Tuning of a shunted electromagnetic vibration absorber based on the maximisation of the electrical power dissipated

This paper investigates a local tuning approach for a shunted electromagnetic vibration absorber, which is based on the maximisation of the electrical power dissipated by the coil and shunt components. The study considers a simplified problem with a single-degree-of-freedom mechanical hosting system, which is excited by a white noise stochastic force. The hosting system is equipped with a coil-magnet seismic transducer, which is connected to a resistive-inductive shunt. The study examines the effectiveness of the shunted electromagnetic vibration absorber with respect to the following cost functions. Firstly, the reference cost function, which is based on the minimisation of the time-averaged kinetic energy of the hosting system. Secondly, the local cost functions, which are based on: the maximisation of the time-averaged vibration power absorbed by the shunted electromagnetic vibration absorber; the maximisation of the time-averaged mechanical power dissipated by the electromagnetic transducer and the maximisation of the time-averaged electrical power dissipated by the coil and the shunt. The study shows that, provided the transducer is lightly damped, the local cost function based on the maximisation of the electrical power dissipated by the coil and the shunt gives the same optimal tuning parameters than the reference cost function. Therefore, provided the electromagnetic transducer is properly designed, the shunt can be suitably tuned by maximising the time-averaged electrical power dissipated by the coil and shunt. This is a rather appealing practical solution since it can be implemented locally without the need of measuring the response of the hosting system and also it can be implemented in the shunt circuit without the need of extra sensors.

Expedited Globalized Antenna Optimization by Principal Components and Variable-Fidelity EM Simulations: Application to Microstrip Antenna Design

Parameter optimization, also referred to as design closure, is imperative in the development of modern antennas. Theoretical considerations along with rough dimension adjustment through supervised parameter sweeping can only yield initial designs that need to be further tuned to boost the antenna performance. The major challenges include handling of multi-dimensional parameter spaces while accounting for several objectives and constraints. Due to complexity of modern antenna topologies, parameter interactions are often involved, leading to multiple local optima as well as difficulties in identifying decent initial designs that can be improved using local procedures. In such cases, global search is required, which is an expensive endeavor, especially if full-wave electromagnetic (EM) analysis is employed for antenna evaluation. This paper proposes a novel technique accommodating the search space exploration using local kriging surrogates and local improvement by means of trust-region gradient search. Computational efficiency of the process is achieved by constructing the metamodels over appropriately defined affine subspaces and incorporation of coarse-mesh EM simulations at the exploratory stages of the optimization process. The resulting framework enables nearly global search capabilities at the costs comparable to conventional gradient-based local optimization. This is demonstrated using two antenna examples and comparative studies involving multiple-start local tuning.

Multiphysics simulations of adaptive metasurfaces at the meta-atom length scale

Adaptive metasurfaces (MSs) provide immense control over the phase, amplitude and propagation direction of electromagnetic waves. Adopting phase-change materials (PCMs) as an adaptive medium allows us to tune functionality of MSs at the meta-atom length scale providing full control over MS (re-)programmability. Recent experimental progress in the local switching of PCM-based MSs promises to revolutionize adaptive photonics. Novel possibilities open new challenges, one of which is a necessity to understand and be able to predict the phase transition behavior at the sub-micrometer scale. A meta-atom can be switched by a local deposition of heat using optical or electrical pulses. The deposited energy is strongly inhomogeneous and the resulting phase transition is spatially non-uniform. The drastic change of the material properties during the phase transition leads to time-dependent changes in the absorption rate and heat conduction near the meta-atom. These necessitate a self-consistent treatment of electromagnetic, thermal and phase transition processes. Here, a self-consistent multiphysics description of an optically induced phase transition in MSs is reported. The developed model is used to analyze local tuning of a perfect absorber. A detailed understanding of the phase transition at the meta-atom length scale will enable a purposeful design of programmable adaptive MSs.

Differentiation of neural-type cells on multi-scale ordered collagen-silica bionanocomposites

Cells respond to biophysical and biochemical signals. We developed a composite filament from collagen and silica particles which combines scaffolding and signaling. We show that local tuning of collagen organization enhances cell differentiation.

A second-order output spectrum based method for detecting bolt-loosening fault in a satellite-like structure

Bolt-loosening faults frequently exist in industrial engineering structures since these bolted structures are often subjected to vibrations or the like in their service process. In this paper, a novel method based on the second-order output spectrum (SOOS) is proposed to detect potential bolt-loosening faults in a complex satellite-like structure. In this method, a general multi-degree-of-freedom (MDOF) model simulating bolt-loosening faults induced non-linearities and inherent boundary or material non-linearities by non-linear forces is built to describe the non-linear behaviour of the structure, and then a local damage indicator is derived for bolt-loosening fault detection through a local tuning approach (LTA) which tunes local structural properties. Results of experimental cases demonstrate that the state of bolted joint in the satellite-like structure with inherent non-linearities can be estimated by this novel SOOS based method effectively and reliably.