In this paper, the possibility of using the static charge that accumulates on aircraft during flight as a source to power monitoring sensors is examined. The assessed methods include using a pair of materials with different air-flow charging rates, contact discharging of the fuselage to neutral metallic bodies, charge motion induction by the fuselage field and inductive harvesting of fuselage-to-air corona discharges at static discharge wicks. The installation and potential advantages of each method are discussed. The feasibility of directly charging a storage capacitor from accumulated static charge is studied experimentally, demonstrating a voltage of 25V on a 25nF capacitor.
Aircraft sensors are typically cable powered, imposing a significant weight overhead. The exploitation of temperature variations during flight by a phase change material (PCM) based heat storage thermoelectric energy harvester, as an alternative power source in aeronautical applications, has recently been flight tested. In this work, a scaled-down and a scaled-up prototype are presented. Output energy of 4.1 J per gram of PCM from a typical flight cycle is demonstrated for the scaled-down device, and 3.2 J per gram of PCM for the scaled-up device. The observed performance improvement with scaling down is attributed to the reduction in temperature inhomogeneity inside the PCM. As an application demonstrator for dynamic thermoelectric harvesting devices, the output of a thermoelectric module is used to directly power a microcontroller for the generation of a pulse width modulation signal.
Energy harvesting - the collection of otherwise unexploited energy in the local environment - is attracting increasing
attention for the powering of electronic devices. While the power levels that can be reached are typically modest
(microwatts to milliwatts), the key motivation is to avoid the need for battery replacement or recharging in portable or
inaccessible devices. Wireless sensor networks are a particularly important application: the availability of essentially
maintenance free sensor nodes, as enabled by energy harvesting, will greatly increase the feasibility of large scale
networks, in the paradigm often known as pervasive sensing. Such pervasive sensing networks, used to monitor
buildings, structures, outdoor environments or the human body, offer significant benefits for large scale energy
efficiency, health and safety, and many other areas. Sources of energy for harvesting include light, temperature
differences, and ambient motion, and a wide range of miniature energy harvesters based on these sources have been
proposed or demonstrated. This paper reviews the principles and practice in miniature energy harvesters, and discusses
trends, suitable applications, and possible future developments.
Multi-project-wafer (MPW) services provide an economical route for prototyping of new electronic circuit designs.
However, addition of MEMS functionality to MPW circuits by post-processing (also known as MEMS-last processing) is
difficult and inefficient because MPW typically yields individual dies. One solution to this problem is to embed the
MPW dies in a carrier wafer prior to MEMS processing. We have developed a process which allows 300 μm-thick
CMOS dies to be embedded in a BSOI (bonded silicon-on-insulator) carrier prior to low-temperature processing for
integration of metal MEMS. Deep reactive ion etching (DRIE) with an STS Multiplex ICP etcher is used to form
cavities in the device layer of a BSOI wafer. By adjusting the passivation and etching cycles, the DRIE process has been
optimized to produce near-vertical sidewalls when stopping on the buried oxide layer. The cavity sizes are closely
matched to the die dimensions to ensure placement of the dies to within ±15 μm. Dies are placed in all the cavities, and
then a photoresist layer is deposited by spin-coating and patterned to provide access to the required IC contact pads. The
photoresist has the dual role of securing the dies and also planarizing the top surface of the carrier. After an appropriate
baking cycle this layer provides a suitable base for multi-level electroplating or other low-temperature MEMS
Rotation of structures fabricated by planar processing into out-of-plane orientations can be used to greatly increase
the 3-dimensionality of microstructures. Previously this has been achieved by a self-assembly process based on surface
tension in meltable hinges. An important application is in fabricating vertical inductors on silicon, to reduce the substrate
coupling and thus increase quality factor and self-resonance frequency. Previous processes have used copper tracks, and
Pb-Sn hinges. However, the use of Cu limits potential applications because of oxidation, since the final structure is not
embedded. Moreover, a substitute hinge material is also required, as a result of legislative restrictions on Pb use. In this
paper, Au is used as an alternative to Cu for the fabrication of self-assembled 3D inductors. A process has been
developed to overcome photoresist deterioration problems due to the alkaline nature of Au electro-deposition solutions.
Furthermore, pure Sn is used instead of Pb-Sn as the hinge material. A Ni metal layer is introduced between the Au coils
and the Sn hinge to prevent inter-diffusion and formation of eutectic Au-Sn compounds. Finally a gold capping
technique is proposed to protect the Sn hinge from oxidation during hinge reflow. The fabrication techniques developed
here are compatible with post-processing on active CMOS circuits, and can be adopted for other MEMS applications.
Among the various possible production techniques of silica- on-silicon integrated optical devices, sol-gel is the one which combines low cost with a great flexibility and the ease of doping the silica matrix with nonlinear and active compounds. In the frame of an European project, we have investigated the application of the sol-gel technique to the realization of an erbium-doped optical amplifier, operating in the third telecommunication window. Here, in particular, we refer to the development of an optimum fabrication strategy for the guiding structure. A strip-loaded configuration was chosen. Design optimization was carried out by means of a MATLAB software code, mainly based on the Effective Index Method. For what concerns the technical side, two different routes were followed: that of the Low Index Load and that of the High Index Load. Pros and cons of both structures were carefully evaluated through numerical simulations as well as experimental analysis, in order to choose the best performing one. Results of the design procedure and the characterization of the fabricated waveguides are described here.
The possible use of sol-gel films and monoliths for optical guided wave components is receiving increasing attention. This paper describes the requirements for such components in fibre communication systems, and reviews the status of the principal integrated optical technologies which compete for these applications. The development of waveguides based on sol-gel, and on sol-gel materials relevant to integrated optics, is reviewed. The issues relating to the future success of sol-gel in this field, i.e. cost, performance and functionality, are discussed, and some areas of current and future work described. Key challenges to competitive success identified.
Optical interferometric monitoring of spin coating (optospinography) has allowed close observation of a thin liquid film temporal evolution (at 500 -2500 rpm, 100 Hz data acquisition), from which its kinematic viscosity can be determined. The data obtained from this procedure is in good agreement with known values for two oil standards, indicating that the method is valid in the range of approx. 0.4 to 150 Stokes. Advantages and limitations are discussed.
Temporal evolution during spin coating is interferometrically monitored, with close regard to gelation at the final stages of the process. Uniform silica films on silicon were produced from an established sol composition, from which slight deviations were taken to produce nonuniform, cracked films. A distinct evolution of the sol to gel transition could then be detected, at speed of rotations of 1000 - 3000 rpm and data acquisition at 100 Hz. Interpretation of a set of experimental results is discussed in terms of a two-phase system, in the light of, and as a test of, current theoretical models.
The use of porous sol-gel films as hosts for semiconductor microcrystals, with applications in integrated optics, has been examined. Techniques are described for characterizing porosity using ellisometric measurements, and the use of this technique to investigate the effects of process parameters is reported. In particular, the effect on pore microstructure of water concentration, catalyst type and concentration and film annealing temperature are presented. A technique for doping the porous host film with CdS crystallites is then described. Absorption spectra for the doped films are presented which given an indication of the size and concentration of these crystallites, and the way in which these are affected by process parameters is also reported. The cadmium counter-ion is shown to strongly influence the doping concentration, and the film annealing temperature is shown to affect the crystallite size.
This paper describes recent progress in the development of a new class of spatial light modulator (SLM). These new SLMs modulate light by the interaction of some active material with a high intensity evanescent field generated by surface plasmon resonance. Such devices have the potential for substantial advantages over conventional SLMs, including higher speed and better response uniformity, as well as high sensitivity in devices with thin active layers. A new optically addressed plasmon device, based on a thin amorphous silicon/liquid crystal sandwich structure, has been developed and tested. The performance characteristics compare favorably with those of conventional liquid crystal SLMs in terms of resolution and speed. The design of more advanced devices based on higher performance ferro-electric and electroclinic liquid crystals is now in progress; in particular, the special pseudo-plasmon modes found in highly birefringent materials, and the application of these to modulation, have been analyzed. Surface plasmon SLMs using electro-optic effects in semiconductor active layers are also discussed.
The status and potential of a new type of device, the surface plasmon spatial light modulator
(SPSLM) is reported. The attractive features of surface plasmon resonance (SPR) for use in SLM's
are explained and results from prototype devices reported. These are of the liquid crystal (LC) light
valve configuration, using nematic LC with a silicon photodiode backplane. Demonstrated advantages
include process simplification and increased response speed. These are obtained due to the thin,
single surface nature of the plasmon active region, whilst high sensitivity is retained due to the
resonant enhancement of the optical field in this region.
The theoretical principle of the liquid crystal SPSLM is described, in terms of the propagation of
plasmons on anisotropic materials. Various alignment configurations are considered to show how both
nematic and smectic materials could provide high sensitivity and speed in future devices.
The need for a grating coupled SPR technology is explained, and the design and fabrication of
holographic gratings for SPSLM's is discussed.
Finally, the present and ultimate performance limitations of these new SLM devices are assessed,
and related to their potential use in optical information processors such as image correlator and
neural network systems.