A substantial challenge in guiding elastic waves is the presence of reflection and scattering at sharp edges, defects, and disorder. Recently, mechanical topological insulators have sought to overcome this challenge by supporting back-scattering resistant wave transmission. In this paper, we propose and experimentally demonstrate a reconfigurable electroacoustic topological insulator exhibiting an analog to the quantum valley Hall effect (QVHE). Using programmable switches, this phononic structure allows for rapid reconfiguration of domain walls and thus the ability to control back-scattering resistant wave propagation along dynamic interfaces for phonons lying in static and finite-frequency regimes. Accordingly, a graphene-like polyactic acid (PLA) layer serves as the host medium, equipped with periodically arranged and bonded piezoelectric (PZT) patches, resulting in two Dirac cones at the K points. The PZT patches are then connected to negative capacitance external circuits to break inversion symmetry and create nontrivial topologically protected bandgaps. As such, topologically protected interface waves are demonstrated numerically and validated experimentally for different predefined trajectories over a broad frequency range. Significance We present a demonstration of topologically protected states using reconfigurable electroacoustic TIs whose design is simple, effective, and straightforward to fabricate. Numerical simulations and experimental measurements illustrate topologically protected wave propagation, free of back-scattering, along edges and interfaces. We anticipate these materials will have broad implications for devices capable of mechanical logic and circuitry, which may have advantages over electronic equivalents in harsh operating conditions, or in replacing wireless systems near propagation dead zones. Due to their dynamic reconfigurability, they may also lead to small-scale multiplexing and demultiplexing devices for use in communication devices, similar to the ubiquitous surface acoustic wave (SAW) devices used to filter electromagnetic energy.

In this paper, we designed and analyzed a piezo-lens to focus flexural waves in thin plates. The piezo-lens is comprised of a host plate and piezoelectric arrays bonded on the surfaces of the plate. The piezoelectric patches are shunted with negative capacitance circuits. The effective refractive indexes inside the piezo-lens are designed to fit a hyperbolic secant distribution by tuning the negative capacitance values. A homogenized model of a piezo-mechanical system is adopted in the designing process of the piezo-lens. The wave focusing effect is studied by the finite element method. Numerical results show that the piezo-lens can focus flexural waves by bending their trajectories, and is effective in a large frequency band. The piezo-lens has the ability to focus flexural waves at different locations by tuning the shunting negative capacitance values. The piezo-lens is shown to be effective for flexural waves generated by different types of sources.

Tailoring the dynamical behavior of wave-guide structures can provide an efficient and physically elegant approach for optimizing mechanical components with regards to vibroacoustic propagation. Architectured materials as pyramidal core kirigami cells combined with smart systems may represent a promising way to improve the vibroacoustic quality of structural components. This paper describes the design and modeling of a pyramidal core with auxetic (negative Poisson’s ratio) characteristics and distributed shunted piezoelectric patches that allow for wave propagation control. The core is produced using a kirigami technique, inspired by the cutting/folding processes of the ancient Japanese art. The kirigami structure has a pyramidal unit cell shape that creates an in-plane negative Poisson’s ratio macroscopic behavior. This structure exhibits in-plane elastic properties (Young’s and shear modulus) which are higher than the out-of-plane ones, and hence this lattice has very specific properties in terms of wave propagation that are investigated in this work. The short-circuited configuration is first analyzed, before using negative capacitance and resistance as a shunt which provides impressive band gaps in the low frequency range. All configurations are investigated by using a full analysis of the Brillouin zone, rendering possible the deep understanding of the dynamical properties of the smart lattice. The results are presented in terms of dispersion and directivity diagrams, and the smart lattice shows quite interesting properties for the adaptive filtering of elastic waves at low frequencies bandwidths.

Time-space modulated media are realized by periodically modulating parameters of the media in both time and space. In this paper, we study frequency conversion induced by time-space modulated media. Two types of frequency conversion are theoretically and numerically demonstrated; their underlying mechanisms are explained by considering the unusual properties of Bloch modes. We find that the first type of conversion is induced by energy transmission between different orders of Bloch modes, which can be observed when waves inside time-space modulated media are reflected by boundaries. The second type is caused by the Bragg scattering effect occurring inside time-space modulated media; it can be observed when external waves are reflected by time-space modulated media. The frequency can be up or down converted, and the difference caused by the conversion depends on the modulation frequency, which is tunable. Therefore, these frequency conversion phenomena could be exploited to manipulate waves' frequencies for particular purposes.

The ongoing improvements in the size and in the power of micro-controllers allow to implement real-time computations of digital filters or control laws. With audio dedicated components, it becomes easier to integrate the control of piezoelectric transducers directly inside structures with discretized feedback controllers. It paves the way to more intelligent systems with adaptive capabilities. Through the z-transform, the behavior of an electrical impedance or of a controller can be written as a recurrent equation directly computable by a micro-controller. Yet the signals are sampled and quantified and it is necessary to run the computations at least twice as fast as the higher frequency f the controlled structure. The delay induced by the computations and the conversion of the signals has to be taken into account to insure the stability of the control. Finally, the type of computation (fixed or floating point) can be a technological problem. This paper highlights the experimental implementation of integrated controlled structures with regards to the technological constraint