Abstract: Practically applied techniques for ultrasonic biomedical imaging employ delay-and-sum (DAS) beamforming which can resolve two objects down to 2.1λ within the acoustic Fresnel zone. Here, we demonstrate a phononic metamaterial lens (ML) for detection of laterally subwavelength object features in tissue-like phantoms beyond the phononic crystal evanescent zone and Fresnel zone of the emitter. The ML produces metamaterial collimation that spreads 8x less than the emitting transducer. Utilizing collimation, 3.6x greater lateral resolution beyond the Fresnel zone limit was achieved. Both hard objects and tissue approximating masses were examined in gelatin tissue phantoms near the Fresnel zone limit. Lateral dimensions and separation were resolved down to 0.50λ for hard objects, with tissue approximating masses slightly higher at 0.73λ. The work represents the application of a metamaterial for spatial characterization, and subwavelength resolution in a biosystem beyond the Fresnel zone limit.
In the paper, titled "Sub-wavelength lateral detection of tissue-approximating masses using an ultrasonic metamaterial lens," the authors pursue a new technical approach because, as they report, traditional methods for ultrasound detection in biomedical application suffer from limited lateral resolution. The authors show that a phononic metamaterial lens can be used for spatial characterisation of subwavelength objects, even beyond the Fresnel zone of the emitting transducer.
The UNT authors included Ezekiel L. Walker, Yuqi Jin, & Arup Neogi. They were joined in publishing this research by Delfino Reyes, a Faculty member of the Autonomous University of the State of Mexico, Campus “El Cerrillo”, Toluca, C.P., 50925, Mexico.