A controllable power conditioning circuit is proposed for battery-free energy harvesting applications. The circuit is designed for piezoelectric energy harvester applications and it has only 11 transistors and consist a simple feedback loop and switched capacitor that conditionally allows the power to be applied to the load (circuit to be powered in this case). The area- and power-efficient digital design that does not include any inductors makes the topology easy to apply to any low-power sensor applications. The power conditioning circuit relies on a digital Schmitt trigger that controls the voltage threshold values of the power supply where the load circuit would operate within. The hysteresis (hence the threshold) levels were set to 435 and 710 mV and the overall energy conversion efficiency is around 65 %. The theory of the piezoelectric harvester was also studied.

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.

We demonstrate selective, two-level metallization of silicon using electroless deposition of copper and gold. In this process, adhesion between the copper and silicon is improved with the formation of intermediary copper-silicide, and the gold layer protects copper from oxidation. The resistivity and residual stress of Au/Cu is 450 Omega nm (220 Omega nm annealed) and 56 MPa (tensile), respectively. These Au/Cu films allow a truly conformal and selective coating of high-aspect-ratio Si structures with good adhesion. We demonstrate the potential of these films in microswitches/relays, accelerometers and sensors by conformally coating the sidewalls of long (up to 1 mm in length), slender microbeams (5 mu m x 5 mu m) without inducing curvature.

We have realized lateral contact switches using electroless deposition of Au/Cu on Si with all the necessary features including source, gate and drain. The metallization approach is simple and effective, allowing for Au/Au contact and inducing near-zero curvature even in long (up to 1 mm length) and slender (5 mu m x 5 mu m) cantilever beams (spring constant is 0.02 N m(-1)). The switching time for these long beams is approximately 80 mu s under ambient conditions. The lifetime of the fabricated switches is a function of current levels applied between the source and the drain (approximately 3000 cycles with a current load of 0.6 mA). The capacitance change between the on-and off-states of the switches is about 3 fF.

Ferrofluid-based liquid manipulation schemes typically actuate an immiscible liquid via a ferrofluid plug, using high magnetic flux (\ensuremath{\sim}1 T) densities and strong field gradients created with bulky permanent magnets. They rely on surface tension effects to maintain the cohesion of the ferrofluid plug, necessitating miniature channels and slow (\ensuremath{\sim}1 \ensuremath{\mu}l/min) flow speeds. Here, we demonstrate direct ferrohydrodynamic pumping using traveling magnetic fields at controllable speeds in a simple, closed-loop geometry without any mechanically actuated components. The pumping approach is compact, scalable, and practical. Using moderate field amplitudes (\ensuremath{\sim}10 mT), we obtained a maximum volumetric flow rate of 0.69 ml/s using a readily available commercial ferrofluid. Our closed-loop pumping approach could lead to integrated and efficient liquid manipulation and cooling schemes based on ferrofluids.

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 εr-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.

We present a low-cost, flow-through nanocytometer that utilizes a colloidal suspension of non-functionalized magnetic nanoparticles for label-free manipulation and separation of microparticles. Our size-based separation is mediated by angular momentum transfer from magnetically excited ferrofluid particles to microparticles. The nanocytometer is capable of rapidly sorting and focusing two or more species, with up to 99% separation efficiency and a throughput of 3 × 10(4) particles/s per mm(2) of channel cross-section. The device is readily scalable and applicable to live cell sorting with biocompatible ferrofluids, offering competitive cytometer performance in a simple and inexpensive package.

Bu makalede yeni bir titresim temelli mikro enerji harmanlayici sistemi onerilmistir. Titresimler ve ani hareketlerin, mekanik yapinin sadece egilmesine degil ayni zamanda gerilmesine yol acmasi prensibine dayanarak, sistemin dogrusal olmayan bolgede calismasi saglanmistir. Tasarlanan ve modellemesi yapilan mekanik yapinin uzeri ince bir piezoelektrik film tabakasi ile kaplanmis ve bu tabaka uzerinde olusan mekanik stres elektrik enerjisine cevrilerek devreleri beslemek icin kullanilmistir. Dogrusal olmayan bolgede calismanin, mikrowatt mertebesindeki guc seviyelerini mm 3 ’luk aletlerle elde edebilecegi goz onune alindiginda, gunes panellerinde elde edilen guc yogunluklari kadar yuksek enerjilerin elde edilebilecegi gorulmustur. Algilayici kabiliyeti sayesinde bilgi depolayabilen, kum tanesi buyuklugunde olan ve uretiminde kullanilan temel malzeme silikon olan bu aletler “zeki kum” olarak isimlendirilmistir. Mekanik yapinin modellenmesi ve tasarimi gelistirilmis ve uretim sonuclari da ayrica verilmistir. Sistemin bilgi gonderebilmesi ve alabilmesi amaciyla iyi bilinen RFID teknolojisi tabanli bir kablosuz haberlesme yontemi onerilmistir. Bu baglamda, paket tasimaciliginda surekli ivme denetleme, sinir guvenligi icin kendinden beslemeli algilayicilar, cabuk bozulan yiyeceklerin tasimaciliginda sicaklik denetleme ve pilsiz kalp atisi algilayici gibi bircok uygulama onerilmistir. RFID devrelerinin tasarimi yapilmis ve benzetim sonuclari elde edilmistir. Oku-yaz bellek olarak manyetik belleklerden yararlanilmistir. Bu sayede, pil kullanilmadan aktif bir sekilde veri yazabilen bir sistem yaratilmistir. “Zeki RFID” olarak isimlendirilen bu sistemde ayrica bilginin iletimi icin de yeni bir modulasyon yontemi onerilmistir. Anahtar Kelimeler: Enerji harmanlayici, RFID, mikroelektronik, MEMS.

We experimentally demonstrate that nonflagellated Escherichia coli strains follow modified Jeffery orbits in shear flow near a surface. We fully characterize their Jeffery orbits as a function of their aspect ratios and distance from that surface. Thanks to the linearity of Navier-Stokes equations under low-Reynolds-number conditions, the hydrodynamic body-wall interactions described here can be superimposed with flagellar motility and Brownian motion to construct models that explain the full picture of bacterial motility near a surface under shear flow.

Interest in vibration energy harvesting technologies has increased significantly in the last decade, primarily due to the possibility of realizing ultra-low power sensor and communication circuits. In such low-power applications, it is paramount to maximize the efficiency of the harvesting system. Here, we propose the use of a simple MEMS cantilever as a power regulating hysteretic switch that allows discharge of the collected voltage within a predetermined range through pull-in and pull-out. This approach enables voltage regulation of the load circuit without the need for any external fixed sources and minimizes losses. We have developed a model to characterize the motion of the beam and verified it by comparing to existing experimental and calculated results. The beam is designed to be immune against possible environmental shock forces; immunity may be increased by deliberately introducing squeezefilm damping. However, there is a tradeoff between shock force immunity and switching time.

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.

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).

We present a rapid and completely label-free cellular manipulation and separation scheme that employs biocompatible, water-based ferrofluids within microfluidic devices. Application of localized magnetic fields through integrated electrodes exerts strong magnetic forces on any micro- particle that forms a magnetic void within the ferrofluid medium in a channel. The magnetic force on each micro-particle depends sensitively on its size (tens of pN for 2 mum diameter) and is an order of magnitude larger than what can be achieved by traditional methods, such as optical tweezers and dielectrophoresis. As such, cellular manipulation and hundreds of microns of separation can easily be accomplished within ferro- microfluidic devices on a time scale of a few seconds, even under low and moderate current values.

In a previous work, we demonstrated that traveling wave excitations from integrated electrodes can continuously pump magnetic liquids within a microfluidic channel. The optimum excitation frequency of this pumping is strongly dependent on the hydrodynamic size of the magnetic nanoparticles, and the effect can be used to detect whenever a molecule or pathogen binds to the magnetic nanoparticles within a ferrofluid. Here, we demonstrate the bio-functionality and pathogen detection capability of a ferrofluid comprised of cobalt-ferrite-silica nanoparticles through the use of biotinylated genetically engineered peptides for inorganics (GEP's). These biotinylated GEPI's are specifically engineered to attach to the silica surface of the magnetic nanoparticles. Binding of streptavidin to the biotinylated GEPI's on the surface of the magnetic nanoparticles shifts the optimum pumping frequency by an amount that corresponds to the increase in the hydrodynamic size of the nanoparticle. The combination of GEPI-enhanced ferrofluids with integrated microfluidic devices finally enables the development of highly sensitive, portable and cheap pathogen sensor chips.

The paper report on the design and test of a low-voltage temperature sensor designed for MEMS power-harvesting systems. The core of the sensor is a bandgap voltage reference circuit operating with a supply voltage in the range of 1-1.5V. The prototype was fabricated on a conventional 0.5mum silicon-on-sapphire (SOS) process. The sensor design consumes 15muA of current at 1V. The internal reference voltage is 550mV. The temperature sensor has a digital square wave output whose frequency is proportional to temperature. A linear model of the dependency of output frequency with temperature has a conversion factor of 1.6kHz/degC. The output is also independent of supply voltage in the range of 1-1.5V. Measured results and targeted applications for the proposed circuit were reported.

Escherichia coli in shear flow near a surface are shown to exhibit a steady propensity to swim towards the left (within the relative coordinate system) of that surface. This phenomenon depends solely on the local shear rate on the surface, and leads to cells eventually aligning and swimming upstream preferentially along a left sidewall or crevice in a wide range of flow conditions. The results indicate that flow-assisted translation and upstream swimming along surfaces might be relevant in various models of bacterial transport, such as in pyelonephritis and bacterial migration in wet soil and aquatic environments in general.