Introducing a novel method to measure the frequency of out-of-plane vibration modes of miscellaneous parts with piezoelectric discs

Modal analysis is a structural method that reveals a structure’s vibrational behavior and offers optimal solutions to improve its performance. This method identifies the system’s intrinsic dynamic properties, including natural frequencies, mode shapes, and damping coefficients. Modal measurement methods are generally categorized into three techniques: experimental modal analysis, operational modal analysis, and impact synchronous modal analysis. This article introduces a novel method for measuring the out-of-plane vibration mode frequency in a structure using two piezoelectric discs. This method positions two piezoelectric discs at different locations on the sample and presses them against it. One piezoelectric disc is used for excitation and the other for data collection. Exciting the input piezoelectric in the frequency of an out-of-plane mode of a sample stimulates natural modes of the output piezoelectric. Since the radial mode of the output piezoelectric has a larger amplitude than the other modes, this frequency is observed in the output voltage of the piezoelectric. Therefore, the output frequency is anticipated to match the input frequency. However, when the input frequency is equal to the sample’s out-of-plane frequencies, the output frequency no longer aligns with the input and instead matches the radial frequency of the output disc. The output disc’s radial mode frequency is known; when it vibrates at this frequency, the input frequency matches the sample’s out-of-plane mode frequency. This method was tested on four samples of varying dimensions and shapes, and all experiments demonstrated that it accurately measures the out-of-plane mode frequency. The advantage of this method over previous methods is that it does not require expensive modal equipment such as shakers, analyzers, hammers and controlled conditions (such as a laboratory environment), and is not sensitive to environmental noise.