: The Internet of Things is anticipated to connect billions of embedded devices equipped with sensors to perceive their surroundings. Thereby, the state of the real world will be available online and in real-time and can be combined with other data and services in the Internet to realize novel applications such as Smart Cities, Smart Grids, or Smart Healthcare. This requires an open representation of sensor data and scalable search over data from diverse sources including sensors. In this paper we show how the Semantic Web technologies RDF (an open semantic data format) and SPARQL (a query language for RDF-encoded data) can be used to address those challenges. In particular, we describe how prediction models can be employed for scalable sensor search, how these prediction models can be encoded as RDF, and how the models can be queried by means of SPARQL.
A new sub-class of composite transducer structures described as 'macrocomposites' have been investigated by finite element modelling and practical experimentation. In current macrocomposites a ferroelectric ceramic is combined with one or more passive components on a macroscopic scale and in a regular geometric configuration to produce new electro-mechanical structures which often have significantly enhanced performance parameters compared to those possessed by their monolithic ferroelectric ceramic components in isolation. Macrocomposites can be used as sensors and actuators. Potential applications include miniature high sensitivity hydrophones, miniature high efficiency sound sources and high strain actuators.
Transmission electron microscopy and X-ray diffraction have been used to characterise the antiferroelectric (AFE) — ferroelectric phase (FE) boundary in PbZrO3-based materials. Bulk ceramics in the solid solution (Pb1-XBax)(Zr1-xTix)O3 (PBZT) and thin films of the general formula, Pb(Zr,Sn,Ti)0.98Nb0.02O3 (PZSNT) were investigated. The phase changes in PBZT as a function of composition and temperature have been studied with a view to understanding the fundamental crystal chemistry across the AFE–FE phase boundary. PZSNT is a potential commercial composition which can be deposited as a thin film using sol-gel spinning. The crystallisation of thin PSZNT from the amorphous gel to the perovskite phase is discussed.
Piezoelectric multi-layer actuators, based on traditional multi-layer capacitor designs, have been designed and tested, and proved robust in service. These devices are manufactured from "soft" piezoelectrics, obtaining larger displacements than hard types, and lend themselves toward d.c. and low frequency applications. Such devices are particularly useful in fast-response applications, where large displacements are less important than operating time (e.g. if the displacement must be achieved in ~ l ms). Such applications include ppm bleed-valves in devices such as mass spectrometers. Multi-layer actuators have also been fabricated from designs based around the unimorph. Applications for these devices include ink-jet printer heads, proportional valve actuation, and adaptive aerofoil technologies. Actuators have been manufactured with thickness ranging from less than I mm, to greater than 5 mm.
Piezoelectric elements as actuators have been extensively used to control struictures with a wide range of sizes. The effect of piezo-actuator thickness on the magnitude of deflection of a cantilever beam has been investigated experimentally and the results compared with a theoretical model. Results indicate that there exists a piezo-actuator thickness which maximises the cantilever deflection, and this optimal thickness is a function of the ratio of the Young's modulus of the actuator and the cantilever. The significance for actuator design is discussed.
Although recent research and development in the area of shape memory alloys (SMA) continues to yield novel and unique results the widespread commercial application of these materials continues to lag. This paper considers strategic and commercial issues for the application of SMA products. Through the use of established product management techniques such as life cycle analysis and bipolar mapping the paper concludes that for SMA applications to become more reactive and less proactive there needs to be a pull from product design and innovation. For this to occur, the differentiating material functions of shape memory must be promoted and perceived as adding value to the product. Consideration is given to the commercialisation of SMA actuators and the role of an R&D/Market interface. The paper shows that for SMA actuators to become commercially viable the physical and mechanical properties of commercially available SMA's must be consolidated and future R&D focused on design properties relevant to applications.
The methods and requirements necessary to perform accurate and reproducible polarisation-field (P-E) measurements are discussed. An introduction to P-E measurements is given outlining the electrical origins of the P-E loop and visual interpretation of loop characteristics. Conventional and computer based measurement systems are reviewed followed by a description of P-E signal analysis techniques. The DynoHYST apparatus, developed at Leeds is introduced and principles of operation are discussed. Methods and uses of electrical breakdown and ferroelectric saturation detection are presented. Particular reference is made to the dual applicability of DynoHYST to both research and production quality assurance and on line testing.
Distributed sensors are shaped sensors which are bonded to the surface of a structure and are continuous over the length and the breadth of the structure. They are designed on the basis of the orthogonality principle of the modes of vibration of a structure. Distributed sensors are designed to monitor specific modes of vibration of the structure and are usually made of polyvinylidene fluoride (PVDF) piezoelectric polymer films. In this paper, PVDF shaped sensors are designed for monitoring the first and the second modes of vibration of a simply supported beam. The design principle for achieving the optimal sensor shape for a particular mode of vibration is based on making the sensor width zero at locations along the length of the beam where the strain is zero. Conversely, the sensor width is maximum where the strain in the beam is maximum for the particular mode of vibration. The vibration responses of the beam as measured by the distributed sensors are compared with the measured vibration responses using an accelerometer. It is shown that by dividing a classical PVDF shaped sensor for mode 1 into two halves, the sensor can be used to monitor modes I and 2 of the flexural vibration of the beam.
Actuators and/or sensors embedded into a host material will disrupt the physical properties of the host. Finite element analysis was used to determine and to minimise the stress concentrations which arise in a 'smart' material system due to the embedded optical fibre sensor. An optimisation routine was used to perform a parametric study to determine the theoretical mechanical and thermal properties of the interface coating that minimise the disruption of the host material properties, due to the optical fibre inclusion. The effects of transverse tensile and thermal loading were studied, including the effect of manufacturing residual stresses. The stress concentrations in the composite host are affected by the dimensions and the mechanical and thermal properties of the interface coating. The results show that with careful selection of the interface coating properties the stress concentrations in the host material caused by the optical fibre inclusion can be reduced to levels similar to those of the pure host material. It is proposed that a set of design curves are produced for a range of host material properties so that the appropriate optical fibre coating can be selected.
Electro-rheological fluids are reviewed with respect to their application in devices that are aimed at featuring electronically designated motion and flexible operation - 3rd wave machines. The article is one engineer's view of what is required in order to promote a successful and unified approach to the interdisciplinary problem amongst scientists and engineers. This is done by setting down the state of the art position of research in the field and the salient factors that determine research trends for fluid developers, whilst at the same time giving some idea of desired machine performance and limitations.
The acoustic radiation from a vibrating structure can be reduced by an active control system provided the system has a suitable sensing capability. The radiation of sound from a structure is in general a spatially distributed phenomenon and it is often necessary to extract information about the behaviour of the structure over its entire surface. The major source of acoustic radiation from a structure at low frequencies is the integrated normal velocity or volume velocity of the structure. For the purposes of active control it is therefore important that this quantity be measured. This can be achieved by using a number of point sensors, but the complexity of the system required to deal with these sensors can become prohibitive. Alternatively, a single distributed PVDF sensor can be used to measure the volume velocity of a structure due to bending, but unfortunately such a sensor is incapable of detecting the whole body motion of the structure. An alternative distributed sensor which uses PVDF as a distributed accelerometer (in the d" mode), can in principle, directly measure the volume velocity of the structure due to any arbitrary motion. Unfortunately, PVDF is very sensitive to strain on the structure's surface and this masks any signal output due to acceleration. Methods of desensitising the PVDF sensor to surface strain are discussed.
An active vibration control system has been developed based upon analogue feedback and optical vibration sensing. ZnO thin films have been deposited using r.f. magnetron sputtering onto silicon substrates and cantilevers fabricated using photolithography. These cantilevers provide a means of actuation and micro-positioning. The system operates such that unwanted vibrations in the cantilever are removed and yet it remains possible to deflect the cantilever statically or dynamically as required. Results are presented for such a system.
The subject of strain measurement has previously been addressed extensively. Most of the existing transducers either rely on low voltage analogue systems (e.g. conventional resistive strain gauge), complicated mechanical assemblies by physically assessing the specimen displacement, optical systems, acoustic systems or pneumatic systems. This paper identifies a new, potentially low cost, non-contact, frequency domain strain sensor utilising SAW (surface acoustic wave) technology for surface strain measurement. The sensor has a short axial length making it flexible in terms of integration into a variety of applications, encompassing both static and dynamic strain measurement. The paper presents a technical description of the resulting strain transducer, regarding it's operation, construction and, in particular application to areas requiring strain measurement. Demonstration of the transducer performance will be addressed utilising test results from existing developed transducers.
The ageing and field-forced deageing characteristics of a commercial cobalt-doped BaTiO3 piezoceramic are reported. It was found that the internal bias field in unpoled specimens reduced according to an exponential time law during field-forced deageing. The time constants associated with the deageing process were 159, 33 and 25 s at 30, 60 and 90 °C respectively, indicating an activation energy of 0.36 eV. In contrast, field-forced deageing of poled specimens yielded a logarithmic behaviour. Furthermore, the internal bias field in poled specimens proved to be extremely resistant to the deageing procedure, with the result that a significant internal bias field (Ei ≈ 0.1 kV mm-1) remained after the application of a continuous AC field of 2 kV mm-1 for 12 000 s at 30 and 60 °C.
PZT sensors are used to detects defect in cylindrical rods using wave propagation techniques. Stress pulses are measured and predicted using the finite element method in rods free of defects and with a defect. The defect is introduced in the rod in the form of a small slot. By analysing the stress wave data for the defect free rod and for the rod with a defect, it is possible to pinpoint the location of the defect. PZT tiles of dimensions 5 x 3 mm, which are cut from standard PZT patches of dimensions 30 x 30 mm, are bonded to the surface of the cylindrical rods and are used for monitoring the propagation of stress pulses induced in the rods by the collinear impact of spherical balls on one of the plane ends of the rods. A finite element analysis is performed to predict the stress pulses in the rods. The results show that the defect can be located using this technique. It is shown that a high degree of correlation is obtained between measured and predicted characteristics.
The paper is concerned with the P—E (polarisation—electric field) switching behaviour of hard PZT (lead zirconate titanate) ceramics. The remanent polarisation Pr , saturation polarisation Ps, and internal bias field Ei were determined at a field amplitude of 3.5 kV mm-1 during ageing and field-driven deaging measurement procedures. It is shown that the rates of increase of Pr and Pr during field-driven deageing, which represents an AC poling process, are dependent both on temperature and on the prior ageing treatment of the unpoled specimens.
The complex shear modulus properties of an electro-rheological fluid, composed of 50 wt.% of starch in 50 wt.% of silicone oil, was determined experimentally by the application of the direct stiffness technique and an ER fluid device consisting of concentric cylinders. The electric field strength, temperature and frequency ranges of the measurements were 0.0 to 2.0 kVmm-1, 0 to 60 °C and 30 to 300 Hz respectively. The results show that the shear modulus of the ER fluid decreased by a factor of up to 20 as the temperature was increased from 0 to 60 °C, whereas the shear loss factor increased from a low value of about 0.05 at 0 °C to a high value of about 1.0 at 60°C. Conversely, as the electric field strength was increased from 0.0 to 2.0 kVmm-1, the shear modulus increased whereas the loss factor decreased. However, both the shear modulus and loss factor increased in value as the excitation frequency was increased. By means of the temperature-frequency superposition principle, master curves of shear modulus and loss factor, which vary with frequency over several decades at a constant reference temperature and for two values of electric field strength, were derived from the measured data.
Over the last decade much effort has gone into forming piezoelectric materials, eg lead zirconate titantate (PZT), on top of micromachined silicon to make sensors and actuators. However the techniques involved in making such devices are complicated and time consuming, reducing their commercial value. Large area silicon p—n and Schottky junctions have been chosen to demonstrate this effect, because they are considered to have well defined junction interfaces. An alternating potential and bias voltage applied across the junction interface would cause an alternating tension and thus a strain in the plane of the junction, so causing the cantilever to vibrate. Initially, experiments were performed with a bias voltage of 2 V over a range of frequencies to determine the frequency response of the cantilever. The experiments clearly show that silicon junctions are piezoelectric actuators, without the need for any additive piezoelectric material.
