RECENT ADVANCES IN THE MEASUREMENT OF STRUCTURAL IMPEDANCE

Abstract
Two devices for measuring mechanical impedance have been developed, one for heavy structures capable of measuring a stiffness of 140 x 10 to the 6th power lb/in. over the frequency range of 5 to 4000 cps and the other for lighter structures capable of measuring a stiffness of 5 x 10 to the 6th power lb/in. over the frequency range of 20 to 8000 cps. Phase angles are measured in the presence of noncorrelated vibrational and electrical noise and distortion. Each device uses two piezoelectric ceramics to sense the applied force and the acceleration response of the structure. The mass associated with the coupling between the impedance transducer and the structure is cancelled electronically. Novel detaipiezoelectric transducers and the reduction of mechanical crosstalk. Manual and automatic phase and impedance measuring systems having a high degree of accuracy are discussed. The report includes procedures for determining the acoustic sensitivity, transverse sensitivity, rocking sensitivity, and strain sensitivity of accelerometers and practical considerations for making mechanical impedance measurements. (Author of the design are presented, such as the elimination of magnetic pickup by the piezoelectric transducers and the reduction of mechanical crosstalk. Manual and automatic phase and impedance measuring systems having a high degree of accuracy are discussed. The report includes procedures for determining the acoustic sensitivity, transverse sensitivity, rocking sensitivity, and strain sensitivity of accelerometers and practical considerations for making mechanical impedance measurements.

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