Self-adaptive metasurface platform based on computer vision.

Programmable metasurfaces allow real-time electromagnetic (EM) manipulation in a digital manner, showing great potential to construct advanced multifunctional EM devices. However, the current programmable metasurfaces typically need human participation to achieve various EM functions. In this Letter, we propose, design, and construct a self-adaptive metasurface platform that can achieve beam control automatically based on image recognition. Such a platform is composed of a metasurface with 36×36 active units, a single-board computer, and two independent cameras that can detect the position of the objects. The single-board computer, Raspberry Pi, is used to calculate the information of the objects and generate the coding sequences to control the digital metasurface based on a low complexity binocular localization algorithm. Such a smart metasurface platform can generate different beams according to the location of the receiver and can be used as intelligent antennas in future communications and radars.

Experimental demonstration of compact spoof localized surface plasmons.

In recent years, the study of generating and detecting localized surface plasmons (LSPs) has been expanded from the optical regime to microwave regime. In this Letter, the compact spoof LSPs are introduced through both numerical simulations and near-field measurements. It is observed that the compact LSP structure could effectively reduce the resonant frequency with a stronger resonance strength (GdBsm) and a higher Q-factor. Both electric near-field and surface-current distributions are monitored to examine the resonance processes of the LSP particle.

Generation of spatial Bessel beams using holographic metasurface.

We propose to use backward radiations of leaky waves supported by a holographic metasurface to produce spatial Bessel beams in the microwave frequency regime. The holographic metasurface consists of a grounded dielectric slab and a series of metal patches. By changing the size of metal patches, the surface-impedance distribution of the holographic metasurface can be modulated, and hence the radiation properties of the leaky waves can be designed to realize Bessel beams. Both numerical simulations and experiments verify the features of spatial Bessel beams, which may be useful in imaging applications or wireless power transmissions with the dynamic focal-depth controls.

Annular focusing lens based on transformation optics.

We propose and design a kind of annular focusing lens based on transformation optics. Based on the method of eigen-mode expansions, closed-form expressions are derived to analyze the proposed annular lens rigorously. We show that the annular lens has excellent focusing property. Even when a barrier (such as a conducting cylinder) exists in the center of the lens, the analytical results demonstrate that the waves are still guided to propagate smoothly and focused on a spot.

Highly homogeneous zero-index metamaterials make devices more compact and perform better.

A highly homogeneous microwave zero-index metamaterial based on high-permittivity SrTiO3 ceramics is demonstrated to realize the small-aperture high-directivity antenna. Such a novel technique is a remarkable step forward to develop compact devices with better performance.

Fully Breaking Entanglement of Multiple Harmonics for Space- and Frequency-Division Multiplexing Wireless Applications via Space-Time-Coding Metasurface.

Harmonic generation and utilization are significant topics in nonlinear science. Although the progress in the microwave region has been expedited by the development of time-modulated metasurfaces, one major issue of these devices is the strong entanglement of multiple harmonics, leading to criticism of their use in frequency-division multiplexing (FDM) applications. Previous studies have attempted to overcome this limitation, but they suffer from designing complexity or insufficient controlling capability. Here a new space-time-coding metasurface (STCM) is proposed to independently and precisely synthesize not only the phases but also the amplitudes of various harmonics. This promising feature is successfully demonstrated in wireless space- and frequency-division multiplexing experiments, where modulated and unmodulated signals are simultaneously transmitted via different harmonics using a shared STCM. To illustrate the advantages, binary frequency shift keying (BFSK) and quadrature phase shift keying (QPSK) modulation schemes are respectively implemented. Behind the intriguing functionality, the mechanism of the space-time coding strategy and the analytical designing method are elaborated, which are validated numerically and experimentally. It is believed that the achievements can potentially propel the time-vary metasurfaces in the next-generation wireless applications.

Design and rigorous analysis of transformation-optics scaling devices.

Scaling devices that can shrink or enlarge an object are designed using transformation optics. The electromagnetic scattering properties of such scaling devices with anisotropic parameters are rigorously analyzed using the eigenmode expansion method. If the radius of the virtual object is smaller than that of the real object, it is a shrinking device with positive material parameters; if the radius of the virtual object is larger than the real one, it is an enlarging device with positive or negative material parameters. Hence, a scaling device can make a dielectric or metallic object look smaller or larger. The rigorous analysis shows that the scattering coefficients of the scaling devices are the same as those of the equivalent virtual objects. When the radius of the virtual object approaches zero, the scaling device will be an invisibility cloak. In such a case, the scattering effect of the scaling device will be sensitive to material parameters of the device.

Optoelectronic Metasurface for Free-Space Optical-Microwave Interactions.

Photon-electron interactions are essential for many areas such as energy conversion, signal processing, and emerging quantum science. However, the current demonstrations are typically targeted to fiber and on-chip applications and lack of study in wave space. Here, we introduce a concept of optoelectronic metasurface that is capable of realizing direct and efficient optical-microwave interactions in free space. The optoelectronic metasurface is realized via a hybrid integration of microwave resonant meta-structures with a photoresponsive material. As a proof of concept, we construct an ultrathin optoelectronic metasurface using photodiodes that is bias free, which is modeled and analyzed theoretically by using the light-driven electronic excitation principle and microwave network theory. The incident laser and microwave from the free space will interact with the photodiode-based metasurface simultaneously and generate strong laser-microwave coupling, where the phase of output microwave depends on the input laser intensity. We experimentally verify that the reflected microwave phase of the optoelectronic metasurface decreases as the incident laser power becomes large, providing a distinct strategy to control the vector fields by the power intensity. Our results offer fundamentally new understanding of the metasurface capabilities and the wave-matter interactions in hybrid materials.

Spatial Power Combination for Omnidirectional Radiation via Anisotropic Metamaterials.

We present an efficient approach to realize the spatial power combination for omnidirectional radiation via metamaterials in the two-dimensional case. We propose a radially anisotropic zero-index metamaterial which can always produce ominidirectional radiation, independent of the number and position of the sources inside the metamaterial. When the radial component of the permeability tensor is approaching zero and the wave impedance is equal to that of free space, waves emitted from all sources inside the metamaterial are transformed into perfectly cylindrical waves without any reflection, and powers from different sources can be combined together to enhance the omnidirectional radiation. We have designed and fabricated such a radially anisotropic metamaterial, and both numerical and experimental results demonstrate the spatial power combination with high efficiency. The proposed idea can be extended to the three-dimensional case to generate perfectly coherent isotropic radiation in nature, which does not exist now. Metamaterial is a unique approach to obtain such a high-efficiency spatial power combination for omnidirectional radiation and isotropic radiation.

A metasurface-based light-to-microwave transmitter for hybrid wireless communications.

Signal conversion plays an important role in many applications such as communication, sensing, and imaging. Realizing signal conversion between optical and microwave frequencies is a crucial step to construct hybrid communication systems that combine both optical and microwave wireless technologies to achieve better features, which are highly desirable in the future wireless communications. However, such a signal conversion process typically requires a complicated relay to perform multiple operations, which will consume additional hardware/time/energy resources. Here, we report a light-to-microwave transmitter based on the time-varying and programmable metasurface integrated with a high-speed photoelectric detection circuit into a hybrid. Such a transmitter can convert a light intensity signal to two microwave binary frequency shift keying signals by using the dispersion characteristics of the metasurface to implement the frequency division multiplexing. To illustrate the metasurface-based transmitter, a hybrid wireless communication system that allows dual-channel data transmissions in a light-to-microwave link is demonstrated, and the experimental results show that two different videos can be transmitted and received simultaneously and independently. Our metasurface-enabled signal conversion solution may enrich the functionalities of metasurfaces, and could also stimulate new information-oriented applications.

Polarization-independent wide-angle triple-band metamaterial absorber.

We report the design, fabrication, and measurement of a microwave triple-band absorber. The compact single unit cell consists of three nested electric closed-ring resonators and a metallic ground plane separated by a dielectric layer. Simulation and experimental results show that the absorber has three distinctive absorption peaks at frequencies 4.06 GHz, 6.73 GHz, and 9.22 GHz with the absorption rates of 0.99, 0.93, and 0.95, respectively. The absorber is valid to a wide range of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarizations. The triple-band absorber is a promising candidate as absorbing elements in scientific and technical applications because of its multiband absorption, polarization insensitivity, and wide-angle response.

Smart Doppler Cloak Operating in Broad Band and Full Polarizations.

Invisibility cloaks, a class of attractive devices that can hide objects from external observers, have become practical reality owing to the advent of metamaterials. In previous cloaking schemes, almost all demonstrated cloaks are time-invariant and are investigated in the system that is motionless, and hence they are limited to hide stationary objects. In addition, the current cloaks are typically static or require manual operation to achieve dynamic cloaking. Here, a smart Doppler cloak operating in broadband and full polarizations is reported, which consists of a time-modulated reflective metasurface and a sensing-feedback time-varying electronic control system. Experimental results show that the smart Doppler cloak is able to respond self-adaptively and rapidly to the ever-changing velocity of moving objects and then cancel different Doppler shifts in real time, without any human intervention. Moreover, the wideband and polarization-insensitive features enable the cloak to be more robust and practical. To illustrate the capabilities of the proposed approach, the smart Doppler cloak is measured in three scenarios with two different groups of linearly-polarized incidences at 3.3 and 4.9 GHz, and one group circularly-polarized incidences at 6.0 GHz, respectively.

[Preliminary research of deqi and the tissue depth of acupoint thread embedding therapy on weight reduction under ultrasonic guidance].

OBJECTIVE: To explore the impacts on weight reduction effect treated with acupoint thread embedding therapy at different tissue levels under ultrasonic guidance. METHODS: A total of 70 patients with overweight or obesity were randomized into a shallow-tissue thread embedding group (35 cases, 5 cases dropped off) and a deep-tissue thread embedding group (35 cases, 4 cases dropped off). Under ultrasonic guidance, the thread was embedded in the shallow tissue level and the deep tissue level respectively. The acupoints were Zhongwan (CV 12), Xiawan (CV 10), Shuifen (CV 9), Zhongji (CV 3), etc. The thread embedding therapy was exerted once every 2 weeks, totally for 3 times. Before and 2 weeks after treatment, body mass, body mass index (BMI), waist circumference and hip circumference were recorded in the patients of the two groups separately. After each treatment, the number and the property of blood vessels under each acupoint were detected by ultrasound. Besides, the needling sensation and the intensity were scored and the adverse events were observed after thread embedding therapy. RESULTS: After treatment, the reduction range of body mass, BMI and waist circumference in the deep-tissue thread embedding group were larger than those in the shallow-tissue thread embedding group successively (P<0.05). The scores of distention and fullness sensation, needling sensation and intensity in the deep-tissue thread embedding group were higher than those in the shallow-tissue thread embedding group successively (P<0.05). Of 29 cases in the shallow-tissue thread embedding group and 27 cases of the deep-tissue thread embedding group, under at least one acupoint, the vessels were found and distributed unevenly (P<0.05). There were no adverse events, i.e. bleeding and infection in the two groups. CONCLUSION: The deep-tissue thread embedding therapy achieves the stronger deqi (needling sensation) and better effect of weight reduction. The acupoint thread embedding therapy under ultrasonic guidance can accurately locate the tissue depth and reduce the incidence of adverse events of thread embedding treatment.

Virtual conversion from metal object to dielectric object using metamaterials.

We propose an illusion device which transforms a perfectly-electric-conducting (PEC) object into a virtual dielectric object with arbitrary material parameters. Such an illusion device has unconventional electromagnetic properties as verified by accurate numerical simulations. The presented illusion device is composed of inhomogeneous and anisotropic media with finite and positive permittivity and permeability components. Hence the designed device is possible to be realized using artificial metamaterials.

[Image and hemodynamical features of pulmonary artery branches in COPD with pulmonary artery hypertension].

OBJECTIVE: To investigate the imaging and hemodynamical features of pulmonary artery branches in chronic obstructive pulmonary disease (COPD) with pulmonary artery hypertension (PAH). METHODS: CT pulmonary angiography (CTPA) with ECG-gating was performed in 13 patients with clinical diagnosed COPD and 25 normal subjects. The thin-slice multiple plane reconstruction in systole and diastole phase was conducted, which in turn was used to generate the InSpace reconstructed images with reference frame of the main pulmonary artery and the first two grades branches, the contour of the branches was depicted. On the base of coordinates, the GAMBIT was used to generate nodes and furthermore meshes, then the software Fluent was used for numerical calculation and flow simulation. The velocity and pressure changes in the main pulmonary artery and the first two grades branches during different periods of cardiac cycle were observed in both groups. RESULT: CTPA showed that the diameter of the main pulmonary before bifurcate and proximal of the first two branches was larger in systole period than that in diastole period. The diameter of the second segmental artery of right upper lobe was larger during diastole period. The length of the main pulmonary and the first two branches showed no significant difference in both diastole and systole periods. There was no significant difference in length of pulmonary arteries between COPD and normal groups. The main pulmonary to distal right pulmonary artery appeared larger in diastole period. Compared with normal, in COPD group several arteries increased in diameter including proximal and distal of the proximal right pulmonary artery and the proximal right pulmonary artery during systole and diastole periods. In systole period only the diameter of the main pulmonary before bifurcate got larger and the back basic segmental artery of both lower lobe show smaller than normal. The flow condition analysis in COPD and normal groups suggested higher pressure in pulmonary arteries during systole period than that in diastole period, both groups showed high pressure area below the branching point. In COPD patients the right lower lobe artery endured the most significant pressure fall during the two periods and high pressure distributed larger area than normal. Flow velocity in main branch was faster than lower grade branches and that in systole period was faster than that in diastole period. The trend of diffusion of high pressure area was more prominent in diastole period than normal and the influence more prominent. CONCLUSION: The distal part of right pulmonary artery to lower lobe artery may be affected earlier when the pulmonary pressure increased. It is feasible to study the changes of flow condition in pulmonary artery branches though the combination of CTPA image and relevant software.

Infrared-controlled programmable metasurface.

Programmable metasurface enables controlling electromagnetic (EM) waves in real time. By programming the states of active device embedded in metasurface element, the EM properties of the digital metasurface can be changed quickly without redesigning their structures. However, large numbers of long-distance wires are required to connect the programmable metasurface to provide the coded signals from field programmable gate array (FPGA) when controlling the metasurface at a long distance, which is complicated and inconvenient. Here, we propose an infrared-controlled programmable metasurface that can be programmed remotely. The infrared transceiver is able to switch the coding sequences stored in the FPGA controller, thus controlling the voltage on the varactors integrated in the metasurface. Experiment is performed at microwave frequencies, and the measured results verify that the scattering beams of the metasurface sample can be changed remotely by using infrared ray. The proposed infrared-controlled programmable metasurface opens up avenues for constructing a new class of remotely-tuning dynamic metasurfaces.

Polarization-Controlled Dual-Programmable Metasurfaces.

Programmable metasurfaces allow dynamic and real-time control of electromagnetic (EM) waves in subwavelength resolution, holding extraordinary potentials to establish meta-systems. Achieving independent and real-time controls of orthogonally-polarized EM waves via the programmable metasurface is attractive for many applications, but remains considerably challenging. Here, a polarization-controlled dual-programmable metasurface (PDPM) with modular control circuits is proposed, which enables a dibit encoding capability in modifying the phase profiles of x- and y-polarized waves individually. The constructed extended interface circuit is able to extend the number of control interfaces from a field programmable gate array by orders of magnitude and also possesses memory function, which enhance hugely the rewritability, scalability, reliability, and stability of PDPM. As a proof-of-concept, a wave-based exclusive-OR logic gate platform for spin control of circularly-polarized waves, a fixed-frequency wide-angle dual-beam scanning system, and a dual-polarized shared-aperture antenna are demonstrated using a single PDPM. The proposed PDPM opens up avenues for realizing more advanced and integrated multifunctional devices and systems that have two independent polarization-controlled signal channels, which may find many applications in future-oriented intelligent communication, imaging, and computing technologies.

Information Metamaterial Systems.

Metamaterials have great capabilities and flexibilities in controlling electromagnetic (EM) waves because their subwavelength meta-atoms can be designed and tailored in desired ways. However, once the structure-only metamaterials (i.e., passive metamaterials) are fabricated, their functions will be fixed. To control the EM waves dynamically, active devices are integrated into the meta-atoms, yielding active metamaterials. Traditionally, the active metamaterials include tunable metamaterials and reconfigurable metamaterials, which have either small-range tunability or a few numbers of reconfigurability. Recently, a special kind of active metamaterials, digital coding and programmable metamaterials, have been presented, which can realize a large number of distinct functionalities and switch them in real time with the aid of field programmable gate array (FPGA). More importantly, the digital coding representations of metamaterials make it possible to bridge the digital world and physical world using the metamaterial platform and make the metamaterials process digital information directly, resulting in information metamaterials. In this review article, we firstly introduce the evolution of metamaterials and then present the concepts and basic principles of digital coding metamaterials and information metamaterials. With more details, we discuss a series of information metamaterial systems, including the programmable metamaterial systems, software metamaterial systems, intelligent metamaterial systems, and space-time-coding metamaterial systems. Finally, we introduce the current progress and predict the future trends of information metamaterials.

Compact-sized and broadband carpet cloak and free-space cloak.

Recently, invisible cloaks have attracted much attention due to their exciting property of invisibility, which are based on a solid theory of transformation optics and quasi-conformal mapping. Two kinds of cloaks have been proposed: free-space cloaks, which can render objects in free space invisible to incident radiation, and carpet cloaks (or ground-plane cloaks), which can hide objects under the conducting ground. The first free-space and carpet cloaks were realized in the microwave frequencies using metamaterials. The free-space cloak was composed of resonant metamaterials, and hence had restriction of narrow bandwidth and high loss; the carpet cloak was made of non-resonant metamaterials, which have broad bandwidth and low loss. However, the carpet cloak has a severe restriction of large size compared to the cloaked object. The above restrictions become the bottlenecks to the real applications of free-space and carpet cloaks. Here we report the first experimental demonstration of broadband and low-loss directive free-space cloak and compact-sized carpet cloak based on a recent theoretical study. Both cloaks are realized using non-resonant metamaterials in the microwave frequency, and good invisibility properties have been observed in experiments. This approach represents a major step towards the real applications of invisibility cloaks.

Analytical design of conformally invisible cloaks for arbitrarily shaped objects.

To design conformally invisible cloaks for arbitrarily shaped objects, we use the nonuniform rational B -spline (NURBS) to represent the geometrical modeling of the arbitrary object. Based on the method of optical transformation, analytical formulas of the permittivity and permeability tensors are proposed for arbitrarily shaped invisible cloaks. Such formulas can be easily implemented in the design of arbitrary cloaks. Full-wave simulations are given for heart-shaped invisible cloaks and perfectly electrical conducting (PEC) objects, in which we observe that the power-flow lines of incoming electromagnetic waves will be bent smoothly in the cloaks and will return to their original propagation directions after propagating around the object. We also show that the scattered field from the PEC object coated with the invisible cloak is much smaller than that from the PEC core. The application of NURBS in the design of arbitrary cloaks shows transformation optics to be a very general tool to interface with commercial softwares like 3D STUDIOMAX and MAYA.