solution for electrical resistance of the conducting media (R(s)), between the disc surface and a distant ground, which is inversely proportional to disk radius [R(s) = 1/(4kappar), where kappa is media conductivity and r is disk radius]. The dependence of spectral impedance on microelectrode radius, however, has not been explored. We verify the analytical solution for resistance using high-frequency (100 kHz) electrochemical impedance data from microelectrodes of varying radius (11-325 microm). For all disc radii, as we approach a lower frequency (--> 10 Hz), we observe a transition from radial to area dependence (e.g., 1/r --> 1/r2). We hypothesize that this transition is driven by the fact that the derivation of the primary distribution ignores concentration gradients, but that these gradients cannot be ignored at lower frequencies.