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Millimeter wave components, such as circulators and isolators, frequently use magnetic fields to break symmetry of the signal propagation and provide unidirectional signal transmission. While effective, these components have not seen the level of miniaturization of other millimeter wave components, primarily due to the discrete nature of the magnets used in the components. Using circulators in the 40-50 GHz range as a motivating application, requirements arise for the deposited films, namely immunity to eddy currents, sufficient magnetization to act as self-biasing magnets, and out-of-plane orientation of the self-biasing field. Based on these required properties, hexaferrite materials are selected for their strong magnetocrystalline anisotropy (MCA) and low conductance. The difficulty of integrating these components monolithically with monolithic microwave integrated circuits (MMIC) originates from the incompatibility of crystal structure with standard semiconductor materials and process conditions. Additive manufacturing using a composite of strontium hexaferrite (SrFe12O19) particles and photoresist has been chosen as a method to overcome the difficulties of integrating hexaferrite material to semiconductor substrates. Due to their large internal anisotropy field, the particles of strontium hexaferrite tend to rotate to the field direction instead of changing magnetization direction under application of an external magnetic field (less than the anisotropy field). We have developed a method for 3D printing composites of high strontium hexaferrite concentration (up to 20% by volume) in a liquid photoresist, SU8. Rotation of hexaferrite particles in polymer matrix and thus magnetic anisotropy has been demonstrated in the composite, which is subsequently cured to hold the physical position and orientation of the particles. The anisotropy of the self-biasing field provided by the films has been experimentally characterized, and a ferromagnetic resonance (FMR) frequency ~43 GHz has been observed. We have also characterized the viscosity of the particle-laden polymer at different particle concentrations. 3D printing of this composite with poling will make it possible to directly print magnetic components that require out-of-plane anisotropic magnetization.

The magnetoelectric properties of exchange-coupled Ni/CoFeB-based composite multiferroic microstructures are investigated. The strength and sign of the magnetoelastic effect are found to be strongly correlated with the ratio between the thicknesses of two magnetostrictive materials. In cases where the thickness ratio deviates significantly from one, the magnetoelastic behavior of the multiferroic microstructures is dominated by the thicker layer, which contributes more strongly to the observed magnetoelastic effect. More symmetric structures with a thickness ratio equal to one show an emergent interfacial behavior which cannot be accounted for simply by summing up the magnetoelastic effects occurring in the two constituent layers. This aspect is clearly visible in the case of ultrathin bilayers, where the exchange coupling drastically affects the magnetic behavior of the Ni layer, making the Ni/CoFeB bilayer a promising next-generation synthetic magnetic system entirely. This study demonstrates the richness and high tunability of composite multiferroic systems based on coupled magnetic bilayers compared to their single magnetic layer counterparts. Furthermore, because of the compatibility of CoFeB with present magnetic tunnel junction-based spintronic technologies, the reported findings are expected to be of great interest for the development of ultralow-power magnetoelectric memory devices.

An unconditionally stable finite-difference time-domain (FDTD) algorithm is proposed to predict and understand the complex response in strain-mediated multiferroic radio frequency devices, such as antennas. A system of three coupled sets of governing equations is solved simultaneously: 1) Maxwell's equations for electromagnetic (EM) wave propagation; 2) Landau–Lifshitz–Gilbert equation for magnetic spin response; and 3) Newton's law for acoustic behavior. The formulation of this algorithm is elaborated on in detail followed by a demonstration of its capability through the simulation of a 1.3- μ m-thick bulk-acoustic-wave (BAW)-based strain-mediated multiferroic antenna. Analysis of the far-field radiation efficiency of this antenna as a function of magnetic dc bias demonstrates the importance of aligning the ferromagnetic resonance (FMR) and the mechanical BAW resonance to enhance EM radiation performance. Results also show that reducing the magnetic loss, or in other words, reducing the FMR linewidth, represents the dominating feature to achieve higher radiation efficiencies in these antennas.

A phenomenological study is presented of the impact, spreading, and arrest of Galinstan droplets on a rigid substrate. The maximum diameter at which contact line arrest occurs is found to be a power law of the speed and a model is presented to rationalize the observations.

In this work, we investigate magneto-acoustic attenuation in thin film multiferroic Lamb wave delay lines. By leveraging magneto-acoustic interactions, multiferroics have potential to realize passive chip-scale alternatives to bulky ferrite devices. For the first time, magnetic field dependence of magneto-acoustic interactions in multiferroic Lamb wave devices is characterized. Multiferroic heterostructures of aluminum nitride and cobalt iron boron are fabricated into Lamb wave delay lines operating at 7.492 GHz to study the effect of strain nonuniformity on the multiferroic coupling. The attenuation of the Lamb waves is characterized as a function of the magnitude and angle of an applied in-plane bias magnetic field. It is found that the bias magnitude for peak attenuation is a strong function of angle, indicating that it is due to coupling between the Lamb waves and spin wave modes. This is in contrast with current models of attenuation in multiferroic SAW delay lines, where the uniform surface strains couple to ferromagnetic resonance, which has no angular dependence on the in-plane bias field magnitude. These results are the first steps towards passive chip-scale alternatives to ferrite devices utilizing Lamb wave devices, which have better coupling and scalability than their SAW counterparts. [2020-0114]

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.

Author(s): Goiriena-Goikoetxea, M; Xiao, Z; El-Ghazaly, A; Stan, CV; Chatterjee, J; Ceballos, A; Pattabi, A; Tamura, N; Lo Conte, R; Hellman, F; Candler, R; Bokor, J | Abstract: We investigate the influence of dislocations and twin walls in BaTiO3 on its ferroelectric response and the resulting effect on the perpendicular magnetic anisotropy (PMA) of a strain-coupled [Co Ni]n film. A dense twinned structure in conjunction with a high dislocation density significantly reduces the converse piezoelectric effect of BaTiO3 by hindering the propagation of newly nucleated domains with an applied electric field. This, in turn, results in a modest reduction of the PMA of the ferromagnetic layer. On the other hand, the ferroelectric polarization reorients from [100] to [001] direction in a dislocation-free BaTiO3, inducing the maximum achievable in-plane compressive strain of 1.1%. A large fraction of this uniaxial strain is transferred to the magnetoelastically coupled ferromagnetic layers whose magnetization switches to in plane via the inverse magnetostriction effect. This work reveals the critical role of the interplay between twin walls and dislocations within a ferroelectric substrate in the performance of multiferroic heterostructures and provides insight into the development of highly energy-efficient magnetoelectric devices.

In the field of beam physics, two frontier topics have taken center stage due to their potential to enable new approaches to discovery in a wide swath of science. These areas are: advanced, high gradient acceleration techniques, and x-ray free electron lasers (XFELs). Further, there is intense interest in the marriage of these two fields, with the goal of producing a very compact XFEL. In this context, recent advances in high gradient radio-frequency cryogenic copper structure research have opened the door to the use of surface electric fields between 250 and 500 MV/m. Such an approach is foreseen to enable a new generation of photoinjectors with six-dimensional beam brightness beyond the current state-of-the-art by well over an order of magnitude. This advance is an essential ingredient enabling an ultra-compact XFEL (UC-XFEL). In addition, one may accelerate these bright beams to GeV scale in less than 10 meters. Such an injector, when combined with inverse free electron laser-based bunching techniques can produce multi-kA beams with unprecedented beam quality, quantified by ~50 nm-rad normalized emittances. These beams, when injected into innovative, short-period (1-10 mm) undulators uniquely enable UC-XFELs having footprints consistent with university-scale laboratories. We describe the architecture and predicted performance of this novel light source, which promises photon production per pulse of a few percent of existing XFEL sources. We review implementation issues including collective beam effects, compact x-ray optics systems, and other relevant technical challenges. To illustrate the potential of such a light source to fundamentally change the current paradigm of XFELs with their limited access, we examine possible applications in biology, chemistry, materials, atomic physics, industry, and medicine which may profit from this new model of performing XFEL science., 80 pages, 24 figures

In this paper we explore parametric amplification on the Lamb wave acoustic platform for the purpose of developing nonlinear and non-reciprocal devices. The strength of the acoustic wave platform over the electromagnetic platform is its low loss and short wavelength at radio frequency which enables devices with a small footprint and high quality factor. Compared to surface acoustic waves, Lamb waves exhibit much higher phase velocity which support higher frequency operation with fabrication tolerance. To realize parametric amplification, the intrinsic nonlinear stiffness of aluminum nitride is used to couple acoustic waves at different frequencies. Novel Lamb wave resonator structures and non-reciprocal devices implementation have been proven in theory and simulation. Experiment of Lamb wave transducers demonstrates parametric effects and proves nonlinearity in AlN thin films.

Lamb wave devices were fabricated and tested to study parametric mixing through a nonlinear elastic modulus. A carrier wave was used to drive the time-variation of the elastic modulus in a traveling wave fashion. The signal wave is launched in the same direction as the carrier wave. The nonlinearity results in the signal to be mixed up and down with the carrier signal generating intermodulation terms. Through optimization, next generation RF components that are 5 orders in magnitude smaller than the current state of the art can be designed, freeing up real estate for larger batteries and additional sensors.

This work demonstrates that magnetoelectric composite heterostructures can be designed at the length scale of 10µms that can be switched from a magnetized state to a vortex state, effectively switching the magnetization off, using electric field induced strain. This was accomplished using thin film magnetoelectric heterostructures of Fe81.4Ga18.6on a single crystal (011) [Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32(PMN-32PT) ferroelectric substrate. The heterostructures were tripped from a multi-domain magnetized state to a flux closure vortex state using voltage induced strain in a piezoelectric substrate. FeGa heterostructures were deposited on a Si-substrate for superconducting quantum interference device magnetometry characterization of the magnetic properties. The magnetoelectric coupling of a FeGa continuous film on PMN-32PT was characterized using a magneto optical Kerr effect magnetometer with bi-axial strain gauges, and magnetic multi-domain heterostructures were imaged using x-ray magnetic circular dichroism—photoemission electron microscopy during the transition to the vortex state. The domain structures were modelled using MuMax3, a micromagnetics code, and compared with observations. The results provide considerable insight into designing magnetoelectric heterostructures that can be switched from an ‘on’ state to an ‘off’ state using electric field induced strain.

In this Letter, we explore a non-degenerate phase independent parametric quality factor (Q)-enhancement technique for aluminum nitride (AlN) Lamb wave resonators. Unlike other active Q-enhancement techniques which require precise phase control of the electronic feedback loop, this technique is implemented by parametrically pumping AlN material stiffness to realize a negative resistance seen at the signal path. The negative resistance is dependent on the nonlinear material modulation and multi-resonance coupling in the device. A nonlinear circuit model is developed to simulate the parametric coupling of each resonance and extract the nonlinearity of AlN from experimental data. With proper pump frequency and pump power, the device quality factor is boosted in both simulation and experiment. The demonstrated Q-enhancement method is simple to implement and can be applied to other types of resonators that have nonlinear behavior and support multi-resonance operation.

Studies on giant magnetostrictive intermetallic compound Tb0.3Dy0.7 Fe1.92 (Terfenol-D) thin films are gaining increasing attention due to the interest in small scale magnetic structures. In this work, polycrystalline Terfenol-D thin films (60 nm) are produced using a Direct Current (DC) magnetron sputtering process and a hybrid thermal annealing approach, i.e. substrate heating and post-annealing. The crystallized Terfenol-D films are micropatterned (3 μm and 20 μm diameters) using a photolithographic method followed by Argon etching. The continuous and micropatterned thin films are characterized with XRD, SQUID and MOKE magnetometers showing properties similar to bulk polycrystalline Terfenol-D. Additional studies are conducted using X-ray absorption spectroscopy and the X-ray magnetic circular dichroism to investigate oxidation. Results show that while the top surface of these Terfenol-D structures are capped with Ta thin films, the side walls of the structures are exposed to ambient atmosphere raising the concern of oxidation issues. This work shows that a passivating oxide layer forms on the side walls of these small-scale Terfenol-D disks which is attributed to both the Ta capping layer as well as residual stresses preventing continued stress corrosion cracking caused by the oxidation process.

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 m2 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.

We demonstrate deterministic multi-step rotation of a magnetic single-domain (SD) state in Nickel nanodisks using the multiferroic magnetoelastic effect. Ferromagnetic Nickel nanodisks are fabricated on a piezoelectric Lead Zirconate Titanate (PZT) substrate, surrounded by patterned electrodes. With the application of a voltage between opposing electrode pairs, we generate anisotropic in-plane strains that reshape the magnetic energy landscape of the Nickel disks, reorienting magnetization toward a new easy axis. By applying a series of voltages sequentially to adjacent electrode pairs, circulating in-plane anisotropic strains are applied to the Nickel disks, deterministically rotating a SD state in the Nickel disks by increments of 45°. The rotation of the SD state is numerically predicted by a fully-coupled micromagnetic/elastodynamic finite element analysis (FEA) model, and the predictions are experimentally verified with magnetic force microscopy (MFM). This experimental result will provide a new pathway to develop energy efficient magnetic manipulation techniques at the nanoscale.

While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for university research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-mm period [1] requires electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K [2] , where collective field effects dominate. In this work, we investigate the behaviour of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis is the one-dimensional FEL theory including space-charge forces. The derived results is compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the one-fourth power while the efficiency grows as the square root of the beam current. This advantage in efficiency may prove critical in the development of very compact short wavelength FELs, such as the Keck Foundation-funded SAMURAI FEL at UCLA.

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.

Robotic surgical platforms have seen increased use among minimally invasive gastrointestinal surgeons (von Fraunhofer et al. in J Biomed Mater Res 19(5):595–600, 1985. doi: 10.1002/jbm.820190511 ). However, these systems still suffer from lack of haptic feedback, which results in exertion of excessive force, often leading to suture failures (Barbash et al. in Ann Surg 259(1):1–6, 2014. doi: 10.1097/SLA.0b013e3182a5c8b8 ). This work catalogs tensile strength and failure load among commonly used sutures in an effort to prevent robotic surgical consoles from exceeding identified thresholds. Trials were thus conducted on common sutures varying in material type, gauge size, rate of pulling force, and method of applied force. Polydioxanone, Silk, Vicryl, and Prolene, gauges 5-0 to 1-0, were pulled till failure using a commercial mechanical testing system. 2-0 and 3-0 sutures were further tested for the effect of pull rate on failure load at rates of 50, 200, and 400 mm/min. 3-0 sutures were also pulled till failure using a da Vinci robotic surgical system in unlooped, looped, and at the needle body arrangements. Generally, Vicryl and PDS sutures had the highest mechanical strength (47–179 kN/cm2), while Silk had the lowest (40–106 kN/cm2). Larger diameter sutures withstand higher total force, but finer gauges consistently show higher force per unit area. The difference between material types becomes increasingly significant as the diameters decrease. Comparisons of identical suture materials and gauges show 27–50% improvement in the tensile strength over data obtained in 1985 (Ballantyne in Surg Endosc Other Interv Tech 16(10):1389–1402, 2002. doi: 10.1007/s00464-001-8283-7 ). No significant differences were observed when sutures were pulled at different rates. Reduction in suture strength appeared to be strongly affected by the technique used to manipulate the suture. Availability of suture tensile strength and failure load data will help define software safety protocols for alerting a surgeon prior to suture failure during robotic surgery. Awareness of suture strength weakening with direct instrument manipulation may lead to the development of better techniques to further reduce intraoperative suture breakage.

Software-defined radio (SDR) requires multi-use or reconfigurable radio-frequency front ends, with filters capable of dynamically shifting their operating frequencies. Current approaches to tunable filters typically require prohibitively large electric fields to achieve large tuning. This study utilizes a multiferroic approach, with an electric field straining magnetoelastic elements to tune the system's magnetic resonance. Furthermore, dipole coupling of the elements yields mode splitting, for additional resonance peaks that depend on element spacing and applied strain. This could lead to innovative types of rf filters for SDR, where communication frequencies are rapidly changing.

As robotic surgery has increased in popularity, the lack of haptic feedback has become a growing issue due to the application of excessive forces that may lead to clinical problems such as intraoperative and postoperative suture breakage. Previous suture breakage warning systems have largely depended on visual and/or auditory feedback modalities, which have been shown to increase cognitive load and reduce operator performance. This work catalogues a new sensing technology and haptic feedback system (HFS) that can reduce instances of suture failure without negatively impacting performance outcomes including knot quality. Suture breakage is common in knot-tying as the pulling motion introduces prominent shear forces. A shear sensor mountable on the da Vinci robotic surgical system's Cadiere grasper detects forces that correlate to the suture's internal tension. HFS then provides vibration feedback to the operator as forces near a particular material's failure load. To validate the system, subjects tightened a total of four knots, two with the Haptic Feedback System (HFS) and two without feedback. The number of suture breakages were recorded and knot fidelity was evaluated by measuring knot slippage. Results showed that instances of suture failure were significantly reduced when HFS was enabled ( p = 0.0078). Notably, knots tied with HFS also showed improved quality compared to those tied without feedback ( p = 0.010). The results highlight the value of HFS in improving robotic procedure outcomes by reducing instances of suture failures, producing better knots, and reducing the need for corrective measures.

The number of procedures performed with robotic surgery may exceed one million globally in 2018. The continual lack of haptic feedback, however, forces surgeons to rely on visual cues in order to avoid breaking sutures due to excessive applied force. To mitigate this problem, the authors developed and validated a novel grasper-integrated system with biaxial shear sensing and haptic feedback to warn the operator prior to anticipated suture breakage. Furthermore, the design enables facile suture manipulation without a degradation in efficacy, as determined via measured tightness of resulting suture knots. Biaxial shear sensors were integrated with a da Vinci robotic surgical system. Novice subjects (n = 17) were instructed to tighten 10 knots, five times with the Haptic Feedback System (HFS) enabled, five times with the system disabled. Seven suture failures occurred in trials with HFS enabled while seventeen occurred in trials without feedback. The biaxial shear sensing system reduced the incidence of suture failure by 59% (p = 0.0371). It also resulted in 25% lower average applied force in comparison to trials without feedback (p = 0.00034), which is relevant because average force was observed to play a role in suture breakage (p = 0.03925). An observed 55% decrease in standard deviation of knot quality when using the HFS also indicates an improvement in consistency when using the feedback system. These results suggest this system may improve outcomes related to knot tying tasks in robotic surgery and reduce instances of suture failure while not degrading the quality of knots produced.

Programming magnetic fields with microscale control can enable automation at the scale of single cells ≈10 µm. Most magnetic materials provide a consistent magnetic field over time but the direction or field strength at the microscale is not easily modulated. However, magnetostrictive materials, when coupled with ferroelectric material (i.e., strain-mediated multiferroics), can undergo magnetization reorientation due to voltage-induced strain, promising refined control of magnetization at the micrometer-scale. This work demonstrates the largest single-domain microstructures (20 µm) of Terfenol-D (Tb0.3 Dy0.7 Fe1.92 ), a material that has the highest magnetostrictive strain of any known soft magnetoelastic material. These Terfenol-D microstructures enable controlled localization of magnetic beads with sub-micrometer precision. Magnetically labeled cells are captured by the field gradients generated from the single-domain microstructures without an external magnetic field. The magnetic state on these microstructures is switched through voltage-induced strain, as a result of the strain-mediated converse magnetoelectric effect, to release individual cells using a multiferroic approach. These electronically addressable micromagnets pave the way for parallelized multiferroics-based single-cell sorting under digital control for biotechnology applications.

Material extrusion 3D printing has long been established for rapid prototyping and functional testing in many research and industry fields. However, its inconsistency and intrinsic defects (surface roughness and geometric inaccuracies) hinder its application in several areas, most notably “certify-as-you-build” small-batch prototyping and large-batch production. In this study, we present an approach to reduce both inconsistency and the 3D geometric inaccuracies of products fabricated by material extrusion. To achieve these improvements in print quality, we developed an in situ metrology system, which scans each layer at the time of printing, providing a 3D model of the as-printed part. We then trained machine learning algorithms with data from this scanning system and predicted 3D geometric inaccuracies in new designs. Eight conditional adversarial network (CAN) machine learning models were trained on a limited number of scanned profile images of different layers, consisting of less than 50 actual images and 50 generated images, to predict the 3D geometric deviations of freeform shapes. The generated images were produced by randomly combining and cropping the actual images without any distortion. These CAN models produced predictions where at least 44.4%, 87.6%, 99.2% of data were within ± 0.05 mm, ± 0.10 mm, ± 0.15 mm of the actual measured value, respectively. A laser sensor was integrated into a material extrusion 3D printer to achieve in situ monitoring of dimensional inaccuracies during printing, which leaves the door open to implement a closed-loop feedback system to compensate geometric errors during printing in the future and fabricate “certify-as-you-build” products.

Frequency conversion is an essential tool in modern communication devices. Traditionally, frequency conversion is achieved through parametric coupling via nonlinear inductors or capacitors whose reactance is modulated by a carrier wave. In this study, nonlinear acoustic Lamb wave devices are explored for simultaneous signal filtering and frequency conversion. Three sets of interdigitated transducers are fabricated on a piezoelectric aluminum nitride (AlN) thin film to provide a carrier wave, a low-power signal wave, and to receive a frequency converted mixed wave. Two devices are fabricated and tested to demonstrate frequency upconversion and downconversion by utilizing mechanical nonlinearity of AlN, and the results are compared to a nonlinear circuit model. The nonlinear circuit model is used to link experimentally observed phenomenon to the acoustic material's intrinsic nonlinearity. The nonlinearity of AlN reaches a maximum of 2.8% with a carrier wave power at 28 dBm. An analytical model is used to predict device performance along with physical dimensions. These analytical results show that nonlinear acoustic mixers and filters can approach sub-millimeter sizes, which is orders-of-magnitude smaller than conventional structures using nonlinear inductors and capacitors.

Precise control and manipulation of nano-beads have various applications, e.g. cell sorter, 3D printing and nano-motors. In this paper we present an approach in which we use voltage on a piezolecetric substrate in order to reorient the magnetization of a nano-disk. In turn this magnetization drives the dynamic of the nano-beads. This is an energy efficient method to control the nano-beads motion since only voltage is applied to the substrate. The mechanism consists of a Ni disk and three pairs of surface electrodes placed on a PZT substrate. By controlling the voltage applied on the different pairs of electrodes, the magnetization of the Ni disk will rotate with constant angular velocity. The rotating magnetization will then generate magnetic force on the soft-magnetic nano-beads driving the motion. For the beads, full 3D dynamics consider both translation and rotation and the forces considered are magnetic, drag, friction and adhesion. With this model we are able to have a realistic description for the particle behavior.

This paper experimentally demonstrates the operating principles of a near-field multiferroic antenna. The antenna uses a piezoelectric lead-zirconate-titanate stack to apply a time varying strain to a magnetoelastic iron gallium Fe80.77Ga19.23 (FeGa) rod. The voltage induced strain controls the net magnetization of the FeGa rod to generate oscillating magnetic fields in free space surrounding the antenna. Direct experimental measurements of the mechanical force, strain, magnetic field, and magnetic flux inside the FeGa rod were collected and show a strong correlation with the dynamic magnetic field measured in free space. Additionally, an analytical dipole model is used to demonstrate that the free space signal originates from the changing magnetization in the FeGa rod, providing a clear multiferroic antenna proof-of-concept demonstration. Finally, analysis is provided to highlight the importance of device geometry and demagnetization fields when optimizing the antenna response.

Realistic modeling of biologic material is required for optimizing fidelity in computer-aided surgical training and assistance systems. The modeling of liver tissue has remained challenging due to its nonlinear viscoelastic properties and high hysteresis of the stress-strain relation. While prior studies have described the behavior of liver tissue during the loading status (in elongation, compression, or indentation tests) or unloading status (in stress relaxation or creep tests), a hysteresis curve with both loading and unloading processes was incompletely defined. We seek to use a single material model to characterize the mechanical properties of liver tissue in a full indentation cycle ex vivo perfused and then sectioned. Based on measurements taken from ex-vivo perfused porcine livers, we converted force-displacement curves to stress-strain curves and developed a visco-hyperelastic constitutive model to characterize the liver's mechanical behavior at different locations under various rates of indentation (1, 2, 5, 10, and 20 mm/s). The proposed model is a mixed visco-hyperelastic model with up to 6 coefficients. The normalized root mean square standard deviations of fitted curves are less than 5% and 10% in low (0.05) and high strain (0.3) conditions respectively.

Wireless multiferroics is an emerging field taking advantage of energy efficient multiferroic coupling to design and develop ultra-conformal, electrically-small antennas. To date, all work on MEMS scale multiferroic devices utilize linear multiferroic coupling. In this work, we present the first demonstration of frequency doubling through nonlinear multiferroics in MEMS resonators. Multiferroic composite cantilevers are fabricated and tested, and it is shown that these resonators can be wirelessly driven to mechanical resonance with magnetic fields at half of the resonant frequency by utilizing perpendicular magnetic poling. This is a potential method for low noise measurement of wireless signals, a problem that plagues all electrically-small wireless devices, which would revolutionize the emerging field of wireless multiferroic devices.

Strain-coupled multiferroic heterostructures provide a path to energy-efficient, voltage-controlled magnetic nanoscale devices, a region where current-based methods of magnetic control suffer from Ohmic dissipation. Growing interest in highly magnetoelastic materials, such as Terfenol-D, prompts a more accurate understanding of their magnetization behavior. To address this need, we simulate the strain-induced magnetization change with two modeling methods: the commonly used unidirectional model and the recently developed bidirectional model. Unidirectional models account for magnetoelastic effects only, while bidirectional models account for both magnetoelastic and magnetostrictive effects. We found unidirectional models are on par with bidirectional models when describing the magnetic behavior in weakly magnetoelastic materials (e.g., Nickel), but the two models deviate when highly magnetoelastic materials (e.g., Terfenol-D) are introduced. These results suggest that magnetostrictive feedback is critical for modeling highly magnetoelastic materials, as opposed to weaker magnetoelastic materials, where we observe only minor differences between the two methods’ outputs. To our best knowledge, this work represents the first comparison of unidirectional and bidirectional modeling in composite multiferroic systems, demonstrating that back-coupling of magnetization to strain can inhibit formation and rotation of magnetic states, highlighting the need to revisit the assumption that unidirectional modeling always captures the necessary physics in strain-mediated multiferroics.

International audience; Composite multiferroic systems, consisting of a piezoelectric substrate coupled with a ferromagnetic thin film, are of great interest from a technological point of view because they offer a path toward the development of ultralow power magnetoelectric devices. The key aspect of those systems is the possibility to control magnetization via an electric field, relying on the magneto-elastic coupling at the interface between the piezoelectric and the ferromagnetic components. Accordingly, a direct measurement of both the electrically induced magnetic behavior and of the piezo-strain driving such behavior is crucial for better understanding and further developing these materials systems. In this work, we measure and characterize the micron-scale strain and magnetic response, as a function of an applied electric field, in a composite multiferroic system composed of 1 and 2 μm squares of Ni fabricated on a prepoled [Pb(Mg 1/3 Nb 2/3)O 3 ] 0.69 −[PbTiO 3 ] 0.31 (PMN−PT) single crystal substrate by X-ray microdiffraction and X-ray photoemission electron microscopy, respectively. These two complementary measurements of the same area on the sample indicate the presence of a nonuniform strain which strongly influences the reorientation of the magnetic state within identical Ni microstructures along the surface of the sample. Micromagnetic simulations confirm these experimental observations. This study emphasizes the critical importance of surface and interface engineering on the micron-scale in composite multiferroic structures and introduces a robust method to characterize future devices on these length scales.

A novel electrically-small bulk acoustic wave (BAW)-mediated multiferroic antenna is proposed based on transverse shear waves instead of the longitudinal ones used in the previously proposed multiferroic antenna [1]. Two in-plane orthogonal pairs of electrodes provide independent excitation of the orthogonal transverse shear modes, enabling the first investigation of polarization control in a BAW-mediated multiferroic antenna. Using this approach, polarization can be controlled simply by adjusting the phase difference between the input RF signals of the two electrode pairs. The proposed design concept is verified numerically via COMSOL simulations and a series of post-processing steps in MATLAB. By assuming ideal input RF signals with equal amplitude and 90° phase difference, broadband circularly polarized radiation is achieved in the sub-GHz band.

Polymer-based pneumatic balloon actuators consisting of novel trapezoidal vertical microballoon fins were fabricated by three-dimensional (3D) printed molds and validated experimentally. The introduction of 3D printed molds for pneumatic actuation provides additional freedom in the design of actuators, removing the limitation of extruded 2D shapes that is present with conventional microfabrication. Whereas conventional balloon actuators exhibit nonlinear response to applied pressure, the presence of balloon fins with 100 s-μm width was shown to produce a linear change in bend angle with the injection of pressurized air. The balloon fins also mitigate stress concentrations that can lead to material failure. Static bending (exceeding 80° bend angle) and the mechanical force of the fabricated microfingers were tested and compared with analytical models. The expanded design space permitted by 3D printing allows actuator designs to achieve a given deflection with less stress in the material as compared to planar designs. Feasibility of this design flexibility and fast prototyping enabled by the 3D printed molding process was demonstrated by fabricating and testing various designs of microfingers. When grouped, the microfingers with balloon fins can successfully accomplish complex object transfer tasks (i.e., multi-directional actuation with independently controlled displacement).

In this work, we experimentally demonstrate deterministic electrically driven, strain-mediated domain wall (DW) rotation in ferromagnetic Ni rings fabricated on piezoelectric [Pb(Mg1/3Nb2/3)O3]0.66-[PbTiO3]0.34 (PMN-PT) substrates. While simultaneously imaging the Ni rings with X-ray magnetic circular dichroism photoemission electron microscopy, an electric field is applied across the PMN-PT substrate that induces strain in the ring structures, driving DW rotation around the ring toward the dominant PMN-PT strain axis by the inverse magnetostriction effect. The DW rotation we observe is analytically predicted using a fully coupled micromagnetic/elastodynamic multiphysics simulation, which verifies that the experimental behavior is caused by the electrically generated strain in this multiferroic system. Finally, this DW rotation is used to capture and manipulate micrometer-scale magnetic beads in a fluidic environment to demonstrate a proof-of-concept energy-efficient pathway for multiferroic-based lab-on-a-chip applications.

This article introduces the use of three-dimensionally (3D) printed molds for rapid fabrication of complex and arbitrary microchannel geometries that are unattainable through existing soft lithography techniques. The molds are printed directly from computer-aided design (CAD) files, making rapid prototyping of microfluidic devices possible in hours. The resulting 3D printed structures enable precise control of various device geometries, such as the profile of the channel cross-section and variable channel diameters in a single device. We report fabrication of complex 3D channels using these molds with polydimethylsiloxane (PDMS) polymer. Technology limits, including surface roughness, resolution, and replication fidelity are also characterized, demonstrating 100-μm features and sub-micron replication fidelity in PDMS channels.

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 $\mu \text{m}$ 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]

This paper describes the design, microfabrication, and characterization of a miniature force sensor for providing tactile feedback in robotic surgical systems. We demonstrate for the first time a microfabricated sensor that can provide triaxial sensing (normal, x-shear, y-shear) in a single sensor element that can be integrated with commercial robotic surgical graspers. Features of this capacitive force sensor include differential sensing in the shear directions as well as a design where all electrical connections are on one side, leaving the backside pristine as the sensing face. The sensor readout is performed by a custom-designed printed circuit board with 24-bit resolution. Experimental results of sensor performance show normal force resolution of 0.055 N, x-shear resolution of 0.25 N, and y-shear resolution of 1.45 N, all of which fall in a range of clinically relevant forces.

We present two key results in this work related to magnetic shielding. First, milliscale single layer magnetic shields were fabricated on 3D printed polymer molds and achieved shielding factors in excess of 4500. Second, microscale multilayer shields of alternating 10 μm layers of Permalloy and copper were microfabricated onto silicon using batch fabrication processes and characterized. While conventional electromagnetic interference (EMI) shielding simply requires a conductor for shielding by image charges, dC magnetic shielding requires high permeability material to provide a low reluctance path, redirecting magnetic fields around its volume. Leveraging our expertise in electroplating thick, high permeability (maximum μ r > 8000) Permalloy over sharp topologies, we have demonstrated two processes of producing conformal electroplated shielding. The size, shape flexibility, and shielding factor of these structures enable compact integration of magnetic devices for magnetic microelectronics and atomic, molecular, and optical (AMO) microsystems.

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.

Leveraging recent advances in microelectromechanical system (MEMS) fabrication technologies, 100 μm gap 400 μm period electromagnetic undulators and 200 μm gap quadrupole optics have been successfully fabricated. Measurement of the electromagnet impedance closely matches simulations, corresponding to 0.135 T peak field on-axis in the undulator and 1400 T/m field gradients in the quadrupole for the initially tested devices. These microfabricated undulators and quadrupoles are envisioned as insertion devices and focusing lattices for future compact light sources.

Lab-on-a-chip (LOC) devices have enabled significant advancements in medical, biological, and chemical analysis. However, widespread adoption of these devices in, clinical settings and academic environments has been impeded by a lack of a reliable, adaptable, and easy-to-use packaging technology. In this work, we introduce a rapid, prototyped modular microfluidic interconnect that addresses these challenges of the, world-to-chip interface. The interconnect, a flexible polymer gasket co-printed with, rigid clamps, eliminates adhesives and additional assembly by direct multi-material 3D, printing from a computer-aided design model. The device represents the first, application of multi-material 3D printing to microfluidic interconnects, and it can be, rapidly re-designed and printed, and has demonstrated the ability to withstand, pressures exceeding 400 kPa.