High Power Synthetic Jet Actuator (SJA) based on compact piezoelectric actuators, have been developed and tested by CEDRAT TECHNOLOGIES (CTEC) and ONERA, under French National funding RAPID from DGA. This publication presents the modelling approach with early breadboarding results, the final design chosen for integration onto an aircraft airfoil mock-up, the performance test results on the SJA device prior integration, and the final aerodynamic performance test demonstration achieved at ONERA wind tunnel test facility.
In many in-situ instruments information about the mass of the sample could aid in the interpretation of the data and portioning instruments might require an accurate sizing of the sample mass before dispensing the sample. In addition, on potential sample return missions a method to directly assess the captured sample size would be required to determine if the sampler could return or needs to continue attempting to acquire sample.
This paper presents an overview of the preliminary design process and findings aimed at morphing of trailing edge (TE) control surfaces for rotorcraft. A design methodology for a camber morphing control surface is presented, although twist can also be induced by applying differential camber of the morphing section span. The concept investigated relies on utilizing conventional aircraft structures and materials for morphing purposes; thus, in essence, has the potential to fulfil the conflicting requirements of lightweight, flexibility and strength at the same time. Based on this concept, the preliminary design work shows that an active trailing edge camber morphing mechanism can be designed after careful considerations of design and actuation requirements. The numerical results presented also indicate that such a morphing scheme increases the 2D aerodynamic efficiency.
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.
To introduce in vivo multifrequency single‐shot magnetic resonance elastography for full‐FOV stiffness mapping of the mouse brain and to compare in vivo stiffness of neural tissues with different white‐to‐gray matter ratios. Brain mechanical properties influence many vital neurological functions including brain development, metabolism, and tissue repair. However, studying brain mechanical properties in a noninvasive fashion encounters a number of challenges including the fact that the brain is protected by the skull as well as the heterogeneous and complex geometry of the brain. At present, magnetic resonance elastography (MRE) is the sole modality allowing noninvasive measurement of in vivo brain mechanical properties in patients and small animals.