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Various mechanical antennas have emerged to overcome the inherently narrower bandwidth and degraded efficiency in electrically small antennas. Among them, multiferroic antennas are expected to realize high-frequency applications and maintain their performance, even with significantly reduced sizes. However, experimental proof of such radiation from multiferroic or magnetoelectric coupling in the GHz range deserves further examination. This paper designs and fabricates a series of multiferroic antenna samples with mechanical resonances at around 3.5 and 6 GHz, and their radiation transmissions are tested at these resonances. Nickel, a magnetoelastic material, consistently exhibits magnetically induced radiation at both resonances. However, magnetic material consisting of Permalloy (Ni78Fe22), known for its much weaker magnetoelastic effects, still shows similar transmission behaviors at 3.67 GHz and enhanced power absorption at 6.42 GHz. Our results indicate that the dynamic response of magnetoelastic materials in the GHz band should differ from their response at the MHz and below bands. This evidence calls for further investigations of the source of magnetoelectric radiation. [ABSTRACT FROM AUTHOR]

We investigate localized in-plane strains on the microscale, induced by arrays of biased surface electrodes patterned on piezoelectrics. Particular focus is given to the influence that adjacent electrode pairs have on one another to study the impact of densely packed electrode arrays. We present a series of X-ray microdiffraction studies to reveal the spatially resolved micrometer-scale strain distribution. The strain maps with micrometer-scale resolution highlight how the local strain profile in square regions up to 250 × 250 μ m 2 in size is affected by the surface electrodes that are patterned on ferroelectric single-crystal [Pb(Mg1/3Nb2/3)O3]x-[PbTiO3]1−x. The experimental measurements and simulation results show the influence of electrode pair distance, positioning of the electrode pair, including the angle of placement, and neighboring electrode pair arrangements on the strength and direction of the regional strain. Our findings are relevant to the development of microarchitected strain-mediated multiferroic devices. The electrode arrays could provide array-addressable localized strain control for applications including straintronic memory, probabilistic computing platforms, microwave devices, and magnetic-activated cell sorting platforms. [ABSTRACT FROM AUTHOR]

The hermeticity and diffusion behavior of “epi-seal” encapsulation [R. N. Candler et al., J. Microelectromech. Syst. 15, 1446 (2006); B. Kim et al., Proceedings of the ASME 2007 InterPACK Conference (InterPACK’07), 33234 (2007)], an epitaxially deposited polysilicon film encapsulation for microelectromechanical systems (MEMSs), were investigated. MEMS resonators with pressure sensitive quality factor were fabricated inside episeal cavities. By measuring the quality factor and inferring cavity pressure, leakage through the encapsulation was studied as a continuation of previous hermeticity investigations [B. Kim et al., Proceedings of the 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE, pp. 413–416 (2004)]. During long-term monitoring performed at 100 °C in a normal atmosphere, the encapsulated cavity pressure increased at a rate of 5–10 mTorr/yr, whereas no measurable pressure change could be detected in our previous room temperature measurement performed with identically designed and encapsulated resonators. To identify the cause of this pressure increase, the diffusive gas species and diffusion pathways in the epi-seal encapsulation were investigated experimentally. Various gas species in the atmosphere were tested in a 400 °C accelerated environment. These tests identified hydrogen and helium as highly diffusive gas species and showed argon and nitrogen to be much less diffusive under these conditions. Also, a series of devices with modifications of encapsulation geometry was tested in a hydrogen environment at 400 °C. Silicon dioxide, used for sacrificial and passivation layers, was identified as the primary diffusion pathway through the epi-seal encapsulation. These experimental results and diffusion pathway models were compared with the diffusion activation energy of various gas species in semiconductor materials, enabling design and process optimization for improved hermeticity of wafer-scale thin-film encapsulation for MEMS devices. [ABSTRACT FROM AUTHOR]

Designing and implementing means of locally trapping magnetic beads and understanding the factors underlying the bead capture force are important steps toward advancing the capture-release process of magnetic particles for biological applications. In particular, capturing magnetically labeled cells using magnetic microstructures with perpendicular magnetic anisotropy (PMA) will enable an approach to cell manipulation for emerging lab-on-a-chip devices. Here, a Co (0.2 nm)/Ni (0.4 nm) multilayered structure was designed to exhibit strong PMA and large saturation magnetization (Ms). Finite element simulations were performed to assess the dependence of the capture force on the value of Ms. The simulated force profile indicated the largest force at the perimeter of the disks. Arrays of Co/Ni disk structures of (4–7) μm diameter were fabricated and tested in a microchannel with suspended fluorescent magnetic beads. The magnetic beads were captured and localized to the edge of the disks as predicted by the simulations. This approach has been demonstrated to enable uniform assembly of magnetic beads without external fields and may provide a pathway toward precise cell manipulation methods. [ABSTRACT FROM AUTHOR]

I recently went to lunch with some friends, and we ended up discussing the lack of female role models in engineering and how that may be limiting the growth of diversity in our field. The discussion went a little further, and the point was made that the role models we already have are not getting enough attention. [ABSTRACT FROM AUTHOR]

Enhancing the magnetoelectric coupling in a strain-mediated multiferroic composite structure plays a vital role in controlling magnetism by electric fields. An enhancement of magnetoelastic coupling between ferroelectric single crystal (011)-cut [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x (PMN-PT, x≈ 0.30) and ferromagnetic polycrystalline Ni thin film through an interposed benzocyclobutene polymer thin film is reported. A nearly twofold increase in sensitivity of remanent magnetization in the Ni thin film to an applied electric field is observed. This observation suggests a viable method of improving the magnetoelectric response in these composite multiferroic systems. [ABSTRACT FROM AUTHOR]

This review examines the state of the art for manufacturing non-planar miniature channels and actuators from PDMS, where non-planar structures are defined here as those beyond simple extrusions of 2D designs, either with rounded or variable cross sections or with an emergence of the channel trajectory out-of-plane. The motivation for 3D PDMS structures and advances in their fabrication are described, focusing on geometries that were previously unachievable through conventional microfabrication. The motivation for non-planar microfluidic channels and actuators is first discussed and the existing literature is grouped into general fabrication themes and described. The structures are organized by their method of fabrication and evaluated based on their relevant properties, including the capability of producing structures with complex geometry, automation of the fabrication process, and minimum feature size. Additional properties are included for work in the more recently emerging field of non-planar PDMS actuators, where the feature size, actuation stroke, and actuation method are the key parameters of interest. In particular, this review considers the impact from recent advances in additive manufacturing, which now allow creation of truly arbitrary 3D structures down to ∼100 μm size scales. [ABSTRACT FROM AUTHOR]

The geometry of a slotted MEMS resonator was optimized using a binary particle swarm optimization technique to reduce energy dissipation from thermoelastic dissipation (TED). The optimization technique combines fundamental physics with bio-inspired algorithms to navigate the complicated design space that arises from multiphysical problems. Fully-coupled thermomechanical simulations were used for optimization of QTED, and a weakly-coupled approach was used for design analysis. Through this approach, a TED-limited Q of 56000 was simulated, showing a 40% improvement over previous designs that were generated from the conventional intuitive design approach. The discovery of non-intuitive designs with these techniques also leads to new insight about the behavior of TED. The design algorithm used in this paper can be readily adapted to a variety of MEMS design problems. [ABSTRACT FROM AUTHOR]

This work presents for the first time a zeolitic imidazolate framework (ZIF)-coupled resonant gas sensor whose sensitivity shows an improvement up to 78 times over bare silicon resonant sensors with identical dimensions. ZIFs are among the highest surface area material used for resonant-based sensing. We utilize high surface area-to-volume ratios of ZIFs to demonstrate how a microresonator coupled with ZIF crystals can provide high sensitivity to chemical vapors. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of dielectric charge on resonant frequency in thermally oxidized silicon resonators hermetically encapsulated using "epi-seal." SiO2 coatings are effective for passive temperature compensation of resonators but make the devices more susceptible to charging-related issues. We present a theoretical model for the electromechanical effects of charge trapped in the dielectrics within the transduction gap of a resonator. Observations of resonance frequency against varying resonator bias voltage are fitted to this model in order to obtain estimates for the magnitude of the trapped oxide charge. Statistics collected from wet- and dry-oxidized devices show that lower fixed oxide charge can be expected upon dry oxidation. In addition, observations of time-varying resonator frequency indicate the presence of mobile oxide charge in a series of voltage biasing and temperature experiments. [ABSTRACT FROM AUTHOR]

This letter investigates the capillary filling in polydimethylsiloxane (PDMS) microchannels using 3-D printed molds to produce channels with circular cross sections. The circular cross sections are prevalent in biology and anatomy, yet they cannot readily be mimicked with existing soft-lithography techniques. The molds are printed directly from computer-aided design files, making rapid prototyping of microfluidic devices possible in hours, demonstrating microscale features in PDMS channels. The PDMS channels with variable channel diameters ranging from 200 to 1000 \mu \textm in a single device that are obtained from four different 3-D printers are compared in terms of capillary flow. Technology limits, including surface roughness and resolution, are also characterized, and estimated as an equivalent contact angle which is a fit parameter dependent on the 3-D printer. [2015-0335] [ABSTRACT FROM PUBLISHER]

The temperature dependence of the quality factor Q of microelectromechanical system (MEMS) resonators is analyzed and measured. For silicon MEMS resonators, there are several energy loss mechanisms that determine the quality factor. These include air-damping, thermoelastic dissipation, and anchor and surface losses. For resonators operating at a low pressure in hermetic wafer-scale encapsulation, the effect of each energy loss mechanism is discussed. The temperature dependence of each mechanism and their contribution to the total quality factor is investigated. MEMS resonators can be designed to have either strong or weak dependence of Q on temperature, which is if the effects of the temperature on the dominant loss mechanisms are well understood. The sensitivity of up to 1% changes in quality factor per degree Celsius change of temperature was demonstrated by experiment. By using Q as the thermometer for temperature compensation, a preliminary experiment demonstrated less than 4-ppm resonant frequency variation over the 0 °C-70 °C temperature range. This indicates that the quality factor can be used as an absolute intrinsic thermometer for temperature compensation in the MEMS resonators. [ABSTRACT FROM AUTHOR]

This paper presents an in-chip thermal-isolation technique for a micro-ovenized microelectromechanical-system resonator. Resonators with a microoven can be used for high-precision feedback control of temperature to compensate for the temperature dependence of resonator frequency over a wide temperature range. However, ovenization requires power consumption for heating, and the thermal time constant must be minimized for effective temperature control. This paper demonstrates an efficient local-thermal-isolation mechanism, which can reduce the power requirement to a few milliwatts and the thermal time constant to a few milliseconds. In this method, the mechanical suspension of the resonator is modified to provide thermal isolation and include an integrated resistive heater. This combination provides mechanical suspension, electrical heating, and thermal isolation in a compact structure that requires low heating power and has a small thermal time constant. A power consumption of approximately 12 mW for a 125 °C temperature rise and a thermal time constant ranging from 7 to 10 ms is reported in this paper, which is orders of magnitude lower than that of commercially available ovenized quartz resonators. A CMOS-compatible wafer-scale encapsulation process is used to fabricate this device, and the thermal-isolation design is achieved without any modification to the existing resonator fabrication process. [ABSTRACT FROM AUTHOR]

We have developed a single-wafer vacuum encapsulation for microelectromechanical systems (MEMS), using a thick (20-μm) polysilicon encapsulation to package micromechanical resonators in a pressure <1 Pa. The encapsulation is robust enough to withstand standard back-end processing steps, such as wafer dicing, die handling, and injection molding of plastic. We have continuously monitored the pressure of encapsulated resonators at ambient temperature for more than 10 000 h and have seen no measurable change of pressure inside the encapsulation. We have subjected packaged resonators to >600 cycles of -50 to 80°C, and no measurable change in cavity pressure was seen. We have also performed accelerated leakage tests by driving hydrogen gas in and out of the encapsulation at elevated temperature. Two results have come from these hydrogen diffusion tests. First, hydrogen diffusion rates through the encapsulation at temperatures 300–400°C have been determined. Second, the package was shown to withstand multiple temperature cycles between room and 300–400°C without showing any adverse affects. The high robustness and stability of the encapsulation can be attributed to the clean, high-temperature environment during the sealing process. [ABSTRACT FROM AUTHOR]

This paper presents two approaches to analyzing and calculating thermoelastic damping in micromechanical resonators. The first approach solves the fully coupled thermomechanical equations that capture the physics of thermoelastic damping in both two and three dimensions for arbitrary structures. The second approach uses the eigenvalues and eigenvectors of the uncoupled thermal and mechanical dynamics equations to calculate damping. We demonstrate the use of the latter approach to identify the thermal modes that contribute most to damping, and present an example that illustrates how this information may be used to design devices with higher quality factors. Both approaches are numerically implemented using a finite-element solver (Comsol Multiphysics). We calculate damping in typical micromechanical resonator structures using Comsol Multiphysics and compare the results with experimental data reported in literature for these devices. [ABSTRACT FROM AUTHOR]

Thermoelastic dissipation (TED) is analyzed for complex geometries of micromechanical resonators, demonstrating the impact of resonator design (i.e., slots machined into flexural beams) on TED-limited quality factor. Zener first described TED for simple beams in 1937. This work extends beyond simple beams into arbitrary geometries, verifying simulations that completely capture the coupled physics that occur. Novel geometries of slots engineered at specific locations within the flexural resonator beams are utilized. These slots drastically affect the thermal-mechanical coupling and have an impact on the quality factor, providing resonators with quality factors higher than those predicted by simple Zener theory. The ideal location for maximum impact of slots is determined to be in regions of high strain. We have demonstrated the ability to predict and control the quality factor of micromechanical resonators limited by thermoelastic dissipation. This enables tuning of the quality factor by structure design without the need to scale its size. thus allowing for enhanced design optimization. [ABSTRACT FROM AUTHOR]

While micromachined accelerometers are widely available and used in various applications, some biomedical applications require extremely small dimensions (

Packaging of micro-electro-mechanical systems (MEMS) devices has proven to be costly and complex, and it has been a significant barrier to the commercialization of MEMS. We present a packaging solution applicable to several common MEMS devices, such as inertial sensors and micromechanical resonators. It involves deposition of a 20 μm layer of epi-polysilicon over unreleased devices to act as a sealing cap, release of the encapsulated parts via an HF vapor release process, and a final seal of the parts in 7 mbar (700 Pa) vacuum. Two types of accelerometers, piezoresistive and capacitive sensing, were fabricated. Piezoresistive accelerometers with a footprint smaller than 3 mm² had a resolution of 10 μg/√Hz at 250 Hz. Capacitive accelerometers with a 1 mm² footprint had a resolution of 1 mg √Hz over its 5 kHz bandwidth. Resonators with a quality factor as high as 14,000 and resonant frequency from 50 kHz to 10 MHz have also been built. More than 100 capacitive accelerometers and 100 resonators were tested, and greater than 90% of the resonators and accelerometers were functional. [ABSTRACT FROM AUTHOR]

This letter examines the dependence of the natural frequency in a microelectromechanical resonator on externally applied acceleration. The particular structure studied is an electrostatically coupled, single anchored, double-ended silicon tuning fork. The authors find that the acceleration dependence in this resonator is primarily due to axial stress on the resonator beams. Measurements show an acceleration sensitivity Δf/f0 of 7×10-9/g, which is comparable to values found for typical quartz crystal resonators. This result was obtained using dynamic (vibration) measurements, and validated using theoretical analysis and finite element simulations. [ABSTRACT FROM AUTHOR]

A model for the amplitude-frequency (A-f) effect in electrostatic microresonators is presented. This effect is an undesired nonlinear phenomenon that sets the maximum usable oscillation current and thereby degrades the resonator’s signal-to-noise ratio and performance. The model developed in this letter provides analytical expressions for the A-f effect and derives an optimal bias condition that maximizes the usable current. In addition, the authors present experimental data for a double-ended-tuning-fork resonator. Using the derived bias condition, an improvement of more than two times in the sustainable oscillation current has been achieved. [ABSTRACT FROM AUTHOR]

As you approach your final year of undergraduate studies and start the process of applying to graduate schools, you will realize that you need at least three letters of recommendation to complete your application. Admissions committees take these letters very seriously, but there is a reasonable chance that you will not think about them until the application comes up. This article describes the ins and outs of how to get letters that will improve your chances of gaining admission to a great graduate program. [ABSTRACT FROM PUBLISHER]