All-Dielectric Integrated Meta-Antenna Operating in 6G Terahertz Communication Window.

Efficient transceivers and antennas at terahertz frequencies are leading the development of 6G terahertz communication systems. The antenna design for high-resolution terahertz spatial sensing and communication remains challenging, while emergent metallic metasurface antennas can address this issue but often suffer from low efficiency and complex manufacturing. Here, an all-dielectric integrated meta-antenna operating in 6G terahertz communication window for high-efficiency beam focusing in the sub-wavelength scale is reported. With the antenna surface functionalized by metagrating arrays with asymmetric scattering patterns, the design and optimization methods are demonstrated with a physical size constraint. The highest manipulation and diffraction efficiencies achieve 84.1% and 48.1%. The commercially accessible fabrication method with low cost and easy to implement has been demonstrated for the meta-antenna by photocuring 3D printing. A filamentous focal spot is measured as 0.86λ with a long depth of focus of 25.3λ. Its application for integrated imaging and communication has been demonstrated. The proposed technical roadmap provides a general pathway for creating high-efficiency integrated meta-antennas with great potential in high-resolution 6G terahertz spatial sensing and communication applications.

Microwave Absolute Distance Measurement Method with Ten-Micron-Level Accuracy and Meter-Level Range Based on Frequency Domain Interferometry.

A microwave absolute distance measurement method with ten-micron-level accuracy and meter-level range based on frequency domain interferometry is proposed and experimentally demonstrated for the first time. Theoretical analysis indicates that an interference phenomenon occurs instantaneously in the frequency domain when combining two homologous broad-spectrum microwave beams with different paths, and the absolute value of the distance difference between the two paths is only inversely proportional to the period of frequency domain interference fringes. The proof-of-principle experiments were performed to prove that the proposed method can achieve absolute distance measurement in the X-band with standard deviations of 15 µm, 17 µm, and 26 µm and within ranges of 1.69 m, 2.69 m, and 3.75 m. Additionally, a displacement resolution of 100 microns was realized. The multi-target recognition performance was also verified in principle. Furthermore, at the expense of a slight decrease in ranging accuracy, a fast distance measurement with the single measurement time of 20 µs was achieved by using a digitizer combined with a Fourier transform analyzer. Compared with the current microwave precision ranging technologies, the proposed method not only has the advantages of high precision, large range, and rapid measurement capability, but the required components are also easily obtainable commercial devices. The proposed method also has better complex engineering applicability, because the ten-micron-level ranging accuracy is achievable only by using a simple Fourier transform without any phase estimation algorithm, which greatly reduces the requirement for signal-to-noise ratio.

All-Dielectric Tunable Terahertz Metagrating for Diffraction Control.

Recently, tunable metagratings have attracted substantial attention in manipulating the diffraction of electromagnetic waves with considerable flexibility, but they are usually limited to inherent ohmic loss due to the metal layers. The all-dielectric schemes can address this issue, but its design and optimization remain challenging in the terahertz regime, especially in the 6G communication window. In this work, an all-dielectric tunable terahertz metagrating is demonstrated in theoretical and experimental investigations. The metagrating operating in the 6G communication window bends the electromagnetic waves beam into the T-1 diffraction order by optimizing the unit cell. In the experiments, more than 72.46% of the transmitted energy is concentrated in the desired diffraction order for p-polarized light and more than 66.60% for s-polarized light, which agrees well with the theoretical design. The tunability by angular deflection is reported in this all-dielectric metagrating. Then, based on the all-dielectric metagrating arrays, a metalens with numerical aperture of NA = 0.39 at 0.14 THz is demonstrated. The subwavelength scale focal spot is obtained as 2.0 mm × 2.0 mm with the focusing distance of 117.8 mm. Imaging capability of the metalens is performed utilizing the transmission imaging manner. The measured and anticipated results are satisfactorily congruous with one another, which could validate our design. This work paves the way toward designing highly efficient and tunable devices with potential applications in terahertz communications, sensors, and super-resolution imaging.

Enhancing the Cycling Stability by Tuning the Chemical Bonding between Phosphorus and Carbon Nanotubes for Potassium-Ion Battery Anodes.

Phosphorus/carbon (P/C) composites as promising potassium-ion storage materials have been extensively investigated for its compound superiorities of high specific capacity and favorable electronic conductivity. However, the effects of different chemical bonding states between P and the carbon matrix for potassium-ion storage and cycling performance still need to be investigated. Herein, three P/C composites with different chemical bonding states were successfully fabricated through simply ball-milling red P with carboxylic group carbon nanotubes (CGCNTs), carbon nanotubes (CNTs), and reduced carboxylic group carbon nanotubes (RCGCNTs), respectively. When used as potassium-ion battery (PIB) anodes, the red P and CGCNT (P-CGCNT) composite deliver the most outstanding cycling stability (402.6 mAh g-1 over 110 cycles) with a favorable capacity retention of 68.26% at a current density of 0.1 A g-1, much higher than that of the phosphorus-CNT (P-CNT) composite (297.5 mAh g-1 and 50.40%). Based on the results of X-ray photoelectron spectroscopy and electrochemical performance, we propose that the existence of a carboxyl functional group will be instrumental for the formation of the P-O-C bond. More importantly, when compared with the P-C bond, the P-O-C bond can lead to a higher reversible capacity and a better long-term cycling stability as a result of the more robust bonding energy of the P-O-C bond (585 KJ mol-1) than that of the P-C bond (264 kJ mol-1). This work provides some insights into designing high-performance P anodes for PIBs.

Simultaneous measurement of the dynamic emissivity and the radiance of the shocked Al/LiF interface in the near-infrared wavelength.

A novel method based on signal superimposing has been presented to simultaneously measure the dynamic emissivity and the radiance of a shocked sample/window interface in the near-infrared wavelength. In this method, we have used three rectangle laser pulses to illuminate the sample/window interface via an integrating sphere and expect that the reflected laser pulses from the sample/window interface can be superimposed on its thermal radiation at the shocked steady state by time precision synchronization. In the two proving trials, the second laser pulse reflected from the Al/LiF interface has been successfully superimposed on its thermal radiation despite large flyer velocity uncertainty. The dynamic emissivity and the radiance at 1064 nm have been obtained simultaneously from the superimposing signals. The obtained interface temperatures are 1842 ± 82 K and 1666 ± 154 K, respectively, the corresponding release pressures are 65.7 GPa and 62.6 GPa, and the deduced Hugonoit temperatures are consistent with the theoretical calculations. In comparison, the fitting temperatures from the gray body model are 300-500 K higher than our experimental measurement results and the theoretical calculations.

A naked eye refractive index sensor with a visible multiple peak metamaterial absorber.

We report a naked eye refractive index sensor with a visible metamaterial absorber. The visible metamaterial absorber consisting of a silver dendritic/dielectric/metal structure shows multiple absorption peaks. By incorporating a gain material (rhodamine B) into the dielectric layer, the maximal magnitude of the absorption peak can be improved by about 30%. As the metamaterial absorber is sensitive to the refractive index of glucose solutions, it can function as a sensor that quickly responds to variations of the refractive index of the liquid. Meanwhile, since the response is presented via color changes, it can be clearly observed by the naked eyes. Further experiments have confirmed that the sensor can be used repeatedly.

Dynamic frequency-domain interferometer for absolute distance measurements with high resolution.

A unique dynamic frequency-domain interferometer for absolute distance measurement has been developed recently. This paper presents the working principle of the new interferometric system, which uses a photonic crystal fiber to transmit the wide-spectrum light beams and a high-speed streak camera or frame camera to record the interference stripes. Preliminary measurements of harmonic vibrations of a speaker, driven by a radio, and the changes in the tip clearance of a rotating gear wheel show that this new type of interferometer has the ability to perform absolute distance measurements both with high time- and distance-resolution.

Note: a novel method to measure the deformation of diamond anvils under high pressure.

A novel and simple method based on optical-fiber frequency domain interferometer to measure the deformation of diamond anvils under high pressure is presented. The working principle and application examples are given in this paper. The deformation of diamond anvils is obtained up to 37.7 GPa, our results verify that the deformation has an obvious difference between uploading and downloading at a given pressure, the maximum difference is up to 4.5 µm at 18.8 GPa, and the cupping effect is observed directly.

Twiddle factor neutralization method for heterodyne velocimetry.

Twiddle factor is considered to be the dominant error source of frequency estimate by Fourier transformation (FT), and thus impacts the accuracy in FT-based heterodyne velocimetry. Here we report a novel data analysis method for heterodyne velocimetry, which utilizes the change law of frequency errors with signals' phases to develop twiddle factor neutralization method, improving the performance of heterodyne velocimetry. Numerical simulations show that this method can improve velocity resolution by many times as compared to the boxcar, Hamming, and Hann window functions under different noise conditions. A 90° optical hybrid is used to generate four phase shifted signals for this method, and 1 m/s level velocity resolution and 100 ps level time resolution are simultaneously achieved in laser-shock experiments.

Optical-fiber frequency domain interferometer with nanometer resolution and centimeter measuring range.

A new optical-fiber frequency domain interferometer (OFDI) device for accurate measurement of the absolute distance between two stationary objects, with centimeter measuring range and nanometer resolution, has been developed. Its working principle and on-line data processing method were elaborated. The new OFDI instrument was constructed all with currently available commercial communication products. It adopted the wide-spectrum amplified spontaneous emission light as the light source and optical-fiber tip as the test probe. Since this device consists of only fibers or fiber coupled components, it is very compact, convenient to operate, and easy to carry. By measuring the single-step length of a translation stage and the thickness of standard gauge blocks, its ability in implementing nanometer resolution and centimeter measuring range on-line measurements was validated.

Note: using an optical phase-locked loop in heterodyne velocimetry.

An optical phase-locked loop was introduced in heterodyne velocimetry to lock the differential frequency between a fiber laser and an external cavity diode laser. An uncertainty less than 1 MHz of the locked beat frequency was achieved during several microseconds, corresponding to a velocity uncertainty at 0.1 m/s level for 1550 nm light. In this way, a measurement with higher precision and better time resolution simultaneously can be obtained during a transient process. Three proof-of-principles shots were performed to measure elastic wave-induced vibrations on surfaces of steel films with submillimeter thicknesses. The surface velocity fluctuations were probed with amplitudes of about 2 m/s and periods of tens of nanoseconds, and propagating times and sound velocities of waves were also well analyzed at a time scale 0.5 µs. A velocity resolution of 0.1 m/s level and a temporal resolution of a few nanoseconds were achieved in these measurements.