Void-Engineered Metamaterial Delay Line with Built-In Impedance Matching for Ultrasonic Applications.

Metamaterials exhibit unique ultrasonic properties that are not always achievable with traditional materials. However, the structures and geometries needed to achieve such properties are often complex and difficult to obtain using common fabrication techniques. In the present research work, we report a novel metamaterial acoustic delay line with built-in impedance matching that is fabricated using a common 3D printer. Delay lines are commonly used in ultrasonic inspection when signals need to be separated in time for improved sensitivity. However, if the impedance of the delay line is not perfectly matched with those of both the sensor and the target medium, a strong standing wave develops in the delay line, leading to a lower energy transmission. The presented metamaterial delay line was designed to match the acoustic impedance at both the sensor and target medium interfaces. This was achieved by introducing graded engineered voids with different densities at both ends of the delay line. The measured impedances of the designed metamaterial samples show a good match with the theoretical predictions. The experimental test results with concrete samples show that the acoustic energy transmission is increased by 120% and the standing wave in the delay line is reduced by over a factor of 2 compared to a commercial delay line.

Direct-to-participant recruitment of mothers and infants: A strategic approach during challenging pandemic times.

Under traditional circumstances, most clinical trials rely on in-person operations to identify, recruit, and enroll study participants and to complete study-related visits. During unusual circumstances, such as the COVID-19 pandemic, the typical clinical trial model is challenged and forced to explore alternative approaches to implementing study recruitment, participant enrollment, and data collection strategies. One such alternative is a direct-to-participant approach which leverages electronic resources and relevant technological devices (e.g., smart phones) available to researchers and patients. This approach functions under the assumption that a participant has access to a device that connects to the internet such as a smart phone, tablet, or computer. Researchers are then able to transition a typical paper-based, in-person model to an electronic-based, siteless, remote study. This article describes the challenges clinicians and researchers faced when implementing a direct-to-participant study approach during the COVID-19 pandemic. The lessons learned during this study of infant populations could help increase efficiency of future trials, specifically, by lessening the burden on participants and clinicians as well as streamlining the process for enrollment and data collection. While direct-to-adult participant recruitment is not a novel approach, our findings suggest that studies attempting to recruit the infant population may benefit from such a direct-to-participant approach.