PZT-hydrogel integrated active non-Hermitian complementary acoustic metamaterials with real time modulations through feedback control circuits

This grant will support research that will generate new fundamental knowledge on the dynamic and acoustic properties of a PZT-hydrogel based active complementary acoustic metamaterial. Such acoustic metamaterials will enable high energy transmission at high frequency through sound barriers, including those with strong intrinsic loss like skull for brain imaging and brain-machine interface.

Transcranial ultrasound (i.e. ultrasound transmission through skull) has many applications including noninvasive surgeries and drug delivery. However, current transcranial ultrasound techniques are all based on sound waves with relatively low frequency and poor spatial resolution, and the energy transmission through the lossy skull is low even for such low frequency sound waves.

Brain imaging and brain-machine interfaces require better spatial resolution, which can be realzied by enabling transmission of high frequency ultrasound through skulls, which is not achievable with existing technologies. Active non-Hermitian complementary acoustic metamaterials (NHCMM) are promising compensation media to complement with the strong transmission loss through skull for high frequency acoustic waves.

This project explores the acoustic and material properties of PZT-hydrogel composites integrated with feedback control circuits for the experimental realization of NHCMM that can compensate the high frequency ultrasound transmission loss through a real skull. This experimental realization will set the foundation for high resolution ultrasound brain imaging and brain-machine interface.

This research will have broader impacts in science, defense, industry and general society by satisfying the critical need for high performance brain imaging and brain-machine interface. In addition, this research will promote the progress of fundamental acoustics, soft matter physics, and metamaterials. This multi-disciplinary research will broaden the participation of underrepresented groups in science and engineering and positively impact STEM education.

The objective of this research is to design, fabricate, and experimentally characterize an active NHCMM by integrating PZT elements, hydrogel, and feedback control circuits that can be used to complement sound barriers, including those with strong intrinsic loss such as skull, to achieve optimal energy transmission for brain imaging and brain-machine interface. The NHCMM has effective density and bulk modulus with negative values of that of the barrier to suppress the strong impedance mismatch and material gain that balances the intrinsic loss in the barrier.

The NHCMM will be realized by integrating piezoelectric elements and hydrogel with electrical circuit components. The integrated feedback control circuit will actively modulate the effective acoustic properties of the metamaterials to realize the desired parameters of NHCMM and compensate impedance mismatch and loss simultaneously. This fundamental research project will pave the road for the realization of noninvasive ultrasonic brain imaging, high intensity focused ultrasound treatments, brain stimulation, and brain-machine interface.

To achieve the proposed objective, the two PIs will utilize their complemented expertise in acoustics, metamaterials, and soft matter to accomplish the following research tasks: 1) Identify the dynamic properties of different types of hydrogels in a wide ultrasonic frequency band; 2) Design and fabricate hydrogel-based active NHCMMs with feedback-circuit-controlled piezoelectric elements to realize any desired effective density and bulk modulus with acoustic gain; 3) Characterize and optimize NHCMMs to enhance acoustic energy transmission through lossy skull for brain imaging and brain-machine interface.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.