We are experts in the development of state-of-the-art algorithms for highly accurate time-of-flight measurement and transducer designs for liquid and gas flow. Through our experience with the technology, we have built specialist knowledge of ultrasonic waveguide and free-field propagation. We use a range of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) packages to aid and accelerate design and we continue to broaden our capabilities in this area through materials analysis.
To validate our models, we continually develop specialist in-house test facilities and use a range of external research test facilities.
Transducer design – materials and compatibility, radiation pattern design, housing design, damping, temperature effects.
Digital signal processing – filter design, frequency domain analysis and algorithm development.
Fluid dynamics for the control of medium flow – fluid dynamics modelling to observe and design for the behaviour of fluids within specific sensor configurations.
Modelling of acoustic propagation – observing the effects of flow profiles and medium interactions to aid sensor design.
Model Validation – we commonly use Laser Doppler Vibrometry and Particle-Image Velocimetry to validate our models.
Acoustic Waveguide Design – to isolate transducers from direct sources of heat, or within a fluid flow measurement sensor.
Cutting Edge Science and Technology – we have collaborated with NPL to develop the acousto-optic effect for ultrasonic frequencies, which also serves as a model-validation tool.
Acoustic measurements use one or more specifically-designed transducers to induce physical motion (a "signal") into a fluid medium such as air or diesel. The signal will propagate through the medium at the longitudinal speed of sound, and at the same time it will undergo various other transformations - such as attenuation, spreading, dispersion, reflection and refraction - depending on the state of the medium. A transducer can then be used to receive the signal after it has travelled some known path through the medium. The signal can be captured, digitally sampled and analysed, and measurements such as the time of flight and total attenuation can be made.
We have developed many different transducer designs for applications such as gas flow, liquid flow and anemometry. A significant amount of protected knowledge has been accrued through overcoming challenges, from fundamental transducer-medium impedance matching, to highly complex and specialist problems, including material’s acoustic property changes over working temperature range, mounting configurations, radiation pattern design, specialist bonding materials, and damping materials that can be used to increase transducer bandwidth.
Captured receive waveforms need to be analysed so that precise timing information can be calculated. Textbook methods such as cross-correlation and autocorrelation are not accurate enough to meet our high measurement specifications, while signal phase data extraction methods may be subject to errors caused by dispersion. Our significant experience has allowed us to develop a signal-processing algorithm that is highly guarded and capable of extremely accurate measurement.
We use COMSOL, ANSYS-CFX, PZ-Flex and OpenFOAM amongst other modelling packages to assist us throughout the acoustic design process, which results in reduced design times. Modelling provides us with insight into the fundamental physics and nature of a system and allows us to identify potential design flaws and solutions. For example, fluid dynamic modelling enabled us to identify an undesirable flow profile in an early design of the fuel flow meter, which would otherwise have been almost impossible to identify; it then allowed us to observe the effects of design changes to improve and eventually perfect the velocity profile. One of our main future challenges is to capture specialist material property information to ensure modelling remains a valuable asset in our toolset.
It is of course important to validate any models where possible. This can be done through bulk parameter measurement, such as measuring the time of flight of a pulse in a prototype unit and comparing with a model of the same situation. Where appropriate, more complex measurement methods can be employed, such as Laser-Doppler Vibrometry (to observe the motion of a vibrating surface for example), Particle-Image Velocimetry (to observe the motion of a fluid around or through a structure) and Acousto-Optic effect (to observe the propagation of ultrasonic waves).
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