A simple configuration of an active Nonreciprocal Gyroscopic Meta-Material (NGMM) is presented. In the proposed NGMM system, a one-dimensional acoustic cavity is provided with piezoelectric boundaries acting as a collocated pair of sensors and actuators. The active piezo-boundaries are controlled by a simple control algorithm that synthesizes a virtual gyroscopic control action to impart desirable non-reciprocal characteristics which are tunable both in magnitude and phase. The dynamic model of a prototype of the NGMM cell is experimentally identified in an attempt to provide means for predicting the characteristics of the virtual gyroscopic controller for various control gains during forward and backward propagations. The theoretical predictions are validated experimentally without the need for any physical dynamic controller which was provided, in previous studies, by using a dummy NGMM cell. Such a simplified arrangement enables the fast execution of the controller with enhanced frequency bandwidth capabilities. The experimental and theoretical characteristics of the NGMM cell are monitored and predicted for different control gain in order to evaluate its behavior for both forward and backward propagation. The obtained experimental results are compared with the theoretical predictions and are found to be in close agreement. The presented concepts provide the foundation necessary for implementation of NGMM that can be employed to more complex 2D and 3D critical structures in order to achieve non-reciprocal behavior in a simple and programmable manner.

This paper presents a class of active non-reciprocal metamaterials (ANMMs) in an attempt to control the flow of acoustic waves along a one-dimensional acoustic duct. The proposed method distinguishes itself from the available approaches where the non-reciprocities are generated either actively or passively by various sources of nonlinearities, circulators and gyroscopic/gyrator components, and/or spatiotemporal modulation. The proposed method relies in its operation on a controller that is designed by simultaneous allocation of both the eigenvalues and eigenvectors. In other words, the entire eigen-structure of the closed-loop system is assigned as deemed necessary. Conventionally, the placement of the eigenvalues has been employed to enhance both the damping and response of the system. However, in this study, the focus is placed on adjusting the eigenvectors in a way that enables the spatial control and redistribution of the wave propagation along the acoustic duct in order to produce any desirable non-reciprocal behavior. During this entire process, the system continues to behave in a linear fashion. The theory governing the operation of this proposed approach is introduced, and a comprehensive experimental validation effort is presented to demonstrate the basic features, non-reciprocal behavior, and control characteristics. Generalization of the presented strategies to two-dimensional acoustic systems is a natural extension of the present work.

Experimental realization of a new class of active Nonreciprocal Gyroscopic Meta-Material (NGMM) is presented. The proposed active NGMM system consists of a one-dimensional acoustic cavity provided with piezoelectric boundaries that act as sensors and actuators. These active boundaries are integrated with linear dynamic control capabilities that virtually synthesize a gyroscopic control action in order to generate desirable non-reciprocal characteristics of tunable magnitude and phase shift. The dynamics of a prototype of the NGMM cell are identified experimentally and the theoretical characteristics of the virtual gyroscopic controller are predicted for various control gains for both forward and backward propagations. The theoretical predictions are validated experimentally using a dummy NGMM cell to act as a physical dynamic controller. Such a preferred arrangement is coupled with analog controllers in order to enable fast execution of the controller and, in turn, enhance the bandwidth of its operating frequency. The time and frequency response characteristics of the NGMM cell are measured for different control gain and the behavior is evaluated for both forward and backward propagations. The obtained experimental results are found to be in close agreement with the theoretical predictions. The presented concept, controller design, and implementation of the NGMM can be extended to various critical structures to achieve realistic acoustic diode configurations in a simple and programmable manner.

During the drilling process in oil and gas fields, slender drill strings often experience a multitude of complex and simultaneous vibrational phenomena. Drill string vibrations hinder the drilling process and can cause premature wear and damage to the drilling equipment. Here, the suppression of drill string vibrations during drilling operations is experimentally investigated using a novel drill string design, based on the use of innovative periodic inserts that control the vibration transmissibility in different directions. These inserts are equipped with viscoelastic rings that act as sources of local resonances, surrounding piezoelectric actuators that generate internal axial loading when electrically excited. An experimental prototype that combined all these details was constructed and tested to demonstrate the periodic drill string's feasibility and effectiveness in minimizing undesirable vibrations. The obtained results indicate that the periodic inserts' careful design can effectively enhance the drill strings' dynamic behavior and conveniently regulate its bandgap characteristics. Both radial and axial vibrations were controlled, and the vibrations' amplitude was reduced significantly over a wide range of frequencies. The proposed approach appears to present a viable means for designing intelligent drill strings with tunable bandgap characteristics.

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