Alaeddin S. Abu-Abed

CAPACITIVE INTERDIGITAL SENSOR WITH INHOMOGENEOUS NEMATIC LIQUID CRYSTAL FILM

The performance of capacitive interdigital sensors involved with anisotropic and inhomogeneous nematic liquid crystal (LC) film is investigated. These sensors have potential applications in chemical and biological systems. The theory for modeling the permittivity tensor of the LC film as a function of the molecular orientation is presented. The LC film is handled as inhomogeneous material where molecules are assumed to have different orientations with respect to the frame axes. Under these conditions, fringing field capacitances as functions of the molecular deformations are calculated. Examples of modeled capacitive interdigital sensors in the present of different inhomogeneous distributions of LC films will be studied and discussed.

Capacitive Transduction for Liquid Crystal-Based Sensors, Part I: Ordered System

In this paper, the theory for tracking the average molecular orientation of a liquid crystal (LC) material via capacitive sensing of anisotropic media is presented. The candidate LC sensor structure utilizes interdigital electrodes. Two capacitive measurements in orthogonal direction can track the director axis of nematic LC material in a homogenous ordered LC film. The sensitivity for the sensor at different alignments is studied. The candidate sensors have been fabricated and experimentally verified. Both experimental and calculated values for capacitances of selected interdigital fingers sensor structures are presented.

Capacitive Techniques to Monitor of Anchoring Energy for Liquid Crystal Sensors

Using the orientation order of the liquid crystal molecules in chemical and biological sensors has been widely investigated. In this paper, a capacitive technique to monitor the functionality of anchoring energy in liquid crystal alignment layers is presented. Sensing changes in the anchoring energy of a liquid crystal film can significantly improve sensitivity of liquid crystal based sensors. The method and theory is presented. Preliminary experimental results are provided using UV irradiation and the concentration dependence of cetyltrimethyl-ammonium bromide (CTAB) self-assembled monolayer to alter the anchoring energy of known alignment structures.

Liquid Crystal Sensors with Capacitive Transduction

In this paper, the theory for tracking the average molecular orientation of a liquid crystal material via capacitive sensing of anisotropic media is presented. Tracking the director axis of a nematic liquid crystal material can be achieved by two capacitance measurements. The sensitivity for the sensor at different alignments is studied. Both the experimental and calculated values for fringing capacitances of a selected interdigitated fingers sensor are presented.

Capacitive Transduction for Liquid Crystal Based Sensors, Part II: Partially Disordered System

This paper presents the capacitive transduction technique involved with liquid crystal (LC) based sensors in partially disordered systems. These sensors have the potential applications in chemical and biological systems. The theory for tracking the average molecular deformation (state of alignment) and degree of ordering of anisotropic and partially disordered LC film via capacitive sensing is investigated. This system is modeled using the Q-tensor approach in modeling uniaxial LC material. The proposed sensor design is an interdigitated electrodes structure. Transverse and fringing capacitances as function of the molecular deformation are calculated. It is verified that three capacitance measurements are required to track the average molecular orientation and the degree of disorder in the LC film. The sensitivity for the sensor at different alignments and ordering degree is also studied. Toward practical sensor, neuro-fuzzy system is modeled to simulate the capacitive transduction and to monitor the LC profile. Sensors are fabricated and tested. Both the experimental and calculated capacitances are presented and compared.

Optical waves in partially ordered anisotropic media

This paper investigates light wave propagation in partially ordered birefringent optical media, with focusing on the influence of the degree of molecular ordering on the propagating modes. The double refraction at isotropic/partially ordered interface is also studied, where the impact of the order parameter on the ordinary and extraordinary refracted waves is discussed. This paper also demonstrates the importance of involving the order parameter in studying the total internal reflection (TIR).

Utilizing critical angles in sensing partially ordered liquid crystal profile

This paper investigates a new approach for tracking nematic uniaxial liquid crystal (LC) profile in partially ordered LC based sensors. This approach utilizes measuring critical angles for total internal reflection (TIR) at the interface of optically isotropic and partially ordered LC film. The proposed optical transduction requires measuring of the ordinary critical angle and two extraordinary critical angles in orthogonal directions to report the LC degree of ordering and the director axis orientation.

Enhanced cooperative coding for relay-based MIMO-OFDM systems

In this paper, we propose a 2 × 2 cooperative multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) scheme based on Alamouti space-time coding. In this scheme, the the relay and the destination antennas receive the transmitted symbols from the source during the first stage. Then, both the relay and the destination generate their own decision variables using an Alamouti decoding procedure by the end of the first stage. In the second stage, the relay sends its own decision variables to the destination to enhance the destination decision variables and therefore improves the performance of the system. Our results show the superiority of the proposed cooperative Alamouti scheme by improving the system performance in terms of average BER, frame error rate (FER), and spectral efficiency.

Capacitive Transduction in Partially Disordered Systems: Application to LC-Based Biosensors

Capacitive transduction is investigated for use in a liquid crystal (LC) based sensors with potential applications to biological systems. The theory for tracking the average molecular orientation of a partially disordered liquid crystal film via capacitive transduction in an inhomogeneous, anisotropic media is presented. The sensitivity for the sensor at different alignment is discussed. Both the experimental and calculated values for fringing capacitance of a selected structure are presented.

Coupled surface plasmon resonance sensor with sensitive liquid crystal layer

This paper presents an optical sensor based on the surface plasmon resonance (SPR) phenomenon, involved with liquid crystal (LC) sensitive layer. This sensor has potential applications in chemical and biological systems. We present a tracking method for the state of alignment and degree of ordering of the partially ordered LC film. This can be achieved via the SPR propagation constant and the critical angle at the interface between a metal and an LC film. The proposed idea is also investigated experimentally. For this purpose, we fabricated gold nano-dots array on an optical fiber tip for localized SPR sensing. The spectral position of the maximum loss in the transmission spectra depends on the refractive index of the medium surrounding the sensor fiber tips. This allows for tracking the LC profile parameters.