There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Singular Integral Equations. By N.I. Muskhelishvili. Translated fromthe 2nd Russian edition by J.R.M. Radok. Pp. 447. F1. 28.50. 1953. (Noordhoff, Groningen)

Energy harvesting generators are attractive as inexhaustible replacements for batteries in low-power wireless electronic devices and have received increasing research interest in recent years. Ambient motion is one of the main sources of energy for harvesting, and a wide range of motion-powered energy harvesters have been proposed or demonstrated, particularly at the microscale. This paper reviews the principles and state-of-art in motion-driven miniature energy harvesters and discusses trends, suitable applications, and possible future developments.

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Energy Harvesting From Human and Machine Motion for Wireless Electronic Devices

Guided Lamb waves for identification of damage in composite structures: A review

The objective of this study is to model the diagnostic transient waves in an integrated piezoelectric sensor/actuator plate with a view to using it as a first step towards establishing an entire structural health monitoring system and to provide experimental verification of the proposed models. PZT ceramic disks are surface mounted on an aluminum plate acting as both actuators and sensors to generate and collect A0 mode Lamb waves. Mindlin plate theory is adopted to model the propagating waves by taking both transverse shear and rotary inertia effects into account. Actuator and sensor models are both proposed. The interaction between an actuator and the host plate is modeled based on classical lamination theory. The converse piezoelectric effect of the actuator is treated as an equivalent bending moment applied to the host plate. The sensor acts as a capacitor that converts the sensed strain change into a voltage response. An analytical expression for the sensor output voltage in terms of the given input excitation signal is derived, and then experimental work is performed to verify the accuracy of the analytical model. Experimental results show that single-mode Lamb waves in the plate can be successfully generated and collected through the integrated PZT disks. The experiment also shows that the predicted sensor output for both amplitude and phase agrees well with experimentally collected data.

Diagnostic Lamb waves in an integrated piezoelectric sensor/actuator plate - Analytical and experimental studies

This article presents a reverse-time migration technique to image damage by cross-correlating forward and backward propagating wavefields in composite structures using flexural wave signals. First,...

Damage identification for composite structures using a cross-correlation reverse-time migration technique:

A new class of vibrational energy harvester based on Magnetostrictive material (MsM) Metglas 2605SC is deigned,
developed, and tested in building practical energy harvesting wireless sensor networks. Compared to piezoelectric
material, Metglas 2605SC offers advantages including ultra-high energy conversion efficiency, high power density,
longer life cycles without depolarization issue, and flexibility to operate in strong ambient vibrations. To enhance the
energy conversion efficiency and shrink the size of the harvester, Metglas is annealed in the direction normal to the axial
strain direction without the need of electromagnet for applying bias (static) magnetic field. To seamlessly integrate with
a newly developed wireless sensor at NC State 1 , a prototype design for the MsM harvester is proposed. An analytical
model is developed for the harvesting using an equivalent electromechanical circuit. The model resulting in achievable
output performances of the harvester powering a resistive load and charging a capacitive energy storage device,
respectively, is quantitatively derived. An energy harvesting module, which powers a wireless sensor, stores excess
energy in an ultracapacitor is designed on a printed circuit board (PCB) with dimension 25mm x 35mm. The main
functionalities of the circuit include a voltage quadrupler, a 3F ultracapacitor, and a smart regulator. The output DC
voltage from the PCB can be adjusted within 2.0~5.5V. In experiments, the maximum output power and power density
on the resistor can reach 200 mW and 900 mW/cm 3 , respectively. For a working prototype, the average power and power
density during charging the ultracapacitor can achieve 576 mW and 606 mW/cm 3 respectively, which are much higher
than those of most piezo-based harvesters.

Fuh-Gwo Yuan

Papers

Diagnostic Lamb waves in an integrated piezoelectric sensor/actuator plate - Analytical and experimental studies

Damage identification for composite structures using a cross-correlation reverse-time migration technique:

Energy harvesting by magnetostrictive material (MsM) for powering wireless sensors in SHM

A 3D collision avoidance strategy for UAV with physical constraints

Design of novel plug-type triggers for composite square tubes: enhancement of energy-absorption capacity and inducing failure mechanisms