Acoustic delocalization sensing by scattering of surface acoustic waves
Micro- and nanomechanical resonators are widely used for chemical and biological detection. Mode localization sensing, based on the distribution of energy between two or more coupled resonators, has demonstrated enhanced sensitivity with respect to the conventional frequency shift method. In contrast, this work introduces an alternative sensing concept based on acoustic delocalization, where energy redistribution is induced in initially uncoupled surface acoustic wave (SAW) cavities by particle-triggered acoustic scattering. We implement this concept using two orthogonally arranged SAW resonators operating with a center frequency of around 415 MHz. Particle adsorption at the intersection region generates wave scattering that effectively couples the resonant cavities. This scattering-driven interaction leads to a redistribution of acoustic energy that was initially confined to a single cavity, enabling detection through the signal emerging in the non-driven cavity and providing information on the mechanical properties of the particles. Devices were fabricated to validate the proposed mechanism and demonstrated the detection of particle arrays. Finite element simulations agree well with experimental results and further reveal how the acoustic scattering coefficient depends on the mechanical properties of the particles and their spatial distribution. These results demonstrate the feasibility of acoustic delocalization sensing using SAW scattering and highlight its potential for robust and sensitive detection of micro- and nanoparticles.