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Nonlinear propagation of short terahertz pulses in the layered structures dielectric -graphene -dielectric … is investigated theoretically on the base of direct simulations of the Maxwell equations and the hydrodynamic equations for electrons in graphene layers. The using of the nonlinear hydrodynamics is justified from a comparison of quasi -classical kinetics, quantum kinetics, and the hydrodynamics. The effective electron mass has been determined for the hydrodynamics. The numerical FDTD scheme is proposed to consider the boundary conditions at graphene sheets. The resonant generation of odd harmonics of THz radiation has been investigated.

The excitation of short electric monopulses of space charge waves with wide frequency spectrum of terahertz range in nitride films has been theoretically investigated. The excitation of these pulses with duration ≤ 5 ps and high peak values of electric fields is possible in n-GaN or n-InN films of submicron thickness in the presence of negative differential conductivity. The simulation of nonlinear dynamics of pulses was performed with due regard for the nonlocal dependence of the drift electron velocity on the average electron energy. Optimal values of the applied constant electric fields and equilibrium electron concentration for excitation of monopulses are specified. The monopulse dynamics is weakly dependent on the film width and also on the value and waveform of input excitation pulses. Short electric monopulses differ from domains of strong electric field in Gunn diodes built on bulk crystals with negative differential conductivity.

This article presents the design and implementation of a micropositioning system actuated by three piezoelectric stacks to control its displacements on XYZ axes. The use of conventional piezoelectric buzzers allows us to reduce fabrication costs. The working or mobile platform is the base for objects that will be manipulated, for example, in automated assembling. The micropositioner can be integrated into a microgripper to generate a complete manipulation system. For micropositioner fabrication, at first, Polylactic Acid (PLA) was chosen as the structural material, but after simulation and some experimental tests performed with a micropositioner made of Acrylonitrile Butadiene Styrene (ABS), it showed larger displacement (approx. 20%) due to its lower stiffness. A third test was performed with a positioner made with Polyethylene Terephthalate Glycol (PETG), obtaining an intermediate performance. The originality of this work resides in the geometrical arrangement based on thermoplastic polymer compliance mechanisms, as well as in the use of additive manufacturing to fabricate it. An experimental setup was developed to carry out experimental tests. ANSYS™ was used for simulation.

The design of a novel electrothermal microgripper device is shown, which is based on an improved chevron type actuator developed considering their elements parameterization, whose resistive model is also provided. The performance of the microgripper&rsquo, s parameters, such as displacement, force, and temperature distribution, with convection for the voltage range from 0 up to 5 V, is evaluated through numerical and analytical simulation. Microgripper design was also improved with aid of parameterization. The effect on the microgripper performance due to its thickness is also analyzed, finding a considerable increment in force, when thickness increases. Its main advantage is given by the simplicity of the compliance arrangement of the microgrippers jaws. Considering convection, when 5 V are applied, 37.72 &deg, C was generated at the jaw&rsquo, s tips of the Improved Microgripper 2 (IMG2), implemented with silicon, this relatively low temperature increases its capabilities of application. When the IMG2 is implemented with polysilicon, its response is competitive comparing with a more complex microgripper, increase of displacement (50%) is shown, but a decrement of force (30%). The diameters allowed for the subjection objects are found between 84.64 &micro, m and 108 &micro, m, with weights lower than 612.2 &micro, g. Some tests of subjection were performed using microcylinders of Au, glass ceramic, polycarbonate and carbon fiber, showing a permissible stress on them, considering its Young&rsquo, s modulus, as well as the total reaction force induced. All simulations were done on Ansys software. The results demonstrate the feasibility of the future microgripper fabrication.

In this paper a novel microgripper device is shown. It is based on a chevron type actuator, and a simple configuration of compliance beams. It is also considered a source of thermal energy, which in this case is 2 V, which generates a temperature of 92.7°C at the jaw’s tips. It is main advantage is given by the simplicity and the reduced number of beams, which composed the compliance arrangement of the microgrippers jaws. It is response competitive with other ones, more complex, found it in literature, both in displacement and force. The structural material is Silicon. The effect on the microgripper performance due to its thickness is also analyzed. Some applications of the microgripper are detected, for example, subjection of microwires and manipulation of micro objects with diameters smaller than 85$\mu$m, until 68 $\mu$m, and weights lower than 38.63 $\mu$g. All microgrippers simulations were done on Ansys software.

In this paper, simulated and experimental analysis of an accelerometer with beams based on arrangements of segments of different width is performed. A comparison with an accelerometer of uniform beams is carried out. Micro accelerometers were scaled to obtain millimeter lengths to obtain low cost prototypes and the possibility to test them, also using an experimental set-up of low cost. The simulation tool employed is Ansys. For experimental validation, additive manufacture using PLA, a type of thermoplastic polymer, is considered. The parameter under analysis is the displacement the proof mass of accelerometers. The larger displacement was obtained for the case of symmetrical beams, with a thinner width equals to 1/3 of width the uniform beam, but a decrease in the natural frequency of the system was also obtained.

In this paper, a novel microgripper based on two perpendicular arrangements of beams and a chevron actuator is shown. In each perpendicular arrangement, the constrained displacement of the double clamped beams, joined at their endpoint, produces a buckling in each beam, which favors the displacement of each arm of the microgripper, normally open. These arrangements constitute the highly flexible structures of the microgripper. Their buckling is produced by the force applied by chevron arrow, producing a reaction force in the range of 174.44 $\mu$ N in the microgripper jaws. Chevron actuator is fed by a thermal source. Temperature in microgripper tips is of 34.42°C and the operation frequency is 33.966 kHz, at maximum load thermal applied of 200°C. The mechanical, thermal and modal analyses of this integrated structure was supported by SIMSOLIDTM, based on Finite Element Analysis. The simulation was developed with Polysilicon as structural material.

Using Poly-Silicon, the implementation of novel Displacement-amplifying Compliant Mechanisms (DaCM), in two geometries of accelerometers, allows for remarkable improvements in their operation frequency and displacement sensitivity, with different proportions. Similar DaCM´s geometries were previously implemented by us with Silicon. In all mentioned cases, the geometries of DaCM´s are adjusted in order to use them with Conventional Capacitive Accelerometer (CCA) and Capacitive Accelerometer with Extended Beams (CAEB), which operate in-plane mode, (y-axis). It should be noted that CAEB shows improvements (95.33%) in displacement sensitivity compared to ACC. Simulations results, carried out using Ansys Workbench software, validate the system’s performance designed with Poly-Silicon. Finally, a comparison with the similar systems, previously designed with Silicon, is also carried out.

In this paper, a modified U-shaped micro-actuator with a compliant mechanism is proposed. It was analyzed with a uniform and modified thin arm, as well as a similar variation in the corresponding flexure, in order to observe the impact of the compliant lumped mechanism. The use of these compliant mechanisms implies an increment in the deformation and a reduction in the equivalent stress of 25% and 52.25%, respectively. This characterization was developed using the Finite Element Method (FEM) in ANSYS Workbench. The design, analysis and simulation were developed with Polysilicon. In this study, the following performance parameters were also analyzed: force and temperature distribution. This device is supplied with voltage from 0 V up to 3 V, at room temperature. The modified U-shaped actuator was applied in both arms of a microgripper, and to evaluate its electrothermal performance, a static structural analysis has been carried out in Ansys Workbench. The microgripper has an increment in deformation of 22.33%, an equivalent stress reduction of 50%, and a decrease in operation frequency of 10.8%. The force between its jaws is of 367 &micro, N. This low level of force could be useful when sensitive particles are manipulated.

In this paper, the dynamic and electric analysis of a novel electrostatically actuated microdevice is presented. This device consist of an arrangement of four parallel microcantilevers, which is fed with 1 V. The analysis was carried out by Finite Element Method (FEM) in Ansys Workbench in order to obtain: current intensity, temperature distribution, Joule effect, structural deformation, natural frequency, and reaction force, which characterize the microgripper performance. The material used in the analysis was Silicon. A thermoelastic model, that describes the behavior mechanical of the device, is developed. The device had an initial gap of 28 µm and a final gap of ~ 4 µm, the force of subjection in grippers is 0.4 µN.

Excitation of nonlinear acoustic monopulses, or baseband waves, is theoretically analyzed. The monopulses have a wide spectrum up till the gigahertz range ≤ 1 GHz. The propagation of waves is along the interface between a solid lm and a solid substrate. A quadratic elastic nonlinearity in both contacting media of the system is taken into account. The nonlinear dynamics of waves depends essentially on the thickness of the lm. The transverse inhomogeneity of the wave pro le in the interface plane and the wave di raction are taken into account, too. The baseband waves are not true solitons and manifest as single shock-like pulses in the case of an excitation from initial long rectangular pulses. The transverse inhomogeneity a ects the dynamics of the shocks, and there is a possibility to focus the nonlinear monopulses.

Accelerometers are widely used in several mechanisms of high sensitivity. They are employed for example in tilt-control in spacecraft, inertial navigation, oil exploration, seismic monitoring, etc. In order to improve the sensitivity of the measurements, implementation of Displacement-amplifying Compliant Mechanisms (DaCMs) in a capacitive accelerometer have been reported in the literature. In this paper, a system composed of two elements; capacitive accelerometer with extended beams (CAEB) and a DaCM geometry, of single and souble layer, are analysed. Three materials were considered, in the case, for the second layer. The DaCM implementation improves the operation frequency and displacement sensitivity, under different proportions, at the same time. Furthermore, three sweeps were performed: a range of thickness from 25 µm up to 30 µm (to determine the appropriate silicon mass value, using SOI technology), a range of second layer thickness (to choose the more appropriate material and its thickness) and a range of gravity values (to determine the maximum normal stress in the beams, which defines the superior value of the g operation range). The in-plane mode (y-axis) was considered in all analysed cases. This characterization was developed using the Finite Element Method. Structural and modal analysis responses were under study.

This paper reports on the first investigation to design, build and characterize a dual vertical and horizontal microactuator based on the topology of a thermal chevron actuator. The chevron-based vertical actuator displays superior performance in comparison to existing electrostatic and electrothermal vertical actuators. The device has the capacity to produce linear vertical motion without deformation of the upper beam surface and is well suited for a variety of optical and microassembling applications. A methodology that may extend the capabilities of standard surface micromachining MEMS technology to design three-dimensional structures is also presented.

Due to the diversity and multiple energy domains involved, Micro-Electromechanical Systems MEMS devices are vulnerable to several mechanical failures such as fatigue. They been widely used in military applications, radio frequency systems, pressure sensors, automotive industry, among several others. Most MEMS devices contain moving parts that are subjected to cyclic loading, which degrade the device´s efficiency. Due to the high importance of MEMS in various applications, it is necessary to know their lifetime to prevent any damage or process discontinuity to which the system is subject. There have been several investigations in particular on the fatigue analysis in presence of cracks, however in terms of lifetime under cycling load, information is not abundant. The fatigue analysis can be performed for characterizing the ability of materials to support many cycles. Some parts of systems are exposed to strong stress level experiences during its usable lifetime, so the analysis must be focused on them. In this paper, a simulated fatigue analysis of classic, Z-shape and optimized chevron with Z shape arms is shown. Simulations are made using Ansys 15.0, to obtain the arms lifetime of the system because they are subjected to greater stresses in the presence of cyclic loading.

Volume and based on surface oriented integrated p-i-n-structures modulators have demonstrated high efficiency in millimeter wave range as quasi-optical modulators and phase shifters. These structures possess high modulation and high-speed properties; sustain great EM powers. However, the modulation characteristics of p-i-n modulators of both mentioned types in millimeter wave range have not been investigated yet. Here, a comparison and criteria of volume and integrated based on Si surface oriented structure modulators in millimeter wave range are presented.

This work reports the analysis of vacuum-solid microwave diodes and triodes. It shows the possibility to use these devices as amplifiers and generators in the millimetre and submillimetre ranges. It is also possible to create multipliers with a large multiplication factor and small multiplication losses. Additionally, the analysis of the basic parameters of these vacuum-solids microwave diodes with different types of cathodes, shows that the efficiency and the frequency band of diodes with P++–N cathode are smaller than for the case of tungsten diodes.

The design of nanometric electronic devices requires novel materials for improving their electrical performance from stages of design until their fabrication. Until now, several DC electrical conductivity models for composite materials have been proposed. However, these models must be valued to identify main design parameters that more efficiently control the electrical properties of the materials to be developed. In this paper, four different models used for modeling DC electrical conductivity of carbon nanotube-polymer composites are studied with the aim of obtaining a complete list of design parameters that allow guarantying to the designer an increase in electrical properties of the composite by means of carbon nanotubes.

The NiTiNOL diaphragm, under two geometries, were simulated on a Silicon wafer and controlled by an external heat source. As the substrate bottom wall heats and conducts heat, the thermal expansion raises the thin layer which can be used as an actuator. The case of heat source applied on the top walls was also considered. The simulations were realized by means of the mechanical and thermal properties of materials. A comparison among the performance of the diaphragm based on the geometries with a plane layer, a layer with a primary boss, and finally with primary and secondary bosses is presented. Each process was simulated in COMSOL Multiphysics. The distribution of deformation using bosses is similar to the analyzed cases using pressure instead of heat. The maximum obtained displacement for NiTiNOL is of approximately 2.5 micrometers at 343°K, at the same conditions, Silicon case reaches 0.9 μm. The diaphragm behavior is also compared with the cases of Silicon and Cu-Al-Ni. Our interest in the development of MEM actuators only controlled by external heat sources is due to several reasons. At first, because these clean energy sources sometimes reaches high density values, but they have not been well-spent. The most of MEMS thermal actuators need a current flow to heat the MEM device, by means of the Joule effect, and produce the corresponding thermal expansion. In this paper, the displacement depends on the external source, in accordance with the mechanical and electrical properties of the used materials.

In this research, experimental tests were realized in order to demonstrate the feasibility to use of epoxy resin as patch antenna radome. The interest in this material is due to its low cost and availability, two desirable characteristics for the prototypes fabrication. In the fists group of tests, the effect of three pieces of epoxy resin of different colors as interference object between a receiver and transmitter antenna is analyzed, that means, its effect on the electromagnetic wave propagation. In the second one, the measurements of parameter S21 were realized considering patch antennas with and without cover made of epoxy resin in order to analyze the effect of the cover on the patch antenna performance. The obtained results allow us to confirm the feasibility to use this material as patch antenna radome.

Applications of Multimode Interference (MMI) effects in optical devices have been increased today due their excellent properties and easy fabrication. Incorporation of these effects in optical fiber has been achieved through a single-mode - multimode - single-mode (SMS) fiber structure showing high sensitivity to bending-loss phenomenon. The latter has been efficiently implemented in pressure sensing application such as is presented in this work. Basically, the SMS structure is embedded in a pressure-sensitive membrane to convert pressure in a mechanical displacement resulting in an attenuation of the transmitted intensity proportionally to the applied pressure. Under this configuration, an all-fiber pressure sensor with high sensitivity and repeatability is obtained into a pressure range from -13 psi to +13 psi. The max pressure range can be varied to 140 psi with our configuration when the membrane thickness is changed. Important features of the proposed all-fiber MMI pressure sensor are its easy-fabrication and low-cost since an inexpensive instrumentation is required.

We discuss a structured 3D Dielectric Photonic Crystal with both a metallic core and a metallic shell. We discuss the role of each one, the stack, the core as well as the cavity formed between the core and the shell. The low frequency metallic core features becomes much more significant as it gets smaller and get diluted by the cavity.

This paper describes the design and experimental characterization of two optimized thermal actuators devised to operate by means of scavenging heat from the environment. Different from the traditional MEMS thermal actuator that relies on electric current to generate heat by Joule effect, the devices herein presented have been optimized to absorb external heat and convert it into mechanical displacement and force. The behavior of vertical and horizontal microactuators fabricated in a standard surface micro-machining process (PolyMUMPs) demonstrates the viability of exploiting heat from the surrounding medium to realize batteryless microsystems. Analytical and finite element models are provided in support of the design. Results show that fairly large and useful displacements can be achieved at commonly available operating temperatures.

This paper presents a novel thermally-actuated vertical micromirror for optical communications. Fabricated in a standard surface micromachining process, this micromirror can achieve low insertion loss (< 1 dB) and is capable of operating at CMOS-compatible voltage levels. It has a measured maximum power consumption of only 50-mW and a switching speed in the order of 16 ms with 5-V drive.

We discuss a 3D Spherical Dielectric Photonic Crystal with a Metallic Core. Previous works have shown a distinctive transmission characterization for such a system. We show a continuous evolution that is explained by its dispersion relation.

The MEM actuator is controlled by an external heat source, such as the heat gradients present in some electronic systems. As the substrate bottom is heated, the thermal expansion rises the membrane, which can be used as an actuator. The analysis was realized by means of mechanical and thermal properties of materials. We also present the effect of the physical dimensions of the walls and, thickness and the length of the membrane. The process was simulated in COMSOL multiphysics. The membrane central deflection results, using different membrane materials, had been shown the use of Cr membrane as the best choice.

In this work we present the basis of the solar concentrator design, which has is located at Temixco, Morelos, Mexico. For this purpose, this place is ideal due to its geographic and climatic conditions, and in addition, because it accounts with the greatest constant illumination in Mexico. For the construction of the concentrator we use a recycled parabolic plate of a telecommunications satellite dish (NEC). This plate was totally covered with Aluminum. The opening diameter is of 332 cm, the focal length is of 83 cm and the opening angle is of 90°. The geometry of the plate guaranties that the incident beams, will be collected at the focus. The mechanical treatment of the plate produces an average reflectance of 75% in the visible region of the solar spectrum, and of 92% for wavelengths up to 3μm in the infrared region. We obtain up to 2000°C of temperature concentration with this setup. The reflectance can be greatly improved, but did not consider it as typical practical use. The energy obtained can be applied to conditions that require of those high calorific energies. In order to optimize the operation of the concentrator we use a control circuit designed to track the apparent sun position.

The analysis and simulation of the coupling between microstrips is realized, showing the corresponding capacitive or inductive walls. We analyze their interference and the changes produced in the electric and magnetic fields, as well as the distance dependence of the interference. The conductive lines on silicon and their crosstalk, produced when their distance is shorter that their width, is considered. The simulations were carried out with FEMLAB.

Annular Photonic structures, which occur on bulk and fibers, are Bragg structures that share both Bragg resonances and waveguiding. They are related to Photonic crystals because of their large enough refraction difference indexes (n 2 - n 1 ) that makes unavoidable to consider in full the reflected wave, well beyond the approximations required for analytical gap solitons. Effectively, their confining capabilities are or primary importance, however, the potential of those structures are substantial and deserves to be further explored. Waveguiding occurs where the structure is homogenous, and may be handled on well known methods. Nonlinear propagation has been observed on solid core Bragg fibers and the soliton distribution on a nonlinear circular and annular region have been described [1]. Linear Photonic annular structures, such as resonators, have been studied by A. Yariv [2] as well as on omniguide fibers. The propagation along the direction where the material is inhomogenous, and that correspond to the beam profile, is a complex task and it is the objective of this paper.

The study of nonlinear photonics crystals is quite complex and cumbersome, because of their inherent architectural complexity and, in addition, because of the nonlinearity that couples propagating and counterpropagating waves. However, they are quite attractive because of their potential capabilities, and that has lead to use different approximated methods. In a one dimensional stack, it has been successfully demonstrated that they show switching, bistability and chirping as nonlinear characteristics. Band gap solitons are a well established feature of the coupled wave equations. We have extended a method that have previously shown its success for a stack with a Kerr nonlinearity, to a much more complex structure such as an omniguide fiber, as part of our suggestion that such method could be applied to numerical or analytical methods as long as the linear solution were available. Such a restriction, hinder our ability of getting analytical solution beyond their enabling approximations, however, it is completely adequate for the purpose of to develop devices. A comparative numerical analysis of a one dimensional photonic crystal and an omniguide fiber, made of a dielectric and stratified linear and nonlinear media, has been carried out. They were considered as multilayer arrangements with a finite numbers of periods: linear-linear, nonlinear-linear and nonlinear- nonlinear in order to study and isolate those features. Finally, a comparison of multilayer systems with variations in the diffraction indexes profiles is presented.

A new technique, based on Optical Methods, has been tested for the evaluation of the lithium bromide (LiBr) concentration, a corrosive substance frequently used in heat pumps. Those solutions have large oxidizing capabilities. This technique avoids the direct contact between the electrodes and the LiBr aqueous solution within a thermodynamic absorption cycle. The viability of this technique in a potential commercial device, resides on its capability to detect working fluid concentrations within a temperature range from 25 °C up to 70 °C, those limiting temperature values correspond to the operating wavelengths of 1.33 μm and 1.55 μm, respectively. Our system determines the correlation among the signal and temperature data, for various concentrations, between 49 and 58 mass percentages. This function of two variables is represented as a surface with the transmittance, concentration and temperature as parameters and wavelength as reference. We discuss the adequate parameters characterization used in this technique.

A modulator on the base of a surface oriented p-i-n structure in an oversize waveguide is researched theoretically and experimentally. It uses a matrix surface oriented structure with "deep" contacts which is like a window in oversize waveguides of the millimeter frequency range. This modulator is also the electrically controlled lens of the microwave branch.

The propagating properties of dielectric waveguides (DW) working in millimeter wave range are investigated. The interest and attention are focused on the peculiarities of a propagation of electromagnetic waves in dielectric waveguides in the region of weak retardings. The losses in DWs in 3 mm wavelength range have been experimentally measured. The results of the experiment demonstrate the promising use of these lines in communication systems in mm and sub mm range.

We describe the design and experimental characterization of two optimized thermal actuators devised to operate by means of scavenging heat from the environment. Different from the traditional MEMS thermal actuator that relies on electric current to generate heat by Joule effect, the devices presented here are optimized to absorb external heat and convert it into mechanical displacement and force. The behavior of vertical and horizontal microactuators fabricated in a standard surface micromachining process (PolyMUMPs, Research Triangle Park, North Carolina) demonstrates the viability of exploiting heat from the surrounding medium to realize batteryless microsystems. Analytical and finite element models are provided in support of the design. Results show that fairly large and useful displacements can be achieved at commonly available operating temperatures.

We discus the changes introduced in switching, bistability and chirping of a one dimensional photonics crystal made up of conducting nanoparticles composites modelled classically and quantum mechanically.

We present near soliton propagation in an optical fiber with a core doped conducting nanoparticles.

Using p-i-n-structures in terahertz range faces some problems. Namely, a change of the frequency dependent effective dielectric permittivity due to injected carriers in terahertz range is not so great as in millimeter wave one. Moreover, the parameters of p-i-n-structure, like the shape and sizes of injecting junctions, the depth of the structure, and matching layers, should differ from the case of millimeter wave range. Therefore, some optimization of modulation properties at higher frequencies must be done.