PhD position: Design of high efficiency power amplifier for ultrasonic transducers dedicated to medical applications
Centre for Nanoscience and Nanotechnology C2N
جامعة حكومية, تصفح الفرص المماثلة
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جامعة حكومية, تصفح الفرص المماثلة
Context of the research work: For a long time, ultrasounds have been exploited for various applications under water and underground for the detection of objects as well as for the measurement of distance and depth. In the medical field, ultrasounds are traditionally used for medical imaging, but in more recent years therapies using High Intensity Focused Ultrasound (HIFU) have emerged. These new therapies have already found several applications such as cancer treatment and targeted medication. Treatments based on this technique are attracting more and more interest around the world and HIFU is a very innovative field with very active research. It is in this context that we obtained financial support from the French National Research Agency (ANR) for our research project in this field in collaboration with two research teams specialized in electronics and imaging of the University of Strasbourg as well as a French company IGT (Imaging-Guided Therapy) specialized in medical equipment assisted by Magnetic Resonance Imaging (MRI) in Bordeaux. Associated with this ANR research project, a doctoral research grant was attributed to the Center for Nanosciences and Nanotechnologies (C2N) attached to the University of Paris-Saclay.
State of the arts:
Currently, most HIFU driver circuits are still based on a linear power amplifier. This is because in HIFU applications, ultrasonic transducers must be driven by pure sine wave signals with phase controlled so that the ultrasound signals can be concentrated in a restricted area called the focal point. Even if a linear power amplifier has the advantage of producing a sinusoidal signal of great purity, it suffers from low energy efficiency, that is to say 50% in the best case. This low energy efficiency brings two disadvantages: more power loss in each amplifier and the difficulty of integration because of the dissipated heat. An increase in the number of total transducers will lead to an increase in the total power consumed and a more complex implementation to remain compatible with an MRI system. In addition, for this type of amplifier, an impedance matching network is required, which not only makes the HIFU system bulky, but also brings more restrictions on the number of transducers. In general, the impedance adaptation used is a static one, because the values of the components used are fixed at the level of the realization of the device. However, with the technological dispersions, as well as the variations of ambient temperature, the real values of the transducers are modified, which degrades the precision of the focusing.
In the literature, different approaches have been published to achieve high conversion efficiency. Class D amplifier is one of them. In theory, the efficiency of a class-D amplifier can reach more than 90%. However, a class-D amplifier has a digital output, i.e. a square wave signal instead of a sinusoidal signal which is essential for HIFU applications. These are considerations for designing a HIFU amplifier.
Required work:
One of the challenges in designing the driver circuit of the transducer is to produce a sinusoidal signal with a high conversion efficiency that will allow future integration. In our previous study, a high energy conversion topology was proposed in order to power the ultrasonic transducer. In particular, an original technique called synchronous self-tuning has been proposed so that dynamic impedance matching might be offered and energy transmission could always remain in an optimal state.
This present doctoral study will still be around the same high energy conversion topology. But the study will be devoted in particular to the design of a high efficiency power amplifier being compatible with the HIFU application. The choice of power transistors and their control is an important aspect. As MRI equipment is typically used for both cancer localization and temperature rise monitoring for HIFU application, the system must of course be compatible with the strong magnetic fields produced by the MRI device in addition to compatibility with CMOS technologies.
Before designing the circuit, for a given ultrasonic transducer, having a good knowledge of the equivalent electrical model of the transducer can help to properly size the power transistors avoiding an unbalanced design. For this purpose, the characterization and the modeling of certain transducers under different conditions are naturally part of the research work.
Before everything, a complete research of the latest publications on the subject is mandatory for the required circuit design. The existing structures will be reviewed and analyzed. Then based on the analysis results, different configurations of a high power conversion amplifier will be proposed, studied, compared, implemented and tested.
The candidate should have a good knowledge on electronics, microelectronics, analog and mixed signal
circuit design. The candidate should also have a good English level in writing as well as in speaking. A
good practice with the CAD design tools, such as CADENCE, SPICE and Altium Designer, will also be
appreciated.
For application send the following documents to Dr ZHANG:
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