ELECTROMAGNETIC MULTIFUNCTIONAL STAND FOR MEMS APPLICATIONS

Transcription

1 ELECTROMAGNETIC MULTIFUNCTIONAL STAND FOR MEMS APPLICATIONS 1 Cristian Necula, Gh. Gheorghe, 3 Viorel Gheorghe, 4 Daniel C. Comeaga, 5 Octavian Dontu 1,,3,4,5 Splaiul Independenței 313, Bucharest 06004, Romania cristianecula@yahoo.com, geo@cefin.ro, viorel_gheorghe@yahoo.com, comeaga@hotmail.com, octavdontu@yahoo.com Abstract - This paper deals with electromagnetic generators employ electromagnetic induction arising from the relative motion between a magnetic flux gradient and a conductor. Electromagnetic generators presented in the literature are reviewed including large scale discrete devices and wafer-scale integrated versions. Electrostatic generators utilize the relative movement between electrically isolated charged capacitor plates to generate energy. In this study describes a electromagnetic multifunctional stand for MEMS applications used for energy harvesting applications. Keywords: energy harvesting, electromagnetic, magnetoelectric transducer, magnetic force. 1. Introduction Electromagnetic induction, first discovered by Faraday in 1831, is the generation of electric current in a conductor located within a magnetic field. The conductor typically takes the form of a coil and the electricity is generated by either the relative movement of the magnet and coil, or because of changes in the magnetic field. In the former case, the amount of electricity generated depends upon the strength of the magnetic field, the velocity of the relative motion and the number of turns of the coil. One of the most effective methods for energy harvesting is to produce electromagnetic induction by means of permanent magnets, a coil and a resonating cantilever beam. In principle, either the magnets or the coil can be chosen to be mounted on the beam while the other remains fixed. It is generally preferable, however, to have the magnets attached to the beam as these can act as the inertial mass. The generalized schematic diagram depicted in figure 1 is applicable to describe the operation of electromagnetic generators. [1]. The damper, c, effectively represents the electromagnetic transduction mechanism, i.e. the magnet and coil arrangement. Figure 1 shows a general example of such a system based on a seismic mass, m, on a spring of stiffness, k. Energy losses within the system (comprising parasitic losses, cp, and electrical energy extracted by the transduction mechanism, ce) are represented by the damping coefficient, ct. These components are located within the inertial frame which is being excited by an external sinusoidal vibration of the form: y( = Y sin(ω. This external vibration moves out of phase with the mass when the structure is vibrated at resonance resulting in a net displacement, z(, between the mass and the frame. Assuming that the mass of the vibration source is significantly greater than that of the seismic mass and therefore not affected by its presence, and also that the external excitation is harmonic, then the differential equation of motion is described as: m z( c z( k z( my( (1) Since energy is extracted from relative movement between the mass and the inertial frame, the following equations apply. The standard steady-state solution for the mass displacement is given by: z( k ct m m Y sin t Ø () Figure 1. Model of a linear, inertial generator [1] where Ø is the phase angle given by: The Romanian Review Precision Mechanics, Optics & Mechatronics, 016, Issue

2 -1 c Ø tan T ( k m) (3) Maximum energy can be extracted when the excitation frequency matches the natural frequency of the system, ωn, given by: (4) n k / m The power dissipated within the damper (i.e. extracted by the transduction mechanism and parasitic damping mechanisms) is given by [3] 3 m TY n Pd 1 T n n 3 (5) where ζ T is the total damping ratio (ζt = ct/mωn). Maximum power occurs when the device is operated at ωn and in this case Pd is given by the following equations: P P 3 my n 4 d (6) n T ma 4 d (7) T Equation (7) uses the excitation acceleration levels, A, in the expression for Pd which is simply derived from A = ω n Y. Since these are steady-state solutions, power does not tend to infinity as the damping ratio tends to zero. The maximum power that can extracted by the transduction mechanism can be calculated by including the parasitic and transducer damping ratios as: result in a broader bandwidth response and a generator that is less sensitive to frequency. Excessive device amplitude can also lead to nonlinear behavior and introduce difficulties in keeping the generator operating at resonance. It is clear that both the frequency of the generator and the level of damping should be designed to match a particular application in order to maximize the power output. Furthermore, the mass of the mechanical structure should be maximized within the given size constraints in order to maximize the electrical power output. It should also be noted that the energy delivered to the electrical domain will not necessarily all be usefully harvested (e.g., coil losses). Since the power output is inversely proportional to the natural frequency of the generator for a given acceleration, it is generally preferable to operate at the lowest available fundamental frequency. This is compounded by practical observations that acceleration levels associated with environmental vibrations tend to reduce with increasing frequency. Application vibration spectra should be carefully studied before designing the generator in order to correctly identify the frequency of operation given the design constraints on generator size and maximum permissible z(. [1] Jin Young et al. described in his paper [], a new broadband vibration energy harvester using magnetoelectric transducer, which takes advantage of multi-cantilever beams and the non-linear behavior of the magnetic force to expand the working bandwidth in ambient low-frequency vibration. And a theoretical model is developed to analyze the non-linear vibration and the electrical-output performances of the harvester, whose results agree closely with the experimental results. The harvester showed a bandwidth of 5.6 Hz and a maximum power of 0.5mW under an acceleration of 0. g. The principle may be generally applied to improve the frequency bandwidth of the energy-harvesting system that works using ME transductions. P e m ea (8) 4n p e Pe is maximized when ζ p = ζ e. Some parasitic damping is unavoidable and it may be useful to be able to vary damping levels. For example, it may indeed be useful in maintaining z( within permissible limits. However, conclusions should not be drawn without considering the frequency and magnitude of the excitation vibrations and the maximum mass displacement z( possible. Provided sufficient acceleration is present, increased damping effects will Figure.Schematic diagram of the proposed vibration energy harvester. [] In order to achieve the 5 degrees of freedom of multifunctional stand MEMS we used a positioning system with vertical guide, which acts as a translational 184 The Romanian Review Precision Mechanics, Optics & Mechatronics, 016, Issue 50

3 of M-105 and M-106 micro meter-driven translation stages with travel ranges of 18 mm and 5 mm, respectively. Precision crossed roller bearings guarantee straightness of travel of better than µm. The M-106 is equipped with a differential micrometer drive providing resolution of 0.1 µm. The vertical stage in the XYZ assembly supports the load through the micrometer spindle providing excellent stability, translatand with high accuracy support that is located a coil. To optimize translational movements and for improved accuracy on positioning assembly can be added for each micro meter-driven a linear actuator M-31 DC that can be programmed. The M-31 is an ultra-high-resolution linear actuator providing linear motion up to 17 mm with sub-micron resolution in a compact package. It consists of a leadscrew which is driven by a closedloop. Figure 3. Designing an electromagnetic multifunctional stand for MEMS applications For controlling vibration it was used a vibration system. It is a system available for experiments produced by TIRA GmbH, Germany, type TIRA Vib S 513. Vibration testing system is therefore composed of vibrator (S 513), power amplifier (647B) and accessories (accelerometers and special cables). The system is equipped with sinusoidal regimes control and random shocks. Maximum acceleration of vibrations depend on the current applied to the command coil and and effective total weight which must be moved. It should be emphasized that for low frequency vibration, the allowable limits of speed and of the amplitude are reached faster than the corresponding acceleration. Figure 4. 3D representation of TIRA Vib S 513 Figure 5. Dependence on acceleration/frequency vibrant area[4] The Romanian Review Precision Mechanics, Optics & Mechatronics, 016, Issue

4 In the figure above is described (in logarithmic scale) dependence between the moveable printed acceleration and vibration frequency generated specific to the vibrant area. The speed limit (3 Area) of the mobile element of the vibrating area (maximum amplitude attainable) is represented as a straight line (1) with a slope of 1 db/octave. Vibration speed limit (4 area) is a function dependent on the elastic constants of membranes and compositionof springs vibrated area and maximum output voltage of the power amplifier. This speed limit vibration is represented graphically as a straight line (1) with a slope of 6 db / octave. The upper limit of the accelerations which can be generated (5 area) depends on the frequency of its own resonance of the movable member of the vibrating table. For the achievement of tests and determine some specific parameters, the mobile element of the vibrated area must execute movements with amplitudes and accelerations clearly defined and controlled. The response curve for vibrated of area for large range of frequencies, it is not straight or flat and shows peaks corresponding to resonant frequencies. Other objects are specific resonant frequencies tested or measured on the vibrant surface, producing peaks in the frequency response curve. For these reasons, the control signal and amplifying the signal must be changed with the change if we maintain defaults frequency vibration area. In principle are compared, in real time, the vibration parameters of vibration area with standard parameters predetermined for each situation. The control of the vibrating area consists mainly of: a frequency generator, a system of real-time measurement of the movable vibration area and a control system and gain control signal of the mobile element. The magnets array is fixed in the middle of flange, being oriented by a Thorlabs tip-tilt table. The TTR001(/M), axis tilt and rotation stage provides ±5 uncoupled tilt adjustment in pitch and roll, together with ±10 rotation (yaw) adjustment. These adjustments allow optical components and fixtures to be aligned with a plane and then rotated within that plane. The center of rotation axis is located at a line normal to the center of the platform. Both the tip and tilt axes will move with respect to a point located 1 mm below the top surface of the stage on the rotation axis. The top plate features an array of (M4) threaded holes on a 1/" (1.5 mm) pitch. An 8-3 to 6-3 thread adapter is included with imperial stages for use with the PM3 and PM4 clamping arms sold below. The metric stages are directly compatible with the PM3/M and PM4/M metric clamping arms, and therefore do not require an adapter. Figure 6. Displacement directions of M-105 micro meter-driven, positioning magnets The electromagnetic multifunctional stand for MEMS applications can be used for energy harvesting applications using the principle of electromagnetic autoinduction. This assembly can be used in conception and stage design for: 1. Analyzing of the mechanical response. During this stage we studied a concept of the cantilever actuator is provided with an array of permanent magnets at the free end of a elastic blades, which is constructed of a material type Polyimide (PI) (super) paramagnetic. The magnets interacts with the magnetic field produced by electric current flowing through a flat coil, and a cantilever support made of silicone. Electric current is adjustable and ensures flexible adjustment of PI clamp deflection. This may cause a terminal voltage generated by a relative movement of the coil. 186 The Romanian Review Precision Mechanics, Optics & Mechatronics, 016, Issue 50

5 Figure 7. Measurement electromechanical response. Measuring the mechanical response depending on the relative vibration between excitatory device and cantilever Figure 8. Measuring the mechanical response 3. Last phase of the study is to determine the overall response of the final product. Figure 9. The overall response of the the finished product The Romanian Review Precision Mechanics, Optics & Mechatronics, 016, Issue

6 For the interpretation of results and frequency domain it was used a signal analyzer SR785 type. It is a device that ensures accurate analysis of the dynamics of a signal with full characterization of signal parameters. For measurements involving vibration analysis, vibration testing systems or actuators, a control systems or acoustic analyzer, SR785 has all the features and specifications necessary to perform complete tests and measurements. This example investigates the frequency response of the test filter using FFT measurements. We used the SR785 source to provide a broad band chirp and both input channels to measure the input to and output from the device under test. For this type of measurement Time/Histogram records in the sample set time signals are processed to provide a statistical description of the input signals and measurements for Octave signals wich are recorded after that, are passed through a set of parallel filters and then mediated. The measurement mode using sweeping frequency (Swept-itself mode) is an optimum analysis schemes involving high dynamic range or high frequency limits. The gain or amplification (gain) is optimized at each measurement point, ensuring a dynamic range of up to 145 db. It is also possible to provide a frequency resolution of up to 000 points. Establishing automatic boundaries frequency source can be used simultaneously with automatic soothing signal control to maintain a constant command signal at a certain level Any changes or modifications of the amplitude exceeding the limits are automatically measured with a resolution corresponding to high frequencies, while small changes are measured using larger frequency increments between points. Figure 10. Low frequency signal analyzer SR 785 [5]. Conclusions This work presented the design, analysis, and experimental testing of electromagnetic multifunctional stand for MEMS applications used for energy harvesting applications. These analyses are well conformed by experiments on energy-harvesting devices. 3. References [1] S P Beeby, M J Tudor and N M White, " Energy harvesting vibration sources for microsystems applications" March 005, in final form 19 July 006, Published 6 October 006, Online at stacks.iop.org/mst/17/r175. [] JIN YANG,* YUMEI WEN AND PING LI "Magnetoelectric Energy Harvesting from Vibrations of Multiple Frequencies", Journal of Intelligent Material Systems and Structures 011 : 1631 originally published online 5 August 011 [3] Williams C B and Yates R B 1996 Analysis of a micro-electric generator for microsystems Sensors Actuators A [4] [5] 785m.pdf 188 The Romanian Review Precision Mechanics, Optics & Mechatronics, 016, Issue 50