Showing papers on "Bimorph published in 2004"

A polymeric piezoelectric micropump based on lamination technology

Abstract: This paper presents the first micropumps assembled using polymeric lamination technology. Each pump consists of two 100 µm thick, 10 mm diameter SU-8 discs; two 1.5 mm thick, 15 mm diameter polymethylmethacrylate (PMMA) discs; and one piezo disc. The SU-8 parts were fabricated by a two-mask polymeric surface micromachining process with silicon as the sacrificial material. Each SU-8 disc has one micro check valve. The valve is a 1 mm plate suspended on a compliant orthoplanar spring. The cross section of the spring beam has a dimension of 100 µm × 100 µm. The PMMA parts were machined from an extrusion PMMA sheet by CO2 laser. An off-the-shelf piezo bimorph disc worked as both actuator and pump membrane. The pump was assembled using adhesive bonding. The adhesive tapes were cut by the same laser system. Alignment pins were used in the assembly process. With a drive voltage of ±150 V the fabricated micropumps have been able to provide flow rates up to 2.9 ml min−1 and back pressures up to 1.6 m of water. The pump design and the polymeric technologies prove the feasibility of making more complex microfluidic systems based on the presented lamination approach.

Multifunctional transducer using poly (vinylidene fluoride) active layerand highly conducting poly (3,4-ethylenedioxythiophene) electrode: Actuator and generator

Abstract: Monomorph and bimorph multifunctional transducers such as actuators and generators were fabricated using a piezoelectric poly (vinylidene fluoride) (PVDF) films as the active layer and a highly conducting poly (3,4-ethylenedioxythiophene)∕poly (4-styrenesulfonate) [PEDOT∕PSS (DMSO for solvent)] as the electrode. In order to enhance the adhesion of the films, either the PVDF films or PEDOT∕PSS (DMSO) electrodes were modified using an ion-assisted-reaction (IAR) method. The direct (generator) and inverse piezoelectric (motor) effects as well as the pyroelectric effect in the PVDF-PEDOT∕PSS based devices were observed. The tip displacement of the 12mm by 30mm bimorph device made with the PEDOT∕PSS (DMSO) electrodes was 3.5mm at the resonance frequency with an appled potential of 40Vrms. The sinusoidal output voltage of the bimorph type generator consisting of the PVDF active layers and PEDOT∕PSS (DMSO) electrodes increased with increasing tip displacement induced by a vibrator. A maximum output voltage of 4....

A piezoelectric linear actuator formed from a multitude of bimorphs

Abstract: This paper describes the design, construction, and testing of a linear actuator using a multitude of cantilever bimorphs. Each beam is vibrated both in the fundamental axial mode and a high-order flexural mode using piezoelectric material with a specific electroding pattern to obtain both axial and flexural motion from each bimorph. Bidirectional linear sliding velocities and forces reached 27.7 cm/s and 0.09 N, respectively, from a single bimorph, while up to 17.6 cm/s velocity and 0.15 N in either direction, at approximately 1% efficiency, were obtained from an actuator composed of four closely-matched bimorphs.

Integrated self-assembling and holding technique applied to a 3-D MEMS variable optical attenuator

Abstract: The application of polysilicon/gold bimorph stress-induced curved beams for three-dimensional self-assembly of MEMS devices is reported. The mechanical principle behind this self-assembling procedure is presented and comparison with current assembling methods are made. With this self-assembling technique, no postprocessing is required. A free-space optical MEMS device in the form of a variable optical attenuator (VOA) has been fabricated and self-assembled using this technique. The angular elevation of the self-assembled structures and the attenuation characteristics of the optical MEMS device are reported. The VOA has a measured dynamic attenuation range of 44 dB at 1.55 /spl mu/m optical wavelength. The bending of the bimorph beams is also temperature controllable, and the thermal behavior of the beams is also reported.

Modelling of non-symmetric piezoelectric bimorphs

Abstract: This paper deals with the modelling of non-symmetric piezoelectric bimorphs used in micromechanics or microsystems (MEMs). An analytical modelling including the elastic and geometric parameters of the substrate, bonding material, piezoelectric layer and electrodes is carried out. This model has been applied to bimorphs having different types of boundary conditions, that is clamped edges (CC), clamped and free edges (CF) or simply supported edges (SS). When the bimorph is used as an actuator, the resonance frequency and displacement of different types of bimorphs are calculated. Open circuit voltage, displacement and resonance frequency are determined when the bimorph is used as a sensor. The influence of the parameters of the bonding layer has been determined. A new method for calculating the global quality factor of bimorphs versus the quality factor of each layer is given. This method can easily be applied to all types of bimorphs (CC, CF, SS). The analytical form of the evolution of the resonance frequency and the sensitivity is deduced from the general modelling and theoretical models and are compared to those given by the finite element method and discussed.

On the electromechanics of a piezoelectric transducer using a bimorph cantilever undergoing asymmetric sensing and actuation

Abstract: This paper presents an analytical, numerical and experimental study of an asymmetric piezoelectric actuator/sensor cantilever beam. The structure consists in a three-layered laminate with a piezoceramic acting as actuator, an elastic material layer and a second piezoceramic layer that can operate as a sensor or actuator. The coupled expansion-bending motion of the system is analytically resolved, where the governing electromechanical expansion and bending motion equations are obtained. Explicitly analytic solutions for longitudinal and transverse displacements, and also the mechanical/electrical frequency response of the structure are calculated. A finite element model (FEM) is developed and used to evaluate the accuracy of the analytic model. Experimental results are used to verify the frequency response of the structure, and validate the theoretical and FEM models.

Switchable cantilever for a time-of-flight scanning force microscope

Abstract: We have developed a cantilever device for applying a time-of-flight scanning force microscope (TOF–SFM) system. The cantilever device consists of a switchable cantilever with an integrated bimorph actuator, an integrated extraction electrode to minimize the ion extraction voltage, and an interlocking structure for precise tip–EE alignment. The TOF–SFM with the cantilever device allows quasisimultaneous topographical and chemical analyses of solid surfaces to be performed in the same way as with the conventional scanning probe technique. The switching properties of the bimorph actuator are demonstrated for use in two operating systems. Field emission measurements and a TOF analysis of a Pt-coated tip are conducted with the TOF–SFM.

Constitutive relations for piezoelectric benders under various boundary conditions

Abstract: In this article, the constitutive relations of three types of piezoelectric bender—the unimorph bender, bimorph bender and triple-layer bender—are derived based on beam theory under the quasi-static equilibrium condition. The relation coefficients are expressed in terms of the geometrical and material properties of the benders. Constitutive relations are derived for a range boundary conditions (fixed-free, fixed-roll and fixed-simply supported) under conditions allowing different lengths of the piezoelectric and elastic layers. The complicated constitutive relations can be easily formulated and verified by using the function for handling symbolic calculations. The derived constitutive relations may assist in the determination of the optimal values of geometrical parameters in the design of actuators and sensors for particular applications.

Multistate latching MEMS variable optical attenuator

Abstract: A multistate latching variable optical attenuator (VOA) is demonstrated using microelectromechanical systems (MEMS) technology. The mechanism is used to fix the position of a shutter inserted into the optical path between two single-mode fibers. The mechanism and fiber mounts are fabricated in 85 /spl mu/m thick silicon using bonded silicon-on-insulator material, by deep reactive ion etching. The device can be continuously adjusted or latched into a discrete set of attenuation states using a rack-and-tooth mechanism driven by electrothermal shape bimorph actuators. Electromechanical and optical characterization is performed to demonstrate a latching VOA function, with a maximum attenuation of 30 dB.

Bimorph MEMS devices

Abstract: A micro-electromechanical dimensioned bimorph structure includes a first element layer structure, and a second element layer structure. The element layer structures are provided in various combinations, including piezoelectric/piezoelectric, antiferroelectric/antiferroelectric or antiferroelectric/piezoelectric. The layer thickness of the element structure is less than 100 μm. A bonding layer bonds the first element structure directly to the second element structure, and the bonding layer thickness is less than 10 μm. The bimorph structure can be made in various forms including a cantilever or a diaphragm. Microfluidic devices using the bimorph structures may also be constructed.

Capacitive-type chemical sensors using thin silicon/polymer bimorph membranes

Abstract: Capacitive-type chemical sensing devices based on a silicon/polymer bimorph structure have been fabricated and evaluated. Upon exposure to analytes, the polymer covering the thin silicon membrane swells, inducing a deflection on the membrane, which is measured as a capacitance change between membrane and substrate. Five different polymer layers [poly-hydroxy-ethyl-methacrylate (PHEMA), poly-methyl-methacrylate (PMMA), poly-vinyl-acetate (PVAc), epoxydized novolac (EPN) and poly-dimethylsiloxane (PDMS)] were used. Exposure to water, methanol and ethanol vapors was used for evaluating performance. Sensitivities ranging from 4.5 fF/%RH for PDMS to 29 fF/%RH for PHEMA-covered devices are reported. Devices covered with PHEMA, PVAc and PMMA also exhibit strong response upon exposure to methanol and ethanol atmospheres.

Induced-strain multimorphs for microscale sensory actuation design

Abstract: The paper proposes an analytic model that evaluates the levels of actuation and sensing by microbenders formed of several sandwiched layers (multimorphs) of active/sensitive materials such as piezoelectric (PZT) and shape memory alloys (SMA) interspersed with structural materials which only react to thermal variations. The model is generic, such that any type of induced strain can be incorporated into it, and its prediction gives the deformed (bent) shape, the corresponding tip bending moment, as well as the position of the neutral axis (NA) and the composite bending rigidity. The generic model reduces to the well-known Timoshenko 'bi-metal thermostat' model in the case of two layers of which one is thermally heated. Finite element simulation produces results that are very close to the analytic model predictions for a three-layer (trimorph) bender when all layers are heated. Concrete examples are further studied that can be encountered in small-scale (MEMS) applications, such as an antisymmetric PZT trimorph with either unilateral actuation and sensing or just antisymmetric actuation, a SMA-actuated bimorph and a hybrid PZT–SMA trimorph that can act as a simultaneous sensory actuator microdevice. Numerical simulations are performed for all examples in order to highlight trends in performance as a function of the microcantilever geometry.

Normally closed microgrippers using a highly stressed diamond-like carbon and Ni bimorph structure

Abstract: A normally closed microgripper with a radius of curvature of 18–50 μm using a diamond-like carbon (DLC) and stress free electroplated Ni bimorph structure has been demonstrated. The large curvature in the fingers of the microgrippers is due to the high compressive stress of the DLC layer. The radius of curvature of the figures can be adjusted by the thickness ratio, and the closure of the devices can also be adjusted by varying the finger length. This device works much more efficiently than other bimorph structures due to the large difference in thermal expansion coefficients between the DLC and the Ni layers. Preliminary electrical tests have shown these microgrippers can be opened by 60°–90° at an applied power of <20mW.

Robust latching MEMS translation stages for micro-optical systems

Abstract: A multi-state latching translation stage is demonstrated using microelectromechanical systems technology. The mechanism is fabricated in bonded silicon-on-insulator material with an 85 µm thick bonded layer, by single-layer patterning, deep reactive ion etching, undercutting and metallization. The table position can be continuously adjusted by electrothermal buckling mode actuators or latched into a discrete set of states using a rack-and-tooth mechanism driven by electrothermal shape bimorph actuators. A travel range of more than 100 µm and a latching precision of 10 µm are demonstrated. The load carrying capacity of the device is in the milligram range, corresponding to the mass of many microoptical components.

Oscillating micromirror with bimorph actuation

Abstract: The present invention relates to a micromirror comprising a mobile part with a reflecting area, a fixed part, two torsion arms originating from the mobile part materializing an axis about which the mobile part can oscillate, this axis being approximately parallel to a principal plane of the mobile part and passing through the mobile part while being offset from the center of mass of the mobile part, each torsion arm having one end connected to the fixed part through bimorph actuation means. The bimorph actuation means comprise a solid stack with deposited or add-on layers for each torsion arm, including a part made of an active material capable of changing volume and/or shape under the effect of an excitation, co-operating with a passive flexible structure.

The effects of ionizing radiation on microelectromechanical systems (MEMS) actuators: electrostatic, electrothermal, and bimorph

Abstract: The effects of ionizing radiation on the operation of polysilicon microelectromechanical systems (MEMS) electrostatic, electrothermal, and bimorph actuators were examined All devices were irradiated up to a total ionizing dose of 1 megarad(Si) using both a low energy X-ray source (LEXR) and Cobalt-60 (Co-60) gamma source The electrostatic actuators exhibited a decrease in capacitance and thereby an increase in voltage per deflection when subjected to the LEXR radiation environment Devices irradiated with the Co-60 source showed no changes in the capacitance/voltage relationship after irradiation The electrothermal actuator operation was not affected by exposure to either type of ionizing radiation The tip deflection measurements of the bimorph actuators showed a slight decrease between pre- and post characterization

An integrated electrochemical sensor–actuator system

Abstract: The use of bimorph actuators based on conducting polymers (CP) in an integrated oxygen control system is explored with practical focus on the control of a fruit storage atmosphere at 5% oxygen. A low-cost oxygen sensor is integrated with a simple actuator valve to limit the influx of atmospheric oxygen to the storage package. For this task, electrochemical oxygen sensors as used in the study, such as zinc–air cells with output potentials up to 1 V, appear to be well suited to drive trilayer strips based on CPs that actuate over a similar range. The actuator used, based on polypyrrole (Ppy), gave reliable and repeatable mechanical behaviour for about 50 h. Two sensor–actuator systems have been trialled. In one, the output from a lead-oxygen sensor was electronically augmented to drive a conducting polymer trilayer actuator valve. The desired oxygen concentration was easily maintained with response times of tens of seconds. The other system used the output from a zinc–air cell directly to drive an actuator valve that limited the diffusion of air into the enclosure. Positive oxygen concentration control was achieved but at lower rates of oxygen flux and longer response times. Good sealing of the orifice at closure was found to be critical.

Near-resonance wide-range operating electromechanical motor

Abstract: The present invention combines bending mode mechanical (frm) and electrical (fre) resonances, whereby a relatively good efficiency can be achieved within a relatively broad frequency range (Δf3). An electrical resonance (fre) or mechanical resonance is designed to be situated in the same order of magnitude as another mechanical resonance (frm), but separated therefrom. Preferably, the separation (Δf2) is smaller than 2f1 / Q 1, where f1 is the resonance frequency for the resonance having lowest quality value, and Q1 is the corresponding quality value of the mechanical resonance. An electromechanical motor comprising a driving element and electrical resonance circuit according to the above ideas may comprise a double bimorph driving element having one single actuating point influencing a body to be moved. The double bimorph driving element is excited in bending vibrations perpendicular to a main displacement direction, whereby both tangential and perpendicular motions are created by bending mode vibrations.

Piezoelectric sounder and electronic apparatus

Abstract: PROBLEM TO BE SOLVED: To provide a piezoelectric sounder suppressing deterioration in a sound pressure characteristic attended with a low profile, and also to provide an electronic apparatus with the sounder. SOLUTION: The housing 10 of a mobile phone has a plurality of sounding holes 12 formed thereon. The inside of positions where the sounding holes 12 are formed is an air chamber 14 wherein fitting parts 16 fitted with a piezoelectric sounding element 20 are formed. The piezoelectric sounding element 20 adopts a bimorph structure wherein piezoelectric elements 24, 26 are respectively made to adhere to both sides of a diaphragm 22, and the diaphragm 22 is made to adhere to the fitting parts 16 by using an adhesive 18 to act like a speaker. The sound pressure characteristic of the piezoelectric sounder as above relates to a part at which the housing 10 and the piezoelectric sounding element 20 are overlapped, that is, an overlap width W of a mount part, and selecting the overlap width W to be 2 mm or below prevents deterioration in the sound pressure characteristic due to vibration of the housing and ensures the required acoustic characteristic. COPYRIGHT: (C)2006,JPO&NCIPI

A Study of Displacement Distribution in a Piezoelectric Heterogeneous Bimorph

Abstract: Piezoelectric heterogeneous bimorphs have extensive applications in the MEMS area. In order to formulate their displacement distribution more conveniently, a concise analytical solution is described herein. This solution integrates all of the important influence factors, such as geometry and material properties, into a single expression. Secondary effects such as shear, residual stress induced curvature, and electrostiction, are not considered, but they are found to be minimally important based on the accuracy of the predicted results. The expression is verified using the finite element method, and shown to be straightforward compared to the more complicated couple-field FEM analysis for a specific range of materials and thicknesses. The method is subsequently shown to be capable of quickly estimating the displacement in a bimorph beam, making it a useful tool for designing piezoelectric structures.

Electrothermal scs micromirror with large-vertical-displacement actuation

Abstract: This paper reports a novel large-vertical-displacement (LVD) microactuator that can generate large piston motion at low driving voltage. A LVD micromirror device has been fabricated by using a unique DRIE CMOS-MEMS process that can simultaneously provide thin-film and single-crystal silicon microstructures. With only a 0.7 mm by 0.32 mm sized device, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at an actuation voltage of 6 V d.c. This device can also perform bidirectional rotational scanning through the use of two bimorph actuators. The micromirror can rotate ± 20q, and has negligible initial tilt angle and high scanning speeds (~2 kHz).

Analytical and Numerical Modelling of Laminated Composites with Piezoelectric Elements

Abstract: We propose an accurate and efficient approach to laminated piezoelectric plates based on a refinement of elastic displacement and electric potential through the plate thickness. More precisely, the model accounts for a shearing function and a layerwise approximation for the electric potential. The layerwise approach becomes a necessity in order to accommodate electric potential at the electrode interfaces. The equations of motion for the piezoelectric composite are deduced from a variational formulation incorporating the continuity conditions at the layer interfaces by using Lagrange multipliers. Different situations are investigated among them (i) bimorph and (ii) sandwich structures for two kinds of electro-mechanical loads applied (density of force and electric potential) and are compared to the finite element computations performed on the 3D model. The vibration problem is also presented and the frequencies for the axial and flexural modes are obtained. At last performance and effectiveness of the model are also discussed and applications to control of the structure shape and vibration are proposed.

Development of a piezoelectric actuator for presentation of various tactile stimulation patterns to fingerpad skin

Abstract: In order to investigate tactile perception characteristics of the human fingerpad for the optimal design of a sensory substitution system, we have developed a small piezoelectric bimorph actuator that possesses flat frequency characteristics in the vibratory frequency of tactilely perceivable bandwidth. The parameters for the design of the bimorph were determined by using a mechanical simulation model of a piezoelectric bimorph and a fingerpad skin. To evaluate the performance of the bimorph, we measured frequency-displacement relationships when the skin of a fingerpad was vibrated by the piezoelectric bimorph. The experimental results showed that the frequency-displacement relationships were almost the same as the estimation obtained from the mechanical simulation model.

Highly symmetric tri-axis piezoelectric bimorph accelerometer

Abstract: This paper describes the design, fabrication and test results of a novel bimorph tri-axis piezoelectric accelerometer (built on symmetric quad Parylene beams with ZnO film). Because of its highly symmetric quad-beam bimorph structure and single proof mass, this tri-axis piezoelectric accelerometer has high sensitivity, low cross-axial sensitivity, good linearity and compact size. The un-amplified sensitivities of the X, Y and Z-axis electrodes in response to accelerations in X, Y and Z-axis are 0.93 mV/g, 1.13 mV/g and 0.88 mV/g, respectively. The minimum detectable signal is measured to be 0.04 g over a subHz /spl sim/100 Hz bandwidth. The cross-axial sensitivity among the X, Y and Z-axis electrodes is less than 15%.

Flow sight meter and measurement method using flow sight meter

Abstract: PROBLEM TO BE SOLVED: To measure fluorescence or scattered light from a sample with high accuracy by aligning a sample flow with high accuracy with respect to the center position of a flow cell. SOLUTION: A bimorph piezoelectric element is distorted by impressing a voltage on the piezoelectric element, thereby distorting an internal flow tube with the piezoelectric element stuck thereon together with the piezoelectric element. The position of an opening end of the flow tube is displaced to adjust the position of the sample liquid flow with respect to the flow cell. COPYRIGHT: (C)2006,JPO&NCIPI

Time domain simulation and measurements for piezoelectric bimorphs

Abstract: The method of normal-mode expansion has been extended for time domain simulation of a piezoelectric bimorph, for arbitrary voltage excitations. An experimental method for time domain measurements is proposed and the logarithmic decrement technique is used for the estimation of the damping factor near the first resonance. The experimental setup consists of an auto-balancing bridge circuit and requires only an oscilloscope for measuring the input and output voltages. Resonant frequencies of the bimorph were also obtained by taking the FFT of the measured output voltage. For comparison purposes the method of normal-mode expansion in frequency domain was applied to obtain the driving point impedance of the bimorph near the first resonance. The value of the damping factor, computed through impedance measurements, was in agreement with the value computed using the logarithmic decrement technique.