1,721,023 research outputs found
Modelling of a novel high-impedance matching layer for high frequency (>30 MHz) ultrasonic transducers
No full textThis work describes a new approach to impedance matching for ultrasonic transducers. A single matching layer with high acoustic impedance of 16 MRayls is demonstrated to show a bandwidth of around 70%, compared with conventional single matching layer designs of around 50%. Although as a consequence of this improvement in bandwidth, there is a loss in sensitivity, this is found to be similar to an equivalent double matching layer design. Designs are calculated by using the KLM model and are then verified by FEA simulation, with very good agreement Considering the fabrication difficulties encountered in creating a high-frequency double matched design due to the requirement for materials with specific acoustic impedances, the need to accurately control the thickness of layers, and the relatively narrow bandwidths available for conventional single matched designs, the new approach shows advantages in that alternative (and perhaps more practical) materials become available, and offers a bandwidth close to that of a double layer design with the simplicity of a single layer design. The disadvantage is a trade-off in sensitivity. A typical example of a piezoceramic transducer matched to water can give a 70% fractional bandwidth (comparable to an ideal double matched design of 72%) with a 3 dB penalty in insertion loss.<br/
Acoustic power output measurements for thick-film PZT transducers
Full text linkDirect acoustic measurements have been performed on a range of thick-film PZT ultrasonic transducer constructions, and these are compared with their electrical impedance and calculated input powers. They show good efficiency when driving into water, and a significant improvement over a similarly constructed bulk PZT transducer
Screen-printable porous glass: a new material for electrochemical sensors
No full textA screen-printable porous paste is described. Its use in the development of a solid-state Ag/AgCl electrochemical reference electrode is reported as an example of a typical application. Potassium chloride salt crystals are homogenously dispersed in a commercial thick-film glass paste and printed through a stainless steel stencil. Printed features are fired at 600 °C; a lower temperature than the melting point of the salt crystals, which remain intact. After firing, embedded salt crystals are dissolved away in warm water. The resultant features have a sponge-like appearance, with pore density and size distribution governed by the volume and grain sizes of the salt. In the application described, the porous paste is used as an electrolyte containment structure and membrane support scaffold; key components for miniaturisation of the Ag/AgCl reference electrode. Experiments show the best performing reference electrode maintained a potential with <5 % change over more than five decades of chloride concentratio
The influence of carrier layer material in ultrasonic particle manipulation devices
No full textThe use of acoustic radiation forces for the manipulation of particles, bacteria and cells is drawing increasing interest. Resonators using quarter-wavelength sized fluid chambers have been developed, where an acoustic pressure node is positioned near the reflector layer surface such that particles may be pushed close to or onto this surface. The thickness of the reflector layer has already been shown to greatly influence the performance of such resonators. These devices have applications in bio-sensing where a concentrate of particulates can be collected or particulates can be contacted with a sensor surface directly. A coupling layer is usually incorporated into the device and is located between the transducer and fluid layer. The ability of this layer to act as an acoustic matching layer depends on its acoustic properties and thickness. Here, the performance of various carrier layer materials in a near quarter-wavelength device is investigated and compared using modelled and experimental data. Results indicate that where the carrier layer thickness is selected for optimum performance, the resonator performance is comparable for most high Q factor carrier layer materials. However, for some materials the performance of the resonator, is highly sensitive to the coupling layer thicknesses and in turn can constrain the flexibility of the acoustic design.<br/
An efficient indoor photovoltaic power harvesting system for energy-aware wireless sensor nodes
No full textWireless sensor nodes are autonomous devices which sense parameters and communicate them wirelessly. Their independent operation precludes the use of wired power supplies, and energy harvesting is becoming an attractive alternative to batteries. This paper presents the circuit design and embedded software of a photovoltaic power harvesting system for indoor wireless sensor nodes, which delivers energy-awareness and improved efficiency levels
Water quality monitoring, control and management (WQMCM) framework using collaborative wireless sensor networks
No full textImproving water quality is of global concern, with agricultural practices being the major contributors to reduced water quality. The reuse of nutrient-rich drainage water can be a valuable strategy to gain economic-environmental benefits. However, currently the tools and techniques to allow this do not exist. Therefore, we have proposed a framework, WQMCM, which utilises increasingly common local farm-scale networks across a catchment, adding provision for collaborative information sharing. Using this framework, individual sub-networks can learn their environment and predict the impact of catchment events on their locality, allowing dynamic decision making for local irrigation strategies. Since resource constraints of network nodes (e.g. power consumption, computing power etc.) require a simplified predictive model for discharges, therefore low-dimensional model parameters are derived from the existing National Resource Conservation Method (NRCS), utilising real-time field values. Evaluation of the predictive models, developed using M5 decision trees, demonstrates accuracy of 84-94% compared with the traditional NRCS curve number model. The discharge volume and response time model was tested to perform with 6% relative root mean square error (RRMSE), even for a small training set of around 100 samples; however the discharge response time model required a minimum of 300 training samples to show reasonable performance with 16% RRMS
Modelling for the robust design of layered resonators for ultrasonic particle manipulation
No full textSeveral approaches have been described for
the manipulation of particles within an ultrasonic
field. Of those based on standing waves, devices in
which the critical dimension of the resonant chamber
is less than a wavelength are particularly well suited to
microfluidic, or “lab on a chip” applications. These
might include pre-processing or fractionation of
samples prior to analysis, formation of monolayers for
cell interaction studies, or the enhancement of
biosensor detection capability.
The small size of microfluidic resonators typically
places tight tolerances on the positioning of the
acoustic node, and such systems are required to have
high transduction efficiencies, for reasons of power
availability and temperature stability. Further, the
expense of many microfabrication methods precludes
an iterative experimental approach to their
development. Hence, the ability to design subwavelength
resonators that are efficient, robust and
have the appropriate acoustic energy distribution is
extremely important.
This paper discusses one-dimensional modelling
used in the design of ultrasonic resonators for particle
manipulation and gives example of their uses to
predict and explain resonator behaviour. Particular
difficulties in the modelling of quarter wave systems
are highlighted.
Keywords: acoustic radiation force, layered
resonators, robust design, particle manipulatio
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