Smart Doppler Cloak Operating in Broad Band and Full Polarizations

Abstract

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.

Self-Powered Photoelectrochemical (Al,Ga)N Photodetector with an Ultrahigh Ultraviolet/Visible Reject Ratio and a Quasi-Invisible Functionality for 360° Omnidirectional Detection

“…The highest transmissivity can reach 82%, which is higher than those of the most reported GaN-based devices (Table ). Due to the high transparency in the whole visible range, PD-B could be regarded to have the quasi-invisible functionality, which is significant for the omnidirectional detection. ,,,, To intuitively demonstrate the transparency, we use a camera as Figure S5a to take pictures through the PDs. From Figure S5b,c, no obvious changes are obtained between the two images with and without PD-B, which demonstrate the quasi-invisible performance.…”

“…As a longstanding fantastic dream for humans, invisibility is now within the realm of possibilities because of the development of metamaterials, which are artificially structured materials exhibiting extraordinary properties that are not observed in natural materials. − Invisible and quasi-invisible devices can provide many novel functionalities and have the potential to open up a new branch of industry, such as invisibility cloaks, wearable intelligent electronics, automobile windshield navigation, IoT (Internet of Things) applications, and so on. ,− However, it is very challenging to realize an invisible or quasi-invisible device at all angles over a wide range, such as realizing an optoelectronic semiconductor in the visible range from 380 to 800 nm. ,, …”

A Self-Powered Transparent Photodetector Based on Detached Vertical (In,Ga)N Nanowires with 360° Omnidirectional Detection for Underwater Wireless Optical Communication

“…As clearly illustrated in Figure 3b, the maximum transmissivity of PD was over 60%, which is high compared with the most-reported GaN-based devices (Table 2). Due to the high transparency, the PD could be used for the omnidirectional detection [7,[18][19][20][21]. To intuitively demonstrate the transparency, we used a camera as Figure 3b to take pictures through the PDs.…”

Flexible Self‐Powered Photoelectrochemical Photodetector with Ultrahigh Detectivity, Ultraviolet/Visible Reject Ratio, Stability, and a Quasi‐Invisible Functionality Based on Lift‐Off Vertical (Al,Ga)N Nanowires

“…[1] Furthermore, invisibility is a longstanding fantastic dream for humans, which should lie in the development of non-natural/ artificially structured materials, including metamaterials. [2,[20][21] Thus, it is essential but highly challenging to realize the selfpowered (Al,Ga)N PEC PDs with both high flexibility and invisible functionality.…”