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2023-07-28 PIER Vol. 177, 127-137, 2023. doi:10.2528/PIER23042502

Two-Dimensional Acoustic Asymmetric Vortex Focusing Lens by Binary-Phase Mode Converters

Yin Wang, Hong-Yu Zou, Yu-Jing Lu, Shuai Gu, Jiao Qian, Jian-Ping Xia, Yong Ge, Hong-Xiang Sun, Shou-Qi Yuan, and Xiao-Jun Liu

Recently, the study of acoustic vortex beams has attracted a great attention owing to its potential applications in medical ultrasound imaging and trapping particles. In some special applications of medical ultrasound, it generally needs the simultaneous realization of vortex focusing and asymmetric propagation in three-dimensional (3D) space. However, the design of a two-dimensional (2D) device with asymmetric acoustic vortex focusing (AAVF) remains a challenge. To overcome it, we experimentally demonstrate a 2D AAVF lens composed of three types of binary-phase mode converters. By simultaneously introducing the phase profiles of acoustic focusing and vortex caused by the mode converters, we design a 2DAAVF lens with the topological charge n = 2, i.e., the sound energy can pass through the lens from the upper side and forms a vortex focus in 3D space; however, it cannot transmit through the lens from the other side. The vortex focusing and asymmetric transmission arise from the phase manipulation and the conversion between the zero-order and first-order waves caused by the mode converters, respectively. The measured fractional bandwidth can reach about 0.19. The proposed lens has the advantages of high-performance AAVF, broad bandwidth and complex sound modulation in 3D space, which provides diverse routes for designing 3D multi-functional sound devices with promising applications in medical ultrasound.

2023-07-19 PIER Vol. 177, 107-126, 2023. doi:10.2528/PIER23032403

Remote Material Characterization with Complex Baseband FMCW Radar Sensors

Ahmed M. Hegazy, Mostafa Alizadeh, Amr Samir, Mohamed Basha, and Safieddin Safavi-Naeini

This paper presents the theoretical basis and experimental validation for a technique to remotely characterize materials using FMCW radar sensors with complex baseband architecture. Our theoretical work proves that the magnitude and phase of the input reflection coefficient of a material can be accurately extracted from the baseband data of a complex-baseband FMCW radar. This complex reflection coefficient can be used to calculate the dielectric constant, loss tangent, thickness, and layer setup of a material with high accuracy due to the extra information obtained from the phase of the reflection coefficient. The analysis starts with a theoretical model for the complex reflection coefficient of a flat material slab suspended in air. We then introduce a formulation for the complex reflection coefficient existing in the complex baseband of an FMCW radar signal. We finally present the experimental testing preformed using TI mmWave radar on two different material samples and introduce the test results for extracting the material dielectric properties and thickness using three different extraction methods compared against nominal values from literature. The test results prove the high accuracy of our technique resulting from the utilization of both magnitude and phase information of the input refection coefficient, despite the relatively long free-space measurement distance and the multi-path reflections test environment.

2023-07-03 PIER Vol. 177, 95-105, 2023. doi:10.2528/PIER23012203

Transverse Orbital Angular Momentum of Spatiotemporal Optical Vortices

Miguel Angel Porras

Spatiotemporal optical vortices (STOVs) are electromagnetic wave packets that transport a phase line singularity perpendicular to their propagation direction. We address the problem of the transverse orbital angular momentum (OAM) actually transported by STOVs propagating in free space or non-dispersive media, the most frequent experimental situation. An elliptically symmetric STOV of topological charge l and carrier frequency ω0 carries an intrinsic transverse OAM per unit energy γl/2ω0, where γ is the STOV ellipticity. Intrinsic stands for the OAM about a moving transverse axis passing permanently through the STOV center. For circular STOVs (γ = 1) this value is half the intrinsic longitudinal OAM of monochromatic light beams of the same charge and frequency. This result agrees with that in Phys. Rev. Lett. 127, 193901 (2021). The formula (γ+1/γ)l/2ω0 for the intrinsic transverse OAM in Phys. Rev. A 107, L031501 (2023) yields infinite values and is not conserved on propagation for particular STOVs. When STOVs propagate losing their elliptical symmetry, they preserve the intrinsic transverse OAM γl/2ω0 despite the phase singularity may split, the split singularities may disappear, or even change the sign of their topological charges. The total transverse OAM of a STOV about a fixed transverse axis crossing its center vanishes because the extrinsic transverse OAM is opposite to the intrinsic OAM, which may preclude applications such as setting particles into rotation, but STOVs could transmit their intrinsic OAM to the photons of other waves, as in nonlinear frequency conversion processes.

2023-06-19 PIER Vol. 177, 85-94, 2023. doi:10.2528/PIER23031001

Terahertz Plasmonic Metagrating Design Simultaneously Enabling Broadband Extraordinary Transmission and Field Enhancement

Chi Wang, Shurun Tan, Xiao Lin, Hongsheng Chen, and Fei Gao

Metagratings, consisting of subwavelength-aperture arrays (SAAs), provide a powerful platform to manipulate electromagnetic waves. Typical examples include extraordinary optic transmission (EOT) in the far field, and field enhancements (FEs) in the near field. These capabilities promise applications in beam steering and wave-matter interactions, but are not extended to broad bandwidth simultaneously. Here, we transplant the concept of broadband light harvesting devices from optic to terahertz frequency and by exploring one-dimensional arrays of spirally textured metallic cylinders supporting multiple designer localized surface plasmon resonances. Theoretical analysis reveals that the interaction between localized plasmons leads to the broadband THz EOTs in the far field as well as large field enhancements in the near field. The bandwidth of the EOT and the magnitude of field enhancements can be flexibly designed by changing the geometry of the plasmonic-like resonators. This design promises applications in THz broadband beam-steering, absorbers, and sensing, topological devices.

2023-06-06 PIER Vol. 177, 75-84, 2023. doi:10.2528/PIER23030802

Research on the Radiation Properties of Tapered Slot Magnetoelectric Antenna

Tianhao Han, Biao Dong, Yong Zhang, Yu Wang, Zhongming Yan, Hongcheng Zhou, Jinhua Feng, and Yulong Liu

The advent of acoustically mediated magnetoelectric (ME) antennas offers a new idea for miniaturizing antennas. The ME antenna operates at mechanical resonant frequencies, so its dimension can be reduced by three orders of magnitude compared to an electric antenna counterpart. However, the poor directional radiation property of the reported magnetoelectric antennas, which is similar to an ideal magnetic dipole, limits the use of the ME antennas. In this paper, we propose a tapered slot magnetoelectric (TSME) antenna which is composited of PZT-5H and Metglas with dimensions of 50 mm × 30 mm × 0.596 mm and an operating frequency of around 30 kHz. Inspired by the structure of the slot-coupled antenna, the structure of the magnetostrictive layer of the ME antenna has been modified, and the front-back radiation difference in the near field has been improved by 7.9 dB compared to a normal ME antenna. The different operating principles between the TSME antenna and normal ME antennas have been analyzed and verified in the paper. In addition, we have successfully implemented amplitude modulation (AM) signals transmission using TSME antennas. This work provides new ideas for improving the radiation performance of ME antennas and lays the foundation for their practical application.

2023-06-04 PIER Vol. 177, 53-73, 2023. doi:10.2528/PIER23011302

The Effects of Obscuration in Passive 3-D Millimeter-Wave Imaging for Human Security Screening

Xuelei Sun, Neil Anthony Salmon, Xiaodong Zhuge, and Jungang Miao

The possibility of near-field passive 3-D imaging using the aperture synthesis technique is theoretically proven and highlights the opportunity for imaging the entire human body by an antenna receiving array that surrounds the body. In these scenarios there will be partial obscuration of some regions of the body, by other parts of the body. This results in some receivers in the array being able to measure emission from certain parts of the body, while others are obscured from a measurement. A model is presented which enables the e ects of obscuration to be assessed for planar-like, cylindrical-like, and concave-like regions of the human body. The e ect the obscuration has on the spatial resolution of the imager is evaluated by examining the 3-D point spread function, as determined by a near-field aperture synthesis imaging algorithm. It is shown that over many areas of the human body, the Abbe microscope resolution of λ/2 (5 mm@30 GHz) in a direction transverse to the human body surface is achievable, an attractive proposition for security screening. However, the spatial resolution in a direction normal to the human body surface is shown to be close to λ(10 mm@30 GHz). In regions of greater obscuration, such as in the armpits, the resolution may fall to λ(10 mm@ 30 GHz) and 5λ (50 mm@30 GHz) in the directions transverse and normal to the human body surface respectively. It is also shown by simulation using a human body solid model and the 3-D aperture synthesis imaging algorithm how the image quality changes with the number of receiving antennas.

2023-05-25 PIER Vol. 177, 43-51, 2023. doi:10.2528/PIER23030703

Broad-Tuning, Dichroic Metagrating Fabry-Perot Filter Based on Liquid Crystal for Spectral Imaging

Tingbiao Guo, Zijian Lin, Xinan Xu, Zhi Zhang, Xiao Chen, Nan He, Guoqing Wang, Yi Jin, Julian Evans, and Sailing He

Dynamic structural color can empower devices with additional functions like spectrum and polarization detection beyond display or imaging. However, present methods suffer from narrow tuning ranges, low throughput, or bulky volumes. In this work, a tunable filter composed of a dichroic metagrating Fabry-Perot cavity and liquid crystal (LC) material is proposed and investigated. By modulating the polarization of the incident light with the LC, the color response can change from blue to green and deep red due to the `mode jumping' effect, with a tuning range of around 300 nm. Besides, we experimentally demonstrate the use of this device as a spectral imager in the visible range. Experimental results show that spectral resolvability can be around 10 nm, with the largest peak wavelength in accuracy of ~5 nm. This approach shows superior performance over traditional liquid crystal tunable filters in low light conditions and indicates the potential of dynamic structural color for miniaturized spectroscopic applications.

2023-04-04 PIER Vol. 177, 33-42, 2023. doi:10.2528/PIER22112703

Systemically Delivered, Deep-Tissue Nanoscopic Light Sources

Xiang Wu, Fan Yang, Sa Cai, and Guosong Hong

Light is widely used in life science in both controlling and observing biological processes, yet a long-standing challenge of using light inside the tissue lies in the limited penetration depth of visible light. In the past decade, many in vivo light delivery methods using photonics and materials science tools have been developed, with recent demonstrations of non-invasive, deep-tissue light sources based on systemically delivered luminescent nanomaterials. In this perspective, we provide an overview for the principles of intravital nanoscopic light sources and discuss their advantages over existing methods for in vivo light delivery. We then highlight their recent applications in optogenetics neuromodulation and fluorescent imaging in live animals. We also present an outlook section about the feasibility of combining these non-invasive light sources with other modalities to expand the utilities of light in biology.

2023-03-23 PIER Vol. 177, 21-32, 2023. doi:10.2528/PIER23012902

Highly Sensitive Temperature Sensing via Photonic Spin Hall Effect

Shuaijie Yuan, Jin Yang, Yong Wang, Yu Chen, and Xinxing Zhou

In this work, we propose a highly sensitive temperature sensor based on photonic spin Hall effect (PSHE). We find that, by involving the liquid crystal (LC) material, the spin spatial and angular shifts in PSHE are very sensitive to the tiny perturbation of temperature when the incident angle of light beam is near the Brewster and critical angles. Importantly, the phase transition from liquid crystal state to liquid state across the clearing point (CP) will lead to the transition of strong spin-orbit interaction to the weak one. During this process, we reveal that the sensitivity of our designed temperature sensor can reach a giant value with 8.27 cm/K which is one order of magnitude improvement compared with the previous Goos-Hänchen effect-based temperature sensor. This work provides an effective method for precisely determining the position of CP and actively manipulating the spin-orbit interaction.

2023-02-13 PIER Vol. 177, 1-20, 2023. doi:10.2528/PIER22101202

Topological Edge Modes in One-Dimensional Photonic Artificial Structures (Invited)

Jiajun Zheng, Zhiwei Guo, Yong Sun, Haitao Jiang, Yunhui Li, and Hong Chen

In recent years, topological states in photonic artificial structures have attracted great attention due to their robustness against certain disorders and perturbations. To readily understand the underlying principles, topological edge modes in one-dimensional (1D) system have been widely investigated, which bring aboutthe discovery of novel optical phenomena and devices. In this article, we review our recent advances in topological edge modes. We introduce the connection between topological orders and effective electromagnetic parameters of photonic artificial structures in band gaps, discuss experimental demonstration of robust topological modes and their potential applications in wireless power transfer, sensing and field of optics, and give a brief introduction of future opportunities in 1D topological photonics.