Search

A method is presented to determine the low-frequency sound field in a duct with a cross-section of arbitrary shape and area that varies gradually without discontinuities. The duct is modeled as several fictitious segments, each of which has a cross-sectional area that is a quadratic function of position along its axis. A closed-form solution does not exist for arbitrary quadratic variation. Therefore, a series solution with two coefficients that depend on the boundary conditions and the radius of convergence (ROC) of the series is presented. Losses due to absorption are included. The solution corresponds to standing waves and is recast in terms of traveling waves. A transfer matrix is developed and used to express the pressure and velocity at the throat of a segment in terms of the pressure and velocity at its mouth. The series solution converges very rapidly when the length of the segment is less than half the ROC. The transfer matrix for the entire duct is the product of the transfer matrices of the segments. Numerical results are presented for open-closed ducts with the same length but different variations in area to illustrate the effect of the latter on the lowest resonance frequency and the pressure amplification.

In this paper, a machine learning based acoustic source localization in an indoor environment is presented. Acoustic source localization is considered as a supervised learning problem and is solved by random forest regressor. Experiments have been conducted to collect narrow band audio signals from an acoustic source placed at different angles using a linear array of 8 microphones. The model is trained using the signals captured by the microphone array. Finally, the performance of the model has been evaluated on an independent test set and results show that the random forest regressor model can be effectively used for indoor acoustic source localization.

A method is presented to design an optimal unimorph beam that flexes and generates voltage in response to a distributed load acting over its length using an analytical model. The objective is to design a beam that resonates at a specified frequency at which there is a peak in the excitation. The associated open-circuit voltage sensitivity and gain bandwidth product are functions to be maximized. For specific boundary conditions and pairs of materials, the dimensional ratio of the thickness of the piezoelectric layer to the square of the length of the beam is chosen such that the beam resonates at the specified frequency. The two optimum values of the dimensionless ratio of the thicknesses of the elastic and piezoelectric layers associated with the maximum values of the two functions of interest are determined through a simple one-dimensional search. Figures of merit and numerical results are used to show the effect of boundary conditions and properties of materials on the functions of interest. All beams with the optimum ratio of thicknesses are equally good and the dimensions of a beam for a specific application are to be chosen by considering principles of design for manufacture and the external electronic circuit.

This work seeks to put forward an approach to enhance the voltage generated by an acoustic based piezoelectric energy harvester. When a flexible triangular foil is attached perpendicular to the PVDF cantilever beam there is an increase in strain in the beam, also there is an increment in the acoustic pressure amplification rate of the Helmholtz resonator due to the dimensional modification of its neck. The integrated effects of these modifications of the harvester on the output voltage have been investigated. When sound incident on the surface of the neck of the resonator, an oscillatory pressure is produced in the cavity, which in turns vibrates the PVDF cantilever beam and voltage generates. By amending the structure of the PVDF cantilever with a polyester foil attached perpendicular to it, the cantilever is driven into concurrent bending and twisting by the cavity pressure and therefore makes a noteworthy increase in the output voltage

Acoustic energy is an important form of energy which is generated and unused all around us. Despite the prevalence of acoustic energy a major challenge of energy harvesting is the low power density in typical acoustic noise fields. With a larger focus on green energy, acoustic energy is one of the vastly available energy sources and so harvesting this energy plays an important role in research. Unconventionally a thermoacoustic engine converts thermal energy to acoustic energy via its core, comprising a porous material that is sandwiched between two heat exchangers. The induced acoustic wave can be converted into electricity by introducing novel environment friendly energy converters. Integration of the thermoacoustic technology with piezoelectricity tends to be promising, since the piezoelectric ceramics are sensitive and operating efficiently at high frequencies. Thermoacoustic technology is receiving growing interest in research for its many advantages, such as having no moving parts, being environment friendly and the possibility of using other renewable energy for its operation. This paper aims at providing a review on various acoustic and thermoacoustic energy harvesting techniques and the maximum power generated from each of these techniques.

Good indoor air quality (IAQ) can contribute to the safety, health and comfort of the people. Since indoor exposure to air contaminants penetrating from the indoor air contaminant sources depends on a number of parameters such as the ventilation rate, the geometric characteristics of the indoor environment, the indoor removal mechanisms and the concentration of air contaminants released, the implementation of smart sensor network is a promising solution to ensure good indoor air quality. This paper focuses on the application of CAN (controller Area Network) in forming a smart sensor network. The nodes are physically distributed where the serial common bus communication network CAN provides a robust means of interconnecting the nodes in the network. This paper proposes Atmel CANary based sensor nodes and motor control node for the monitoring and control of indoor air quality. The system output is a prototype of IAQ monitoring and control system which is evaluated through hardware tests.

Indoor air quality (IAQ) is a key factor for ensuring the safety, health and comfort of the people. Since physical variables describing IAQ, such as the concentration of volatile organic compounds (VOCs), concentrations of gaseous air contaminants and that of other toxic gases need to be closely monitored, concept of distributed monitoring and control network needs to be implemented. In this paper, a framework of sensor network for monitoring IAQ is explained where sensors are physically distributed and the serial common bus communication network CAN is used to exchange system information. CAN (Controller Area Network) is a high integrity serial bus protocol that is designed to operate at high speeds ranging from 20kbit/s to 1Mbit/s which provide an efficient, reliable and very economical link between sensor nodes and display node. This paper proposes Atmel CANary based sensor nodes and display node for the monitoring of indoor air quality. The communication between the sensor nodes and the display node through the CAN bus is evaluated through hardware tests.