6,396 research outputs found
Performance of a micro-engineered ultrasonic particle manipulator
No full textAn ultrasonic microfluidic particle manipulator has been modeled and its experimentally measured separation performance has been compared with the modeled results for 1 µm latex particles, and yeast particles in water
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/
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
Acoustic power output measurements for thick-film PZT transducers
No full textDirect 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
Investigation of two-dimensional acoustic resonant modes in a particle separator
No full textWithin an acoustic standing wave particles experience acoustic radiation forces, a phenomenon which is exploited in particle or cell manipulation devices. When developing such devices, one-dimensional acoustic characteristics corresponding to the transducer(s) are typically of most importance and determine the primary radiation forces acting on the particles. However, radiation forces have also been observed to act in the lateral direction, perpendicular to the primary radiation force, forming striated patterns. These lateral forces are due to lateral variations in the acoustic field influenced by the geometry and materials used in the resonator. The ability to control them would present an advantage where their effect is either detrimental or beneficial to the particle manipulation process.The two-dimensional characteristics of an ultrasonic separator device have been modelled within a finite element analysis (FEA) package. The fluid chamber of the device, within which the standing wave is produced, has a width to height ratio of approximately 30:1 and it is across the height that a half-wavelength standing wave is produced to control particle movement. Two-dimensional modal analyses have calculated resonant frequencies which agree well with both the one-dimensional modelling of the device and experimentally measured frequencies. However, these two-dimensional analyses also reveal that these modes exhibit distinctive periodic variations in the acoustic pressure field across the width of the fluid chamber. Such variations lead to lateral radiation forces forming particle bands (striations) and are indicative of enclosure modes.The striation spacings predicted by the FEA simulations for several modes compare well with those measured experimentally for the ultrasonic particle separator device. It is also shown that device geometry and materials control enclosure modes and therefore the strength and characteristics of lateral radiation forces, suggesting the potential use of FEA in designing for the control of enclosure modes in similar particle manipulator devices
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
A multilayer thick-film PZT actuator for MEMs applications
No full textThis paper describes a technique for replacing the conventional bonded bulk PZT transducer, commonly used in MEMS devices, with a screen printed equivalent. Previously, the piezoelectric activity available from screen printed PZT has been considerably lower than the bulk material, but recent developments in material composition and device structure have allowed screen printed structures to deliver powers equivalent to bulk devices. An actuator using the multilayer screen printed technique was designed for use in an ultrasonic flow-through separator, and its successful use is reported
A silicon microfluidic ultrasonic separator
No full textUltrasonic standing waves can be used to generate forces on particles within a fluid. Such forces have a number of potential applications in microfluidic devices. This paper describes such a device providing filtration on a microfluidic scale. It is microfabricated and uses ultrasound in the megahertz frequency range to concentrate particles at a node within the flow. It offers the possibility of a functional equivalent of a centrifugal separator for microfluidic systems. It is constructed using silicon and Pyrex, and hence is highly compatible with established microfabrication techniques. The modelling, design, fabrication and control of the device are discussed
A dual frequency, ultrasonic, microengineered particle manipulator
No full textUltrasonic standing waves can be used to generate forces on particles within a fluid. Recent work has concentrated on developing devices that manipulate the particles so that they are concentrated near the centre of the cavity. It is also possible to design a device that concentrates the particles at the wall of a cavity. This paper describes a device that has the capability of operating in several modes to allow concentration of particles at either the cavity wall or the centre of the cavity, depending on the driving frequency
Fluid modelling of microfluidic separator channels
No full textIn a microfluidic ultrasonic separator device, the microchannel geometry is inherently angular due to the anisotropic etch processes used. A CFD model is used to investigate eddy formation induced by this angular geometry. Results are applicable to various microfluidic devices and show that certain etch patterns significantly reduce eddy formation
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