arXiv subjects

Sam Keller

Publications and source records attributed to Sam Keller.

5 recordsLinked to original sources

arXiv2026

Steerable Radiation Forces with Frequency-Detuned Acoustic Metasurfaces

We demonstrate that acoustic waves can induce controlled translation and rotation of macroscopic objects through small, but deliberate, detuning of the driving wave frequency. When an object is patterned with a suitably designed acoustic metasurface, small changes in the incident frequency $\omega \pm \delta \omega$ are converted into directional radiation forces and torques, enabling steerable motion even for objects much larger than the acoustic wavelength. We present the concept of a force-optimal metasurface topology and show that it enables fully reversible forces in real time: the object is moved in one direction for positively detuned incident frequency $\omega+\delta \omega$ and in the opposite direction for negatively detuned frequency $\omega-\delta \omega$, where $\omega=22.5 \textrm{ kHz}$ and $\delta \omega =2.5 \textrm{ kHz}$ for a proof of concept at inaudible frequencies. This mechanism is demonstrated experimentally at ultrasonic frequencies with 3D-printed metasurfaces. The proposed concept is scalable across frequencies and materials, offering a building block for realizing complex, remote-controlled, dynamical behaviors that can be programmed by reconfiguring material surface patterns.

physics.app-ph↗

arXiv2026

Adaptive and ultrabroadband thermal control with solid-state nanophotonic emitters

Managing the emission and absorption of thermal radiation is crucial for a wide range of technologies, from radiative cooling of buildings and vehicles to thermal regulation of satellites and future lunar and Mars habitats. Despite this universal and critical need, thermal emitters capable of adaptively modulating emissivity in a broadband, high-contrast, and fully solid-state manner remain elusive. Here, we leverage neural-network-guided photonic design to enable adaptive, solid-state thermal emitters based on chalcogenide phase-change materials capable of emissivity switching with extreme spectral contrast and bandwidth. These engineered nanophotonic emitters operate over a broad spectrum$-$from solar through thermal infrared$-$providing very low solar absorptivity while enabling switchable thermal infrared emissivity with high contrast. We experimentally demonstrate the core functionality of our approach in the space-like radiative environment in the stratosphere, observing a 31.5 {\deg}C temperature differential between the two solid-state phases of a simplified chalcogenide GeSbTe-225 thermal emitter. Our results point to even more significant capabilities, such as the potential to modulate >600 W/m$^2$ of radiative heat (at 100 {\deg}C) with minimal solar heating in the vacuum of space. The proposed nanophotonic solid-state adaptive emitter could provide high-power and high-speed heat modulation while requiring no power to maintain state, offering transformative capabilities for thermal control in dynamic radiative environments on Earth and in space.

physics.app-ph↗

arXiv2025

Multifunctional Lightweight Radiators for Small-Satellite Thermal Control

Thermal management in small satellites is constrained by limited radiative area and strict mass budgets, necessitating the development of radiator structures that are simultaneously lightweight, thermally conductive, and mechanically robust. Here, we present a topology-optimization and design-space analysis framework for multifunctional lightweight radiators that achieve high specific stiffness and high effective thermal conductivity through simultaneous structural and thermal optimization. Density-based optimization produces hierarchical architectures that naturally form continuous cavities suitable for high-conductivity channels such as embedded heat pipes. The resulting microarchitectures exhibit Pareto behavior indicating efficient trade-offs between mass, stiffness, and thermal conductivity, while maintaining dynamic stability across a broad range of design parameters. Coupled structural-thermal analysis shows that voids used as thermal channels yield nearly isothermal radiating surfaces, confirming efficient lateral and transverse heat flow through the radiator. This integrated framework contributes toward the development of thermo-mechanically optimized radiator panels for small-scale spacecraft, enabling compact and efficient thermal control solutions.

physics.class-ph↗

arXiv2022

3D Printing via material extrusion on an acoustic air bed

Additive manufacturing, such as 3D printing, offers unparalleled opportunities for rapid prototyping of complex three-dimensional objects, but typically requires simultaneous building of solid supports to minimize deformation and ensure contact with the printing surface. Here, we theoretically and experimentally investigate the concept of material extrusion on an "air bed", a judiciously engineered acoustic field that supports the material by contactless radiation force. We study the dynamics of polylactic acid filament (PLA), a commonly used material in 3D printing, as it interacts with the acoustic potential during extrusion. We develop numerical models to determine optimal transducer arrangements and printing conditions, and we build and demonstrate a concept prototype that integrates a commercial 3D printer and open-source control code. Our results point towards alternative, contactless support mechanisms with potential benefits such as fewer surface defects, less material waste, lower cost, and reduced manufacturing time. These features could become crucial as additive manufacturing continues to evolve into a foundational tool in engineering and beyond.

physics.app-ph↗

arXiv2022

Shaping contactless forces through anomalous acoustic scattering

Waves impart momentum and exert force on obstacles in their path. The transfer of wave momentum is a fundamental mechanism for contactless manipulation, yet the rules of conventional scattering intrinsically limit the radiation force based on the shape and the size of the manipulated object. Here, we show that this intrinsic limit can be overcome for acoustic waves with subwavelength-structured metasurfaces, where the force becomes controllable by the arrangement of surface features, independent of the object's overall shape and size. Harnessing such anomalous metasurface scattering, we demonstrate complex actuation phenomena: self-guidance, where a metasurface object is autonomously guided by an acoustic wave, and contactless pulling, where a metasurface object is pulled by the wave. Our results show that bringing metasurface physics, and its full arsenal of tools, to the domain of mechanical manipulation opens the door to diverse actuation mechanisms that are beyond the limits of traditional wave-matter interactions.

physics.app-ph↗