PVDF loudspeakers are used for some applications in audio and could be used for applications in active control where light structures are needed, for example in aeronautics. For all these applications, it is necessary to be able to predict the acoustic response of such systems in order to help the designer. Some papers propose models for calculating the acoustic pressure radiated by these loudspeakers.
The following paper is based upon the latest improvements of MSPA Module of Stepping Piezo Actuator to provide an option for appropriated linear and rotary motional applications. Starting from breadboards, MSPA modules and stages have been developed to reach series of complex mechanisms.
Required improvements of piezoelectric elements actuation and measurement system efficiency and robustness are introduced as a critical feature for structural health monitoring (SHM) applications. An electronic module (Lamb wave detection system: LWDS) allowing to use each piezoelectric element in an array either in emission or reception mode is presented. The high commutation rate between these two states, for each transducer separately, is a key enhancement for SHM methods. The robustness of the sensor integration is also studied considering the patches size and bonding method. Coupled dispersion curve are introduced Comparison of FEM simulation and experiments of the piezo-electric coupling are presented. This work takes part of the H2020 REMAP project about adaptive aircraft maintenance planning.
This paper presents comparison between two excitation solutions for tubular ultrasonic transducer. The axial excitation is widespread in conventional ultrasonic transducer. The radial excitation is proposed in order to have an uniform acoustic energy all along the tube. This excitation approach is also proposed to allow the modularity by adding several tubes.
This paper investigates the use of Optimal Control (OC) theory to design Radio-Frequency (RF) pulses that actively control the spatial distribution of the MRI magnetization phase. The RF pulses are generated through the application of the Pontryagin Maximum Principle and optimized so that the resulting transverse magnetization reproduces various non-trivial and spatial phase patterns. Two different phase patterns are defined and the resulting optimal pulses are tested both numerically with the ODIN MRI simulator and experimentally with an agar gel phantom on a 4.7 T small-animal MR scanner. Phase images obtained in simulations and experiments are both consistent with the defined phase patterns. A practical application of phase control with OC-designed pulses is also presented, with the generation of RF pulses adapted for a Magnetic Resonance Elastography experiment. This study demonstrates the possibility to use OC-designed RF pulses to encode information in the magnetization phase and could have applications in MRI sequences using phase images.
This article presents a new motion encoding strategy to perform magnetic resonance elastography (MRE). Instead of using standard motion encoding gradients, a tailored RF pulse is designed to simultaneously perform selective excitation and motion encoding in presence of a constant gradient. The RF pulse is designed with a numerical optimal control algorithm, in order to obtain a magnetization phase distribution that depends on the displacement characteristics inside each voxel. As a consequence, no postexcitation encoding gradients are required. This offers numerous advantages, such as reducing eddy current artifacts, and relaxing the constraint on the gradients maximum switch rate. It also allows to perform MRE with ultra-short TE acquisition schemes, which limits T2 decay and optimizes signal-to-noise ratio. The pulse design strategy is developed and analytically analyzed to clarify the encoding mechanism. Finally, simulations, phantom and ex vivo experiments show that phase-to-noise ratios are improved when compared to standard MRE encoding strategies.
This study aims at evaluating Magnetic Resonance Elastography (MRE) as a reliable technique for the characterization of viscoelastic properties of soft tissues. Three phantoms with different concentrations of plastisol and softener were prepared in order to mechanically mimic a broad panel of healthy and pathological soft tissues. Once placed in a MRI device, each sample was excited by a homemade external driver, inducing shear waves within the medium. The storage (G’) and loss (G’’) moduli of each phantom were then reconstructed from MRE acquisitions over a frequency range from 300 to 1,000 Hz, by applying a 2D Helmholtz inversion algorithm. At the same time, mechanical tests were performed on four samples of each phantom with a High-Frequency piezo-Rheometer (HFR) over an overlapping frequency range (from 160 to 630 Hz) with the same test conditions (temperature, ageing). The comparison between both techniques shows a good agreement in the measurement of the storage and loss moduli, underlying the capability of MRE to noninvasively assess the complex shear modulus G* of a medium and its interest for investigating the viscoelastic properties of living tissues. Moreover, the phantoms with varying concentrations of plastisol used in this study show interesting rheological properties, which make them good candidates to simulate the broad variety of viscoelastic behaviors of healthy and pathological soft tissues.
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