1,721,080 research outputs found
Multiple-level digital loudspeaker array
No full textAbstractIn modern audio systems, the signal path is generally digital in nature, with the notable exception being the analogue loudspeaker. Digital Loudspeaker Arrays (DLA) have been proposed as an alternative approach. Generally, they have a relatively poor acoustic output, as high audio quality requires an impractically large number of speaklets (tiny loudspeakers). We address this limitation by proposing an increase in the number of quantizing levels, thus requiring fewer speaklets. A comprehensive system simulation has demonstrated the feasibility of such a system to produce high quality sound, with a hardware implementation currently being investigated
Empirical modeling and simulation for discharge dynamics enabling catchment-scale water quality management
No full textExcessive or poorly timed application of irrigation and fertilizers, coupled with inherent inefficiency of nutrient uptake by crops result in nutrient fluxes into the water system. Due to the recent adoption of WSNs in precision agriculture, it is proposed that existing networked agricultural activities can be leveraged into an integrated mechanism by sharing information about discharges and predicting their impact, allowing dynamic decision making for irrigation strategies. Since resource constraints on network nodes (e.g. battery life, computing power etc.) require a simplified predictive model, low-dimensional model parameters are derived from the existing National Resource Conservation Method (NRCS). An M5 decision tree algorithm is then used to develop predictive models for depth (Q), response-time (t1) and duration (td) of the discharge. 10-fold cross-validation of these models demonstrates RRSE of 10.2%, 30% and 9.6% for Q, t1 and td respectively. Furthermore, performance of these models is validated using multiple linear regression metho
A Thick-film Piezoelectric Multimorph Cantilever
Full text linkFree-standing thick-film cantilevers have the potential to be used as micro-generators as well as self-generating resonant sensors. Earlier versions of free-standing devices were implemented by fabricating in the form of multilayer structures. Instead of structures with a plate of PZT sandwiched between upper and lower electrodes, multimorph structures consist of three individual PZT plates having equal thicknesses (of about 40 ?m each). Ag/Pd conductors form the separators between the layers, also acting as electrodes on the upper and lower layers of the structure. Each piezoelectric plate was polarised in its thickness direction with two different modes: parallel and series. In the parallel mode, both the upper and lower PZT plates were polarised in the opposite direction, while in the series mode the upper plates and the lower plates were polarised in the same direction. The centre plate of PZT acts as the neutral axis of the structure. Using the direct piezoelectric effect, a voltage was generated when the multimorph structures were bent by the application of a harmonic excitation. An output power of 10 ?W was measured for the parallel polarised sample. Series multimorphs, however, exhibited a non-linear effect, where the output power was 21 ?W for an up-sweeping frequency, but was reduced by a factor of 50 for a down-sweeping frequency
Sensor Networks for Maritime Deployment: Modeling and Simulation
No full textSimulation is widely used in Wireless Sensor Networks to assess the feasibility and performance of design decisions before the deployment, assisting the development of optimal solutions or trade-offs. In this paper, we address the particular case of a sensor network deployed at sea, where hundreds or thousands of sensing nodes drift with the stream and organise into a network capable of transmitting results to a remote station. A new simulator was built to address the particularities of the wireless models required to correctly understand the application scenario. The models provide realistic channel simulation, along with additive interference from other sources, where all transmissions are considered independently. The receiver decides which transmission was first and what is the level of noise from the environment and contending nodes. Network algorithms were implemented and compared using different network sizes and parameters. Results show that algorithms are sensitive to deployment conditions and respond differently to each set of environmental parameters
Free-standing thick-film piezoelectric multimorph cantilevers for energy harvesting
No full textPiezoelectric materials provide one approach for converting mechanical to electrical energy and can therefore be used to harvest energy from ambient vibration sources. Typically, piezoelectric materials are fabricated onto thin substrates, such as aluminum and stainless steel. These serve as mechanical support platforms to function as a cantilever beam structure. The platforms, however, are non-electro-active and they do not contribute directly to the electrical power output. The aim of this paper is to describe a novel multimorph cantilever structure in a free-standing form. Multimorphs consist of three laminar sections of lead zirconate titanate (PZT) of equal thickness 40 µm and length 18 mm were polarized in two modes; series and parallel. An optimum output power of 42 µW was measured when the series polarized sample was excited at its resonant frequency of 400 Hz
Collaborative catchment-scale water quality management using integrated wireless sensor networks
No full textThe challenge of improving water quality (WQ) is a growing global concern. Poor WQ is mainly attributed to poor water management and outdated agricultural activities. We propose that collaborative sensor networks spread across an entire catchment can allow cooperation among individual activities for integrated WQ monitoring and management. We show that sharing information on critical parameters among networks of water bodies and farms can enable identification and quantification of the contaminant sources, enabling better decision making for agricultural practices and thereby reducing contaminants fluxes
Data-driven low-complexity nitrate loss model utilizing sensor information – towards collaborative farm management with wireless sensor networks
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