Hur Koser

Label-free cellular manipulation and sorting via biocompatible ferrofluids

We present a simple microfluidic platform that uses biocompatible ferrofluids for the controlled manipulation and rapid separation of both microparticles and live cells. This low-cost platform exploits differences in particle size, shape, and elasticity to achieve rapid and efficient separation. Using microspheres, we demonstrate size-based separation with 99% separation efficiency and sub-10-μm resolution in <45 s. We also show continuous manipulation and shape-based separation of live red blood cells from sickle cells and bacteria. These initial demonstrations reveal the potential of ferromicrofluidics in significantly reducing incubation times and increasing diagnostic sensitivity in cellular assays through rapid separation and delivery of target cells to sensor arrays.

Smart Sand—a wide bandwidth vibration energy harvesting platform

We propose a concept for true wide bandwidth vibration energy harvesting. Our approach exploits nonlinear stretching of fixed-fixed beams in an off-resonance mode, effectively expanding the operational frequency range well beyond the narrow bandwidth of linear resonators. Our initial prototype demonstrates operation between 160–400 Hz, without the need for frequency tuning. A simple dynamic model shows good agreement with measurements. Optimized device geometry will allow for even lower frequency operation (starting at 60 Hz) at strain levels above 1e-3 (ideal for piezoelectric transduction).

Direct Upstream Motility in Escherichia coli

We provide an experimental demonstration of positive rheotaxis (rapid and continuous upstream motility) in wild-type Escherichia coli freely swimming over a surface. This hydrodynamic phenomenon is dominant below a critical shear rate and robust against Brownian motion and cell tumbling. We deduce that individual bacteria entering a flow system can rapidly migrate upstream (>20 μm/s) much faster than a gradually advancing biofilm. Given a bacterial population with a distribution of sizes and swim speeds, local shear rate near the surface determines the dominant hydrodynamic mode for motility, i.e., circular or random trajectories for low shear rates, positive rheotaxis for moderate flow, and sideways swimming at higher shear rates. Faster swimmers can move upstream more rapidly and at higher shear rates, as expected. Interestingly, we also find on average that both swim speed and upstream motility are independent of cell aspect ratio.

Magnetic induction micromachine-part II: fabrication and testing

This paper presents the realization of a magnetic induction machine. The development of this machine is part of an ongoing project to create high-power density electric microgenerators for use in portable-power applications. The results reported here focus on testing a first-generation nonlaminated electromagnetic actuator, a metrology device designed for exploring and characterizing the fabrication process and the operating behavior of the magnetic induction micromachine. Achieving high power density requires large electrical currents and magnetic fluxes, which necessitate thick, multilayered microstructures that are difficult to fabricate. The batch-fabrication schemes developed as part of this work are based on low-temperature micromolding that makes extensive use of various ultra-thick photoresists and electroplating of electrical conductors (Cu) and ferromagnetic materials (Ni-Fe 80%-20%), resulting in the successful fabrication of a multilayer two-phase planar stator and a planar rotor. To evaluate the performance of the complete machine (stator plus rotor), a 4-mm-diameter, 500-/spl mu/m-thick electroplated Ni-Fe rotor is tethered to a series of flexible structures that prevent it from making a complete revolution, but allow accurate torque performance extraction. The tethered induction micromotor studied here exhibits torque production as high as 4.8 /spl mu/N/spl middot/m.

Overcoming the Diffusion Barrier: Ultra-Fast Micro-Scale Mixing Via Ferrofluids

We report on the design, development, fabrication and characterization of a novel, micro-scale mixing device based on stable water suspensions of magnetic nanoparticles (i.e. ferrofluids). The micromixer prototypes are built using standard microfabrication and simple soft-lithography, and the design can be incorporated as a sub-system into any chemical micro-reactor or a miniaturized biological sensor. The devices achieve mixing virtually instantaneously and may be used to greatly increase mass transport towards chemically or biologically active sites on lab-on-a-chip devices for rapid incubation and highly improved detection sensitivity.

A New Batteryless Active RFID System: Smart RFID

Since RFID systems start to share the supply chain market with the barcodes, new application areas have become attractive where the wireless radio-frequency communication and identification is possible. Unlike the passive systems, active RFID systems can be used as sensor nodes and they can monitor and store environment data, such as acceleration or temperature. However, the need of external battery limits their applications to where battery replacements are only possible. In this paper, a new batteryless active RFID transponder system has been proposed based on a MEMS (Micro-Electro Mechanical Systems) energy scavenger. The mechanical part of the system has been designed and fabricated. The circuit level simulations have been performed. In this context, a new modulation scheme has been proposed and a magnetic random access memory (MRAM) has been used for the data storage.

Characterization of ferroelectric material properties of multifunctional lead zirconate titanate for energy harvesting sensor nodes

We propose a microsystem integration technique that is ideal for low-cost fabrication of vibration energy harvesting sensor nodes. Our approach exploits diverse uses of sol-gel deposited lead zirconate titanate, effectively combining fabrication of several microsystem components into a single process and significantly reducing manufacturing cost and time. Here, we measure and characterize thin film parameters—such as the piezoelectric coefficient e31 (−4.0 C/m2), the dielectric constant er-eff (219 at 3.3 V), and the total switching polarization (2Pr;52 μC/cm2)—in order to verify this material’s potential for energy harvesting, energy storage, and nonvolatile memory applications simultaneously on the same device.

Magnetic induction micromachine-part I: Design and analysis

Most microscale electric and magnetic machines studied in the last decade lack the power density to support many practical applications. This paper introduces a design for a magnetic induction machine that offers power densities in excess of 200 MW/m/sup 3/ and efficiencies of up to 50%, while providing more than 10 W of mechanical power. This is a substantial performance increase in MEMS electromagnetic machines studied to date.

Magnetic induction micromachine-part III:Eddy currents and nonlinear effects

The magnetic induction micromachine fabricated in Part II was not laminated, as designed in Part I. Consequently, eddy currents in the stator core, and the associated nonlinear saturation, significantly decreased its performance from that predicted in Part I. To investigate and explain these phenomena and their consequences, this paper models the behavior of the solid-stator-core machine fabricated in Part II using a finite-difference time-domain numerical analysis. The inherent stiffness in the time-domain integration of Maxwells equations is mitigated via reducing the speed of light artificially by five orders of magnitude, while taking special care that assumptions of magneto-quasi-static behavior are still met. The results from this model are in very good agreement with experimental data from the tethered magnetic induction micro motor.

An integrated MEMS ferrofluid pump using insulated metal substrate

A novel ferrofluid micropump utilizing traveling magnetic fields is designed based on previous numerical analysis. A cost-effective fabrication process combining insulated metal substrate etching and soft lithography is used to realize the prototype ferrofluid micropump. Preliminary results show good agreement of pumping characteristics between theory and experiment.