Index of content:
Volume 119, Issue 5, May 2006
- ARCHITECTURAL ACOUSTICS 
The influence of circumferential edge constraint on the acoustical properties of open-cell polyurethane foam samples119(2006); http://dx.doi.org/10.1121/1.2185494View Description Hide Description
In this paper, a three-dimensional Laplace domain finite element model with four-node tetrahedral porous elements is developed and applied for the investigations. Without the incident acoustic field, the exact acoustical properties of a laterally infinite planar foam, which is backed with a rigid plane, are accurately predicted by assuming the circumferential edge constraints as rollers. It is found that the rigidity of the circumferential edge constraint has a profound effect on the predictions. If the circumferential edge constraints are all fixed, the amplitude of the first sound absorption peak is increased, and the peak is moved to a lower frequency as compared with the exact solutions.Measurements obtained by the two-microphone impedance tube method are bounded by the predictions of samples with roller as well as with fixed constraints. They are much closer to that predicted with fixed edge constraints. Upon increasing the diameter-to-thickness ratio of the sample, the influence of the fixed edge constraint is reduced. The measured acoustic results can be the representatives of the laterally infinite planar foam from which the sample was cut only if the roller edge constraint of the sample is managed or the diameter-to-thickness ratio of the sample is increased.
Piezoelectric vibration control by synchronized switching on adaptive voltage sources: Towards wideband semi-active damping119(2006); http://dx.doi.org/10.1121/1.2184149View Description Hide Description
Synchronized switch damping (SSD) principle and derived techniques have been developed to address the problem of structural damping. Compared with standard passive piezoelectric damping, these new semi-passive techniques offer the advantage of self-adaptation with environmental variations. Unlike active damping systems, their implementation does not require any sophisticated signal processing nor any bulky power amplifier. This paper presents an enhancement of the SSD technique on voltage source (SSDV) which is the most effective of the SSD techniques. The former SSDV technique uses a constant continuous voltage sources whereas the proposed enhancement uses an adaptive continuous voltage source which permits fitting the mechanical braking force resulting from the SSDV process to the vibration level. A theoretical analysis of the SSDV techniques is proposed. Experimental results for structural damping under single frequency and for vibration control of a smart board under white noise excitation are presented and confirm the interest of the enhanced SSDV compared to other SSD techniques. Depending on the excitation type, a 4- to 10-dB damping gain can be achieved.