A nonlinear ultrasonic method for real-time bolt looseness monitoring using PZT transducer–enabled vibro-acoustic modulation

TLDR

The authors develop a real‑time nonlinear ultrasonic technique using vibro‑acoustic modulation with piezoceramic transducers to quantitatively detect early bolt looseness, replacing the conventional shaker with a low‑cost PZT patch. The method modulates a high‑frequency probing wave with a low‑frequency pumping wave, generating sidebands that reflect bolt looseness, and examines how low‑frequency voltage amplitude affects the modulation. Experiments confirm that the PZT‑enabled vibro‑acoustic modulation reliably and continuously identifies bolt looseness and outperforms a time‑reversal linear ultrasonic method.

Abstract

A real-time nonlinear ultrasonic method based on vibro-acoustic modulation is applied to monitor early bolt looseness quantitatively by using piezoceramic transducers. In addition to the ability to detect the early bolt looseness, a major contribution is that we replaced the shaker, which is commonly used in a vibro-acoustic modulation method, by a permanently installed and low-cost lead zirconate titanate patch. In vibro-acoustic modulation, when stimulating two input waves with distinctive frequencies, namely the high-frequency probing wave and the low-frequency pumping wave, the high-frequency probing wave will be modulated by the low-frequency pumping wave to generate sidebands in terms of bolt looseness. Thus, the influence of low-frequency voltage amplitudes on the modulation results, which is ambiguous in previous research, is also analyzed in this article. The results of experiment demonstrated that the lead zirconate titanate–enabled vibro-acoustic modulation method is reliable and easy to implement to identify the bolt looseness continuously and quantitatively. In addition, low-frequency amplitudes of actuating voltage should be selected in a reasonable range. Finally, we compared the vibro-acoustic modulation method with the time-reversal method based on the linear ultrasonic theory, and the result illustrates that vibro-acoustic modulation method has better performance in monitoring the early bolt looseness.