Sound propagation through bone tissue

Effect of perforation on structure borne sound propagation through rigid porous materials has been investigated. Experimental works has been carried out on rigid porous materials with and without perforations. A low frequency vibration has been applied to excite the material structure by using a force transducer connected a shaker to detect the changes in resulting response. Applied vibration on sample surface causes structure borne sound wave to propagate through the material. The resulting response of this structural borne vibration is detected by using an accelerometer. The results with and without perforation of the sample have been compared. The results show that changing the structure of the material has an effect on the amplitude, shape and arrival time of the transmitted acoustic wave

Behaviour of ultrasonic waves in porous rigid materials: anisotropic Biot-Attenborough model

The anisotropic pore structure and elasticity of cancellous bone cause wave speeds and attenuation in cancellous bone to vary with angle. Anisotropy has been introduced into Biot theory by using an empirical expression for the angle-and porosity-dependence of tortuosity. Predictions of a modified anisotropic Biot–Attenboorugh theory are compared with measurements of pulses centred on 100 kHz and 1 MHz transmitted through water-saturated porous samples. The samples are 13 times larger than the original bone samples. Despite the expected effects of scattering, which is neglected in the theory, at 100 kHz the predicted and measured transmitted waveforms are similar

THE INSERTION LOSS OF POROELASTIC PLATE SILENCERS IN A FLOW DUCT

Idealized silencers consisting of cavity-backed clamped porous elastic plates parallel to the direction of flow can result in low frequency attenuation of noise in the duct. The insertion loss of perforated and non-perforated poroelastic plate silencers have been measured with and without mean air flow. Peak IL when the plate is not perforated has a value of 4.1 dB at 1 kHz without air flow. With perforations the peak IL is 3.2 dB at 630 Hz. In the presence of mean air flow, without self-noise, peak IL have values of 17 dB at 250 Hz and 7 dB at 400 Hz for the air flow speeds of 37.65 m/s and 5.5 m/s respectively. Peak IL of perforated and non perforated porous plate has values of 11 dB and 11.5 dB at 160 Hz with noise and air flow at speed of 37.65 m/s. The displacements of a perforated and non-perforated porous elastic plates separated from duct wall by an air cavity in the duct have been measured and compared with those of the duct wall

Arithmetic Nullstellensatz and Nonstandard Methods

In this study we find height bounds for polynomial rings over integral domains. We apply nonstandard methods and hence our constants will be ineffective. Then we find height bounds in the polynomial ring over algebraic numbers to test primality of an ideal. Furthermore we consider unique factorization domains and possible bounds for valuation rings and arithmetical functions

Behaviour of acoustic waves in a duct with Helmholtz resonator in presence of a temperature gradient

Understanding the behaviour of one-dimensional acoustical wave propagation in ducts is very important for controlling combustion instabilities in propulsion, household burners, gas turbine combustors, and designing engineering mufflers. This paper is concerned with ducts in which temperature gradient exist. Computational Fluid Dynamics (CFD) simulation of the acoustic wave propagations through a duct with Helmholtz resonators in the presence of a mean temperature gradient without mean air flow has been investigated. Acoustic pressure and axial velocity amplitudes have been calculated as a function of time. Time and axial distance dependent acoustic pressure and velocity are visualised as 3D surface plots

A review of the state of art in applying Biot theory to acoustic propagation through the bone

Understanding the propagation of acoustic waves through a liquid-perfused porous solid framework such as cancellous bone is an important pre-requisite to improve the diagnosis of osteoporosis by ultrasound. In order to elucidate the propagation dependence upon the material and structural properties of cancellous bone, several theoretical models have been considered to date, with Biot-based models demonstrating the greatest potential. This paper describes the fundamental basis of these models and reviews their performance

Investigation of sound propagation in a duct with a mean temperature gradient

This paper presents an analytical and numerical investigation of an impedance tube in the presence of a mean temperature gradient. Full Navier-Stokes simulation of the acoustic wave propagations through an impedance tube in the presence of a mean temperature gradient without mean air flow is investigated. Results from the simulations are compared with an analytical model of the behaviour of one-dimensional oscillations in an impedance tube with an axial temperature gradient in the absence of mean flow. Time and axial distance dependent acoustic pressure and velocity are visualised as 3D surface plots. The agreement between simulation and the analytical model is shown to be very good and represents a baseline validation of the numerical methodology for the simulation of impedance tubes in the presence of temperature gradients

Sound propagation through bone

Effect of perforation on structure borne sound propagation through rigid porous materials has been investigated. Experimental works has been carried out on rigid porous materials with and without perforations. A low frequency vibration has been applied to excite the material structure by using a force transducer connected a shaker to detect the changes in resulting response. Applied vibration on sample surface causes structure borne sound wave to propagate through the material. The resulting response of this structural borne vibration is detected by using an accelerometer. The results with and without perforation of the sample have been compared. The results show that changing the structure of the material has an effect on the amplitude, shape and arrival time of the transmitted acoustic wave

Development of universal software radio peripheral amplifier for underwater acoustic platform using software defined radio

First and foremost, the development of a modem using the USRP has applications in oceanographic monitoring and communication. Improved acoustic connecting would allow more efficient transfer of information between Underwater Acoustic (UWA) equipment such as autonomous vehicles, piloted vehicles, and underwater profilers. Therefore it can easily be modified in order to be employed for the testing of different UWA. This project describes the full system of an underwater acoustic modem with underwater wireless connection starting with the most critical component of the system which is the USRP amplifier for the receiver and the transceiver. In this project we focused on the development of the USRP amplifier. This amplifier is expected to enhance the signal of the transceiver to Universal Software Radio Peripheral (USRP) modem and the GNU radio. The platform that we proposed uses the Software Defined Radio (SDR) as the main controller. This is due to its flexibility in modulation and able to support coding. Since this is an initial stage, in this work we only use Gaussian Minimum Shift Keying (GMSK) as the modulation techniques. The performance of the UWA platform had been tested and we found that as the frequency increases the attenuation increased as well but with the USRP amplifier we have managed to decrease it. UWA communication research will benefit greatly from the adaption of the USRP as an underwater acoustic modem. The USRP amplifier amplifies the signal that has send by the transceiver and detected by the receiver will effectively demodulate the signal and analyze the received data in the USRP modem. GNU radio and USRP SDR has been successfully implemented. The results demonstrate that the objectives of this research are archived. It is proved that by implementing GNU radio and USRP SDR in the new generation of underwater acoustic communication technology, and improves the utilization of the underwater communication. We conclude that the proper design of the USRP Amplifier is crucial to obtain high quality performance. This project has successfully developed a USRP amplifier and the underwater acoustic communication testbed with expected results

A review of the state of art in applying Biot theory to acoustic propagation through the bone

Understanding the propagation of acoustic waves through a liquid-perfused porous solid framework such as cancellous bone is an important pre-requisite to improving the diagnosis of osteoporosis by ultrasound. In order to elucidate the propagation dependence upon the material and structural properties of cancellous bone, several theoretical models have been considered to date, with Biot-based models demonstrating greatest potential. This paper describes the fundamental basis of these models and reviews their performance