Luiz Otávio Saraiva Ferreira

A silicon micromechanical galvanometric scanner

Abstract The design, fabrication, characterization and modeling of a micromechanical optical scanner driven electromagnetically is described. This microscanner, based on the galvanometric principle, consists of a thin film mirror surrounded by a planar coil deposited on a Si base that is able to rotate around suspended torsion bars and all is immersed in an external magnetic field. This design has no transverse force acting on the rotation axis during scanning, which provides good mechanical characteristics as low distortion and damping, high optical angular deflection (≥22° peak-to-peak) and large Q quality factor at the resonant frequency. Variations in the design are presented and shown to enhance the deflection angle, the speed response and decrease the power consumption.

A novel Si micromachined moving-coil induction actuated mm-sized resonant scanner

A novel silicon micromachined moving-coil scanner with electromagnetic induction actuation principle is presented. It was manufactured by the Si-LIG process, silicon-lithography-electroforming (Galvanoformung, from German), where its mechanical structure was made by bulk silicon micromachining of 200 µm thick (1 0 0) silicon substrate, and its armature was patterned by deep UV lithography and Au electroplating. The monolithic mechanical structure is a 12 × 24 mm2 rectangular frame connected by 4.5 mm long torsion bars to a 4 × 10 mm2 rectangular rotor. On one face of the rotor is the armature, a 70 µm thick, single turn, electroplated Au coil with 3.3 mΩ electrical resistance. The other face of the rotor was mirrored by a 1480 A thick Al film. An external magnetic circuit generated a constant 0.115 T magnetic field parallel to the coil plane and a 0.01 T (peak value) field normal to the coil plane. A maximum mechanical deflection angle of 9.0° pp at the 1311.5 Hz resonance frequency was measured, and a quality factor, Q, of 347 was achieved in air. A mathematical model for the device was derived and a dimensioning procedure was developed. The results show that electromagnetic induction actuation is adequate for mm-sized systems and capable of producing resonant scanners with performance compatible with applications such as bar code readers.

Analysis of a complete model of rotating machinery excited by magnetic actuator system

Rotating machines have a wide range of application involving shafts rotating at high speeds that must have high confidence levels of operation. Therefore, the dynamic behavior analysis of such rotating systems is required to establish operational patterns of the equipment, providing the basis for controller development in order to reduce vibrations or even to control oil instabilities in lubricated bearings. A classical technique applied in parameter identification of machines and structures is the modal analysis, which consists of applying a perturbation force into the system and then to measure its response. However, there are mainly two problems in modal analysis concerning the excitation of rotating systems. First, there are limitations to the excitation of systems with rotating shafts when using impact hammers or shakers, due to friction, undesired tangential forces, and noise that can be introduced in the system response. The second problem relies in the difficulty of exciting backward whirl modes, an inherent characteristic from these systems. Therefore, the study of a non-contact technique of external excitation, also capable of exciting backward whirl modes, becomes of high interest. In this sense, this article deals with the study and modeling of a magnetic actuator, used as an external excitation source for a rotating machine, mainly in backward whirl mode. Special attention is given to the actuator model and its interaction with the rotor system. Differently from previous works with similar proposal, which uses current and air gap measurements, here the external excitation force control is based on the magnetic field directly measured by hall sensor positioned in the pole center of the magnetic actuator core. The magnetic actuator design was completely developed for this purpose, opening different paths to experimental application of this device, for example, fault detection analysis based on directional modes. It is also presented a comparison between the numerical simulations and practical tests obtained from a rotor test rig and an experimental evidence of the backward whirl was accomplished based on the numerical simulation results.

Constant Boundary Elements on graphics hardware: a GPU-CPU complementary implementation

Numerical simulation of engineering problems has reached such a large scale that the use of a parallel computing approach is required to obtain solutions within a reasonable time. Recent efforts have been made to implement these large scale computational tasks on general-purpose programmable graphics hardware (GPGPU). The Graphics Processing Unit (GPU) is specially well-suited to address problems that can be formulated in form of data-parallel computations with high arithmetic intensity. This work addresses the implementation of the direct version of the Boundary Element Method (DBEM) on a complementary GPU-CPU system. In this article, constant elements were used for the solution of 2D potential problems. A serial implementation of the BEM was rewritten under the SIMT (Single Instruction Multiple Thread) parallel programming paradigm. The code was developed on an NVidiaTM CUDA programming environment. The efficiency of the implemented strategies is investigated by solving a representative 2D potential problem. The paper reviews in detail the classical BEM formulation in order to be able to address the possible parallelization steps in the numerical implementation. The article reports the performance of the GPU-CPU system compared to the classical CPU-based system for an increasing number of boundary elements.

Manufacturing of miniature fluidic modules for lab-on-a-chip using UA photoresin from flexographic platemaking process

A new technique of fabrication of miniaturized fluidic devices was developed using a photoresin based on urethane and acrylate (UA) oligomers used to platemaking for flexographic printers on graphic industry. Fluidic mixers and reactors modules measuring 10´10 mm2 were manufactured, with channels width in the 0.25 to 1.00 mm range and 0.75 mm depth. Top covers 4.00 mm thick, with 1.26 mm diameter inlet and outlet holes were used to seal the channels. The sealed channel structures were formed using a film of photoresin as adhesive. Interconnections of 1.20 mm diameter and 10 mm long steel tubes were fixed into inlet and outlet holes. All fluidic modules were manufactured by photolithography of UA, sealed by ultraviolet cure of an UA adhesion layer, package in an UA container and successfully tested for leakage under 2´105 Pascal air pressure.

Design and modeling of an acoustically excited double-paddle scanner

Dynamic analysis is an essential factor in the design, fabrication and optimization of micro-systems. Micro-scanners are currently subjected to wide research work. In this paper, the dynamic behavior of a monolithic single-crystal silicon microstructure is investigated. The microstructure used is a double-paddle scanning mirror for laser applications. It consists of two similar plates (wings) connected to another plate (mirror) and is suspended by one torsion bar. The dynamic analysis is conducted numerically, using finite element analysis. The numerical modeling is described. The numerical results are validated experimentally by measuring the frequency response functions collected at some points on the scanner surface. The experimental modal analysis is performed using a laser Doppler vibrometer and an acoustic excitation device. The excitation device consists of a polyester resin mount with two conic-shaped ducts which give access to the back of the two wings from one side and to two mini loudspeakers on the other side. This excitation device was used and good agreement was found between the numerically predicted and the experimentally identified modal parameters. The non-intrusive excitation mechanism and the optical measurement techniques used in the experiments are discussed. A high quality factor is identified for the chosen operational mode shape.

Dynamic Analysis of Silicon Micromachined Double-Rotor Scanning Mirror

The use of MEMS-based technologies for producing scanning mirrors enables its batch production with a consequent increase in the throughput and a decrease in the manufacturing costs per device. However, the use of Silicon as a structural material could introduce non-linearities in the device behavior due to the variation of its mechanical properties according to the crystalline orientation. The orthotropic properties when taken into account in the finite element model of the device could enhance the accuracy in the design of micromachined scanning mirrors. The model used in this paper does not take into account the orthotropic behavior, however, satisfactory results were obtained. To validate the finite element model, a modal analysis of the device was performed using the Laser Doppler Vibrometry method. The normal modes of the structure were identified and the results agree well with the finite element model. This work presents the FE model and experimental modal analysis results of a Silicon micromachined double-rotor scanning mirror.

Si-LiG process for inductive meso systems

A new process for microelectromechanical systems (MEMS) has been developed and employed in the microfabrication of inductive actuators. The process combines deep UV lithography and metal electroplating with bulk silicon micromachining. The lithography is based on an AZ-4260 photoresist with a thickness of 50 μm, while electroplating is accomplished by using a gold bath; the bulk silicon is micromachined in an aqueous KOH solution (28% w/w) at 80 °C. This process has been successfully applied in the micromachining of an oscillating mirror actuated by induction. The results show compatibility between the microfabrication process of the metallic structures and the KOH bulk silicon micromachining process. The photoresist mold remained intact after the electroplating step, and the electroplated structures were uniform in thickness, surface uniformly smooth, and presented good adhesion, maintaining these features also after KOH micromachining.

Micromachined scanner actuated by electromagnetic induction

A novel micromachined scanner with electromagnetic induction actuation principle is presented. It was manufactured by Si-LIG technique, where its mechanical structure was made by bulk silicon micromachining of 200μm thick (100) silicon substrate, and its electric circuit was made by deep UV lithography and Au electroplating. The monolithic mechanical structure is a 12×24 mm2 rectangular frame connected by 4.5mm long torsion bars to a 4×10mm2 rectangular rotor. On one face of the rotor is the electric circuit, a 70μm thick, single turn, electroplated Au coil with 3.3mΩ electrical resistance. The other face of the rotor was mirrored by a 1480Å thick Al film. An external magnetic circuit generated a constant 1150 Gauss magnetic field parallel to the coil plane and a 100 Gauss (peak value) field normal to the coil plane. Maximum deflection angle of 6.5°pp at the 1311Hz resonance frequency was measured, and the quality factor Q was 402. The results shown that electromagnetic induction actuation is adequate for meso-scale systems and capable of producing resonant scanners with performance compatible with applications like bar code readers.

Magnetic Actuator Modelling for Rotating Machinery Analysis

Rotating machines have a wide range of application such as airplanes, factories, laboratories and power plants. Lately, with computer aid design, shafts finite element models including bearings, discs, seals and couplings have been developed, allowing the prediction of the machine behavior. In order to keep confidence during operation, it is necessary to monitor these systems, trying to predict future failures. One of the most applied technique for this purpose is the modal analysis. It consists of applying a perturbation force into the system and then to measure its response. However, there is a difficulty that brings limitations to the excitation of systems with rotating shafts when using impact hammers or shakers, once due to friction, undesired tangential forces and noise can be present in the measurements. Therefore, the study of a non-contact technique of external excitation becomes of high interest. In this sense, the present work deals with the study and development of a finite element model for rotating machines using a magnetic actuator as an external excitation source. This work also brings numerical simulations where the magnetic actuator was used to obtain the frequency response function of the rotating system.