Abstract
By designing tailor-made resonance modes with structured atoms, metamaterials allow us to obtain constitutive parameters outside their limited range from natural materials. Nonetheless, tuning the constitutive parameters depends on our ability to modify the physical structure or external circuits attached to the metamaterials, posing a fundamental challenge to the range of tunability in many real-time applications. Here, we propose the concept of virtualized metamaterials on their signal response function to escape the boundary inherent in the physical structure of metamaterials. By replacing the resonating physical structure with a designer mathematical convolution kernel with a fast digital signal processing circuit, we demonstrate a decoupled control of the effective bulk modulus and mass density of acoustic metamaterials on-demand through a software-defined frequency dispersion. Providing freely software-reconfigurable amplitude, center frequency, bandwidth of frequency dispersion, our approach adds an additional dimension to constructing non-reciprocal, non-Hermitian, and topological systems with time-varying capability as potential applications.
Highlights
By designing tailor-made resonance modes with structured atoms, metamaterials allow us to obtain constitutive parameters outside their limited range from natural materials
Tuning can be extended to the level of each individual atom when backend electronics such as an FPGA chip or a computer are used to store and alter the state of the controlling parameters[22,23,24]. For most of these metamaterials, tuning largely depends on the actual mechanism for modifying the metamaterial resonance of the physical structures. This poses a fundamental challenge in terms of the degree of flexibility or range of tunability, which is crucial in many applications requiring real-time reconfigurability
By replacing the frequency resonating response of a physical metamaterial structure with a mathematically designed frequency dispersion implemented by digital convolution in the time domain within a microprocessing unit, the impulse response and the form of atomic response of a metamaterial structure is virtualized using a software code for digital representation
Summary
By designing tailor-made resonance modes with structured atoms, metamaterials allow us to obtain constitutive parameters outside their limited range from natural materials. In the context of tunability and reconfigurability, acoustic metamaterials mainly programmable by electronically controlled elements can be used to achieve a wide range of tunable effective parameters[25,26,27,28,29] These acoustic metamaterials have proved useful as a platform for many intriguing wave phenomena, such as unidirectional invisibility[26], sound isolation[27], Willis coupling[28], and highly tunable mechanical properties[29]. These works point to the direction that programmable control with external circuits or microprocessors can be used to provide a higher level of abstraction of the physical properties of metamaterials. While the artificial physical structures of metamaterials mimic the working of natural atoms with engineering degrees of freedom, the concept of virtualization generalizes this analogy to a digital representation with tunability based solely on software modification, assigning another level of meaning to “meta”
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