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Active control of the spatial MRI phase distribution with optimal control theory
7 November 2019
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.
A bistable piezoelectric harvester for wideband mechanical frequency excitation
19 June 2023
The developments of autonomous systems such as for self health monitoring, embedded systems are increasingly used in industrial applications. The energy supply is a key point for the development of such systems. Solutions based on battery have limited life time and the power supplies through wires aren’t always appropriate and easy to install. Furthermore, the battery recycling is complex and an expensive process. The researches on power supply through harvesting systems are increasing in the same way the autonomous systems.
Active control of vibrations of a space truss using amplified piezoelectric actuators
19 June 2023
The new piezo actuators manufactured by Cedrat Technologies have been developed for the positioning control of space optics but they are spreading widely in various engineering fields such as precise positioning, intelligent control of shapes and generation or control of vibrations. Their ability for the control or active damping of vibrations has been successfully demonstrated at the lab scale in space applications. In a first case, the piezo actuators were used for both for the control of launching vibrations and the positioning control in orbit of a telescope mirror. In a second set of space applications, these piezo actuators have been successfully integrated in a space truss using active tendons for control of micro vibrations, as publicly released at the Industry Space Days (ISD2001, Noordwijk, 9-10 Mai 2001) and as presented in this paper.
Fast and fine Steering Mirrors based on piezoelectric & magnetic actuator technologies for Air and Space
8 August 2022
This review presents CEDRAT TECHNOLOGIES (CTEC) solutions developed for more than 20 years for Fast & fine Steering Mirrors (FSM) as required in air, space, defence & other embedded or demanding applications: Typical appli-cations are for example Lidar, free space optical communication (FSO) and Laser interferometry.
Active flap device for helicopters based on Cedrat Amplified Piezoelectric Actuators
19 June 2023
A project called RPA (Rotor à Pales Actives) was launched three years ago to study the possible benefits of implementing active trailing edge flaps on a helicopter main rotor. The main objectives of this project are to decrease BVI noise in descent flight and improve the dynamic behavior of the rotor throughout the largest possible flight domain. After a first phase dedicated to the design of the best flap configuration at scale 1, the second phase of the project deals with the design of a wind-tunnel scale model of a rotor equipped with active flaps. An off-the-shelf piezo-electric actuator is used together with a specific patented flap-driving mechanism. Such an active device was tested under centrifugal loads as well as under aerodynamic loads in order to prepare future wind-tunnel tests. The results obtained under centrifugal loads allowed to clear the active device but the aerodynamic testing showed that some improvements were needed. Corresponding modifications are under way to fully clear the active device to be used on a complete rotor model.
Rotating piezoelectric motors for high precision positioning & space applications
19 June 2023
Piezo-electric motors have been successfully developed for various applications like autofocus drives in camera lenses and handling equipment for semiconductor production. Their high speed and accurate positioning capability, combined with a favourable holding torque in unpowered condition, make piezomotors also very attractive for actuation purposes in spacecraft mechanisms. The paper introduces a new concept of a versatile ultrasonic piezomotor. The testing campaign carried out on the designed rotating piezomotor has validated the vacuum compatibility and the lifetime of the motor in air.
