PhD grants : Low-power converter dedicated to capacitive ultrasonic energy harvesters: application to ultrasonic-based wireless power transmission (EMSTU)

• 36 months doctoral funding (October 2021 to September 2024)
• Keywords

High efficiency converter, cMUT transducer, piezoelectric generator, energy harvesting

• Profile ans skills required

The candidate must hold a Master's of Research degree or an engineering degree in one of the following specialties:

- Engineering Sciences with specialization in Electronics

- Engineering Sciences with specialization in Electrical Engineering

During his/her curriculum, the candidate will have had experience in electronics, acoustics, signal processing and instrumentation. A good knowledge of this field is essential to the success of the proposed work. Complementary competence in one of the following areas would be greatly appreciated:

- Software experience: PSpice or LTSpice; Matlab or Scilab; Octave

- Experience in instrumentation

• Project description

Capacitive Micro-machined Ultrasonic Transducers (cMUT) are micro-capacitors (typically 50x50 µm2), one electrode of which is mobile and the other fixed. When this capacitor is polarized and receives an ultrasonic wave, the received mechanical energy is converted into electrostatic energy. If a high number of micro-capacitors (typically a few hundred) are combined in parallel, then the amount of energy harvested is likely to be able to power electronic devices with very low consumption. This area is commonly referred to as AET for Acoustic Energy Transfer. This energy transfer, performed at ultrasonic frequencies, can be done classically over a distance of a few centimeters in biological tissues. AET thus appears to be a promising avenue for powering Implanted Medical Devices (IMDs).

The electrostatic energy recovered by the cMUT receiver still needs to be converted to a form suitable for the targeted electronic load. This results in precise specifications in terms of shape and level of voltage and current. An electronic converter must therefore be interposed between the harvester and the load, and must have very low power consumption. In addition, the cMUTs must be polarized by a DC voltage at the beginning of the cycle, so a power source of a few µJ is required to start operation. For this initial energy, one approach consists of integrating a composite piezoelectric layer (here based on ZnO nanowires) on the membrane of the cMUT.

In the framework of this thesis, the aim is to propose original low-power conversion structures dedicated to cMUTs used for the conversion of energy from ultrasonic waves in the range [40 kHz, 400 kHz]. Among the possible tracks, non-linear converters of SECE (Synchronous Electric Charge Extraction) type, initially designed for piezoelectric harvesters, also give good performances on electrostatic harvesters. In addition, Totem-pole converters allow the voltage to be raised in a similar way to SECE type converters, but with the advantage of better efficiency by replacing the rectifier stage with the switching cell. Particular care will be taken in the development of the control electronics, which will have to be ultra low power consumption.

• References

1] G. V. B. Cochran et al., “Piezoelectric internal fixation devices: A new approach to electrical augmentation of osteogenesis,” J. Orthop. Res., vol. 3, no. 4, pp. 508–513, 1985.

[2] S. Ozeri et al., “Ultrasonic transcutaneous energy transfer using a continuous wave 650 kHz Gaussian shaded transmitter,” Ultrasonics, vol. 50, no. 7, pp. 666–674, 2010

[3] G. Poulin-Vittrant et al., “Challenges of low-temperature synthesized ZnO nanostructures and their integration into nano-systems,” Materials Science in Semiconductor Processing 91 (2019) 404-408

[4] EnSO, “Energy for Smart Objects,” financement ECSEL-JU 2016-2020, http://enso-ecsel.eu/

[5] S. Boisseau et al., “Microstructures électrostatiques de récupération d’énergie vibratoire pour les microsystèmes,” Techniques de l'ingénieur Innovations en énergie et environnement, RE160, 10 octobre 2010

[6] A. Morel et al., “A unified N-SECE strategy for highly coupled piezoelectric energy scavengers,” Smart Materials and Structures, IOP Publishing, 2018, 27 (8), pp.4002

[7] M. Perez et al., “Triboelectret-based aeroelastic flutter energy harvesters,” Journal of Physics: Conference Series 773 (2016) 012021

[8] S. Jacques, C. Reymond, J.-C. Le Bunetel and G. Benabdelaziz, 'Comparison of the power balance in a Totem-Pole Bridgeless PFC topology with several inrush current limiting strategies', Journal of Electrical Engineering 72 (2021)

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