Non-Hermitian elastodynamics

Project Information

EXCEPTIONAL

Grant agreement ID: 101045494

DOI

10.3030/101045494

EC signature date 28 April 2022

Start date 1 September 2022

End date 31 August 2029

Funded under

• European Research Council (ERC)

Total cost

€ 1 594 166,25

EU contribution

€ 1 594 166,00

Coordinated by

TECHNION - ISRAEL INSTITUTE OF TECHNOLOGY
Israel

Periodic Reporting for period 1 - EXCEPTIONAL (Non-Hermitian elastodynamics)

Reporting period: 2022-09-01 to 2025-02-28

Summary of the context and overall objectives of the project

The properties of artificial materials can be tailored to exhibit extraordinary properties by cleverly engineering their composition. The development of such metamaterials is a prominent thrust in engineering today. One of the greatest challenges is to engineer metamaterials that manipulate waves by design. Of particular interest are elastic waves, since numerous mechanical applications require their control; vibration isolation, ultrasonography, energy harvesting and cloaking, to name a few. The forefront of research in wave control emerged from a seemingly unrelated theory, quantum mechanics, with the development of its non-Hermitian formalism, describing nonconservative systems that exchange energy with their environment. By drawing analogies between this formalism and those of classical systems, researchers have discovered phenomena that defy intuition, phenomena such as zero reflection and chiral absorption, and have exploited them to control light, sound, and elastic waves. This project goes beyond these analogies by exploiting the rich nature of elastodynamics, a nature that is unparalleled in other physics, in order to access unexplored non-Hermitian features and harness them for unprecedented wave control.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We have discovered a new form of elastic waves, known as axially frozen elastic waves, since their axial (group) velocity is zero, in spite of the fact that their transmittance is finite and can even reach unity.
We have developed simplified models for metamaterials whose linear momentum is coupled with electric field, a coupling that termed "the electromomentum coupling" and can be exploited for wave manipulation. Our models elucidate the physical origins of the electromomentum coupling, illustrate its mechanism, and identify local resonances which lead to elevated Willis and electromomentum coupling in narrow frequency bands. The results provide intuitive guidelines for the design of this coupling in piezoelectric metamaterials, and set the stage for future design of non-Hermitian features via odd electromomentum tensors.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our results on axially frozen elastic waves pave the way for robust manipulation (i.e. guiding, harvesting etc.) of mechanical energy. Our results on the electromomentum coupling bring it closer towards its usage in sensing applications, as it enables inertial sensing directly from the material’s motion without requiring parasitic elements such as proof masses, providing a compact way of measuring both pressure and velocity fields; and inherently supports direction- and frequency-selective transduction responses, which can be tailored for a wide range of technological and defense-relevant applications. The ability to enable extreme forms of coupling with reconfigurable features opens an entirely uncharted design space for next-generation transduction devices, which can be used to detect, generate, and transport elastic and electromagnetic signals in efficient ways.

Breaking of axial symmetry and high-order mode degeneracy

Axially frozen elastic waves with unity transmittance

non-Hermitian odd electromomentum constitutive operators in elastodynamics