Reference Acoustic Envelope Detector

Assess the acoustic emission from product testing - How the Acoustic Envelope Detector works

In response to requests from both university and commercial research departments, Stable Micro Systems developed a method of measuring the acoustic energy release during a physical test. The acoustic system, which utilises a microphone and pre-amplifier from Danish sound and vibration experts Brüel & , Kjær, has high sensitivity to the frequencies emitted by brittle products but has low sensitivity to mechanical noise emitted by the Texture Analyser.

The system contains all the necessary components for connection to a TA.XTplus Texture Analyser, which will generate synchronised force, and sound profiles for individual tests to provide the "4th dimension in texture analysis".

The Production of Sound

When a force is applied to any material, resulting movements within the structure form sound waves. These sound waves can be monitored as acoustic emissions. The definition of acoustic emission is the transient elastic wave generated by rapid release of energy within a material. Another way to describe this is that when a load is applied to a specimen, energy is stored as strain energy. When an inherent critical point is reached in the sample, there is a sudden redistribution of the energy. At this point some of the strain energy is converted into acoustic energy.

The Marketing of Sound

Advertisers use onomatopoeia so consumers will remember their products – words for things are created from representations of the sounds these objects make. In English, for example, there is the universal fastener which is named for the sound it makes: the zip.

In the past few years, advertisers have made use of the crispness and crunchiness of foods. Television viewers cannot experience the taste or the smell of a product being advertised. They can only see it and, of course, hear it. Advertising the aural assets of a food acquaints the potential customer with this most important quality attribute of many products.The structure of a food and the mechanical properties of that structure are related to crispness by their capability to generate the appropriate sound and their ability to dampen or amplify this sound. The Acoustic Envelope Detector provides a tool for the quantification of this sound emission whilst measuring the textural properties of the product.

The Application of Sound

Whilst much work in this area has focussed on measuring crispness of brittle foods, potential applications include the quantification of:

• The ‘Snap’ of a biscuit (whilst measuring its breaking strength)
• The ‘Pop’ of a cork (whilst measuring its ease of removal)
• The ‘Fizz’ of a bath bomb or ‘Alka-Seltzer’ (whilst measuring its firmness
• The ‘Snap’ of a pencil (whilst measuring its breaking strength
• The ‘Click’ of a switch (whilst measuring its actuation force)