All electric and magnetic stimulation of the brain deposits thermal energy in the brain. This occurs through either Joule heating of the conductors carrying current through electrodes and magnetic coils, or through dissipation of energy in the conductive brain.Objective.Although electrical interaction with brain tissue is inseparable from thermal effects when electrodes are used, magnetic induction enables us to separate Joule heating from induction effects by contrasting AC and DC driving of magnetic coils using the same energy deposition within the conductors. Since mammalian cortical neurons have no known sensitivity to static magnetic fields, and if there is no evidence of effect on spike timing to oscillating magnetic fields, we can presume that the induced electrical currents within the brain are below the molecular shot noise where any interaction with tissue is purely thermal.Approach.In this study, we examined a range of frequencies produced from micromagnetic coils operating below the molecular shot noise threshold for electrical interaction with single neurons.Main results.We found that small temperature increases and decreases of 1∘C caused consistent transient suppression and excitation of neurons during temperature change. Numerical modeling of the biophysics demonstrated that the Na-K pump, and to a lesser extent the Nernst potential, could account for these transient effects. Such effects are dependent upon compartmental ion fluxes and the rate of temperature change.Significance.A new bifurcation is described in the model dynamics that accounts for the transient suppression and excitation; in addition, we note the remarkable similarity of this bifurcation's rate dependency with other thermal rate-dependent tipping points in planetary warming dynamics. These experimental and theoretical findings demonstrate that stimulation of the brain must take into account small thermal effects that are ubiquitously present in electrical and magnetic stimulation. More sophisticated models of electrical current interaction with neurons combined with thermal effects will lead to more accurate modulation of neuronal activity.

We report performance results on a MEMS outof-plane gyroscope suitable for platform stabilization. Angle random walk (ARW) less than 0.006 deg/rt-hr and median bias stabilities over temperature of 0.2 deg/hr have been achieved. Sensor bandwidth as characterized by drive and sense mode frequency separation is >700 Hz allowing system level bandwidth greater than 300 Hz. The HG6900 IMU will integrate these sensors and serve platform stabilization applications in a 259 cm3 volume.

Sprays are a class of multiphase flows which exhibit a wide range of drop size and velocity scales spanning several orders of magnitude. The objective of the current work is to experimentally investigate the prospect of dynamical similarity in these flows. We are also motivated to identify a choice of length and time scales which could lead towards a universal description of the drop size and velocity spectra. Towards this end, we have fabricated a cohort of geometrically similar pressure swirl atomizers using micro-electromechanical systems (MEMS) as well as additive manufacturing technology. We have characterized the dynamical characteristics of the sprays as well as the drop size and velocity spectra (in terms of probability density functions, p.d.f.s) over a wide range of Reynolds ($Re$) and Weber numbers ($We$) using high-speed imaging and phase Doppler interferometry, respectively. We show that the dimensionless Sauter mean diameter ($D_{32}$) scaled to the boundary layer thickness in the liquid sheet at the nozzle exit ($\unicode[STIX]{x1D6FF}_{o}$) exhibits self-similarity in the core region of the spray, but not in the outer zone. In addition, we show that global drop size spectra in the sprays show two distinct characteristics. The spectra from varying $Re$ and $We$ collapse onto a universal p.d.f. for drops of size $x$ where $x/\unicode[STIX]{x1D6FF}_{o}>1$. For $x/\unicode[STIX]{x1D6FF}_{o}<1$, a residual effect of $Re$ and $We$ persists in the size spectra. We explain this characteristic by the fact that the physical mechanisms that cause large drops is different from that which is responsible for the small drops. Similarly, with the liquid sheet velocity at the nozzle exit ($u_{s}$) as the choice of velocity scale, we show that drops moving with a velocity $u$ such that $u/u_{s}<1$ collapse onto a universal p.d.f., while drops with $u/u_{s}>1$ exhibit a residual effect of $Re$ and $We$. From these observations, we suggest that physically accurate models for drop size and velocity spectra should rely on piecewise descriptions of the p.d.f. rather than invoking a single mathematical form for the entire distribution. Finally, we show from a dynamical modal analysis that the conical liquid sheet flapping characteristics exhibit a sharp transition in Strouhal number ($St$) at a critical $Re$.

A whispering gallery mode resonator based magnetometer using chip-scale glass microspherical shells is described. A neodynium micro-magnet is elastically coupled and integrated on top of the microspherical shell structure that enables transduction of the magnetic force experienced by the magnet in external magnetic fields into an optical resonance frequency shift. High quality factor optical microspherical shell resonators with ultra-smooth surfaces have been successfully fabricated and integrated with magnets to achieve Q-factors of greater than 1.1 × 107 and have shown a resonance shift of 1.43 GHz/mT (or 4.0 pm/mT) at 760 nm wavelength. The main mode of action is mechanical deformation of the microbubble with a minor contribution from the photoelastic effect. An experimental limit of detection of 60 nT Hz−1/2 at 100 Hz is demonstrated. A theoretical thermorefractive limited detection limit of 52 pT Hz−1/2 at 100 Hz is calculated from the experimentally derived sensitivity. The paper describes the mode of action, sensitivity and limit of detection is evaluated for the chip-scale whispering gallery mode magnetometer.

We present a novel magnetometer consisting of chip-scale whispering gallery mode resonators with high-g factors (>106) realized using MEMs fabrication techniques. A permanent magnet is elastically coupled to a whispering gallery mode borosilicate microbubble. Magnetic forces from applied external magnetic fields induce deformation in the microbubble which can be sensitively monitored through changes in the optical resonance characteristics. We calculate the force and simulate the resultant deformation in the microbubble. The effect of different permanent magnet orientations and microbubble shell thickness is experimentally investigated and modeled. We experimentally demonstrate a large sensitivity of 1.9 GHz/mT on a microbubble with 1.1 μm shell thickness.

A comprehensive investigation of magnetostriction optimization in Metglas 2605SA1 ribbons is performed to enhance magnetoelectric performance. We explore a range of annealing conditions to relieve remnant stress and align the magnetic domains in the Metglas, while minimizing unwanted crystallization. The magnetostriction coefficient, magnetoelectric coefficient, and magnetic domain alignment are correlated to optimize magnetoelectric performance. We report on direct magnetostriction observed by in-plane Doppler vibrometer and domain imagining using scanning electron microscopy with polarization analysis for a range of annealing conditions. We find that annealing in an oxygen-free environment at 400 ◦ C for 30 min yields an optimal magnetoelectric coefficient, magnetostriction and magnetostriction coefficient. The optimized ribbons had a magnetostriction of 50.6 ± 0.2 μ m m − 1 and magnetoelectric coefficient of 79.3 ± 1.5 µm m−1 mT−1. The optimized Metglas 2605SA1 ribbons and PZT-5A (d31 mode) sensor achieves a magnetic noise floor of approximately 600 pT H z − 1 / 2 at 100 Hz and a magnetoelectric coefficient of 6.1 ± 0.03 MV m−1 T−1.

In this Article, we experimentally measure the adsorption kinetics of human serum albumin (HSA) on a hydrophobic hexadecanethiolated gold surface. We use micromachined quartz crystal resonators with fundamental frequency of 83 MHz to accomplish these measurements in real time. In this work, we focus on two key results: (i) asymptotic behavior of the sensor responses upon HSA adsorption and (ii) the jamming limit of adsorbed layer formed by both single-injection and multi-injection experiments with the same value of final concentration. We develop a new interface-depletion modified random sequential adsorption (RSA) model to elucidate the adsorption kinetics and the transport properties of the protein molecules. Analysis of the experimentally measured data shows that the results can be explained on the basis of the exponentially depleting interfacial layer RSA model. To better understand the origin of the formation of the interfacial depletion region where the supply of protein molecules is dramatically reduced, we performed a series of molecular dynamics (MD) simulations using the ReaxFF method. These simulations predict that the resulting adsorption of the protein molecules on the thiolated surface results in a specific orientation at the interface and the diffusion constant of the protein molecules in this layer is significantly reduced. This interplay between the surface adsorption rate and the reduced diffusion coefficient leads to the depletion of the protein molecules in the interfacial layer where the concentration of the protein molecules is much less than the bulk concentration and explains the observed slowdown of the HSA adsorption characteristics on a hydrophobic surface.

Via optimization of the mechanical coupling, alignment of Metglas® magnetic domains, relief of residual stress, and operation of the PZT-5A under a DC electric field of 2 kV/cm an unprecedented magnetoelectric voltage coefficient of 9.52 V/cm-Oe is achieved; resulting to a magnetic field sensitivity of 150 pT at 20 Hz for a d3i Metglas®/PZT-5A laminate. Mechanical coupling is improved by reducing the thickness and porosity of the epoxy. The Metglas® residual stress reduction and easy axis alignment is accomplished by a 30 minute 400 °C anneal under a 1600 Oe magnetic field in vacuum. Finally, a DC electric field bias is applied to increase the <¡3i coefficient of the PZT-5A piezoelectric.

Arrays of on-chip spherical glass shells of hundreds of micrometers in diameter with ultra-smooth surfaces and sub-micrometer wall thicknesses have been fabricated and have been shown to sustain optical resonance modes with high Q-factors of greater than 50 million. The resonators exhibit temperature sensitivity of −1.8 GHz K−1 and can be configured as ultra-high sensitivity thermal sensors for a broad range of applications. By virtue of the geometry’s strong light-matter interaction, the inner surface provides an excellent on-chip sensing platform that truly opens up the possibility for reproducible, chip scale, ultra-high sensitivity microfluidic sensor arrays. As a proof of concept we demonstrate the sensitivity of the resonance frequency as water is filled inside the microspherical shell and is allowed to evaporate. By COMSOL modeling, the dependence of this interaction on glass shell thickness is elucidated and the experimentally measured sensitivities for two different shell thicknesses are explained.

This paper reports the first experimental observations of whispering gallery mode (WGM) resonance in on-chip glass microbubble structures. Using microfabrication methods, chip-scale glass microbubbles with ultra-smooth surface and sub-micrometer wall thickness are shown to support optical resonance modes with ultra-high Q-factors of >10 7 . The resonance is highly sensitive to temperature, with measured sensitivity of -1.8 GHz/°C. Based upon the signal to noise performance, this corresponds to a temperature resolution of 55 μK.

Highly sensitive, wirelessly powered, and maintenance-free sensors are of great interest to the biomedical, geological, hazardous environment, and traffic control communities. This work demonstrates the passively-powered wireless operation of a magnetoflexoelastic magnetometer. The wireless coupling is achieved using a coupled near-field resonant loop antennas, which excite the high Q-factor (~6000) micromachined quartz resonator. Magnetostrictive curves are acquired both wired and wirelessly at distances up to 45 mm to confirm the phenomenon is magnetoflexoelastic in nature. A 49.1 Hz/Oe sensitivity was achieved in wireless operation and the ultimate detectable limit was 7 μT at 0.5 Hz.

We present a new packaging method for improving the lifetime of ferrofluid-based magnetoviscous magnetometer. The concept of a ferrofluid based magnetometer has been previously reported where the viscoelastic response of a thin interfacial ferrofluid layer loaded atop a high frequency shear wave quartz resonator to applied magnetic field is monitored. The magnetic field can be sensitively quantified by the changes in the at-resonance admittance characteristics of the resonator. However, under open conditions, continuous evaporation of the ferrofluid compromises the long term performance of the magnetometer. In this work, we integrate glass hemispherical microbubbles, used as vessels of ferrofluid, on the resonator chip to seal and prevent the evaporation of the ferrofluid liquid and drying out. A layer of high relative permeability thin film Metglas (Fe 85 B 5 Si 10 ) is deposited on the resonator chip to improve the sensitivity. Using these improvements, a minimum detectable field of 650 nT/yHz at 1 Hz is achieved. Moreover, comparing with the unsealed ferrofluid device, the lifetime of the glass microbubble integrated chip packaged device improved significantly from only few hours to over a month and continuing.

Materials exhibiting electronic phase transitions have attracted widespread attention. By switching between metallic and insulating states under external stimuli, the accompanying changes in the electrical and optical properties can be harnessed in novel electronic and optical applications. In this work, a laterally confined conductive pattern is inscribed into an otherwise insulating VO2 thin film using ultraviolet light, inducing an almost four orders of magnitude decrease in electrical resistivity of the exposed area. The metallic imprint remains in VO2 after ultraviolet light exposure and can be completely erased by a short low temperature anneal. The ability to optically pattern confined metallic structures provides new opportunities for reconfigurable photonic and plasmonic structures, as well as re‐writable electric circuitry.

The intrinsic field effect, the change in surface conductance with an applied transverse electric field, of prototypal strongly correlated VO(2) has remained elusive. Here we report its measurement enabled by epitaxial VO(2) and atomic layer deposited high-κ dielectrics. Oxygen migration, joule heating, and the linked field-induced phase transition are precluded. The field effect can be understood in terms of field-induced carriers with densities up to ∼5×10(13)  cm(-2) which are trongly localized, as shown by their low, thermally activated mobility (∼1×10(-3)  cm(2)/V s at 300 K). These carriers show behavior consistent with that of Holstein polarons and strongly impact the (opto)electronics of VO(2).

We report the growth of (001)-oriented VO2 films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO2 surface. Another key limitation is interdiffusion with the (001) TiO2 substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO2 films with abrupt MIT behavior.