SWIIRL: SWarm Intelligence
of Independent aRtificially active particLes

Project: PN-III-P4-ID-PCE-2020-1301
Contract number: 176/2021

Project Description

Project executive summary

We propose to investigate the swarm intelligence of independent individual artificial active particles (particles that are capable of propelling themselves with their own motor force). Such swarms of particles can explore unknown landscapes (for example a swarm of rescue robots sent into an unknown landscape affected by an earthquake), escape from or pass through obstacles (nano sized robots delivering nutrients or drugs passing through biological barriers) or be stopped by well designed obstacle configurations (limiting the spread of bacteria). Our project will investigate the topic with an interdisciplinary approach, from a Computer Science perspective, running computer simulations of the phenomena, from a Physics and Robotics perspective of building small (cm sized) robot swarms (of 80-100 robots) with microcontrollers where the individual robots that can alter their behavior based on local interaction measurements, and from a Chemical perspective of building a system of micron sized polystyrene beads acting as Quincke rotors in a switched electric field mimicking the run and tumble motion of bacteria.

Project Description

Swarms of Independent Active Matter particles forming cooperative ensembles with emergent behavior


In this research grant, we investigate multiple active matter particles passing through a quenched disordered landscape (a series of obstacles). These particles have a tendency to form a large cluster and move together. This partcile swarm exhibits interesting emergent behavior that is more complex than the simple rules that the individual particles obey. Using a Brownian Dynamics simulation code developed by our research group, we studied the interaction of such a particle swarms with a heterogeneous pinning substrate and observed a novel phenomena of shepherding. We also studied a system where the substrate is modified by the particles above it that "consume it", finding different interesting regimes or collective motion as a function of the consumption and recovery rates in out system as well as the density and the ratio of active/passive particles in the system. We are also looking into a slightly more complex behavior of an SIR epidemiologic model applied to our active matter system where the individual changes of behavior affects the way the entire swarm responds to the spreading of an infection.

To complement the simulation studies, we designed and built small robots (about 12 centimeters in diameter) capable of running an algorithm independently on their processors. They have wireless and bluetooth capability, they can sense the color and intensity of the surface they are moving on in multiple points thus being capable of following a gradient and have a series of IR LEDs and sensors along their perimeter that they can use to detect the proximity of other robots as well as a communication channel with neighboring robots. They have two independenly controller motors driving its wheels that allows it tu turn and move. It knows its heading from a magnetometer and can signal different states to a camera above it via several smart RGB LEDs.

Another interesting experiment we will perform is to observe small (40 micron) PMMA particles undergoing Quincke rotation and self-propulsion in an electric field. This is a microscopic realization of the active particle swarms and we will be able to place defects in their paths and observe the behavior of the swarm when encountering these defects and navigating through them. Here the particles undergo an alignment due to hydrodynamic interactions and it should be possible to induce directionality changes by switching the electric field on/off.

Realizations

We studied the behavior of a mix of active and passive partciles by simulating active particles with elastic disc interactions on a landscape that consisted of a half space filled with obstacles and another half space free of obstacles. We found an emergent behavior of the system where the active particles prefer to stay in the half-plane with the obstacles and gradually shepherd the passive particles out from among them into the open obstacle-free region. We studied this new phenomenon we call shepherding as a funtion of particle density and active motor force. We have published our results in the article: Phys. Rev. E 104, 044613 (2021).
We studied a system of an active substrate that is modified by the partciles that are moving above it. The particles consume the substrate grid points they cover at a given rate and move towards the direction of the substrate gradient, and teh substrate recovers at a fixed rate. The system echibits interesting collecive behaviors depending on the consumption and recovery rates as well as the particle density. We have published our results in the article: Phys. Rev. Research 4, 013061 (2022).
We constructed a robot prototype. We designed a four-layer printed circuit board that will hold the main microcontroller and all the peripherical chips that will allow the robot to communicate via wireless and bluetooth, signal the camera with RGB LEDs, drive two wheels, light up the array of IR LEDs on its perimeter for both distance measurement as well as inter-robot communication and also read the IR signal in multiple places around its perimeter. It also has sensors mounted underneath that can observe the pattern and gradients it is moving over. The robot is designed with the possibility of being extended with a shield for future modularity.

Publications resulting from this grant

P. Forgács, A. Libál, C. Reichhardt, and C. J. O. Reichhardt.
Active matter shepherding and clustering in inhomogeneous environments.
Phys. Rev. E 104, 044613 (2021)

L Varga, A Libal, CJO Reichhardt, C Reichhardt
Active Phases for Particles on Resource Landscapes
Phys. Rev. Research 4, 013061 (2022).

P. Forgács, A. Libál, CJO Reichhardt, C Reichhardt
Effects of clustering on disease spreading in active matter
(manuscript in preparation)

Objectives for 2021

Objective : Simulations

We have adapted our simulations to study the interplay of active matter with inhomogeneous pining landscapes, finding new interesting collective behaviors emerging. We investigated a novel system of an active substrate that is modified by the particles passing over it. We also incorporated an SIR model over our active particles to study the dynamics of a disease spreading over our active system, showing the link between the individual protocol and the emergent swarm behavior.

Objective : Active Robots

We designed a four-layer printed circuit board for the smart active robots and built the proptotypes testing their functionality. We have tested all the subsystems on the robot from the wireless to the bluetooth to the IR sensing capabilities as well as the sensors incorporated and the processors that run the code of a single actor insode the swarm. These robots are very versatile encompassing behavior from simple active matter particles to complex agents.

Objective : Quincke rollers

We acquired all the materials necessary for the assembly of the Quincke roller experiment, the PMMA beads, a high voltage source, microscope glass plates coated with ITO for the capacitor, hexadecane and AOT salt for the calibration of the liquid and uniform glass beads of 180-220 microns to act as spacers between the plates. We also assembled the system in a test mode and we designed PCBs to hold our cells together and make it easy to apply the 1000V voltage.

Research Team

András Libál

Group leader

András coordinates the group effort, the weekly group meetings with team members and our collaborators abroad. His expertise is writing of the simulation code, evaluation of the results, definition of the measurements and analysis of the data resulting from the simulations.

Réka Barabás

Senior researcher

Réka coordinates the effort towards creating the Quincke roller setup and experiment, choosing the equipment and materials needed. Her expertise is in the chemical aspects,the correct handling of the materials and in the sythesis of differently shaped and functionalized rollers.

Arthur Tunyagi

Senior researcher

Arthur designed and tested the intelligent robots, chose and ordered the components and built the prototypes. His expertise is in the engineering aspects of these components as well as the development of the libraries necessary for the coding and deploying the robots in the experiments.

Levente Varga

Senior researcher

Levente rewrote and adapted the code to accomodate a pinning surface that is influenced by the particles moving over it as well as optimized the code for running on CPUs. He is an expert in coding and optimization as well as in the visualization of the data. He also has an engineering background and will participate in coding the robot systems as well as image processing and extracting the data from the cameras observing the robotic and the Quincke setup.

Noémi-Izabella Farkas

PhD student (Chemistry)

Noémi is responsible for assembling the cells for the Quincke experiments, setting the correct distance between the ITO covered glasses with spacers, creating a seal and filling the system with hexadecane and the PMMA Quincke rollers and gathering the video data from the cameras on the position of the particles during the experiment. Her expertise is in the chemistry of the components used in the experiment and handling experimental setups.

Péter Forgács

MSc student (Physics)

Péter adapted the code to run the simulations for the active matter on the half-occupied pinning landscape, generated the results and made the figures and the corrections necessary for the publication. He also rewrote and adapted the active matter code to handle the overlaying SIR model. His expertise is in coding, adding the necessary statistical tools and analyzing the results from the simulations as well as preparing the figures for the publications.

Contact

You are welcome to reach us at the provided email address(es) to discuss science.

We are also available at our office for in person meeting at previously agreed times.

Dr. Libál András

Group Leader, Associate Professor
Faculty of Mathematics and Computer Science
Department of the Hungarian Line
of Mathematics and Computer Science
Babes-Bolyai University

Mathematica Building 210
Babes-Bolyai University
Faculty of Mathematics and Computer Science
Ploiesti Street No. 23-25,
RO-400157 Cluj-Napoca, Romania