The benchmark
The National Physical Laboratory (NPL) was set up in 1900 in Teddington, Middlesex, and is the UK's National Measurement Institute. It connects the latest scientific innovation with the real world by creating measurement standards for industries to maintain an accurate infrastructure for new technology.
Over the years, NPL has been involved in many significant projects. For example, research into the force of wind was used in 1908 to study the effects on flight. This allowed rapid advances in the efficiency and safety of the aeroplane. Later, in 1919, a wind tunnel was built at NPL and Sir Thomas Stanton, Superintendent of the Engineering Department, pioneered the science of wind.
Early tests of the bouncing bomb were undertaken in the NPL ship tanks in 1942. The bombs were designed to bounce across the water surface to avoid torpedo nets and were successfully deployed in 1943. Part of the 1955 movie The Dam Busters, about the bombs and the second world war, was filmed at NPL.
In 1976, NPL designed and fitted fail-safe brakes for the quarter-chiming mechanism of London's iconic Big Ben. Nowadays, NPL is the largest applied physics organisation in the UK and is managed by Serco on behalf of the Department for Business, Innovation and Skills. It continues to be involved in developments in all industries from hospital equipment to F1 racing.
More recently, NPL announced results for a new technique to measure time using optical frequency, which could provide a tenfold improvement in time measurement accuracy. The technique involves freezing single strontium atoms to about -273°C. The atom then moves precisely between two energy states, like the ticking of a clock. A laser beam is locked onto this 'ticking', providing a measurable optical frequency.
New dimensions
One type of device NPL works with is ear simulators. These are used to set up (or calibrate) audiometers, which in turn are used to test hearing. They are also used to check hearing aids and to design and test a wide range of other devices, such as telephone handsets, audio headphones and earplugs.
There are many types of ear simulator. Some look nothing like a real (human) ear, but are designed to make the best possible measurement of a specific type of device. Others are more general-purpose and have some anatomically correct features such as the shape of the pinna (the external part of the ear) and the width of an average human head. NPL have recently measured sound-pressure levels produced by ordinary in-ear headphones, to ensure they do not damage people's hearing.
Other facilities at NPL include the hemi-anechoic chamber, used to measure sound in air. The 8x8x5m room is covered in soft fibreglass wedges (a similar materialto loft insulation) that absorb sound waves. The chamber provides the perfect environment in which to test acoustic equipment for industries as varied as medical ultrasound and oceanographic research. Food manufacturers have even used it to test the 'crunch' properties of their crisps and biscuits.
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