MSc thesis project proposal

[2021] Ultrasonic Scalp – towards high-precision transcranial ultrasound brain stimulation

Low intensity focused ultrasound (LIFU) is an emerging non-invasive brain stimulation modality showing improved performance when compared to its traditional alternatives such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (TdCS), since it has the unique property of combining high depth of penetration in brain tissue with high spatial resolution1.

One of the current challenges in this field is on advancing ultrasound transmitter technology, from hand-held and mechanically focused transducers to flexible electronically focused transducers by means of constructive wave interference. This would enable a wearable brain stimulator where the stimulation location could be electronically changed in 3D and in real time2 (Fig.1), with millimeter spatial resolution, for both whole-brain neuroscience studies in large animals, or precise treatment of neurological diseases in humans. The key challenge of transcranial LIFU is the ability for the ultrasound waves to pass through the skull and propagate to the desired region of the brain with high-spatial resolution.

However, the interface between typical piezoelectric ultrasound transducers and the skull is heavily mismatched in the acoustic domain, which translates into very high reflections from incoming ultrasound. Given that acoustic impedance is the product of the material density with its characteristic speed of sound, we hypothesize that by manufacturing ultrasound transducers by combining materials with different ratios of density and speed of sound, we will be able to acoustically match ultrasound transmitters and the skull, towards an “ultrasonic-scalp” device, combining high-efficient, precise, and wearable brain stimulation.

Why additive manufacturing (AM)? Here, we envision that AM can be the key technology to tailor the acoustic properties of ultrasound transducers to a “skull-like” material density, so that reflections are minimized at the transducer/skull interface are minimized. The advent of AM technologies has created a host of unparalleled opportunities to design and fabricate patient-specific medical devices with complex geometries. In particular, multi-material AM techniques have enabled additional functionalities with precise control over the spatial distribution of properties at ultrafine resolutions3. This allows to effectively connect multiple materials (such as metals and polymers) with several order of magnitude stiffness mismatches, which is necessary to maximize the acoustic coupling between transducers and the skull.

The goal of this project is to investigate the optimal piezocomposite materials and AM techniques towards high efficient, precise and wearable ultrasonic brain stimulators.


1. Literature review of piezoelectric composites and AM techniques
2. Design of piezocomposites transducers optimized for skull acoustic matching, and integration into a flexible printed circuit board
3. Ultrasound characterization of focused ultrasound propagation through skull phantom

This work will be done under the supervision of Dr. Mohammad J. Mirzaali (3me– Tissue Biomechanics department) and Dr. Tiago Costa (EWI – Microelectronics department)

1 Tyler, W. J., et al, Current Opinion in Neurobiology 50, 222--231, (2018).
2 Costa, T., et al, in 2019 IEEE Custom Integrated Circuits Conference (CICC). 1-4.
3 Mirzaali, M. J. et al. Composite Structures 237, 111867, (2020).
4 Yoshizawa, M., et al, in IEEE Ultrasonics Symposium, 2004.


Highly driven and enthusiastic MSc students from Microelectronics, Biomedical Engineering or Mechanical Engineering with interest in microfabrication and biomedical devices should contact Dr. Mohammad J. Mirzaali ( and Dr. Tiago Costa ( and include a motivation letter and a list of courses attended.


dr. Tiago Costa

Bioelectronics Group

Department of Microelectronics

Last modified: 2021-02-10