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.

This work demonstrates the design, fabrication, and characterization of the first piezoelectric micromachined ultrasonic transducers (PMUTs) based on bilayer X-cut lithium niobate (LiNbO3). A comparison of PMUT materials based on different figures of merit (FoMs) is presented, highlighting LiNbO3 as a promising and well-balanced alternative to more conventional materials. To leverage its superior material properties, PMUTs were designed based on bilayer X-cut LiNbO3 to fully harnesses the in-plane stress associated with the bending of the structure, thereby enhancing transduction. The fabricated devices show high electromechanical coupling (k2t ) of 4:6 %, albeit significantly lower than the simulated value due to parasitic effects. Mechanical vibration characterization shows a high static displacement of 0:88 nm=V and excellent linear dynamic range. Based on this design, an 8 × 1 array is demonstrated showing excellent consistency among the elements, with a frequency spread of 0:006 MHz and a displacement sensitivity spread of 0:15 nm=V. Our devices show comparable performance to monocrystalline PZT-based PMUTs, and substantially outperform ScAlN-based PMUTs in terms of static displacement sensitivity by a factor of 5. These results underscore the strong potential of LiNbO3 for high-performance PMUTs.

This work identifies the optimal orientation of lithium niobate (LiNbO3, LN) for piezoelectric micromachined ultrasonic transducers (PMUTs) operating in lateral-field excitation (LFE) and thickness-field excitation (TFE) modes. Geometry-independent material figures of merit (FoMs), representing the round-trip signal-to-noise ratio (SNR), are evaluated by sweeping rotated material tensors across the full orientation space. Finite element method (FEM) simulation is then used to quantify the electromechanical coupling k_t² under consistent device stacks and electrode layouts. The FoMs peak at 140°Y-cut LiNbO3 (≈120% of PZT-5H); the best commercial TFE option, 128°Y-cut, attains ~65% of that maximum. Under the shared baseline design, the highest k_t² is achieved with X-cut LiNbO3 (≈7.2%) using elongated rectangular membranes, about 70% of the PZT-5H reference. Our results provide clear design guidance for LiNbO3 PMUTs to maximize performance: optimal cut, in-plane rotation, and membrane geometry.