Vibrational Power Flow Measurement in a Beam Using Electronic Speckle Pattern Interferometry

Vibrational power flow or structural intensity analysis is used to study the many paths of vibrational energy flow around complex flexible lightweight structures such as cars and aircraft. The vibrational power flow approach was developed so that the various paths of energy flow in the structure could be ranked in a rational way. A series of fundamental studies of power flow in simple structural elements, such as beams and plates, has been conducted over the last 25 years. These methods of measuring power flow have relied heavily on arrays of accelerometers mounted directly onto the structure. However, the practical application of power flow analysis has been limited by the lack of suitable measuring equipment. This paper reports on a preliminary case study which demonstrates the application of Electronic Speckle Pattern Interferometry (ESPI) also known as 'TV holography' to measure the vibrational power flow due to flexural vibrations in an experimental beam with anechoic terminations. Results obtained from the ESPI based measurements at three different frequencies are compared to conventional two-accelerometer power flow measurements and also to the measured power input to the structure. Although it is difficult to draw general conclusions about the ESPI based system from a single case study under ideal "infinite" beam conditions a number of observations about using the measurement system are summarised at the end of the paper.