Mehdi Shadaram

Ferrocenylenesilylene Polymers as Coatings for Tapered Optical-Fiber Gas Sensors

In this paper we report the use of ferrocenylenesilylene polymers as coatings for tapered optical-fiber sensors. The principle of operation of this device is based upon environmentally induced changes in the refractive index of the polymer layer which change the power transmitted through the tapered fiber. The results for two sensor arrays fabricated using the ferrocenylenesilylene polymer [(η5-C5H4)Fe(η5-C5H4)MePhSi]m and copolymer {[(η5-C5H4)Fe(η5-C5H4)SiPhMe]n[(η5-C5H4)Fe(η5-C5H4)Me2Si]m are presented. We also show that the sensitivity of this device is a function of the taper beat length.

Probe beam deflection technique as acoustic emission directionality sensor with photoacoustic emission source.

The goal of this paper is to demonstrate the unique capability of measuring the vector or angular information of propagating acoustic waves using an optical sensor. Acoustic waves were generated using photoacoustic interaction and detected by the probe beam deflection technique. Experiments and simulations were performed to study the interaction of acoustic emissions with an optical sensor in a coupling medium. The simulated results predict the probe beam and wavefront interaction and produced simulated signals that are verified by experiment.

Characterization of pressure transients generated by nanosecond electrical pulse (nsEP) exposure

The mechanism(s) responsible for the breakdown (nanoporation) of cell plasma membranes after nanosecond pulse (nsEP) exposure remains poorly understood. Current theories focus exclusively on the electrical field, citing electrostriction, water dipole alignment and/or electrodeformation as the primary mechanisms for pore formation. However, the delivery of a high-voltage nsEP to cells by tungsten electrodes creates a multitude of biophysical phenomena, including electrohydraulic cavitation, electrochemical interactions, thermoelastic expansion, and others. To date, very limited research has investigated non-electric phenomena occurring during nsEP exposures and their potential effect on cell nanoporation. Of primary interest is the production of acoustic shock waves during nsEP exposure, as it is known that acoustic shock waves can cause membrane poration (sonoporation). Based on these observations, our group characterized the acoustic pressure transients generated by nsEP and determined if such transients played any role in nanoporation. In this paper, we show that nsEP exposures, equivalent to those used in cellular studies, are capable of generating high-frequency (2.5 MHz), high-intensity (>13 kPa) pressure transients. Using confocal microscopy to measure cell uptake of YO-PRO®-1 (indicator of nanoporation of the plasma membrane) and changing the electrode geometry, we determined that acoustic waves alone are not responsible for poration of the membrane.

Modeling and performance evaluation of ferrocene-based polymer clad tapered optical fiber gas sensors

The possibility of utilizing certain polymers, known as variable-index materials, as cladding in tapered optical fibers for gas sensing is explored. We have shown that any small variation in the refractive index of the cladding of a tapered single-mode fiber has a direct influence on the transmission characteristic of the tapered region. A 4% deviation in the refractive index of a certain polymer is obtained upon the exposure of the polymer to ammonia. Sensitivity, repeatability, and selectivity of several fabricated sensors are also illustrated.

Phase and amplitude stability of broadband analog fiber optic links

The phase and amplitude stability of directly and externally modulated analog fiber optic links are investigated and factors which limit link stability are discussed. Link gain, phase noise, and phase delay fluctuation measurements have been performed on fiber-optic links which are currently being considered for Navy shipboard antenna remoting and phased array antenna applications. Measurements indicate that good amplitude and adequate phase stability can be obtained using either directly or externally modulated analog photonic links provided certain design considerations are met.

Flexible Spectrum and Power Allocation for OFDM Unlicensed Wireless Systems

Future generations of communication systems will benefit from cognitive radio technology, which significantly improves the efficient usage of the finite radio spectrum resource. In this paper we present a wireless unlicensed system that successfully coexists with the licensed systems in the same spectrum range. The proposed unlicensed system determines the level of signals and noise in each frequency band and properly adjusts the spectrum and power allocations subject to rate constraints. It employs orthogonal frequency-division multiplexing (OFDM) modulation and distributes each transmitted bit energy over all the bands using a novel concept of bit spectrum patterns. A distributed optimization problem is formulated as a dynamic selection of spectrum patterns and power allocations that are better suited to the available spectrum range without degrading the licensed system performance. Bit spectrum patterns are designed based on a normalized gradient approach and the transmission powers are minimized for a predefined quality of service (QoS). At the optimal equilibrium point, the receiver that employs a conventional correlation operation with the replica of the transmitted signal will have the same efficiency as the minimum mean-squared error (MMSE) receiver in the presence of noise and licensed systems. Additionally, the proposed approach maximizes the unlicensed system capacity for the optimal spectrum and power allocations. The performance of the proposed algorithm is verified through simulations.

TECHNIQUE FOR STABILIZING THE PHASE OF THE REFERENCE SIGNALS IN ANALOG FIBER-OPTIC LINKS

The effects of temperature and longitudinal stress on the phase delay of reference signals in a fiber-optic link are discussed. A feedback system that uses a fiber-optic phase modulator is used to compensate for the phase fluctuations of a reference signal in the link. The phase deviations of a 50-MHz reference frequency that are caused by temperature variations of the link is reduced by more than 95% on optimization of the correction system. The advantages of this technique are that the fiber-optic phase modulator has a greater stability compared with the electronic phase modulators, and signal conversions from electric to optic and optic to electric are avoided.

Cross-entropy Histogram Equalization

This paper introduces a novel cross-entropy Histogram Equalization method. The new algorithm is based on separating the density spectrum of an image and then minimizing the so-called Cross-Entropy between the brightness and darkness components. Cross-entropy is used to measure the information-theoretic distance between the images brightness and darkness. Experimental results show that the cross-entropy histogram equalization method has better performance than Bi-histogram equalization and its modified weighted form.

An innovative Fiber Bragg Grating sensor capable of fault detection in radial power systems

In this paper, a fiber optic based sensor capable of fault detection in power systems is presented. This sensor uses Bragg wavelength shift to measure current in power systems. Magnetic fields generated by currents in power transmission lines cause a strain in magnetostrictive material which is then detected by Fiber Bragg Grating (FBG). Interrogators sense the reflected FBG signals, and the Bragg wavelength shift is calculated. It is shown that the faults in the systems cause a detectable wavelength shift on the Fiber Bragg Grating.

Cost effective portable system for sign language gesture recognition

This paper presents a standalone system that converts static gestures into voice. It is also known as GesTALK. The primary input device is the self design and cost effective Data Glove. It operates in two basic modes. In first mode the system speaks a single alphabet for a static gestures made by the user, while in second mode the system speaks complete string by concatenating words. Various gestures of alphabets are made to spell out the words involved in string. This system has been shown to work for both American Sign Language (ASL) and Pakistan Sign Language (PSL) and other language models. Results show that the system recognizes 24 out of 26 letters; an overall accuracy of 90% is achieved.