High-resolution ultrasonic imaging is of much interest in Non-invasive Diagnosis (NID) in biomedicine and Non-Destructive Evaluation (NDE) of components in safety-critical industries. However, imaging conventional ultrasonic methods suffer from poor resolution imposed by the diffraction limit. Thus ways to overcome the diffraction limit are of much interest. The authors also have recently demonstrated the use of Holey Structured Metamaterials (HSM) to enable resolution beyond the diffraction limit in the ultrasonic regime. In HSM, the holes act as pixels for imaging and are of subwavelength dimension in terms of the wavelength used. Thus, the use of HSM lenses requires the acquisition of data at fine spatial intervals. Although Laser Doppler Vibrometers (LDV) can serve as a receiver in such requirements, they suffer from signal-to-noise ratio (SNR) issues and are also expensive, hampering a wider practical implementation. This paper proposes a cost-effective methodology which utilizes conventional ultrasonic transducers (for reception) for the practical implementation of HSM. Here we propose an attachment of mechanical filter in the form of a conical hollow acoustic waveguide or horn to the conventional  
transducer, thereby yielding spatially narrowband reception. The proposed conical hollow horn has an opening at its apex, with an aperture comparable to the hole size of the HSM. The implementation of the proposed methodology is experimentally demonstrated and validated against previous work using LDV as the receiver. A study on the optimal geometrical parameters  
of the conical attachment is also carried out using Finite Element Simulations. The proposed methodology offers a feasible solution for the practical implementation of HSM for achieving subwavelength resolution imaging at a relatively higher speed and minimal cost.


Technique for Implementing Holey Metalenses Using Conventional Ultrasonic Transducers

No proceedings papers in 2020. Video only.

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