MEASUREMENT AND APPLICATION OF MECHANICAL IMPEDANCE DATA - 2. MEASUREMENT TECHNIQUES.

This article is the second in a three-part treatment of measurement and application of mechanical impedance data. There are several methods by which mechanical impedance data may be measured experimentally. The most straightforward approach is simply to impose a sinusoidally varying force on the structure under test and to measure the similarly sinusoidal response. This basic procedure is repeated over a range of frequencies in order to obtain the complete impedance curve. A number of alternative methods have been developed using nonperiodic excitations - such as an impulse, a short transient or a burst of random excitation - and these methods are useful when the duration of on-test vibration must be limited: for example, to minimize the risk of damage. In view of the somewhat specialized nature of alternative methods, only the basic sinusoidal excitation technique is described in this paper. Details of alternative methods may be found in the appropriate references listed in the bibliography section.