The yearly increase in government R&D investment and top-down national R&D investment allocation requires a more quantitative decision-making system that maximizes R&D performance and efficient budget allocation. Sound decision-making is necessary at both the selection stage and the pursuit stage in order to maximize limited national R&D resources. We study Korean smart farms as an example to examine national R&D investment from the various R&D actors (academia, industry, and research institutes) perspectives. The objective of our research is to evaluate the theoretical efficiency of R&D investment on specific technologies in smart farms and compare the results with expert opinions where the reality is reflected. To be specific, our study is to provide the quantitative approach in making decision among policymakers by reflecting the field experiences and opinions. We use a data envelopment analysis with an assurance region model, which integrates an analytic hierarchy process and a data envelopment analysis. The weights of output in DEA model by the R&D actors are similar to the overall weight by all actors, implying that investment allocation decisions in the smart farm sector are not significantly affected by the R&D actors. We realized that the relative efficiency of some R&D technologies increases after reflecting qualitative ideas of experts. In reality, it is necessary to invest in these technology groups, but they excluded from top-down decision-making. This also shows that a government's top-down decision-making can distort its investment allocation. This study proposes a new approach to compensate for the difference between theoretical virtual prices and actual prices in data envelopment analysis. In particular, when comparing the only quantitative results on investment priorities with analysis results by additionally reflecting the opinions of experts in each sector, we found that the Korean government's investment priorities in the smart farm field are considerably distorted. Therefore, this study is expected to be used as an alternative for policy makers to compensate for the quantitative distortion might be caused by top-down national R&D investment decisions.
Budgets , Investments , Farms , Organizations , Technology
Surgical design in personalized medicine is often based on native anatomy, which may not accurately reflect the interaction between native musculoskeletal tissues and biomechanical artifacts. To overcome this problem, researchers have developed alternative methods based on affordance-based design. The design process can be viewed in terms of action possibilities provided by the (biological) environment. Here, we use the affordance-based approach to address possibilities for action offered by biomechanical artifacts. In anterior crucial ligament (ACL) reconstruction, the design goal is to avoid ligament impingement while optimizing the placement of the tibial tunnel. Although in the current rationale for tibial tunnel placement roof impingement is minimized to avoid a negative affordance, we show that tibial tunnel placement can rather aim to constrain the target bounds with respect to a positive affordance. We describe the steps for identifying the measurable invariants and provide a mathematical framework for the surgery affordances within the knee.
Vibration energy harvesters based on the resonance of the beam structure work effectively only when the operating frequency window of the beam resonance matches with the available vibration source. None of the resonating MEMS structures can operate with low frequency, low amplitude, and unpredictable ambient vibrations since the resonant frequency goes up very high as the structure gets smaller. Bistable buckled beam energy harvester is therefore developed for lowering the operating frequency window below 100Hz for the first time at the MEMS scale. This design does not rely on the resonance of the MEMS structure but operates with the large snapping motion of the beam at very low frequencies when input energy overcomes an energy threshold. A fully functional piezoelectric MEMS energy harvester is designed, monolithically fabricated, and tested. An electromechanical lumped parameter model is developed to analyze the nonlinear dynamics and to guide the design of the nonlinear oscillator based energy harvester. Multilayer beam structure with residual stress induced buckling is achieved through the progressive residual stress control of the deposition processes along the fabrication steps. Surface profile of the released device shows bistable buckling of 200µm which matches well with the amount of buckling designed. Dynamic testing demonstrates the energy harvester operates with 50% bandwidth under 70Hz at 0.5g input, operating conditions that have not been demonstrated by MEMS vibration energy harvesters before.
Most portable electronic devices are power-limited by battery capacity, and recharging these batteries often interrupts the user's experience with the device. The product presented in this paper provides an alternative to powering portables by converting regular human walking motion to electricity. The device harvests electric power using air bulbs, distributed in the sole of a shoe to drive a series of micro-turbines connected to small DC motors. The number and position of air bulbs is optimized to harvest the maximum airflow from each foot-strike. The system is designed to continuously drive the micro-turbines by utilizing both outflow and inflow from the air bulbs. A prototype combat boot was fitted on the right foot of a 75 kg test subject, and produced an average continuous power on the order of 10 s of mW over a 22 Ω load during walking at 3.0 mph. This combat boot provides enough electric power to a passive GPS tracker that periodically relays geographical coordinates to a smartphone via satellite without battery replacement.
Photocatalytic nanostructures loaded with metallic nanoparticles are being considered as a potential candidate for designing efficient water splitting devices. Here, we aim to unveil the plasmonic behavior of a device made of Au-TiO2 nanostructures through in-depth investigations combining electron energy loss spectroscopy (EELS) and cathodoluminescence (CL). The experiments confirm the existence of Au bulk plasmon excitation, intrinsic interband transitions, and plasmon losses over a wide range of energies (0.6-2.4 eV). Depending on the size and the shape of the obtained nanostructures, such as fishing hook (FH), asymmetric nanorod (AR), and a/symmetric nanoparticles, in our devices, the dephasing times and the quality factors of the modes vary. Finite difference time domain simulations were then carried out on FH and AR structures. These simulations indicate good agreement between the electric field enhancement and the obtained plasmon excitation as observed in EELS. Moreover, the plasmonic activity obtained by CL and EELS was correlated with the photocurrent measurements recorded with the device, which confirmed that the localized plasmons in Au generate hot electrons and enhance the photoresponse of the device. This study confirms the functionality of the metal dielectric photocatalyst device over a wide range of wavelengths ranging from UV to near IR.
We recently reported that an Au/TiO2 photonic crystal device for photochemical energy conversion showed a sub-bandgap photoresponse centered at the surface plasmon polariton (SPP) resonant wavelength of this device. Here we developed a theoretical modeling of the internal photoemission in this device by incorporating the effects of anisotropic hot electron momentum distribution caused by SPP. The influences of interband and intraband transition, anisotropic momentum distribution of hot electrons by SPP are integrated to model the internal quantum efficiency (IQE) of this device. Near resonant wavelength, SPP dominates the electric field in the thin Au layer, which generates hot electrons with high enough momentum preferentially normal to the Schottky interface. Compared with the widely used Fowler's theory of internal photoemission, our model better predicts hot electron collection in Schottky devices. This model will provide a design guidance for tuning and enhancing photoresponse of Schottky hot carrier devices.
Plasmon assisted photoelectric hot electron collection in a metal-semiconductor junction can allow for sub-bandgap optical to electrical energy conversion. Here we report hot electron collection by wafer-scale Au/TiO2 metallic-semiconductor photonic crystals (MSPhC), with a broadband photoresponse below the bandgap of TiO2. Multiple absorption modes supported by the 2D nano-cavity structure of the MSPhC extend the photon-metal interaction time and fulfill a broadband light absorption. The surface plasmon absorption mode provides access to enhanced electric field oscillation and hot electron generation at the interface between Au and TiO2. A broadband sub-bandgap photoresponse centered at 590 nm was achieved due to surface plasmon absorption. Gold nanorods were deposited on the surface of MSPhC to study localized surface plasmon (LSP) mode absorption and subsequent injection to the TiO2 catalyst at different wavelengths. Applications of these results could lead to low-cost and robust photo-electrochemical applications such as more efficient solar water splitting.
The increasing demand for wearable electronic devices has made the development of highly elastic strain sensors that can monitor various physical parameters an essential factor for realizing next generation electronics. Here, we report an ultrahigh stretchable and wearable device fabricated from dry-spun carbon nanotube (CNT) fibers. Stretching the highly oriented CNT fibers grown on a flexible substrate (Ecoflex) induces a constant decrease in the conductive pathways and contact areas between nanotubes depending on the stretching distance; this enables CNT fibers to behave as highly sensitive strain sensors. Owing to its unique structure and mechanism, this device can be stretched by over 900% while retaining high sensitivity, responsiveness, and durability. Furthermore, the device with biaxially oriented CNT fiber arrays shows independent cross-sensitivity, which facilitates simultaneous measurement of strains along multiple axes. We demonstrated potential applications of the proposed device, such as strain gauge, single and multiaxial detecting motion sensors. These devices can be incorporated into various motion detecting systems where their applications are limited to their strain.
Elasticity , Electronics/instrumentation , Monitoring, Physiologic/instrumentation , Movement , Nanotechnology/instrumentation , Nanotubes, Carbon/chemistry , Clothing , Humans
An analytical Mason equivalent circuit is derived for a circular, clamped plate piezoelectric micromachined ultrasonic transducer (pMUT) design in 31 mode, considering an arbitrary electrode configuration at any axisymmetric vibration mode. The explicit definition of lumped parameters based entirely on geometry, material properties, and defined constants enables straightforward and wide-ranging model implementation for future pMUT design and optimization. Beyond pMUTs, the acoustic impedance model is developed for universal application to any clamped, circular plate system, and operating regimes including relevant simplifications are identified via the wave number-radius product ka. For the single-electrode fundamental vibration mode case, sol-gel Pb(Zr0.52)Ti0.48O3 (PZT) pMUT cells are microfabricated with varying electrode size to confirm the derived circuit model with electrical impedance measurements. For the first time, experimental and finite element simulation results are successfully applied to validate extensive electrical, mechanical, and acoustic analytical modeling of a pMUT cell for wide-ranging applications including medical ultrasound, nondestructive testing, and range finding.
Increase in conductivity and mechanical properties of a carbon nanotube (CNT) fiber inspired by mussel-adhesion chemistry is described. Infiltration of polydopamine into an as-drawn CNT fiber followed by pyrolysis results in a direct insulation-to-conduction transformation of poly(dopamine) into pyrolyzed-poly(dopamine) (py-PDA), retaining the intrinsic adhesive function of catecholamine. The py-PDA enhances both the electrical conductivity and the mechanical strength of the CNT fibers.
We report the design of dielectric-filled anti-reflection coated (ARC) two-dimensional (2D) metallic photonic crystals (MPhCs) capable of omnidirectional, polarization insensitive, wavelength selective emission/absorption. Using non-linear global optimization methods, optimized hafnium oxide (HfO2)-filled ARC 2D Tantalum (Ta) PhC designs exhibiting up to 26% improvement in emittance/absorptance at wavelengths λ below a cutoff wavelength λc over the unfilled 2D TaPhCs are demonstrated. The optimized designs possess high hemispherically average emittance/absorptance εH of 0.86 at λ < λc and low εH of 0.12 at λ > λc.
A metallic dielectric photonic crystal with solar broadband, omni-directional, and tunable selective absorption with high temperature stable (1000 °C, 24 hrs) properties is fabricated on a 6" silicon wafer. The broadband absorption is due to a high density of optical cavity modes overlapped with an anti-reflection coating. Results allow for large-scale, low cost, and efficient solar-thermal energy conversion.
The design and simulation of a wide angle, spectrally selective absorber/emitter metallic photonic crystal (MPhC) is presented. By using dielectric filled cavities, the angular, spectrally selective absorption/emission of the MPhC is dramatically enhanced over an air filled design by minimizing diffraction losses. Theoretical analysis is performed and verified via rigorous coupled wave analysis (RCWA) based simulations. An efficiency comparison of the dielectric filled designs for solar thermophotovoltaic applications is performed for the absorber and emitter which yields a 7% and 15.7% efficiency improvement, respectively, compared to air filled designs. The converted power output density is also improved by 33.5%.
In this work, the deflection equation of a piezoelectrically-driven micromachined ultrasonic transducer (PMUT) is analytically determined using a Green's function approach. With the Green's function solution technique, the deflection of a circular plate with an arbitrary circular/ring electrode geometry is explicitly solved for axisymmetric vibration modes. For a PMUT with one center electrode covering ≈60% of the plate radius, the Green's function solution compares well with existing piece-wise and energy-based solutions with errors of less than 1%. The Green's function solution is also simpler than them requiring no numerical integration, and applies to any number of axisymmetric electrode geometries. Experimentally measured static deflection data collected from a fabricated piezoelectric micro ultrasonic transducer (PMUT) is further used to validate the Green's function model analysis. The center deflection and deflection profile data agree well with the Green's function solution over a range of applied bias voltages (5 to 21 V) with the average error between the experimental and Green's function data less than 9%.
An electric circuit model for a clamped circular bimorph piezoelectric micromachined ultrasonic transducer (pMUT) was developed for the first time. The pMUT consisted of two piezoelectric layers sandwiched between three thin electrodes. The top and bottom electrodes were separated into central and annular electrodes by a small gap. While the middle electrode was grounded, the central and annular electrodes were biased with two independent voltage sources. The strain mismatch between the piezoelectric layers caused the plate to vibrate and transmit a pressure wave, whereas the received echo generated electric charges resulting from plate deformation. The clamped pMUT plate was separated into a circular and an annular plate, and the respective electromechanical transformation matrices were derived. The force and velocity vectors were properly selected using Hamilton's principle and the necessary boundary conditions were invoked. The electromechanical transformation matrix for the clamped circular pMUT was deduced using simple matrix manipulation techniques. The pMUT performance under three biasing schemes was elaborated: 1) central electrode only, 2) central and annular electrodes with voltages of the same magnitude and polarity, and 3) central and annular electrodes with voltages of the same magnitude and opposite polarity. The circuit parameters of the pMUT were extracted for each biasing scheme, including the transformer ratio, the clamped electric impedance, and the open-circuit mechanical impedance. Each pMUT scheme was characterized under different acoustic loadings using the theoretically developed model, which was verified with finite element modeling (FEM) simulation. The electrode size was optimized to maximize the electromechanical transformer ratio. As such, the developed model could provide more insight into the design, optimization, and characterization of pMUTs and allow for performance comparison with their cMUT counterparts.
Algorithms , Computer-Aided Design , Electrodes , Electronics/instrumentation , Micro-Electrical-Mechanical Systems/instrumentation , Models, Theoretical , Ultrasonography/instrumentation , Computer Simulation , Equipment Design , Equipment Failure Analysis , Miniaturization
The effect of plate electrode area on the deflection of a symmetric circular bimorph piezoelectric micromachined ultrasonic transducer (pMUT) with clamped and simply supported boundary conditions was studied for the first time. Distinct plate displacement shape functions were defined for the regions underneath and outside the active electrodes. The plate shape functions were solved analytically using classic plate theory in conjunction with the external boundary conditions and the internal ones between the two regions in order to calculate the exact plate displacement under both external voltage stimulus and acoustic pressure. The model was used to study the effect of the electrode area on the overall plate deflection per unit input voltage such that the electromechanical coupling is optimized. While the center plate deflection increased monotonically with the electrode area for a simply supported plate, it followed a parabolic shape for a clamped one with a maximum deflection when the electrode radius covered 60% of the total plate radius. The simply supported plate exhibited four times the plate deflection capability of its clamped counterpart, when both are operating at their optimal electrode size. Both an experimental clamped bimorph aluminum nitride (AlN) pMUT, recently reported in the literature, and Finite Element Modeling (FEM) were used to verify the developed model. The theoretical model predicted a static displacement per unit voltage of 10.9nm/V and a resonant frequency of 196.5kHz, which were in excellent agreement with the FEM results of 10.32nm/V and 198.5kHz, respectively. The modeling data matched well with the experimental measurements and the error ranged from 2.7-22% due to process variations across the wafer. As such, the developed model can be used to design more sensitive pMUTs or extract the flexural piezoelectric coefficient using piezoelectrically actuated circular plates.
An electric circuit model for a circular bimorph piezoelectric micromachined ultrasonic transducer (PMUT) was developed for the first time. The model was made up of an electric mesh, which was coupled to a mechanical mesh via a transformer element. The bimorph PMUT consisted of two piezoelectric layers of the same material, having equal thicknesses, and sandwiched between three thin electrodes. The piezoelectric layers, having the same poling axis, were biased with electric potentials of the same magnitude but opposite polarity. The strain mismatches between the two layers created by the converse piezoelectric effect caused the membrane to vibrate and, hence, transmit a pressure wave. Upon receiving the echo of the acoustic wave, the membrane deformation led to the generation of electric charges as a result of the direct piezoelectric phenomenon. The membrane angular velocity and electric current were related to the applied electric field, the impinging acoustic pressure, and the moment at the edge of the membrane using two canonical equations. The transduction coefficients from the electrical to the mechanical domain and vice-versa were shown to be bilateral and the system was shown to be reversible. The circuit parameters of the derived model were extracted, including the transformer ratio, the clamped electric impedance, the spring-softening impedance, and the open-circuit mechanical impedance. The theoretical model was fully examined by generating the electrical input impedance and average plate displacement curves versus frequency under both air and water loading conditions. A PMUT composed of piezoelectric material with a lossy dielectric was also investigated and the maximum possible electroacoustical conversion efficiency was calculated.
New developments in digital mirror devices (DMDs) require suspension hinges with a good damping and high temperature stability. Carbon nanotubes (CNTs) offer these unique properties. Herein it is shown how CNT hinges can be integrated in micromirrors. The image illustrates a micromirror with a CNT suspension, and a typical overdamped stepresponse (Q-factor < 0.5).
Nanotechnology/methods , Nanotubes, Carbon/chemistry
Scanning probe microscopy (SPM) has been one of the most important tools to image and, hopefully, to manipulate bio-structures at micro/nanoscales. However, the current out-of-plane cantilever design makes it very difficult to extend the spectrum of the current SPM technology to meet many new functionalities arising from bio-engineering applications. An in-plane scanning probe concept is developed to accommodate the new functional requirements. It is designed to have a single-strand multi-walled carbon nanotube (CNT) tip assembled at the end of the probe, a built-in actuator and a tip deflection sensor, all in the same plane. The coplanar design is compatible with most of the standard MEMS processes and would facilitate the assembly of a carbon nanotube tip to the micromachined probe. The in-plane design features a switchable stiffness which adapts the scanning probe's stiffness to the changing surface hardness of the sample. This paper describes how the variable stiffness is accomplished by engaging or disengaging electrostatically actuated clutches, in addition to the discussions on many possible benefits of the in-plane scanning platform.
We present a microfabricated grating whose period can be tuned in analog fashion to within a fraction of a nanometer. The tunable angular range is more than 400 microrad in the first diffracted order. The design concept consists of a diffractive grating defined onto a 400-nm membrane, with the membrane subsequently strained in the direction perpendicular to the grating grooves by thin-film piezoelectric actuation. The strain-tuned grating device was fabricated with microelectromechanical processes, utilizing both surface and bulk micromachining. The fabricated piezoelectric film achieved a measured dielectric constant of 1200. Device characterization yielded grating period changes up to 8.3 nm (0.21% strain in the membrane) at 10 V and a diffracted angular change of 486 microrad, in good agreement with the theory. Uniformity across the actuated grating and out-of-plane deflections are characterized and discussed.
