National Physical Laboratory

Underwater acoustical standards under simulated ocean conditions

NPLs Acoustic Pressure Vessel (APV)

This project provides standards for acoustic transducer testing and free field materials testing at simulated ocean conditions by use of the NPL APV (Acoustic Pressure Vessel), and disseminates those standards by operating measurement services. The results of the characterisation of commercial hydrophones will be disseminated to industry to act as guidance of the use of these devices.

The environmental conditions within the APV can be modified to simulate ocean depths down to 700 m (hydrostatic pressure from atmospheric to 7 MPa) and temperatures from 2 °C to 35 °C. With the APV, NPL provides a valuable national facility which is unique within Europe, a fact recognised by the UK underwater acoustic industry. This facility consolidates NPL's already pre-eminent position as the world-leading NMI in underwater acoustics.

As noted earlier, the APV provides a cost-effective alternative to sea-trials which is an order of magnitude less expensive. To maximise savings to industry, it is therefore of considerable importance to be able to maximise the usefulness of the facility in terms of the technical capability. Novel methods will be investigated to increase the frequency range over which measurements may be made in the APV, with particular emphasis on the difficult low frequency range below a few kilohertz.

The materials used in underwater acoustics often have an important influence on the transducer performance, especially if the material properties vary with temperature and depth of immersion (for example for viscoeleastic materials). Methods of characterisation of these materials have been undertaken in the NPL APV, but there is a need to further extend the frequency range of the measurements down below the current limit of 5 kHz.

Last Updated: 11 Feb 2014
Created: 6 Jun 2007

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