Nanostructured AlN/YAlO3 Ceramic Media for Acoustic Signal Processing and Hardware Cryptography: A Grain-Boundary Entropy Model for Acoustic Physical Unclonable Functions

We propose a nanostructured AlN/YAlO3 ceramic metamaterial as a new class of Physical Unclonable Function (PUF) that unifies acoustic signal processing and hardware authentication in a single passive component. Unlike the optical PUF platforms in our prior work (LiNbO3, CsPbBr3), entropy here is extracted from the stochastic, thermodynamically unclonable distribution of the YAlO3 grain-boundary phase formed during ceramic consolidation, read out as a correlation-filter response to an incident acoustic wave. We derive an entropy model structurally analogous to our optical PUF framework, substituting ionic-radius dopant mismatch with coefficient-of-thermal-expansion (CTE) mismatch between AlN grains and the YAlO3 interphase as the driver of acoustic scattering. We calibrate the baseline (undoped-analog) term against real elastic and acoustic-mode Grüneisen data for ceramic AlN, and motivate the linear form of the scattering-vs-phase-fraction relationship by an established precedent from nonlinear ultrasonic characterization of second-phase content in engineering materials. We explicitly flag which parameters are calibrated against literature data and which remain theoretical predictions requiring direct measurement. Preliminary literature evidence indicates AlN retains its piezoelectric response under substantial neutron and gamma irradiation, supporting the extreme-environment motivation for this platform, while also showing that its elastic constants can degrade by up to 30% under high neutron fluence — a limitation we treat with the same honesty standard as the service-life analysis in our CsPbBr3 work. This is a theoretical proposal (pre-fabrication stage): no experimental entropy, NIST, or BER data exist yet for this platform. All PUF-relevant claims are predictions requiring the validation programme (V1-V8) described in the paper, not established results.