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Showing papers on "Active vibration control published in 2008"


Journal ArticleDOI
TL;DR: In this paper, the optimal placement of collocated piezoelectric actuator?sensor pairs on flexible beams using a model-based linear quadratic regulator (LQR) controller is considered.
Abstract: This paper considers the optimal placement of collocated piezoelectric actuator?sensor pairs on flexible beams using a model-based linear quadratic regulator (LQR) controller. A finite element method based on Euler?Bernoulli beam theory is used. The contributions of piezoelectric sensor and actuator patches to the mass and stiffness of the beam are considered. The LQR performance is taken as the objective for finding the optimal location of sensor?actuator pairs. The problem is formulated as a multi-input multi-output (MIMO) model control. The discrete optimal sensor and actuator location problem is formulated in the framework of a zero?one optimization problem which is solved using genetic algorithms (GAs). Classical control strategies like direct proportional feedback, constant gain negative velocity feedback and the LQR optimal control scheme are applied to study the control effectiveness. The study of the optimal location of actuators and sensors is carried out for different boundary conditions of beams like cantilever, simply supported and clamped boundary conditions.

186 citations


Book
03 Dec 2008
TL;DR: In this article, a comparison of passive, active and hybrid control methods for wind-excitation control in Civil Structures is presented, based on a Lumped Modeling Approach.
Abstract: About the Authors. Preface. Acknowledgements. 1 Active Damping. 1.1 Introduction. 1.2 Structural Control. 1.3 Plant Description. 1.4 Equations of Structural Dynamics. 1.5 Collocated Control System. 1.6 Active Damping with Collocated System. 1.7 Decentralized Control with Collocated Pairs. 2 Active Isolation. 2.1 Introduction. 2.2 Relaxation Isolator. 2.3 Sky-hook Damper. 2.4 Force Feedback. 2.5 Six-Axis Isolator. 2.6 Vehicle Active Suspension. 2.7 Semi-Active Suspension. 3 A Comparison of Passive, Active and Hybrid Control. 3.1 Introduction. 3.2 System Description. 3.3 The Dynamic Vibration Absorber. 3.4 Active Mass Damper. 3.5 Hybrid Control. 3.6 Shear Control. 3.7 Force Actuator, Displacement Sensor. 3.8 Displacement Actuator, Force Sensor. 4 Vibration Control Methods and Devices. 4.1 Introduction. 4.2 Classification of Vibration Control Methods. 4.3 Construction of Active Dynamic Absorber. 4.4 Control Devices for Wind Excitation Control in Civil Structures. 4.5 Real Towers Using the Connected Control Method. 4.6 Application of Active Dynamic Absorber for Controlling Vibration of Single-d.o.f. Systems. 4.7 Remarks. 5 Reduced-Order Model for Structural Control. 5.1 Introduction. 5.2 Modeling of Distributed Structures. 5.3 Spillover. 5.4 The Lumped Modeling Method. 5.5 Method of Equivalent Mass Estimation. 5.6 Modeling of Tower-like Structure. 5.7 Modeling of Plate Structures. 5.8 Modeling of a Bridge Tower. 5.9 Robust Vibration Control for Neglected Higher Modes. 5.10 Conclusions. 6 Active Control of Civil Structures. 6.1 Introduction. 6.2 Classification of Structural Control for Buildings. 6.3 Modeling and Vibration Control for Tower Structures. 6.4 Active Vibration Control of Multiple Buildings Connected with Active Control Bridges in Response to Large Earthquakes. 6.5 Vibration Control for Real Triple Towers Using CCM. 6.6 Vibration Control of Bridge Towers Using a Lumped Modeling Approach. 6.7 Conclusion. References. Index.

152 citations


Journal ArticleDOI
TL;DR: This paper illustrates that MPC can be implemented on inexpensive hardware at high sampling rates using traditional online quadratic programming methods for nontrivial models and with significant control performance dividends.
Abstract: The difficulties imposed by actuator limitations in a range of active vibration and noise control problems are well recognized. This paper proposes and examines a new approach of employing model predictive control (MPC). MPC permits limitations on allowable control action to be explicitly included in the computation of an optimal control action. Such techniques have been widely and successfully applied in many other areas. However, due to the relatively high computational requirements of MPC, existing applications have been limited to systems with slow dynamics. This paper illustrates that MPC can be implemented on inexpensive hardware at high sampling rates using traditional online quadratic programming methods for nontrivial models and with significant control performance dividends.

118 citations


Journal ArticleDOI
TL;DR: Passive means of vibration attenuation have been employed successfully and efficiently in machining systems such as turning and milling as discussed by the authors, and traditional approach to controlling vibration in a milling s...
Abstract: Passive means of vibration attenuation have been employed successfully and efficiently in machining systems such as turning and milling. Traditional approach to controlling vibration in a milling s ...

107 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed an active vibration control scheme for controlling transverse vibration of a rotor shaft due to unbalance and presented a theoretical study, which uses electromagnetic exciters mounted on the stator at a plane, in general away from the conventional support locations, around the rotor shaft for applying suitable force of actuation over an air gap to control transverse vibrations.

86 citations


Journal ArticleDOI
TL;DR: In this paper, the optimum parameters of a dynamic vibration absorber of non-traditional form have been derived for suppressing vibration of a single degree-of-freedom system due to ground motion, and the reduction of transmission of motion from the support to the mass of the structure is compared for the cases of using the traditional and the proposed dynamic absorbers.

80 citations


Journal ArticleDOI
TL;DR: In this paper, an output feedback approach is described that makes use of measured receptances, there being no requirement at all for the M, C, K matrices usually obtained by finite elements.

80 citations


Journal ArticleDOI
TL;DR: In this article, a dual-stage control system design method for the three-axis rotational maneuver control and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensor and actuator is presented.
Abstract: This paper presents a dual-stage control system design method for the three-axis-rotational maneuver control and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensor and actuator. In this design approach, the attitude control system and vibration suppression were designed separately using a lower order model. Based on the sliding mode control (SMC) theory, a discontinuous attitude control law in the form of the input voltage of the reaction wheel is derived to control the orientation of the spacecraft actuated by the reaction wheel, in which the reaction wheel dynamics is also considered from the real applications point of view. The asymptotic stability is shown using Lyapunov analysis. Furthermore, an adaptive version of the proposed attitude control law is also designed for adapting the unknown upper bounds of the lumped disturbance so that the limitation of knowing the bound of the disturbance in advance is released. In addition, the concept of varying the width of boundary layer instead of a fixed one is also employed to eliminate the chattering and improve the pointing precision as well. For actively suppressing the induced vibration, modal velocity feedback and strain rate feedback control methods are presented and compared by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque and parameter uncertainty.

71 citations


Journal ArticleDOI
TL;DR: In this article, a degenerate shell element for modeling and analysis of multilayer composite general shell structures with bonded/embedded distributed PZT sensors and actuators is presented.
Abstract: This paper deals with the formulation of a nine-noded piezolaminated degenerated shell finite element for modeling and analysis of multilayer composite general shell structures with bonded/embedded distributed piezoelectric sensors and actuators. The distributed PZT sensors and actuators used in the composite smart structures are relatively thin and could have arbitrary variation of curvatures and thicknesses. They cannot be modeled with shell elements based on curvilinear shell theories which would need the specification of constant shell curvatures and thicknesses. Modeling them with piezo finite elements available in popular commercial codes like ABAQUS, ANSYS, MARC, etc, would need relatively greater computational effort as they are based on solid element formulation. In view of these, the present proposed degenerated piezoelectric shell element would be a better choice giving good computational accuracy and efficiency. The main advantage of a degenerate shell element is that it is not based on any shell theories and is applicable over a wide range of curvatures and thicknesses. This element is developed by using the degenerate solid approach based on Reissner–Mindlin assumptions which allow the shear deformation and rotary inertia effect to be considered and the 3D field is reduced to a 2D field in terms of mid-surface nodal variables. Uniformly reduced integration is carried out to overcome membrane locking and shear locking and the numerical integration is carried out in all three directions to obtain accurate results. The present element has 45 elastic degrees of freedom and 10 electric degrees of freedom per piezoelectric layer in the element. The potential induced due to bending deformation is more accurately represented by assuming quadratic variation of the electric potential through the thickness of each piezoelectric layer. This is achieved by interpolating using nodal mid-plane electric potentials and one electric degree of freedom representing the potential difference between the top and bottom surfaces of the piezoelectric layer. Few case studies of composite general shells with piezoelectric sensors and actuators have been considered by modeling them with the above elements and the active vibration control performance has been studied using linear quadratic Gaussian (LQG) control.

51 citations


Journal ArticleDOI
TL;DR: In this paper, an analytical methodology is presented to study the active vibration control of beams treated with active constrained layer damping (ACLD), which is based on the conventional theory of structural dynamics.
Abstract: An analytical methodology is presented to study the active vibration control of beams treated with active constrained layer damping (ACLD). This analytical method is based on the conventional theory of structural dynamics. The process of deriving equations is precise and easy to understand. Hamilton's principle with the Rayleigh–Ritz method is used to derive the equation of motion of the beam/ACLD system. By applying an appropriate external control voltage to activate the piezoelectric constraining layer, a negative velocity feedback control strategy is employed to obtain the active damping and effective vibration control. From the numerical results it is seen that the damping performances of the beam can be significantly improved by the ACLD treatment. With the increase of the control gain, the active damping characteristics are also increased. By equally dividing one ACLD patch into two and properly distributing them on the beam, one can obtain better active vibration control results than for the beam with one ACLD patch. The analytical method presented in this paper can be effectively extended to other kinds of structures.

50 citations


01 Jan 2008
TL;DR: In this article, a short review of the rotor-induced vibration problem is given with a link to typical vibration characteristics of Eurocopter helicopters, and the concepts and means to influence and control vibrations are outlined.
Abstract: This paper is about recent advances in Eurocopter’s research activities on passive and active vibration control systems. Emphasis is placed on the reduction of rotor-induced vibrations which is still one of the key challenges in helicopter dynamics. Both passive and active means for the reduction of vibrations are discussed. A short review of the rotor-induced vibration problem is given with a link to typical vibration characteristics of Eurocopter helicopters. The concepts and means to influence and control vibrations are outlined. The main focus of this paper is on recent advances on i) vibration control at the rotor, ii) vibration control at the transmission and iii) vibration control at the fuselage. In the section “vibration control at the rotor”, vibrations are attacked at their source – the rotor itself. Advanced passive and active rotor dynamic layouts are of interest. Here, a 5-bladed bearingless vs. 4bladed main rotor system on EC145 as well as an active flap rotor on the hingeless system of BK117 are discussed. For each system, key parameters of the design, data of the test configuration and test environment and in particular results on vibration reduction are presented. A substantial reduction of the exciting hub loads is achieved thus providing superior airframe vibration levels. In the section “vibration control at the transmission”, a new generation of pylon isolation system is presented. This passive system based on the SARIB principle combines advantages of efficiency, lightness, reliability and low cost design. This technology consists of a compact suspension and a flapping mass integrated in each gear box strut. It provides an important attenuation of the vibrations for all hub loads components and it was successfully tested in-flight. In the section “vibration control at the fuselage”, active anti-vibration control systems (AVCS) installed in the fuselage are presented. The systems rely on single-port active devices which are capable to generate inertia-based control forces which induce a secondary vibration field to compensate the vibration disturbance. Here, systems based on electromagnetic actuation technology for EC225 as well as Piezo-ceramic technology demonstrated on EC135 are presented.

Journal ArticleDOI
TL;DR: In this article, the performance potential of a new hardware combination for active suspension systems is presented, which consists of a low bandwidth actuator and a continuously variable damper, a setup that is shown to be competitive to high bandwidth active suspension system especially if energy, cost and implementability aspects are taken into account.

Journal ArticleDOI
TL;DR: In this article, the active vibration control of a cylindrical shell partially covered by a laminated PVDF actuator (LPA) is studied. And the authors derived the electromechanically coupled equations of the system considering the influences of the bonding layers.
Abstract: Active vibration control of a cylindrical shell partially covered by a laminated PVDF actuator (LPA) is studied. The electromechanically coupled equations of the system are derived considering the influences of the bonding layers. The analytical expressions of the control forces induced by the LPA are obtained and thereafter a parametric study is conducted to evaluate the effects of the physical properties of the actuator on the control forces. The active vibration control of a clamped–free cylindrical shell using an LPA with different layer numbers is simulated and carried out experimentally. It shows that the control forces of the actuator can be significantly enhanced by increasing the PVDF layer number while keeping the driving voltage unchanged. As a result, the modal vibrations of the shell are suppressed quite well (the vibration amplitude is cut by 64.08%) under a relatively low control voltage (40 V) with a five-layer LPA whose area is only 0.21% of that of the shell. Additionally, as the LPA partially covers the shell surface along the circumferential direction, it can exert a radial actuating force on the structure except for the actuating moment, and the former is much larger than the latter and is thus preferable for controlling the structural radial vibration. To make full use of this actuating force, the actuator should not be placed at a point of large surface strain as is usual but at one of large radial deformation.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the application of model predictive control technology based on mixed H2/H-inf control approach for active suspension control of a railway vehicle, the aim being to improve the ride quality of the railway vehicle.
Abstract: This paper investigates the application of model predictive control technology based on mixed H2/H-inf control approach for active suspension control of a railway vehicle, the aim being to improve the ride quality of the railway vehicle. Comparisons are made with more conventional control approaches, and the applicability of the linear matrix inequality approach is illustrated via the railway vehicle example

Journal ArticleDOI
TL;DR: In this paper, a pole placement controller for active vibration suppression of a smart flexible cantilever beam with piezoceramic actuator and sensor by using a nonparametric identification for the dynamics of the first three modes is carried out.
Abstract: This study presents results of multimodal vibration suppression of a smart flexible cantilever beam with piezoceramic actuator and sensor by using a pole placement controller. Piezoceramic PZT (lead zirconate titanate) patches are surface-bonded on the beam and function as actuator and sensor. Nonparametric identification for the dynamics of the first three modes is carried out. From the nonparametric model, a parametric model is identified to assist the control system design. The identified model is used for state estimation and development of control algorithm. A linear pole placement controller is designed and simulated using the identified model. Experimental results demonstrate the effectiveness of observer-based multimodal active vibration control of the structure using piezoceramic smart materials.

Journal ArticleDOI
TL;DR: In this paper, a robust saturation controller is applied to the linear structure with an active mass damper, which involves both control input saturation and structured real parameter uncertainties, and its applicability is verified through experimental tests in the laboratory for a two-story test structure equipped with a hydraulic-type active massdamper.

Journal ArticleDOI
TL;DR: In this paper, an active vibration control technique using seismic masses that are actuated by means of piezo actuators to create forces on the gradient coil counteracting its vibrations is presented. But the method is not suitable for MRI systems.
Abstract: Lorentz-force-induced vibrations in MRI systems cause significant acoustic noise levels during scanning, the main acoustic noise source being the vibrating gradient coil. In this paper, a novel active vibration control technique is presented to reduce vibrations of the gradient coil, and hence, achieve a reduction of acoustic noise during scanning. The active vibration control technique uses seismic masses that are actuated by means of piezo actuators to create forces on the gradient coil counteracting its vibrations. Using four seismic mass actuators, a vibration reduction of 3-8 dB at resonance frequencies is achieved, giving an overall vibration reduction of 3 dB for a typical field gradient (FE)-echo planar imaging (EPI) gradient sequence, as substantiated by measurements. Using eight actuators, an overall vibration reduction of 5 dB is predicted for this sequence.

Journal ArticleDOI
TL;DR: In this article, an active reduction of mechanical vibration using an electrohydraulic actuator has been proposed, where the energy recuperated from the first suspension DOF is transferred by dedicated hydraulic system and stored in an accumulator.
Abstract: Studies of systems with energy regeneration have been carried out for years, because they primarily cover the assemblies with electrodynamic actuators. This paper addresses the issue of active reduction of mechanical vibration using an electrohydraulic actuator. The testing procedure aims to assess the potential use of those assemblies in a different frequency band and force range than in electrodynamic actuators. The paper explains the operating principle of the system, and the findings of laboratory tests are presented. The tested vibration reducing system is the physical model of a 2 degree-of-freedom (DOF) suspension. An initial analysis has been conducted to explore the potential use of the energy produced by the vibration of unsprung mass in the first degree of the suspension system, for power supply to the active component incorporated in the second suspension degree.The energy recuperated from the first suspension DOF is transferred by a dedicated hydraulic system and stored in an accumulator. Res...

Journal ArticleDOI
TL;DR: In this paper, a methodology for calculating the gains of an output feedback controller for active vibration control of flexible rotors is presented, based on modal reduction, which is applied to an industrial gas compressor supported by active tilting-pad journal bearings.
Abstract: This article presents a methodology for calculating the gains of an output feedback controller for active vibration control of flexible rotors. The methodology is based on modal reduction. The proportional and derivative gains are obtained by adjusting the first two damping factors of the system and keeping the lengths of the two eigenvalues constant in the real-imaginary plane. The methodology is applied to an industrial gas compressor supported by active tilting-pad journal bearings. The unbalance response functions and mode shapes of the flexible rotor with and without active control are presented, showing significative improvement in damping reserve with the control. The importance of sensor location is emphasized, on the basis of the energy necessary to operate the active system over the entire frequency range studied. The best results are obtained by a decentralized controller, observing displacement and velocity of the shaft at the bearing positions.

Journal ArticleDOI
TL;DR: In this article, a modal controller is implemented on a digital controller board, and experimental tests with the floor panel and center panel of a car body are carried out to validate the proposed concept.

Journal ArticleDOI
TL;DR: This paper presents a multi-objective fuzzy logic controller (PSO-FLC) for active vibration control of seismically exited buildings by combining a new self configurable multi- objective PSO (particle swarm optimisation) algorithm with fuzzy logic Controller.

Journal ArticleDOI
TL;DR: In this paper, a finite element model is developed for the active control of thermally induced vibration of laminated composite shells with piezoelectric sensors and actuators, which takes into account the mass, stiffness and thermal expansion of the piezothermoelastic patches.
Abstract: Shell type components and structures are very common in many mechanical and structural systems. Modeling and analysis of adaptive piezothermoelastic shell laminates represent a high level of sophistication and complexity. In this paper a finite element model is developed for the active control of thermally induced vibration of laminated composite shells with piezoelectric sensors and actuators. The present model takes into account the mass, stiffness and thermal expansion of the piezoelectric patches. A Co continuous nine-node degenerated shell element is implemented to model the structure. The piezoelectric sensing layer senses the structural vibration and a suitable voltage applied in the piezoelectric actuator layer suppresses the oscillation. Actuator and sensor are coupled together with a control algorithm so as to actively control the dynamic response of the structure in a close loop. Numerical results are generated for a cylindrical shell and it is observed that thermally induced vibration of a laminated cylindrical shell can be suppressed through the application of piezoelectric sensor and actuator. Effects of variation in control gain and piezoelectric layer area coverage (PAC) have been studied. Higher control gain is more effective in damping out the vibration. Although the damping is enhanced by increase in PAC, increase beyond a certain level may not be useful in view of smaller efficacy and increased weight.

Proceedings ArticleDOI
19 Dec 2008
TL;DR: This paper demonstrates an active vibration control system of flexible structures by using piezoelectric sensors and actuators, and a LQR controller is designed based on the independent mode space control techniques to suppress the vibration of the system.
Abstract: This paper demonstrates an active vibration control system of flexible structures by using piezoelectric sensors and actuators. A set of vibration control equations, sensing equations and actuating equations are derived through using the modal theory for piezoelectric flexible structures, then the model is converted into the state space form. With recent developments in sensors/actuators technologies, many researchers have concentrated on control methods for suppressing vibration of the structures using smart materials such as piezoelectric transducers (PZT). In this paper, two piezoelectric patches are collocated on both sides of the same position of the structure which used as modal sensors and actuators, and the optimal location of them is ascertained by the function of displacement deflection, a LQR controller is designed based on the independent mode space control techniques to suppress the vibration of the system. Finally, the paper takes a piezoelectric cantilever beam as an example, and gives the control simulation results which demonstrate the effectiveness of the method in this paper.

Journal ArticleDOI
TL;DR: In this article, a multi-mode structural vibration control in the composite fin-tip of an aircraft is proposed using particle swarm based evolutionary optimization technique for optimal placement of piezoelectric patch actuators.
Abstract: The goal of this study is the multi-mode structural vibration control in the composite fin-tip of an aircraft. Structural model of the composite fin-tip with surface bonded piezoelectric actuators is developed using the finite element method. The finite element model is updated experimentally to reflect the natural frequencies and mode shapes accurately. A model order reduction technique is employed for reducing the finite element structural matrices before developing the controller. Particle swarm based evolutionary optimization technique is used for optimal placement of piezoelectric patch actuators and accelerometer sensors to suppress vibration. H{infty} based active vibration controllers are designed directly in the discrete domain and implemented using dSpace® (DS-1005) electronic signal processing boards. Significant vibration suppression in the multiple bending modes of interest is experimentally demonstrated for sinusoidal and band limited white noise forcing functions.

Journal ArticleDOI
TL;DR: In this paper, a rectangular aluminium plate vibrating in air or in contact with water is investigated, and a filtered-x least mean square (FXLMS) adaptive feedforward algorithm is applied to the system, realising structural vibration control in linear field with a SISO approach.

Journal ArticleDOI
TL;DR: In this article, a study on the vibration attenuation in an isolated platform by combining multi-layer perception (MLP) neural network, radial basis function (RBF), cerebella model articulation controller (CMAC), and fuzzy neural networks (FNN) with error back propagation algorithm to control voice coil actuator is presented.

Journal ArticleDOI
01 Sep 2008-Robotica
TL;DR: Spectral analyses of structural vibrations illustrate that deformations from structural vibration of flexible links are suppressed to a significant extent when the proposed vibration control strategy is employed, while the deflections caused by inertial and coupling forces are not reduced.
Abstract: This paper addresses the dynamic simulation and control of structural vibrations of a 3-PRR parallel manipulator with three flexible intermediate links, to which are bonded lead zirconate titanate (PZT) actuators and sensors Flexible intermediate links are modelled as Euler–Bernoulli beams with pinned-pinned boundary conditions A PZT actuator controller is designed based on strain rate feedback (SRF) control Control moments from PZT actuators are transformed to force vectors in modal space and are incorporated in the dynamic model of the manipulator The dynamic equations are developed based on the assumed mode method for the flexible parallel manipulator with multiple PZT actuator and sensor patches Numerical simulation is performed and the results indicate that the proposed active vibration control strategy is effective Spectral analyses of structural vibrations further illustrate that deformations from structural vibration of flexible links are suppressed to a significant extent when the proposed vibration control strategy is employed, while the deflections caused by inertial and coupling forces are not reduced

Journal ArticleDOI
TL;DR: In this article, the authors developed a novel approach to vibration energy harvesting, including adaptation to non-periodic vibrations so as to extract the maximum amount of vibration energy available, using an off-the-shelf transducer.
Abstract: By scavenging energy from their local environment, portable electronic devices such as MEMS devices, mobile phones, radios and wireless sensors can achieve greater run times with potentially lower weight. Vibration energy harvesting is one such approach where energy from parasitic vibrations can be converted into electrical energy through the use of piezoelectric and electromagnetic transducers. Parasitic vibrations come from a range of sources such as human movement, wind, seismic forces and traffic. Existing approaches to vibration energy harvesting typically utilize a rectifier circuit, which is tuned to the resonant frequency of the harvesting structure and the dominant frequency of vibration. We have developed a novel approach to vibration energy harvesting, including adaptation to non-periodic vibrations so as to extract the maximum amount of vibration energy available. Experimental results of an experimental apparatus using an off-the-shelf transducer (i.e. speaker coil) show mechanical vibration to electrical energy conversion efficiencies of 27–34%.

Journal ArticleDOI
TL;DR: Experimental results on a skin panel of a Boeing 717 aircraft prove the effectiveness of the proposed approach in practical complex applications, with global vibration reduction performances.

Patent
Chienliu Chang1
19 Sep 2008
TL;DR: In this article, an electromechanical transducer includes a vibration membrane with a first electrode, a substrate provided with a second electrode, and a support member adapted to support the vibration membrane in such a way that a gap is formed between the vibrational membrane and the substrate, with the first and second electrodes being arranged in opposition to each other.
Abstract: An electromechanical transducer includes a vibration membrane provided with a first electrode, a substrate provided with a second electrode, and a support member adapted to support the vibration membrane in such a manner that a gap is formed between the vibration membrane and the substrate, with the first and second electrodes being arranged in opposition to each other, wherein a part of the vibration membrane and a part of the substrate are in contact with each other at a contact region, and another region of the vibration membrane other than the contact region is able to vibrate; an overlap region is provided between the first electrode and second electrode in the contact region, and at least one of these electrodes has a through portion formed therethrough in at least a part of the overlap region, and a plurality of protrusions formed within the gap and on at least one of the vibration member and the support member, wherein the contact region is surrounded by the plurality of protrusions.