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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]

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 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]