Department of Physics, University of North Texas, P.O. Box 311427, Denton, TX 76203, USA.
Department of Mechanical Engineering, University of North Texas, 3940 North Elm Suite F101, Denton, TX 76207, USA.
Int J Mol Sci. 2021 Jul 26;22(15):7966. doi: 10.3390/ijms22157966.
This work demonstrates the detections and mappings of a solid object using a thermally tunable solid-state phononic crystal lens at low frequency for potential use in future long-distance detection. The phononic crystal lens is infiltrated with a polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) bulk hydrogel polymer. The hydrogel undergoes a volumetric phase transition due to a temperature change leading to a temperature-dependent sound velocity and density. The temperature variation from 20 °C to 39 °C changes the focal length of the tunable solid-state lens by 1 cm in the axial direction. This thermo-reversible tunable focal length lens was used in a monostatic setup for one- and two-dimensional mapping scans in both frequency domain echo-intensity and temporal domain time-of-flight modes. The experimental results illustrated 1.03 ± 0.15λ and 2.35 ± 0.28λ on the lateral and axial minimum detectable object size. The experiments using the tunable lens demonstrate the capability to detect objects by changing the temperature in water without translating an object, source, or detector. The time-of-flight mode modality using the tunable solid-state phononic lens increases the signal-to-noise ratio compared to a conventional phononic crystal lens.
这项工作展示了使用低频热可调固态声子晶体透镜对固体物体的检测和成像，这可能对未来的远距离检测有应用潜力。声子晶体透镜中填充了一种基于聚乙烯醇的聚 N-异丙基丙烯酰胺（PVA-PNIPAm）块状水凝胶聚合物。由于温度变化，水凝胶会发生体积相转变，导致声速和密度随温度变化。温度从 20°C 变化到 39°C 会使可调谐固态透镜的焦距在轴向方向上改变 1 厘米。这种热可逆可调谐焦距透镜在单基地设置中用于在频域回波强度和时域飞行时间模式下进行一维和二维映射扫描。实验结果表明，在横向和轴向方向上，最小可检测物体尺寸分别为 1.03±0.15λ和 2.35±0.28λ。使用可调谐透镜的实验表明，无需移动物体、源或探测器，通过改变水中的温度即可检测物体。与传统声子晶体透镜相比，使用可调谐固态声子晶体透镜的飞行时间模式可以提高信噪比。
