Sharif Digital Repository

Lost sensory or motor functions can be restored using electrical neural prostheses (NP), which include surface NPs, implanted or subcutaneous NPs and the more recent Stimulus Router System (SRS). The latter type of NP outperforms the other types in its selective excitation and least invasiveness. In each case, the achieved performance depends on a multitude of design factors among which the electrical excitation waveform shape, frequency, duration of pulses, configuration of electrodes, number of intervals, thermal conditions and electrode material. To investigate the effects of these parameters on the distribution of electric current inside biological tissues, numerical modeling can be... 

In this contribution a new approach to perform spatial integration is presented using a dielectric slab. Our approach is indeed based on the fact that the transmission coefficient of a simple dielectric slab at its mode excitation angle matches the Fourier-Green's function of first-order integration. Inspired by the mentioned dielectric-based integrator, we further demonstrate its graphene-based counterpart. The latter is not only reconfigurable but also highly miniaturized in contrast to the previously reported designs [Opt. Commun. 338, 457 (2015)]. Such integrators have the potential to be used in ultrafast analog computation and signal processing. © 2017 Optical Society of America  

A general modeling framework is presented for the development of the frequency equation of a microgyroscope, which is modeled as a suspended cantilever beam with a tip mass under general base excitation. Specifically, the beam is considered to vibrate in all the three directions, while subjected to a base rotational motion around its longitudinal direction. This is a common configuration utilized in many vibrating beam gyroscopes and well drilling systems. The governing equations are derived by using the Extended Hamilton's Principle with a general 6-dof base motion. The natural frequency equation is then extracted in a closed-form for the case where the beam support undergoes longitudinal... 

By virtue of a method of displacement potentials, an analytical treatment of the response of a transversely isotropic substrate-coating system subjected to axisymmetric time-harmonic excitations is presented. In determination of the corresponding elastic fields, infinite line integrals with singular complex kernels are encountered. Branch points, cuts, and poles along the path of integration are accounted for exactly, and the physical phenomena pertinent to wave propagation in the medium are also highlighted. For evaluation of the integrals at the singular points, an accurate analytical residual theory is presented. Comparisons with the existing numerical solutions for a two-layered... 

This paper is devoted to the analysis of nonlinear behavior of amplitude modulation (AM) and frequency modulation (FM) modes of atomic force microscopy. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Using perturbation methods such as Averaging, and Fourier transform nonlinear equations of motion are analytically solved and the advantageous results are extracted from this nonlinear analysis. The results of the proposed techniques for AM-AFM, clearly depict the existence of two stable and one unstable (saddle) solutions for... 

The differential equation governing the motion of an electrically excited capacitive microcantilever beam is a nonlinear PDE [1]. Accurate analysis about its motion is of great importance in MEMS' dynamical response. In this paper first the nonlinear 4th order 2 point boundary value problem (ODE) governing the static deflection of the system is solved using three methods. 1. The nonlinear part is linearized and its exact solution is obtained. 2. For low applied DC voltages (not near pull-in) the solutin is found using the direct straight forward perturbation analysis. 3. Numerical computer solutions which are used for the previous solution's verifications. The next parts are devoted to the... 

This paper presents the modeling steps towards development of frequency equations for a cantilever beam with a tip mass under general base excitations. More specifically, the beam is considered to vibrate in all the three directions, while subjected to a base rotational motion around its longitudinal direction. This is a common configuration utilized in many vibrating beam gyroscopes and well drilling systems. The governing equations are derived using Extended Hamilton's Principle with general 6-DOF base motion. The natural frequency equations are then extracted in closed-form for the case where the base undergoes longitudinal rotation. For validation purposes, the resulting natural... 

Vibration control, especially in cracked rotors, is an important factor that can prevent the occurrence of disastrous failures. In this paper, vibrational control of a cracked rotor with an electromagnetic actuator has been studied with a continuous model of flexural vibration of cracked rotors. The governing equation of motion for the rotor under the external excitation of the electromagnetic actuator, gravity, and unbalanced forces is presented. A control law for the optimal control method to minimize the vibration of the rotor or stress at the crack section was obtained. To this aim, two cost functions have been introduced, based on the overall vibration of the rotor and the maximum... 

The physics and modes of radiation in structures exhibiting extraordinary transmission (ET) can be best studied using Green's function formalism. In this article, we find the electromagnetic response to local excitation of a canonical structure exhibiting ET, and investigate the role of complex waves. The structure is a perfectly conducting slab having a finite or infinite number of through-slits. The solution breaks up the field into even and odd modes, and solves for the fields of the structure with a finite number of slits, by setting up an integral equation. The solution is then extended to find Greens' function of the infinitely periodic structure. The dispersion relations of the... 

This paper discusses the effects of substrate motions on the performance of a microgyroscope modeled as a suspended beam with a tip mass. These motions can be either along or around the three axes. Using the Extended Hamilton's Principle, the equations of motion are derived. In these equations, the effects of beam distributed mass, tip mass, angular accelerations, centripetal and coriolis accelerations are well apparent. The effect of electrostatic forces inducing the excitation vibrations are considered as linear functions of beam displacement. The response of the system to different inputs is studied and the system sensitivity to input parameter changes are examined. Finally, the sources... 

Preciseness and finished surface quality are the significant factors of final products, especially in a number of drilling processes. Burr is usually considered a negative outcome in assembly procedures. One way to reduce or remove burr and improve surface roughness in metal cutting is to employ ultrasonic vibration in the drilling process. In this paper, the effects of ultrasonic vibration on burr size reduction, drilling force and surface roughness with two different vibration systems are investigated. To this end, two vibration structures were built, one to excite the workpiece (the workpiece vibration system) and the other to vibrate the tool (the tool vibration system). Besides, the... 

A new method is presented for the extraction of the bulk and surface parameters of a periodic artificial medium which uses the eigenvectors of the generalized transfer matrix of a unit layer. These eigenvectors correspond to the Bloch modes of the periodic structure. The eigenvector related to the propagating Bloch mode directly yields an expression for the effective, intrinsic wave impedance of the medium. Moreover, the interface between the artificial material and a surrounding, conventional (dielectric) region is described by an interface impedance matrix which accounts for the excitation of higher order, nonpropagating Bloch modes at the interface. Although these modes do not propagate... 

The problem of aperiodic excitation of periodic structures with periods larger than a half-wavelength is revisited. A large number of antennas and other electromagnetic wave propagation problems fall within this category. Because of overlapping branch cuts, the conventional path deformation techniques employed in application of the array scanning method for this type of problem fail when the period is larger than a half-wavelength. A new method based on the subdivision of the integration path and using the double exponential quadrature formula is introduced to alleviate this problem and apply the array scanning method to structures with an arbitrary spatial period. To demonstrate the... 

This paper investigates the stall control over an airfoil employing dual excitation of separated shear layers with dielectric barrier discharge plasma actuators. This novel approach is studied experimentally on the NACA 0015 airfoil at the angle of attack and Reynolds number of 14° and 0.3×106, respectively. To analyze the baseline flow, Time-averaged pressure distributions on the airfoil surfaces are evaluated with 40 pressure taps. Further, the dominant natural frequencies associated with flow structures in the airfoil wake are examined utilizing a hot-wire anemometer. Two plasma actuators, one on the suction side just upstream the separation point and the other on the pressure side at the... 

We present a new approach for depth detection of hidden defects based on the analysis of the frequency spectrum of the output waveform in a nondestructive testing (NDT) system. In our eddy current Superconducting quantum interference device (SQUID) based NDT system, we apply multiple frequencies to its single excitation coil in a magnetically unshielded environment. The excitation coil is a planar D-shaped printed circuit board coil, and a high-Tc gradiometer YBCO rf-SQUID is used as the electromagnetic sensor in this system. An automated two-dimensional nonmagnetic scanning robot is used to test samples with intentional defects at different depths. In this approach, a diagram labeled 'FFT... 

This paper applies the homotopy perturbation method to the simulation of the static response of nano-switches to electrostatic actuation and intermolecular surface forces. The model accounts for the electric force nonlinearity of the excitation and for the fringing field effect. Using a mode approximation in the Galerkin projection method, the nonlinear boundary value differential equation describing the statical behavior of nano-switch is reduced to a nonlinear algebraic equation which is solved using the homotopy perturbation method. The number of included terms in the perturbation expansion for achieving a reasonable response has been investigated. Three cases have been specifically... 

Resolvers as position sensors need a high frequency AC excitation voltage, and the induced voltage in their 2-phase perpendicular windings are amplitude modulated (AM) signals. For calculating the position, it is required to demodulated the output signals and calculate their envelopes. Then, inverse tangent can be used for calculating the position. Despite the advantages of resolvers, there are some drawbacks in their application. Calculating the envelopes is always one of the deep concerns in using resolvers. Furthermore, due to low-amplitude of the excitation flux, the performance of the resolvers is strongly affected by electromagnetic interference by the stray fields of motor and brake....