This paper reviews feasibility of piezoceramic-polymer composite, so called piezocomposite, materials for UUV sonar application. Focus is not only placed on high electro-acoustic transformation performance, also on mass productivity, which is achieved by introducing Powder Injection Molding(PIM) process. Theoretical piezocomposite design method is introduced with FEM verification. Samples, produced via PIM process, are tested and proved their feasibility as UUV sonar sensors.
Numerical modeling of a three-dimensional acoustic field coupled with a piezoelectric-elastic structure demands significant computation load even on modern high speed computers. In particular, when the wavelength is much smaller than the field scale, the size of the coupled model and its computation time can be excessively large. In this paper, MHSV (Modal Hankel Singular Value) based model reduction technique is employed to minimize the size of the coupled model. This model reduction technique enables us to compare both the radiated and reflected waves from a piezoelectric-elastic source in three dimensional space. Thus, it considers the possibility to fully suppress reflected waves by radiating controlled wave in three dimensional space.
Active control of sound reflection on a boundary of acoustic medium is studied based on the electro-acoustic multilayer
model and the feedback control. The acoustic medium boundary is made of multiple layers of elastic materials and two
electro-acoustic transducer layers that can transform acoustic signal to electric signal and vice versa. When acoustic
waves are incident on the boundary, the external control circuit receives the electric signal from the transducer that
measures acoustic pressure level on the boundary surface, properly filters the signal band and actuates the other
transducer so that actuated acoustic waves can suppress the reflection waves. Advantage of this active approach is in the
small thickness of the boundary layer configuration over passive absorption layers and in wider frequency band control
over other control algorithms. This paper discusses the controllability of the active boundary layers from the view of
time delay caused from the thickness of transducers layers, and its affect on the reflection control performance and
This paper presents a model reduction method based on modal coordinates and Modal Hankel Singular Values (MHSV). Model reduction has recently become one of the main topics among many numerical engineers, since a reduced model increases its flexibility and adaptability in synchronizing with other models in many numerical multi-physics applications. On the other hand, a full numerical model from various FEM/BEM tools has pin-point modeling accuracy over their modeling domain. The proposed model reduction method reduces the full size model to a smaller size while maintaining the modeling accuracy. The original model reduction theory is established based on state space model that describes a linear dynamic system as a first order differential matrix equation. The magnitude of each state variable is measured by the Hankel Singular Value (HSV), and the reduced model has state variables with large HSVs. In this paper, the model is described using modal coordinates system instead of state space, since most dynamic system is described as a second order system rather than first order. A modal Hankel singular value for each mode is introduced to measure the magnitude of the mode. A numerical example of coupled acoustic and piezoelectric models is included.
Smart structures incorporate sensors, actuators and control electronics that permit the structures to tailor their response to changes in the environment in an optimal fashion. The sensors and actuators are constructed from functional materials such as piezoelectric, electrostrictive, shape memory alloys and magnetostrictive materials and more recently using MEMS (Micro Electro Mechanical Systems) devices. All functional materials and devices therefrom involve coupled fields involving elastodynamic, viscoelastic, electric, magnetic and thermal fields. The materials are anisotropic and often nonlinear. Finite element modeling has been successfully used to model these complex structures. More recently, closed ioop numerical simulation of the tailored response of a smart structure has become possible by combining the finite element equations of the sensor response to applied dynamical and/or thermal loads to the input voltage or current to the actuators via a control algorithm. This hybrid approach permits us to simulate the response of the structure with feedback control. Simple feedback controllers have now been replaced by robust controllers that provide stability under a range of uncertainties and do not require a very accurate system model. The talk will present an overview of the approaches of various researchers and consider numerical applications and comparison with experiments for active vibration damping, noise control and shape modification.
The optimal control algorithm is one of the feasible feedback algorithms for vibration suppression of flexible structures. One of the commonly encountered problems of the optimal control implementation is the spillover problem. The spillover generally occurs when modeling a continuous structure that has infinite number of resonance modes as a nominal model with finite modes for controller design. This paper presents a design of an optimal controller that is low order and can prevent the spillover problem when the unmodeled resonance modes perturb the feedback control loop. For low order controller design, this paper proposes modal Hankel singular values (MHSV) for efficient nominal model reduction. Low order controller can be derived from the reduced nominal model. For design of more stable controller, this paper applies frequency dependent weight functions to the cost function. The weight functions prevent the spillover by making optimal controller not to excite the resonance modes that are not included in nominal model. The optimal controller is derived from the nominal model. This weight function approach optimizes the control performance and control stability by smoothening the discrepancy between the weights of on the modeled modes to be controlled and unmodeled modes to be stabilized. A finite element model is exploited to develop the controller and to test its control performance and stability against high resonance mode spillover.
Electro-active polymer actuators (EAPA) have been a topic of research interest in the recent decades due to their ability to produce large strains under the influence of relatively low electric fields as compared to commercially available actuators. This paper investigates the feasibility of EAPA for active and passive cabin noise control. The passive damping characteristics of EAPA were determined, by measuring the transmission loss of four samples of various thickness and composition in an anechoic chamber in the 200 - 2000 Hz frequency range. This was then compared to that of Plexiglas and silicone rubber sheets of comparable thickness. The transmission loss of EAPA and Plexiglas were observed to be about the same. The transmission loss of EAPA was greater than that of silicone rubber, of the same thickness. The experimental and theoretical results computed using the mass law agree well. EAPA produces a strain of 0.006 for an applied field of 1 V/m. The ability of EAPA to potentially provide active as well as passive damping in the low to intermediate frequency range, along with being light- weight, pliable and transparent, makes it attractive for noise control applications as active/passive windows or wall papers.
Active Noise Control has been an area of research interest in the recent decades with the goal of providing reduced noise levels in automobile and aircraft enclosures. Although digital controllers are adaptable and efficient, they lack the simplicity of analog controllers due to the requirement of a computer, D/A and A/D boards. Analog controllers on the other hand can be designed to be compact using current IC technology and hence are relatively very cheap. The following paper studies the application of an analog robust controller to abate the noise radiated into a non-reverberant wooden enclosure by a clamped aluminum plate. Since only the odd-odd modes radiate efficiently, a SISO robust analog controller was designed and built inexpensively for a piezoelectric actuator and accelerometer sensor placed at the center of the plate. A reduction of 17 dB is observed when the panel is excited at its fundamental frequency, the dominant radiating mode. When the plate is excited with narrowband noise (40 - 316 Hz), the controller reduces the noise levels in the enclosure by 9 dB. The experimental results agree well with the controller simulation carried out using MATLAB.