Yoav Linzon

Strong enhancement of the Faraday rotation in Ce and Bi comodified epitaxial iron garnet thin films

Ce and Bi comodified iron garnet (Ce2.2Bi0.8Fe5O12) thin films for magneto-optic applications were epitaxially grown on a (111)-oriented Gd3Ga5O12 substrate by pulsed laser deposition. We found that epitaxial film quality could be achieved under a low-pressure Ar atmosphere. Surprisingly, our 1 μm thick epitaxial films showed a record Faraday rotation as high as 0.55 deg/μm, a value strongly dependent on the concentration of Bi3+ ions.Ce and Bi comodified iron garnet (Ce2.2Bi0.8Fe5O12) thin films for magneto-optic applications were epitaxially grown on a (111)-oriented Gd3Ga5O12 substrate by pulsed laser deposition. We found that epitaxial film quality could be achieved under a low-pressure Ar atmosphere. Surprisingly, our 1 μm thick epitaxial films showed a record Faraday rotation as high as 0.55 deg/μm, a value strongly dependent on the concentration of Bi3+ ions.

Efficient parametric excitation of silicon-on-insulator microcantilever beams by fringing electrostatic fields

Large amplitude flexural vibrations have been excited in single layer silicon-on-insulator micromechanical cantilever beams in ambient air environment. Our driving approach relies on a single co-planar electrode located symmetrically around the actuated grounded cantilever. Electrostatic forces are created via tailored asymmetries in the fringing fields of deformed mechanical states during their electric actuation, with strong restoring forces acting in a direction opposite to the deflection. This results in an effective increase in the structure stiffness in its elastic regime. The devices had been fabricated using deep reactive ion etching based process and their responses were characterized in a laser Doppler vibrometer under ambient conditions. Harmonic voltages applied to the electrode result in the periodic modulation of the effective stiffness and lead to strong parametric excitation of the structure. As opposed to close gap actuators, where high-amplitude drives are severely limited by pull-in ins...

Stress-based resonant volatile gas microsensor operated near the critically buckled state

We describe sensing of chemical vapors from the atmosphere using critically buckled polycrystalline silicon doubly clamped mechanical resonators coated on one side with polymethyl methacrylate (PMMA). Our method of sensing is based on stress-induced resonance frequency shifts through volumetric swelling of the 60 nm thick PMMA layer resulting in altered tension in the beams. The stress change produces shifts in the resonance frequency as large as 150% of the baseline frequency. In order to maximize the sensitivity, we tailor residual stress of the polycrystalline silicon resonators to slightly exceed the critical buckling stress. We incorporate a relatively large gap between the bridge and a substrate to provide optical readout and minimize squeezed film effects. We show that the larger gap results in substantial improvements of the quality factor and frequency stability of our resonators under ambient pressure and temperature conditions compared to previous implementations. These lead to resonance freque...

Thermochemical hydrolysis of macroalgae Ulva for biorefinery: Taguchi robust design method.

Understanding the impact of all process parameters on the efficiency of biomass hydrolysis and on the final yield of products is critical to biorefinery design. Using Taguchi orthogonal arrays experimental design and Partial Least Square Regression, we investigated the impact of change and the comparative significance of thermochemical process temperature, treatment time, %Acid and %Solid load on carbohydrates release from green macroalgae from Ulva genus, a promising biorefinery feedstock. The average density of hydrolysate was determined using a new microelectromechanical optical resonator mass sensor. In addition, using Flux Balance Analysis techniques, we compared the potential fermentation yields of these hydrolysate products using metabolic models of Escherichia coli, Saccharomyces cerevisiae wild type, Saccharomyces cerevisiae RN1016 with xylose isomerase and Clostridium acetobutylicum. We found that %Acid plays the most significant role and treatment time the least significant role in affecting the monosaccharaides released from Ulva biomass. We also found that within the tested range of parameters, hydrolysis with 121 °C, 30 min 2% Acid, 15% Solids could lead to the highest yields of conversion: 54.134–57.500 gr ethanol kg−1 Ulva dry weight by S. cerevisiae RN1016 with xylose isomerase. Our results support optimized marine algae utilization process design and will enable smart energy harvesting by thermochemical hydrolysis.

Liquid Mass Sensing Using Resonating Microplates under Harsh Drop and Spray Conditions

We have performed in situ real time mass sensing of deposited liquid volatile droplets and sprays using plate-like microstructures, with robust and reusable performance attained over harsh conditions and multiple cycles of operation. A home-built electrooptical sensing system in ambient conditions has been used. The bimorph effect on the resonant frequency of altered mass loading, elasticity, and strain had been carefully compared, and the latter were found to be negligible in the presence of nonviscous liquids deposited on top of our microplate devices. In resonant mode, the loaded mass has been estimated from measured resonant frequency shifts and interpreted from a simple, uniformly deposited film model. A minimum submicrogram detectable mass was estimated, suggesting the system’s potential for robust, fast, and reusable sensing capabilities, in the presence of volatile liquids under harsh operation conditions.

Trapping dynamics in nonlinear wave scattering by local guiding defects

We study numerically the trapping dynamics of nonlinear waves scattered by local guiding photonic centers with normal eigenmodes which are embedded in uniform nonlinear Kerr waveguides. The linear and nonlinear scattering from a local defect may be treated from either a wave optics approach or a ray optics approach. The former provides a better understanding of the wave dynamics while the latter enables one to perform quasi-analytical estimates of the extent of trapping in a given structure. In the presence of a single-site multi-mode local scattering center, power may localize in a certain normal mode of the center, or periodically oscillate between different normal modes. The degree of trapping and mode of localization can be controlled as function of both the input power and the angle of incidence. With multi-site local scattering centers, the trapping dynamics are strongly dependent on the degree of coupling between the neighboring sites. In the scattering by a local multi-site defect with strongly coupled adjacent sites, two possibilities for nonlinear trapping arise. At intermediate nonlinear powers, periodic tunneling of power between adjacent sites and their normal modes is observed. At highly nonlinear powers, but still within experimental feasibility, the radiation can become strongly localized in a single site. The scattering and trapping dynamics are also described in the context of nonlinear Fabry-Perot etalons, as a function of the local defects refractive index.

Raman-induced localization in Kerr waveguide arrays.

We show that during the spatiotemporal compression in a periodic Kerr waveguide array, stimulated Raman scattering can effectively balance the effects of self-phase modulation, diffraction, and group-velocity dispersion, eliminating collapse and breakup over a wide range of input powers and leading to stable propagation in a single site.

Power-dependent switching of nonlinear trapping by local photonic potentials

We study experimentally and numerically the nonlinear scattering of wave packets by local multisite guiding centers embedded in a continuous dielectric medium as a function of the input power and angle of incidence. The extent of trapping into the linear modes of different sites is manipulated as a function of both the input power and the angle of incidence, demonstrating power-controlled switching of nonlinear trapping by local photonic potentials.

Nonlinear scattering and trapping by local photonic potentials

We experimentally study nonlinear scattering by local photonic potentials embedded in continuous Kerr media, and demonstrate nonlinear trapping in guiding potentials and resonant transmission in anti-guiding potentials. The results are verified by numerical simulations.

Synchronous imaging for rapid visualization of complex vibration profiles in electromechanical microresonators

Synchronous imaging is used for the dynamic space-domain studies of vibration profiles in capacitively driven, thin n + doped polysilicon microbridges oscillating at rf frequencies. Fast and high-resolution actuation profile measurements of micromachined resonators are useful when significant device nonlinearities are present. For example, bridges under compressive stress near the critical Euler value often reveal complex dynamics stemming from a state close to the onset of buckling. This leads to enhanced sensitivity of the vibration modes to external conditions, such as pressure, temperatures, and chemical composition, the global behavior of which can be conveniently evaluated using synchronous imaging combined with spectral measurements. We performed an experimental study of high drive amplitude and ambient pressure effect on the resonant vibration profiles in electrically driven microbridges near critical buckling. Numerical analysis of electrostatically driven post-buckled microbridges supports the r...