Intelligent metasurface imager and recognizer

Abstract

There is an increasing need to remotely monitor people in daily life using radio-frequency probe signals. However, conventional systems can hardly be deployed in real-world settings since they typically require objects to either deliberately cooperate or carry a wireless active device or identification tag. To accomplish complicated successive tasks using a single device in real time, we propose the simultaneous use of a smart metasurface imager and recognizer, empowered by a network of artificial neural networks (ANNs) for adaptively controlling data flow. Here, three ANNs are employed in an integrated hierarchy, transforming measured microwave data into images of the whole human body, classifying specifically designated spots (hand and chest) within the whole image, and recognizing human hand signs instantly at a Wi-Fi frequency of 2.4 GHz. Instantaneous in situ full-scene imaging and adaptive recognition of hand signs and vital signs of multiple non-cooperative people were experimentally demonstrated. We also show that the proposed intelligent metasurface system works well even when it is passively excited by stray Wi-Fi signals that ubiquitously exist in our daily lives. The reported strategy could open up a new avenue for future smart cities, smart homes, human-device interaction interfaces, health monitoring, and safety screening free of visual privacy issues.

Contributions and Risks of Artificial Intelligence (AI) in Building Smarter Cities: Insights from a Systematic Review of the Literature

“…AI systems, in combination with sensors, cameras and other data collection devices, have been developed to monitor the health and wellbeing of individuals [70,87]. Machine learning techniques can be used to improve the cost and efficiency of fall detection devices [99], and detect changes in sleep, mood, heartbeat, respiration, and other vital signs [118,129]. Wearable devices, or 'smart textiles, enabled by AI, can detect changes in the human body and report findings to health care providers [129].…”

Full Manipulation of the Power Intensity Pattern in a Large Space‐Time Digital Metasurface: From Arbitrary Multibeam Generation to Harmonic Beam Steering Scheme

“…[6,7] However, in most of these strategies, the metasurfaces are designed for a specific application and their scattering program remains unchanged after being fabricated. Digital metasurfaces accompanied by reprogrammable functionalities furnish a wider range of wave-matter functionalities which renders them especially appealing in the applications of imaging, [8] smart surfaces, [9] and dynamical THz wavefront manipulation. [10] All the above mentioned digital programmable architectures are spacecoding metasurfaces wherein the coding sequences are generally fixed in time and are controlled through a computerprogrammed biasing networks only to switch the functionalities whenever needed.…”

Metasurface‐Based Spatial Phasers for Analogue Signal Processing

“…One possible approach to achieve the required spatial phasers is the artificial surfaces, [ 20,21 ] or metasurfaces, which comprise periodic or quasi‐periodic arrays of subwavelength elements. They can alter the amplitude, phase, and polarization responses of the incident waves, and thus offer ideal toolkit to realize numerous functions, such as polarization conversion, [ 22 ] subwavelength imaging, [ 23 ] and hologram generation. [ 24,25 ] Since the advent of artificial surfaces, a series of metasurface‐based signal processing devices, such as integrator, [ 26 ] equation solver, [ 27 ] and spatial filter, [ 28 ] have been implemented in spatial domain and considered as promising candidates for future optical analogue computing systems.…”