Non-Hermitian Compliant Metamaterials for Ultrasound Transmission
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Solution Overview
Problem
High frequency ultrasound struggles to transmit effectively through lossy mediums like the skull due to impedance mismatch and strong attenuative effects, limiting its application in biomedical imaging and therapies.
Innovation Solution
Non-Hermitian complementary metamaterials (NHCMM) with resonating structures and active gain elements are used to amplify energy coherently, compensating for energy loss and impedance mismatch, allowing bidirectional acoustic transmission through lossy tissues like the cranium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency ultrasound is used for imaging and therapy, then spatial resolution and precision are improved, but transmission through lossy mediums like skull is severely attenuated
Solution Approach 1:
A complementary metamaterial layer is introduced as an intermediary between the ultrasound source and the skull. This metamaterial layer has acoustic impedance matched to soft tissue and generates surface waves at the skull interface that convert to body waves within the skull, enabling efficient energy transmission through the impedance mismatch barrier
Solution Approach 2:
The acoustic impedance and wave propagation characteristics are changed by using a metamaterial with engineered properties. The metamaterial transforms the incident plane waves into surface waves with different impedance characteristics that are better matched to the skull, thereby reducing attenuation
2Loss of energy
If the skull is treated as an impedance barrier, then transmission of ultrasound energy is limited, but the skull's structural integrity must be maintained
Solution Approach 1:
The complementary metamaterial acts as a mediator that couples the acoustic impedance of soft tissue to the skull. By generating surface waves at the interface, it creates a transition zone that bridges the impedance gap without requiring physical modification of the skull
Solution Approach 2:
The direct mechanical wave transmission through the skull is replaced by a two-stage process: first generating surface waves on the skull exterior, then converting these to body waves inside the skull. This substitution enables efficient energy transfer while preserving skull integrity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables near-perfect transmission and wavefront restoration of high frequency ultrasound through the skull, enhancing diagnostic imaging and therapeutic capabilities by overcoming the impedance mismatch and attenuation issues.
Implementation Method 1
The NHCMM can comprise resonating structures, and active gain elements
Implementation Method 2
the NHCMM is configured to add a first amount of energy amplification coherently to an acoustic wave passing therethrough to account for an energy loss in the acoustic wave
Data Source
AI summary
A non-Hermitian complementary metamaterial (NHCMM). Acoustic transmission systems including an acoustic wave generator configured to generate an acoustic wave and propagate the acoustic wave through a tissue of a specimen, and the NHCMM, which is configured to add a first amount of energy amplification coherently to the acoustic wave to account for energy loss in the acoustic wave as a result of the wave propagating through the tissue of the specimen. The acoustic wave generator can be an ultrasound generator, and the tissue can be a cranium.