Wireless magnetic-based closed-loop control of self-propelled microjets

In this study, we demonstrate closed-loop motion control of self-propelled microjets under the influence of external magnetic fields. We control the orientation of the microjets using external magnetic torque, whereas the linear motion towards a reference position is accomplished by the thrust and pulling magnetic forces generated by the ejecting oxygen bubbles and field gradients, respectively. The magnetic dipole moment of the microjets is characterized using the U-turn technique, and its average is calculated to be 1.3x10-10 A.m2 at magnetic field and linear velocity of 2 mT and 100 μm/s, respectively. The characterized magnetic dipole moment is used in the realization of the magnetic force-current map of the microjets. This map in turn is used for the design of a closed-loop control system that does not depend on the exact dynamical model of the microjets and the accurate knowledge of the parameters of the magnetic system. The motion control characteristics in the transient- and steady-states depend on the concentration of the surrounding fluid (hydrogen peroxide solution) and the strength of the applied magnetic field. Our control system allows us to position microjets at an average velocity of 115 μm/s, and within an average region-of-convergence of 365 μm

Harnessing bacterial power in microscale actuation

This paper presents a systematic analysis of the motion of microscale structures actuated by flagellated bacteria. We perform the study both experimentally and theoretically. We use a blotting procedure to attach flagellated bacteria to a buoyancy-neutral plate called a microbarge. The motion of the plate depends on the distribution of the cells on the plate and the stimuli from the environment. We construct a stochastic mathematical model for the system, based on the assumption that the behavior of each bacterium is random and independent of that of its neighbors. The main finding of the paper is that the motion of the barge plus bacteria system is a function of a very small set of parameters. This reduced-dimensional model can be easily estimated using experimental data. We show that the simulation results obtained from the model show an excellent match with the experimentally-observed motion of the barge

Frequency dependence of surface acoustic wave swimming.

This is the author accepted manuscript. The final version is available from The Royal Society.Surface acoustic waves (SAWs) are elastic waves that can be excited directly on the surface of piezoelectric crystals using a transducer, leading to their exploitation for numerous technological applications, including for example microfluidics. Recently, the concept of SAW streaming, which underpins SAW microfluidics, was extended to make the first experimental demonstration of 'SAW swimming', where instead of moving water droplets on the surface of a device, SAWs are used as a propulsion mechanism. Using theoretical analysis and experiments, we show that the SAW swimming force can be controlled directly by changing the SAW frequency, due to attenuation and changing force distributions within each SAW streaming jet. Additionally, an optimum frequency exists which generates a maximum SAW swimming force. The SAW frequency can therefore be used to control the efficiency and forward force of these SAW swimming devices. The SAW swimming propulsion mechanism also mimics that used by many microorganisms, where propulsion is produced by a cyclic distortion of the body shape. This improved understanding of SAW swimming provides a test-bed for exploring the science of microorganism swimming, and could bring new insight to the evolutionary significance for the length and beating frequency of swimming microbial flagella.Leverhulme Trust Research Projec

Advances in colloidal manipulation and transport via hydrodynamic interactions

In this review article, we highlight many recent advances in the field of micromanipulation of colloidal particles using hydrodynamic interactions (HIs), namely solvent mediated long-range interactions. At the micrsocale, the hydrodynamic laws are time reversible and the flow becomes laminar, features that allow precise manipulation and control of colloidal matter. We focus on different strategies where externally operated microstructures generate local flow fields that induce the advection and motion of the surrounding components. In addition, we review cases where the induced flow gives rise to hydrodynamic bound states that may synchronize during the process, a phenomenon essential in different systems such as those that exhibit self-assembly and swarming

Experimental Framework for the Position Control of Magnetic Microfibers

Magnetic microfibers have been developed in recent years with potential applications to a large number of fields, from MEMS to microfluidics to bio-chemical analyses. Magnetic microfibers based on polymer material like polypropylene and cellulose has been developed at Clemson University that are hollow cylindrical filaments internally coated with superparamagnetic nanoparticles. This internal coating provides the fiber with magnetic properties that allow them to be externally controlled using magnetic fields from a distance. These fibers can align with the external magnetic fields under constraints imposed by elastic properties and boundary conditions. Current work in this field is primarily focused on the use of micro-scale magnetic fibers under a constant homogenous magnetic field. The work presented in this thesis documents the experimental framework to provide precise position control under non-homogenous fields in a much larger scale. The fiber used is several centimeters long and is constrained at one end by being fixed to an acrylic base. Multiple solenoids are used to generate magnetic fields and cameras provide image information to the controller. The controller adjusts the current to the solenoids based on information obtained from the image. Current literature is surveyed to provide an overview of various models of magnetic fibers. Suggestions for improvements to the system are provided and future work that will aid in the transition to a model based control approach is explained

FABRICATION OF MAGNETIC TWO-DIMENSIONAL AND THREE-DIMENSIONAL MICROSTRUCTURES FOR MICROFLUIDICS AND MICROROBOTICS APPLICATIONS

Micro-electro-mechanical systems (MEMS) technology has had an increasing impact on industry and our society. A wide range of MEMS devices are used in every aspects of our life, from microaccelerators and microgyroscopes to microscale drug-delivery systems. The increasing complexity of microsystems demands diverse microfabrication methods and actuation strategies to realize. Currently, it is challenging for existing microfabrication methods—particularly 3D microfabrication methods—to integrate multiple materials into the same component. This is a particular challenge for some applications, such as microrobotics and microfluidics, where integration of magnetically-responsive materials would be beneficial, because it enables contact-free actuation. In addition, most existing microfabrication methods can only fabricate flat, layered geometries; the few that can fabricate real 3D microstructures are not cost efficient and cannot realize mass production. This dissertation explores two solutions to these microfabrication problems: first, a method for integrating magnetically responsive regions into microstructures using photolithography, and second, a method for creating three-dimensional freestanding microstructures using a modified micromolding technique. The first method is a facile method of producing inexpensive freestanding photopatternable polymer micromagnets composed NdFeB microparticles dispersed in SU-8 photoresist. The microfabrication process is capable of fabricating polymer micromagnets with 3 µm feature resolution and greater than 10:1 aspect ratio. This method was used to demonstrate the creation of freestanding microrobots with an encapsulated magnetic core. A magnetic control system was developed and the magnetic microrobots were moved along a desired path at an average speed of 1.7 mm/s in a fluid environment under the presence of external magnetic field. A microfabrication process using aligned mask micromolding and soft lithography was also developed for creating freestanding microstructures with true 3D geometry. Characterization of this method and resolution limits were demonstrated. The combination of these two microfabrication methods has great potential for integrating several material types into one microstructure for a variety of applications

Acoustic Bubble Propulsion and Rotation for MEMS Devices

The goal of this thesis research is to investigate acoustic wave actuated devices’ abilities spatially in different media and with various designs. Self-trapped bubble oscillation generates cavitation at the open end of the micro channel under a continuous sound wave. The cavitation generates propulsion from the opening through to the end of the micro channel. Researchers generally have found bubbles undesirable because of their non-linear effect in many applications. Therefore, there has been much research conducted in the area of eliminating the bubbles in liquid media. However, the use of bubbles can be beneficial in some applications like bubble powered actuators, switchers, and so forth. This research ensures the availability and feasibility of the bubble powered actuator for future medical applications. In the current research, the actuator works with the principle of an oscillating bubble cavitation. The bubble cavitation and oscillation effect create a propulsion effect through the designed tubes. The captured bubbles generate force against to contact surface. The force against this force from the contact surface causes propelling. Different frequencies oscillate the bubbles in different lengths. Thus, the length of the bubble that is captured in the channel has an impact on the oscillation frequency by the sound wave, since the changes in lengths of the bubble also differ the oscillating frequency. In different oscillating frequencies can be used not only for a planar propulsion but also for bilateral and three dimensional propulsion. In addition, with various designs, a device has an ability to substantiate many kind of motion in liquid media which means that propulsion effect can also use for circular or vortex motion purposes. In this research, up to 400 RPM circular and 70 mm/s instantaneous propelling speed are achieved in several designs by self-trapped and blocked micro-bubbles’ oscillations under acoustic wave in water media. In this novel study, availability and feasibility of acoustically oscillated micro-bubble based propulsion is demonstrated in spatial and rotational movement for future MEMS applications