Thermally Programmable Two‐Port Non‐Hermitian Acoustic Metastructure for Broadband and Direction‐Dependent Absorption

ABSTRACT A thermally programmable two‐port non‐Hermitian acoustic metastructure is proposed to realize broadband and direction‐dependent sound absorption by exploiting temperature as a non‐geometric air‐property tuning variable. Within a unified transfer‐matrix and electro‐acoustic circuit modeling framework, the influence of thermal variation in air density, viscosity, and speed of sound on impedance matching and loss–leakage coupling is quantitatively described. The model reveals that thermal modulation shifts the scattering‐matrix eigenvalues and adjusts the critical‐coupling condition, enabling asymmetric absorption associated with exceptional point behavior. Numerical analyses show that, under thermally induced parameter changes, the structure achieves an effective bandwidth of 321 Hz at a deep subwavelength scale, while maintaining robust one‐sided suppression of reflection. Temperature‐driven transitions between under‐damped, critically damped, and over‐damped states further demonstrate how non‐Hermitian coupling can be programmably controlled without any geometric modification. The proposed framework consolidates theoretical modeling and numerical prediction, clarifies the mechanism of thermally programmable asymmetric absorption, and provides a compact route for broadband sound control in extreme or variable‐temperature environments. These results offer fundamental guidance for designing programmable acoustic absorbers and establish a foundation for future material and high‐temperature implementations.