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1. Thermal considerations for microswimmer trap-and-release using standing surface acoustic waves

   https://doi.org/10.1039/D1LC00257K  

   Cui, Mingyang; Kim, Minji; Weisensee, Patricia B.; Meacham, J. Mark (June 2021, Lab on a Chip)

   null (Ed.)

   Controlled trapping of cells and microorganisms using substrate acoustic waves (SAWs; conventionally termed surface acoustic waves) has proven useful in numerous biological and biomedical applications owing to the label- and contact-free nature of acoustic confinement. However, excessive heating due to vibration damping and other system losses potentially compromises the biocompatibility of the SAW technique. Herein, we investigate the thermal biocompatibility of polydimethylsiloxane (PDMS)-based SAW and glass-based SAW [that supports a bulk acoustic wave (BAW) in the fluid domain] devices operating at different frequencies and applied voltages. First, we use infrared thermography to produce heat maps of regions of interest (ROI) within the aperture of the SAW transducers for PDMS- and glass-based devices. Motile Chlamydomonas reinhardtii algae cells are then used to test the trapping performance and biocompatibility of these devices. At low input power, the PDMS-based SAW system cannot generate a large enough acoustic trapping force to hold swimming C. reinhardtii cells. At high input power, the temperature of this device rises rapidly, damaging (and possibly killing) the cells. The glass-based SAW/BAW hybrid system, on the other hand, can not only trap swimming C. reinhardtii at low input power, but also exhibits better thermal biocompatibility than the PDMS-based SAW system at high input power. Thus, a glass-based SAW/BAW device creates strong acoustic trapping forces in a biocompatible environment, providing a new solution to safely trap active microswimmers for research involving motile cells and microorganisms. 

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2. Tunable Organic Polymer/Inorganic Silicon Diode Using an Ionic Liquid Gel Gate Dielectric

   https://doi.org/10.1002/pssa.201900358  

   Rijos, Luis M.; Pinto, Nicholas J. (August 2019, physica status solidi (a))

   A diode is fabricated using poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT‐PSS) and n‐doped Si. Using an ionic liquid (IL) gel as the gate dielectric, the diode rectification ratio is tunable up to four orders of magnitude at very low operating voltages. Both p–n and Schottky type diodes are observed in the same device depending on the polarity of the gate voltage. IL‐gated electrostatic/electrochemical doping in PEDOT‐PSS is believed to be responsible for this switch. The turn‐on voltage in the first quadrant of the current–voltage (I–V) curve for the p–n diode is in the range 0.2–0.4 V. The Schottky diode operates in the third quadrant. This is the first report on a tunable diode using an IL to control its operation, and the low operating voltages make these diodes excellent candidates for use in reduced power consumption electronics. 

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3. Magnetically Assisted Vorticity Production in Decaying Acoustic Turbulence

   https://doi.org/10.3847/1538-4357/adbe38  

   Brandenburg, Axel; Scannapieco, Evan (April 2025, The Astrophysical Journal)

   Abstract We study vorticity production in isothermal, subsonic, acoustic (nonvortical), and decaying turbulence due to the presence of magnetic fields. Using three-dimensional numerical simulations, we find that the resulting kinetic energy cascade follows the ordinary Kolmogorov phenomenology involving a constant spectral energy flux. The nondimensional prefactor for acoustic turbulence is larger than the standard Kolmogorov constant due to the inefficient dissipation of kinetic energy. We also find that the Lorentz force can drive vortical motions even when the initial field is uniform by converting a fraction of the acoustic energy into vortical energy. This conversion is shown to be quadratic in the magnetic field strength and linear in the acoustic flow speed. By contrast, the direct production of vortical motions by a non-force-free magnetic field is linear in the field strength. Our results suggest that magnetic fields play a crucial role in vorticity production in cosmological flows, particularly in scenarios where significant acoustic turbulence is prevalent. We also discuss the implications of our findings for the early Universe, where magnetic fields may convert acoustic turbulence generated during cosmological phase transitions into vortical turbulence. 

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4. Coherent optical coupling to surface acoustic wave devices

   https://doi.org/10.1038/s41467-024-48167-7  

   Iyer, Arjun; Kandel, Yadav P.; Xu, Wendao; Nichol, John M.; Renninger, William H. (May 2024, Nature Communications)

   Abstract Surface acoustic waves (SAW) and associated devices are ideal for sensing, metrology, and hybrid quantum devices. While the advances demonstrated to date are largely based on electromechanical coupling, a robust and customizable coherent optical coupling would unlock mature and powerful cavity optomechanical control techniques and an efficient optical pathway for long-distance quantum links. Here we demonstrate direct and robust coherent optical coupling to Gaussian surface acoustic wave cavities with small mode volumes and high quality factors (>10⁵measured here) through a Brillouin-like optomechanical interaction. High-frequency SAW cavities designed with curved metallic acoustic reflectors deposited on crystalline substrates are efficiently optically accessed along piezo-active directions, as well as non-piezo-active (electromechanically inaccessible) directions. The precise optical technique uniquely enables controlled analysis of dissipation mechanisms as well as detailed transverse spatial mode spectroscopy. These advantages combined with simple fabrication, large power handling, and strong coupling to quantum systems make SAW optomechanical platforms particularly attractive for sensing, material science, and hybrid quantum systems. 

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5. Surface acoustic waves and lattice vibrations in two-dimensional ${\mathrm{Ti}}_3{\mathrm{C}}_2{T}_x$ $(T=\mathrm{O}, \mathrm{F})$ MXene films

   https://doi.org/10.1103/PhysRevB.111.214103  

   Hamilton, Parker; Kalia, Rajiv; Wixom, Ryan; Dingreville, Rémi (June 2025, Physical Review B)

   We investigated surface acoustic wave (SAW) propagation and lattice vibrations in two-dimensional (2D) titanium carbide $\left({\mathrm{Ti}}_3{\mathrm{C}}_2{T}_{\mathrm{x}}\right)$MXene films as a function of surface termination and layer stacking, using atomistic simulations. We found that SAW propagation velocity is highly sensitive to both single-layer properties and interlayer bonding. Surface terminations significantly modulate wave behavior, with oxygen and fluorine terminations producing distinct effects on wave propagation, with oxygen-terminated monolayers exhibiting 20% higher wave speeds than fluorine counterparts due to strengthened intralayer bonds. Key observations include the transition from one to two layers causing wave speed variations, and the development of interlayer modes that generate more dispersed lattice vibrations. As the film layer thickness increases, SAW propagation becomes predominantly confined to the upper surface, with coherence of vibrational modes diminishing in multilayer structures. These findings suggest MXene terminations and layer stacking are crucial parameters for controlling SAW behavior, offering promising avenues for novel acoustic wave device applications. Published by the American Physical Society2025 

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