Active control of a lumped acoustic source driven by various actuators

This paper studies an acoustic source with a relatively small thickness and high bending stiffness. The high bending stiffness is obtained with a sandwich structure in which the face of the sandwich structure internal to the source is perforated to increase the acoustic compliance. Multiple actuators are used to drive the moving component of the acoustic source. Feedback and feedforward damping control techniques are used to actively obtain a smooth frequency response, especially at low frequencies. Such a compensation scheme generally leads to amplification of the lower frequencies and may result in a significant electrical input power. In addition, a part of the input power is stored in mechanical and acoustical elements of the acoustic source. Voice coil and piezoelectric actuators are compared regarding the ability to recover the stored energy. Piezoelectric actuators are particularly attractive from energy recovery point of view because the acoustic source has to operate in the low frequency, quasi-static regime. The two-way energy ?ow between the actuator and a connected ampli?er is investigated. In particular, the effectiveness of energy recovery from the reactive components of the acoustic source is evaluated to improve the overall radiation ef?ciency. A lumped model is used to represent the acoustic source that is excited by a stacked piezoelectric element. The required power supply and resulting radiation ef?ciency are evaluated when a conventional analogue ampli?er is used. The result is compared to the case in which some parts of the stored power are recovered and sent back to the connected switching amplifier. It was found that approximately 66% of the reactive power stored in the acoustic source can be recovered. The study also reveals a significant increase in overall system ef?ciency and more than 80% decrease in the amount of required input power through recovering the reactive power in the system

Numerical modeling of a flexural displacement-converter mechanism to excite a flat acoustic source driven by piezoelectric stack actuators

This paper studies an acoustic source with a relatively small thickness and high bending stiffness. The acoustic source operates in the low frequency, quasi-static regime. The focus of the current study is on the actuation part in order to design an appropriate excitation mechanism. A flexural mechanism is modeled in combination with piezoelectric actuators to convert an in-plane displacement of the actuators to a perpendicular out-of-plane direction. First, an optimization simulation is used to determine the size of the required piezoelectric actuator. Then an equivalent electrical circuit of the lumped acoustic source is developed. This equivalent circuit can directly be connected to the electrical model of a switching amplifier. Finally, a coupled numerical finite element analysis is carried out by using COMSOL Multiphysics software package to model the combination of both flexural mechanism and piezoelectric device. The suggested flexural mechanism is sufficiently narrow to overcome the space limitation challenge in the design

Numerical modeling of a lumped acoustic source actuated by a piezoelectric stack device that is driven by a switching amplifier

This paper studies an acoustic source with a relatively small thickness and high bending stiffness. Piezoelectric actuators are used to drive the moving component of the acoustic source. In the current study, a lumped model is used to represent the acoustic source that is excited by a piezoelectric stacked actuator. The equivalent electrical circuit of the lumped acoustic source can directly be connected to the electrical circuit of a switching amplifier. Various methods are used to estimate the radiation impedance of the acoustic source. The effectiveness of these methods is investigated when they are used in combination with the equivalent electrical circuit of the lumped acoustic source, the actuator and the amplifier. Finally, result of a numerical finite element simulation is compared with the results of the fully-lumped equivalent electrical circuit

Energy-efficient low-frequency flat acoustic source: analysis, design and experimental validation

There is a need for compact acoustic sources that operate at low frequencies. These acoustic sources can be employed to produce good quality sound in the low frequency range. A problem arising when the acoustic sources operate at low frequencies is that the acoustical power is not always enough to allow for sound to be emitted in the form of propagating waves. As a rule of thumb, in the low frequency range the larger the enclosure volume of acoustic sources, the greater the radiated acoustical power. Therefore, in the applications with limited build space it is difficult to compensate for the sufficient acoustic power of the radiators. A thin sandwich acoustic source with a large surface area and a relatively small thickness that is integrated with an internal cavity can fulfill the need for both large enclosure volume and limited build space. The sandwich structure makes the thin acoustic source light-weight and stiff. Therefore, the resulting acoustic source has a reasonably high fundamental resonance frequency. An inefficient acoustic source consumes extra input electric energy, which causes energy loss and high energy expenses. The existence of an appropriate electrical amplifier in combination with the piezoelectric devices is crucial to achieving an energy-efficient thin acoustic source. An appropriate combination of the actuators and amplifiers is investigated in this research. Due to the limited build space in the low-frequency applications, a need for a compact design of the piezoelectric stack actuators arises. An appropriate auxiliary flexural mechanism is investigated for use as an appropriate driver in the limited space of the thin acoustic source. The resulting acoustic source is thin and energy-efficient and can be used in the low frequency operations. The motivation of the present research is to design a compact energy-efficient actuation mechanism for the thin acoustic source that operates in the low-frequency range

An acoustic radiator with integrated cavity and active control of surface vibration

This paper presents a method to realize an acoustic source for low frequencies with relatively small thickness. A honeycomb plate structure which is open on one side combines the radiating surface and the major part of the air cavity. The vibration of the plate is controlled with a decentralized feedback controller. The fundamental resonance is controlled, as well as higher-order bending modes, while avoiding possible instabilities due to the fluid-structure interaction. The smooth and well defined frequency response enables robust feedforward control for further response equalization. The influence of different actuation principles on the overall system efficiency is compared

A low-profile flexural displacement-converter mechanism for piezoelectric stack actuators

A thin flexure-based mechanism is proposed that is useful in applications with limited build space. The proposed mechanism converts the initial in-plane motion of two piezoelectric stack actuators to an out-of-plane translational motion. Two actuators in the symmetric design of the proposed APA can be used to ensure a pure translation output motion. A Finite Element (FE) model is used to analyze the rigid multibody model of the proposed mechanism. The rigid multibody model is used to design the desired flexural mechanism in a three-dimensional space. The proposed design is then manufactured and is subjected to an experimental study. Measurements validate the performance of the proposed design with an error of less than 15%. A parametric study on the effect of the applied voltage to the actuators of the proposed mechanism reveals good agreement between the numerical model and the manufactured mechanism