Henrik C. Pedersen

Characterization of azobenzene chromophores for reversible optical data storage: molecular quantum calculations

Azobenzene chromophores are promising as molecularly engineered materials for reversible optical data storage based on molecular reorientation. In this paper, the optical properties of several different azobenzene chromophores are studied using molecular quantum calculations. Special emphasis is put on molecular anisotropy since a high degree of anisotropy is essential for the storage performance. The trans isomers are all found to be practically one-dimensional whereas the anisotropy of the cis isomers is highly dependent on substituents. Molecular reorientation of chromophores in liquid-crystalline polymers is simulated in order to study the influence of lacking cis anisotropy. It is demonstrated that photoinduced birefringence is significantly reduced in materials characterized by a low degree of cis anisotropy.

Peak-type and dip-type metal-clad waveguide sensing.

Two types of operation for metal-clad waveguide sensors, peak-type and dip-type operation, are described. The newly discovered peak-type operation [Sens. Actuators B 94, 304 (2003)] can be achieved by use of a few-nanometers-thick cladding of a metal with a large imaginary permittivity, whereas conventional dip-type operation is obtained with a metal cladding with small imaginary permittivity some tens of nanometers thick. Both types of operation are described, and the main differences are illustrated.

Measurement of guided light-mode intensity: An alternative waveguide sensing principle

An alternative transduction mechanism for planar optical waveguide sensors is reported. Based on a simple measurement of the mode intensity, the presented transduction is an interesting alternative to the conventional mode-angle transduction, because the expensive, high-precision angular rotation usually employed may be avoided.

Multimode reverse-symmetry waveguide sensor for broad-range refractometry

A sensor design that uses a grating-coupled multimode planar optical waveguide for absolute detection of the refractive indices of liquids or gases is presented. The waveguide consists of a simple 50-microm-thick, free-standing glass plate with air beneath it and the sample to be analyzed on top of it. This design offers a simple alternative to the well-known monomode waveguides, and, owing to its so-called reverse-symmetry configuration, a large detection range can be obtained.

Optimum Design of a Moving Coil Actuator for Fast-Switching Valves in Digital Hydraulic Pumps and Motors

Fast-switching seat valves suitable for digital hydraulic pumps and motors utilize direct electromagnetic actuators, which must exhibit superior transient performance to allow efficient operation of the fluid power pump/motor. A moving coil actuator resulting in a minimum valve switching time is designed for such valves using transient finite-element analysis of the electromagnetic circuit. The valve dynamics are coupled to the fluid restrictive forces, which significantly influence the effective actuator force. Fluid forces are modeled based on transient computational fluid dynamics models. The electromagnetic finite-element model is verified against experimental measurement, and used to design an optimum moving coil actuator for the application considering different voltage-current ratios of the power supply. Results show that the optimum design depends on the supply voltage-current ratio, however, the minimum switching time obtained is nearly independent on this voltage-current ratio. Selecting a suitable power supply based on thermal considerations yields a switching time just above one millisecond for a travel length of 3.5 mm while submerged in oil. The proposed valve has a pressure drop below 0.5 bar at 600 L/min flow rate, enabling efficient operation of digital hydraulic pumps and motors.

Incoherent enhancement of the photorefractive response inBi 12 SiO 20 by subharmonic interaction

A new mechanism for enhancing the photorefractive grating amplitude in Bi(12)SiO(20) is presented. We show experimentally that, by recording two photorefractive running gratings induced by two pairs of mutually incoherent laser beams, it is possible for the two gratings to transfer energy from one to the other. As might be expected, maximum energy transfer is obtained when the phase velocities of the two gratings are equal.

Observation of angularly tilted subharmonic gratings in photorefractive bismuth silicon oxide.

A new subharmonic regime in photorefractive bismuth silicon oxide has been discovered by the use of the running-grating technique. In this regime the subharmonic grating splits into two gratings that are angularly tilted with respect to the fundamental grating. These observations necessitate an extension of previously proposed theories.

Analytical modeling of two beam coupling during grating translation in photorefractive media

We present two analytical methods of solving the coupled wave equations related to two-wave mixing in a photorefractive medium in the case where the illuminating light pattern is rapidly translated with respect to a stationary photorefractive grating. Both methods lead to the same analytical expressions for the intensities of the transmitted beams and for the initial phase of their temporal oscillations. Our analytical expressions cannot, however, confirm earlier numerical and experimental results obtained by Grunnet-Jepsen et al. [Opt. Lett. 22 (1997) 874] regarding the photorefractive phase shift in photorefractive polymers.

Robust Non-Chattering Observer Based Sliding Control Concept for Electro-Hydraulic Drives

Abstract This paper presents an observer-based sliding mode control concept with chattering reduction, generally applicable for position tracking control of electro-hydraulic valve-cylinder drives (VCDs). The proposed control concept requires only common data sheet information and no knowledge on load characteristics. Furthermore the proposed scheme only employ ***piston-and valve spool positions- and pressure feedback, commonly available in industry. The main target is to overcome problems with linear controllers deteriorating performance due to the inherent nonlinear nature of such systems, without requiring extensive knowledge on system parameters nor advanced control theory. In order to accomplish this task, an integral sliding mode controller designed for the control derivative employing state observation is proposed, based on a generalized reduced order model structure of a VCD with unmatched valve flow- and cylinder asymmetries. It is shown that limited attention can be given to bounds on parameter estimates, that chattering is reduced and the number of tuning parameters is reduced to the level seen in conventional PID schemes. Furthermore, simulation results demonstrate a high level of robustness when subjected to strong perturbations in supply pressure and coulomb friction force, and that tracking accuracy may be reduced to the level of noise. Furthermore, the proposed controller tolerates significant noise levels, while still remaining stable and accurate.

Design of energy efficient SMISMO-ELS control strategies

Traditionally mechanical linked meter-in and meterout spool valves are used for velocity control of hydraulic differential cylinders. However with the demand for energy efficient systems the individual meter-in and meter-out valves draws massive attention. This paper propose an energy efficient actuator control and combines this with energy efficient system control. Finally energy neutral performance improvments are suggested for the subjacent actuator in an ELS system.