arXiv subjects

Martin Brandenbourger

Publications and source records attributed to Martin Brandenbourger.

14 recordsLinked to original sources

arXiv2026

On the rectification of oscillatory flows by flexible leaflets in a confined geometry

Inspired by biological systems, extensive research has explored how fluid-structure interactions in compliant channels and confined geometries control fluid transport. While local nonlinearities can be induced by individual components, arranging these elements into larger architectures gives rise to increasingly complex, collective responses. Predicting these collective behaviors, however, remains largely restricted to steady-state characterization, as the dynamic coupling between time-varying flows and multiple interacting structures is difficult to model. In this paper, we investigate numerically the collective interaction of multiple asymmetric leaflets within a channel at low-Reynolds number. By utilizing symmetrically oscillating plates rather than a pressure-driven flow to isolate the system from background asymmetries, we characterize how these interacting structures generate a net fluid transport. We develop an analytical framework to evaluate transport in the steady limit, which we subsequently extend to account for time-dependent channel oscillations, providing a complete dynamic description of the coupled fluid-structure system. Our results demonstrate that high leaflet densities maximize collective interactions and net transport. Furthermore, we define an elastoviscous number comparing viscous hydrodynamic forces to the restorative elastic forces of the leaflets, and uncover an optimal value that maximizes the net flow. This framework establishes a foundation for analyzing how collective slender structures interact dynamically within viscous environments, laying the groundwork for future studies on flow control in biological fluid transport and microfluidic design.

physics.flu-dyn↗

arXiv2026

Real time monitoring of pressure-induced deformation of PDMS to evaluate pressure distribution in microfluidic channels

Accurate pressure measurements in micrometric channels are essential for a wide range of microfluidic applications. Existing approaches rely on a variety of sensing mechanisms, but generally require the integration of additional probes or sensing elements during or after chip fabrication. Here, we introduce a pressure sensing approach based on quantitative phase imaging of the deformation of compliant microfluidic channels. We demonstrate real-time measurements of channel deformation over a large field of view with high sensitivity, without the need for embedded components or modifications of the microfluidic device.

physics.optics↗

arXiv2026

Spontaneous Emergence of Solitary Waves in Active Flow Networks with Elastic Elements

Flow networks are fundamental for understanding systems such as animal and plant vasculature or power distribution grids. These networks can encode, transmit, and transform information embodied in the spatial and temporal distribution of their flows. In this work, we focus on a minimal yet physically grounded system that allows us to isolate the fundamental mechanisms by which active flow networks generate and regulate emergent dynamics capable of supporting information transmission. The system is composed of active units that pump fluid and elastic units that store volume. From first principles, we derive a discrete model -- an active flow network -- that enables the simulation of large systems with many interacting units. Numerically, we show that the pressure field can develop solitary waves, resulting in the spontaneous creation and transmission of localized packets of information stored in the physical properties of the flow. We characterize how these solitary waves emerge from disordered initial conditions in a one-dimensional network, and how their size and propagation speed depend on key system parameters. Finally, when the elastic units are coupled to their neighbors, the solitary waves exhibit even richer dynamics, with diverse shapes and finite lifetimes that display power-law behaviors that we can predict analytically. Together, these results show how simple fluidic elements can collectively create, shape and transport information, laying the foundations for understanding -- and ultimately engineering -- information processing in active flow systems.

physics.flu-dyn↗

arXiv2026

Unidirectional flow from continuous broken symmetries

Locally broken symmetries are used across fields to transport matter, particles and information in preferential directions. Beyond local mechanisms, spatially distributed nonlinearities in crystalline media have enabled non-reciprocal transport, a rectification mechanism that operates continuously across scales and frequencies. Here, we show that this concept applies beyond condensed matter, to fluid transport in living organisms and artificial systems. We take the example of the lymphatic vascular system, which transports interstitial fluid in mammals, and demonstrate that distributed leaflets act as continuous broken symmetries. We build an artificial model of a collecting lymphatic and investigate the naturally richer dynamics of unidirectional transport that arises from spatiotemporal excitations. We observe robust and scalable transport for any waveshape and external pressure gradients. We show experimentally and theoretically that the contraction wavelength, directionality, and pulsatility control the flow rate. In particular, we counterintuitively find waveshapes that maximize transport when propagating against the direction of the flow. Overall, our findings advance the understanding of unidirectional fluid transport in living systems and beyond, and reveal how coupling nonlinearities with spatiotemporal excitations can tune such transport across fields.

cond-mat.soft↗

arXiv2025

Non-reciprocal breathing solitons

Breathing solitons consist of a fast beating wave within a compact envelope of stable shape and velocity. They can propagate and carry information and energy in a variety of contexts such as plasmas, optical fibers and cold atoms, but propagating breathers have remained elusive when energy conservation is broken. Here, we report on the observation of breathing, unidirectional, arbitrarily long-lived solitons in non-reciprocal, non-conservative active metamaterials. Combining precision desktop experiments, numerical simulations and perturbation theory on generalizations of the sine-Gordon and nonlinear Schrödinger equations, we demonstrate that unidirectional breathers generically emerge in weakly nonlinear non-reciprocal materials, and that their dynamics are governed by an unstable fixed point. Crucially, breathing solitons can persist for arbitrarily long times provided: (i) this fixed point displays a bifurcation when a delicate balance between energy injection and dissipation is struck; (ii) the initial conditions allow the dynamics to reach this bifurcation point. Importantly, discrete effects tend to stabilize these non-reciprocal breathers over a wider range of initial conditions. Our work establishes non-reciprocity as a promising avenue to generate stable nonlinear unidirectional waves, and could be generalized beyond metamaterials to optics, soft matter and superconducting circuits.

cond-mat.soft↗

arXiv2023

Self-oscillation and Synchronisation Transitions in Elasto-Active Structures

The interplay between activity and elasticity often found in active and living systems triggers a plethora of autonomous behaviors ranging from self-assembly and collective motion to actuation. Amongst these, spontaneous self-oscillations of mechanical structures is perhaps the simplest and most wide-spread type of non-equilibrium phenomenon. Yet, we lack experimental model systems to investigate the various dynamical phenomena that may appear. Here, we report self-oscillation and synchronization transitions in a centimeter-sized model system for one-dimensional elasto-active structures. By combining precision-desktop experiments of elastically coupled self-propelled particles with numerical simulations and analytical perturbative theory, we demonstrate that the dynamics of single chain follows a Hopf bifurcation. We show that this instability is controlled by a single non-dimensional elasto-active number that quantifies the interplay between activity and elasticity. Finally, we demonstrate that pairs of coupled elasto-active chains can undergo a synchronization transition: the oscillations phases of both chains lock when the coupling link is sufficiently stiff. Beyond the canonical case considered here, we anticipate our work to open avenues for the understanding and design of the self-organisation and response of active artificial and biological solids, e.g. in higher dimensions and for more intricate geometries.

cond-mat.soft↗

arXiv2022

Limit cycles turn active matter into robots

Active matter composed of energy-generating microscopic constituents is a promising platform to create autonomous functional materials. However, the very presence of these microscopic energy sources is what makes active matter prone to dynamical instabilities and hence hard to control. Here, we show that these instabilities can be coaxed into work-generating limit cycles that turn active matter into robots. We illustrate this general principle in odd active media, model systems whose interaction forces are as simple as textbook molecular bonds yet not constrained to be the gradient of a potential. These emergent robotic functionalities are demonstrated by revisiting what is arguably the oldest of inventions: the wheel. Unlike common wheels that are driven by external torques, an odd wheel undergoes work-generating limit cycles that allow it to roll autonomously uphill by virtue of its own deformation, as demonstrated by our prototypes. Similarly, familiar scattering phenomena, like a ball bouncing off a wall, turn into basic robotic manipulations when either the ball or the wall is odd. Using continuum mechanics, we reveal collective robotic mechanisms that steer the outcome of collisions or influence the absorption of impacts in experiments. Beyond robotics, work-generating limit cycles can also control the non-linear dynamics of active soft materials, biological systems and driven nanomechanical devices.

cond-mat.soft↗

arXiv2020

Observation of non-Hermitian topology and its bulk-edge correspondence in an active mechanical metamaterial

Topological edge modes are excitations that are localized at the materials' edges and yet are characterized by a topological invariant defined in the bulk. Such bulk-edge correspondence has enabled the creation of robust electronic, electromagnetic and mechanical transport properties across a wide range of systems, from cold atoms to metamaterials, active matter and geophysical flows. Recently, the advent of non-Hermitian topological systems---wherein energy is not conserved---has sparked considerable theoretical advances. In particular, novel topological phases that can only exist in non-Hermitian systems have been introduced. However, whether such phases can be experimentally observed, and what their properties are, have remained open questions. Here, we identify and observe a novel form of bulk-edge correspondence for a particular non-Hermitian topological phase. We find that a change in the bulk non-Hermitian topological invariant leads to a change of topological edge mode localisation together with peculiar purely non-Hermitian properties. Using a quantum-to-classical analogy, we create a mechanical metamaterial with non-reciprocal interactions, in which we observe experimentally the predicted bulk-edge correspondence, demonstrating its robustness. Our results open new avenues for the field of non-Hermitian topology and for manipulating waves in unprecedented fashions.

cond-mat.mes-hall↗

arXiv2019

Tuning flow asymmetry with bio-inspired soft leaflets

In Nature, liquids often circulate in channels textured with leaflets, cilia or porous walls that deform with the flow. These soft structures are optimized to passively control flows and inspire the design of novel microfluidic and soft robotic devices. Yet so far the relationship between the geometry of the soft structures and the properties of the flow remains poorly understood. Here, taking inspiration from the lymphatic system, we devise millimetric scale fluidic channels with asymmetric soft leaflets that passively increase (reduce) the channel resistance for forward (backward) flows. Combining experiments, numerics and analytical theory, we show that tuning the geometry of the leaflets controls the flow properties of the channel through an interplay between asymmetry and nonlinearity. In particular, we find the conditions for which flow asymmetry is maximal. Our results open the way to a better characterization of biological leaflet malformations and to more accurate control of flow orientation and pumping mechanisms for microfluidics and soft robotic systems.

cond-mat.soft↗

arXiv2019

Non-reciprocal robotic metamaterials

Non-reciprocal transmission of motion is potentially highly beneficial to a wide range of applications, ranging from wave guiding, to shock and vibration damping and energy harvesting. To date, large levels of non-reciprocity have been realized using broken spatial or temporal symmetries, yet only in the vicinity of resonances or using nonlinearities, thereby nonreciprocal transmission remains limited to narrow ranges of frequencies or input magnitudes and sensitive to attenuation. Here, we devise a novel type of robotic mechanical metamaterials wherein we use local control loops to break reciprocity at the level of the interactions between the unit cells. We show theoretically that first-of-their-kind asymmetric standing waves at all frequencies and unidirectionally amplified propagating waves emerge. We demonstrate experimentally and numerically that this property leads to tunable, giant, broadband and attenuation-free non-reciprocal performances, namely a level of 50dB non-reciprocal isolation over 3.5 decades in frequency, as well as one-way amplification of pulses.

physics.app-ph↗

arXiv2017

Elastogranular Mechanics: Buckling, Jamming, and Structure Formation

Confinement of a slender body into a granular array induces stress localization in the geometrically nonlinear structure, and jamming, reordering, and vertical dislocation of the surrounding granular medium. By varying the initial packing density of grains and the length of a confined elastica, we identify the critical length necessary to induce jamming, and demonstrate an intricate coupling between folds that localize along grain boundaries. Above the jamming threshold, the characteristic length of elastica deformation is shown to scale with the length over which force field fluctuations propagate in a jammed state, suggesting the ordering of the granular array governs the deformation of the slender structure. However, over confinement of the elastica will induce a form of stress relaxation in the granular medium by dislocating grains through two distinct mechanisms that depend on the geometry of the confined structure.

cond-mat.soft↗

arXiv2016

Leidenfrost drops on a heated liquid pool

We show that a volatile liquid drop placed at the surface of a non-volatile liquid pool warmer than the boiling point of the drop can experience a Leidenfrost effect even for vanishingly small superheats. Such an observation points to the importance of the substrate roughness, negligible in the case considered here, in determining the threshold Leidenfrost temperature. A theoretical model based on the one proposed by Sobac et al. [Phys. Rev. E 90, 053011 (2014)] is developed in order to rationalize the experimental data. The shapes of the drop and of the substrate are analyzed. The model notably provides scalings for the vapor film thickness. For small drops, these scalings appear to be identical to the case of a Leidenfrost drop on a solid substrate. For large drops, in contrast, they are different and no evidence of chimney formation has been observed either experimentally or theoretically in the range of drop sizes considered in this study. Concerning the evaporation dynamics, the radius is shown to decrease linearly with time whatever the drop size, which differs from the case of a Leidenfrost drop on a solid substrate. For high superheats, the characteristic lifetime of the drops versus the superheat follows a scaling law that is derived from the model but, at low superheats, it deviates from this scaling by rather saturating.

physics.flu-dyn↗

arXiv2016

Physics of a toy geyser

A geyser can be reproduced by a toy experiment composed of a water pool located above a water reservoir, the two being connected by a long and narrow tube. When the bottom reservoir is heated, the system experiences periodic eruptions of hot water and steam at the top similarly to the geyser effect occurring in nature. The eruption frequency of a toy geyser is inspected experimentally as a function of the heating power and the height of the set-up. We propose a thermodynamic model of this system which predicts the time between eruptions. Besides, the geometric and thermodynamic conditions required to observe a geyser effect are discussed. The study of the toy geyser is then extended to the case of two reservoirs connected to the same tube. In such a configuration, an eruption in a reservoir may entrain the eruption of the other. Such a coupled system adopts a complex time-evolution which reflects the dynamics of natural geysers. We analyze the behavior of a toy geyser with two reservoirs by the way of statistical tools and develop a theoretical model in order to rationalize our observations.

physics.flu-dyn↗

arXiv2013

Electrically charged droplet: Influence of the generator configuration and the nature of the liquid

We studied how to charge droplets by induction and how to maximize this charge. In order to aim this objective, we developed an innovative device that avoids non-linear effects and that is able to charge liquids of different nature. The device developed resembles a planar capacitor. The influence of the nature of the liquid (i.e. presence of ions in solution, polarity, surface tension and conductivity) on the charge induced was measured. We deduced that there exists a threshold of electrical conductivity for the fluid below which it does not charge according to the "perfect conductor" model.

physics.flu-dyn↗