Working in the dark

Professional engineers work as experts who influence the work of others. They rarely have direct contact with the products of an enterprise. They work with analogues such as graphs, algorithms and simulations, and engage in discussions in specialized languages, which develop alongside the technological changes they promote or oppose. The engines of linguistic development are metaphors and analogies, however there is no system for creating them. Some metaphors and analogies become so familiar that they are treated as literal terms or literal explanations and become embedded in engineering language games. The field of electrical engineering offers hosts of examples. Students wishing to practice in engineering will need to become fluent in the language games of the profession. The haphazard evolution of language games offer students little help. As with acquisition of any language, repeated rehearsal is vital and practice in playing specialised language games is a primary part of engineering education

Power Flow Modelling of Dynamic Systems - Introduction to Modern Teaching Tools

As tools for dynamic system modelling both conventional methods such as transfer function or state space representation and modern power flow based methods are available. The latter methods do not depend on energy domain, are able to preserve physical system structures, visualize power conversion or coupling or split, identify power losses or storage, run on conventional software and emphasize the relevance of energy as basic principle of known physical domains. Nevertheless common control structures as well as analysis and design tools may still be applied. Furthermore the generalization of power flow methods as pseudo-power flow provides with a universal tool for any dynamic modelling. The phenomenon of power flow constitutes an up to date education methodology. Thus the paper summarizes fundamentals of selected power flow oriented modelling methods, presents a Bond Graph block library for teaching power oriented modelling as compact menu-driven freeware, introduces selected examples and discusses special features.Comment: 12 pages, 9 figures, 4 table

Strong 4-mode coupling of nanomechanical string resonators

We investigate mechanical mode coupling between the four fundamental flexural modes of two doubly-clamped, high-Q silicon-nitride nanomechanical string resonators. Strong mechanical coupling between the strings is induced by the strain mediated via a shared clamping point, engineered to increase the exchange of oscillatory energy. One of the resonators is controlled dielectrically, which results in strong coupling between its out-of-plane and in-plane flexural modes. We show both, inter-string out-of-plane-in-plane and 3-mode resonance of the four coupled fundamental vibrational modes of a resonator pair, giving rise to a simple and a multimode avoided crossing, respectively.Comment: 5 pages, 4 figure

Hybridizing matter-wave and classical accelerometers

We demonstrate a hybrid accelerometer that benefits from the advantages of both conventional and atomic sensors in terms of bandwidth (DC to 430 Hz) and long term stability. First, the use of a real time correction of the atom interferometer phase by the signal from the classical accelerometer enables to run it at best performances without any isolation platform. Second, a servo-lock of the DC component of the conventional sensor output signal by the atomic one realizes a hybrid sensor. This method paves the way for applications in geophysics and in inertial navigation as it overcomes the main limitation of atomic accelerometers, namely the dead times between consecutive measurements

On the Efficiency of Multi-Source Energy Harvesters

Energy harvesters can be used to provide small amounts of power in remote locations. Applications include powering wireless sensor networks and powering microelectromechanical systems. A wealth of different designs exists for harvesting energy from different sources, including designs which harvest from multiple sources simultaneously. However, there are no universally accepted metrics for assessing the performance of energy harvesters; this can make it impossible to compare designs in any meaningful way. The first part of this thesis develops a domain-neutral framework for describing and analysing the behaviour of energy harvesters. This involves introducing a system of dimensionally consistent analogies into energy harvesting. Using this domain-neutral and dimensionally consistent framework, it is possible to come up with general expressions for the behaviour of single-source energy harvesting systems. This approach is then validated experimentally for single-source energy harvesters. The second part of this thesis involves extending the theoretical analysis to multi-source energy harvesters. Using the system of analogies defined in the first part of the thesis it is possible to create an n-degree-of-freedom matrix representation of a multi-source energy harvester. This enables us to derive expressions which are valid for both single-source and multi-source energy harvesters. The expressions for the maximum power absorbed by an energy harvesting device are shown to be independent of the number of sources, as well as any static coupling or coupling through material effects (e.g. piezoelectric). Numerical simulations are used to explore the validity of these expressions for various system configurations driven with a mixed stochastic-deterministic input signal. From the results of these numerical simulations, a practical approach for estimating the efficiency of an energy harvester using the maximum power absorbed as a theoretical limit is described. The third part of this thesis describes experiments which validate the theoretical analysis. These experiments are used to provide an example of how to calculate and compare the efficiency of energy harvesting designs

Molecular motors: design, mechanism and control

Biological functions in each animal cell depend on coordinated operations of a wide variety of molecular motors. Some of the these motors transport cargo to their respective destinations whereas some others are mobile workshops which synthesize macromolecules while moving on their tracks. Some other motors are designed to function as packers and movers. All these motors require input energy for performing their mechanical works and operate under conditions far from thermodynamic equilibrium. The typical size of these motors and the forces they generate are of the order of nano-meters and pico-Newtons, respectively. They are subjected to random bombardments by the molecules of the surrounding aqueous medium and, therefore, follow noisy trajectories. Because of their small inertia, their movements in the viscous intracellular space exhibits features that are characteristics of hydrodynamics at low Reynold's number. In this article we discuss how theoretical modeling and computer simulations of these machines by physicists are providing insight into their mechanisms which engineers can exploit to design and control artificial nano-motors.Comment: 11 pages, including 8 embedded EPS figures; Invited article, accepted for Publication in "Computing in Science and Engineering" (AIP & IEEE