Resonance Introduction

March 29, 2018

Because resonance is an important concept in sine testing, we return to that concept now. Earlier, we defined resonance as the state of a system in which an abnormally large vibration is produced in response to an external stimulus, occurring when the frequency of the stimulus is the same, or nearly the same, as the natural vibration frequency of the system. In Figure 4.1, three resonances stand out, at 67.99Hz, 142.1Hz, and 538.1Hz. When, for instance, the shaker vibrated at 538.1Hz (538.1cycles per second)—the external stimulus—the end of the beam responded with a much greater vibration. The amplitude of the external stimulus was about 1G. The amplitude of the vibration of the end of the beam vibrated at 33.11G. The frequency of the stimulus was the same, or nearly the same, as the natural vibration frequency of the metal beam. There are several measurements that are used to describe a resonance: transmissibility, bandwidth, and Q-factor. To these measurements, we now turn.

Figure 18: Resonances of a metal beam

Figure 4.1. Resonances of a metal beam.