Two electro-mechanical actuators are examined for a semi­ active Helmholtz resonator acoustic device. The device is used to reflect narrowband noise back to the source in an acoustic duct. The controller and actuator are used to tune the system on-line allowing optimum performance over a range of operating conditions. Actuator. dynamics play an important role in the controller design and the op...

Sound can be described as the propagation of pressure variations in compressible media that involves compression and expansion and induces a change in the density of the medium. This change in acoustic pressure as it induces a change of the refractive index can be measured by optical methods, the most recent being the optical feedback interferometry. With this technique, a laser diode is beamin...

Present work focuses on experimental acoustic characterization of an engine beauty cover in far field and near field conditions. Specifically, a comparison between results coming from the two different experimental measurement techniques is presented. Experimental campaign has been carried out on a car engine compartment at different operating conditions, by using on one hand a typical pressure...

In this article the calculation, along with practical examples of near and far fields of acoustic antennas are presented. Knowing the near and far fields is important because the radiation patterns and physical measurements of the antennas depend on them. These antennas designed for measurements in air consist of transducers in flexural vibration, which give the best possibility to match acoust...

What are shock waves? Extracorporeal shock waves are pressure waves generated outside the body that can be focused at a specific site within the body. Shock waves are characterized by high positive pressures, up to 100 MPa (over 100 times atmospheric pressure), and negative pressures of 5-10 MPa. They have a rapid rise time of 30-120 nanoseconds (10-9) and a short, 5 microsecond (10-6) pulse du...

An acoustic energy density probe is a sensor that uses multiple pressure transducers to measure acoustic energy density. Calibrating each pressure transducer an acoustic energy density probe at the same time is a difficult problem because the pressure transducers have a unique location and orientation. Two main issues arise that are involved in simultaneous calibration. The first issue is a uni...

Reversible and localized blood-brain barrier disruption (BBBD) using focused ultrasound (FUS) in combination with intravascularly administered microbubbles (MBs) has been established as a non-invasive method for drug delivery to the brain. Using two-photon fluorescence microscopy (2 PFM), we imaged the cerebral vasculature during BBBD and observed the extravasation of fluorescent dye in real-ti...