47 research outputs found
A comparison of optical sensing methods for the high precision 3D surface profile measurement of grooved surfaces
No full textA non-contact method has been shown to be the preferred solution for the scanning of valuable early sound recordings, such as wax cylinders and flat discs for the purpose of cultural preservation [1]. This paper describes the operating principles and compares the performances of four different sensing techniques, including scanning white light interferometer (SWLI), con-focal laser (CL), con-focal white light sensor (WL), and atomic force microscope (AFM), in a range of measurement tasks. The con-focal systems described in this paper are used in a 3 dimensional (3D) cylinder scanning system for the measurement of wax cylinder recordings, where the 3D data is used to create a map of the measured surface. The generation of the map allows the sound recorded on the surface to be decoded without physical contact to the surface. The main advantage of the con-focal system is the scanning speed. Reference samples with sinusoidal and rectangular profiles are used to investigate the effects of surface inclination angle and the interaction between the sensor head and the measured surface. The effects of precision mode, grid spacing and spot size on surface height measurements are investigated
A quantitative analysis of signal reproduction from cylinder recordings measured via noncontact full surface mapping
No full textSound reproduction via a noncontact surface mapping technique has great potential for sound archives, aiming to digitize content from early sound recordings such as wax cylinders, which may otherwise be “unplayable” with a stylus. If the noncontact techniques are to be considered a viable solution for sound archivists, a method for quantifying the quality of the reproduced signal needs to be developed. In this study, a specially produced test cylinder recording, encoded with sinusoids, provides the basis for the first quantitative analysis of signal reproduction from the noncontact full surface mapping method. The sampling and resolution of the measurement system are considered with respect to the requirements for digital archiving of cylinder recordings. Two different methods of audio signal estimation from a discrete groove cross section are described and rated in terms of signal-to-noise ratio and total harmonic distortion. Noncontact and stylus methods of sound reproduction are then compared using the same test cylinder. It is shown that noncontact methods appear to have distinct advantages over stylus reproduction, in terms of reduced harmonic distortion and lower frequency modulation
Peak-finding methods for improving the resolution of a sonar-based correlation velocity log
No full textParticle separation with ultrasonic standing waves
No full textUltrasonic standing wave fields are able to trap and manipulate biological cells and other micron scale particles. The ability to levitate and move cells is of fundamental importance in a wide variety of life sciences applications. The gradients of pressure and velocity within a standing wave interact with small scatterers, such as cells, to generate time-averaged forces, in addition to the oscillatory acoustic forces. These steady-state radiation forces comprise: i) a component that acts towards the acoustic velocity maximum for a dense scatterer (relative to the surrounding fluid) and ii) a component that acts towards the acoustic pressure minimum for a relatively stiff particle. The resultant of these components will move the majority of scatterers, such as cells in aqueous suspension, towards the pressure nodes of a plane standing wave.This presentation discusses the second order terms that lead to the radiation forces and describes different approaches to modelling the forces, both numerical and analytical. The magnitude and scale of the potential wells that can be created within the standing waves complement other approaches to cell manipulation such as optical traps and dielectrophoresis. In addition, ultrasonic excitation is particularly suitable for integration into lab-on-a-chip devices and at low intensities cell damage has been shown to be negligible, making the approach ideal for handling biological cells in microfluidic devices.A number of potential applications of the technology will be described, including filtration and concentration, biosensor enhancement, and fractionation of particles on the basis of size, material properties and geometr
A novel binary particle fractionation technique
No full textAn interesting development towards a robust particle fractionator is presented. Typically acoustic fractionators rely on time of flight in a constant acoustic field to separate different populations . Such a system requires all particles to be concentrated to an initial known point before entering the acoustic field. As the particle population enters the acoustic field, the particles will move towards the nodal point at velocities dictated by their relative size. If the size of the acoustic chamber, flow rates and radiation forces are carefully adjusted, particles can be graded across the width of the chamber when they exit the acoustic field.
In this work we describe a technique that allows a more robust fractionation technique which is less sensitive to residence time and allows particle populations to be split in a binary fashion. Modelling results and initial experimental results are presented.<br/
Processing techniques for the recovery of audio from Edison cylinder recordings, via noncontact surface measurement
No full textA non-contact method for the recovery of audio signals from early acoustic cylinder recordings is presented.
The cylinder surface is scanned via optical displacement sensor, capable of submicron axial resolution. Sound recovery
is achieved by estimating the trajectory of a playback stylus over the measured surface. The processing methods
required to extract audio from a discrete height map are described. The signal to noise ratio of the extracted signal as a
function of position across the groove cross-section is examined, for a Blue Amberol cylinder, (circa 1912)
An Algorithmic Approach to the Optimal Extraction of Signals from Intelligent Sensors
No full textThis paper describes the development of an intelligent sensor architecture, where signal conditioning is performed onboard the sensor itself, in software. Our proposed architecture uses data-based models of the sensor for signal conditioning and fault detection, so that the sensor is robust to degradation and its processed output includes an estimate of uncertainty with each measurement value for higher level sensor management processes such as data fusion. We use a data-based kernel representation for the signal conditioning system, which avoids deriving physical models of the sensor from first principles. A sparse realisation of the kernel model provides fast predictions and opportunities for efficient updating of the sensor model to enable reconfiguration of the sensor model based on incoming data. We show that these techniques have the ability to detect degradation in a MEMS sensor, using elevated temperatures in laboratory conditions
An ultrasonic transducer array for velocity measurement in underwater vehicles
No full textA correlation velocity log (CVL) is an ultrasonic navigation aid for marine applications, in which velocity is estimated using an acoustic transmitter and a receiver array. CVLs offer advantages over Doppler velocity logs (DVLs) in many autonomous underwater vehicle (AUV) applications, since they can achieve high accuracy at low velocities even during hover manoeuvres. DVLs require narrow beam widths, whilst ideal CVL transmitters have wide beam widths. This gives CVLs the potential to use lower frequencies thus permitting operation in deeper water, reducing power requirements for the same depth, or allowing the use of smaller transducers.Moving patterns in the wavefronts across a 2D receiver array are detected by calculating correlation coefficients between bottom reflections from consecutive transmitted pulses, across all combinations of receiver pairings. The position of the peak correlation value, on a surface representing receiver-pairing separations, is proportional to the vessel's displacement between pulses.A CVL aimed primarily for AUVs has been developed. Its acoustical and signal processing design has been optimised through sea trials and computer modelling of the sound field. This computer model is also used to predict how the distribution of the correlation coefficients varies with distance from the peak position.Current work seeks to increase the resolution of the peak estimate using surface fitting methods. Numerical simulations suggest that peak estimation methods significantly improve system precision when compared with simply identifying the position of the maximum correlation coefficient in the dataset. The peak position may be estimated by fitting a quadratic model to the measured data using least squares or maximum likelihood estimation. Alternatively, radial basis functions and Gaussian processes successfully predict the peak position despite variation between individual correlation datasets.This paper summarises the CVL's main acoustical features and signal processing techniques and includes results of sea trials using the device. <br/
Improvement of velocity estimate resolution for a correlation velocity log using surface fitting methods
No full textA Correlation Velocity Log (CVL) is an acoustical navigation aid, consisting of a transmitter and a receiver array. Moving patterns in the wave fronts across the receiver army, indicative of motion, are detected by calculating correlation coefficient between bottom reflections from consecutive transmitted pulses. A velocity vector map is constructed by plotting the correlation coefficient on a grid representing the, velocity vector spacing. The peak position on this map surface provides an estimate of the velocity vector of the vessel.The resolution of the velocity vector map is limited by the minimum diameter of the receiving elements and the maximum size of the array. Current research is focused on exploiting the full potential of the CVL by investigating surface fitting techniques to' interpolate peak position estimates between measurement points.Detailed simulations and sea trials of a prototype CVL have demonstrated that the correlation coefficient surface is subject to high variance at only a modest distance from the peak. This paper presents numerical comparisons between different surface-fitting methods for performing peak finding on the data. Different least squares schemes are investigated, together with a non-liner iterative implementation of Maximum Likelihood Estimation. The performance of these methods is compared both in terms of rms error and mean, error in peak estimation.It is shown that CVL performance can he improved significantly by the use of an appropriate peak finding technique
