image: The LIG based metasurface with a size of 5 × 5 cm2 can be rapidly prepared in just 5 minutes under ambient atmosphere. The continuous modulation between wave transmission/shielding in an ultra-wide range of 9.66%–99.78% is achieved.
Credit: ©Science China Press
Electromagnetic shielding materials are often referred to as the “protective coat” of electronic devices, preventing external electromagnetic interference. However, conventional materials possess fixed physicochemical properties and thus provide only static protection, limiting their adaptability to real-time electromagnetic environments.
In response to the demand for next-generation adaptive smart electronics, the group led by Professor Daping He at Wuhan University of Technology has demonstrated a laser-induced graphene (LIG)–based strategy that enables the direct “drawing” of highly precise, patterned electromagnetic metasurfaces. Remarkably, a 5 × 5 cm2 metasurface can be fabricated within just 5 minutes. In practical application, simple rotation continuously tunes the shielding effectiveness from 9.66% to 99.78%, allowing rapid switching between wave transmission and shielding. Building upon this, the group designed a novel electromagnetic information encryption and encoding system derived from the LIG metasurface.
- Laser-focused/defocused-dependent properties of LIG
Laser pulses simultaneously trigger photothermal and photo-etching effects. When the laser is focused, energy is more concentrated with a higher energy density, resulting in a more pronounced photoetching effect. Consequently, the surface of PI rapidly forms a deep pit (steep cliff), where the photothermal effect causes heat to diffuse to surrounding areas, resulting in increased LIG thickness but insufficient crystalline domains. As a result, LIG exhibits more defects and lower electrical conductivity. When laser is defocused, the enlargement of the laser-irradiated area improves energy distribution with lower energy density, resulting in decreased photoetching effect. Meanwhile, the photothermal effect is enhanced which lead to enhanced growth of crystalline domains, resulting in less defects and better electrical conductivity.
- Electromagnetic modulation performance and mechanism
The LIG metasurface exhibits excellent switching behavior across the X-, Ku-, and K-bands (8–26.5 GHz). The minimum achievable SET is only 0.441 dB at 9.85 GHz, corresponding to a shielding efficiency of 9.66%. In contrast, the metasurface exhibits SET of 26.6 dB (shielding efficiency of 99.998%) upon Off-state at this frequency. This achievement is critical as it not only shows remarkable Off-state performance, but also addresses the challenge of suboptimal On-state performance in reported works, where the shielding efficiency is too high with the majority exceeding 50%.
Evaluated using the newly proposed reconfigurability factor (r), the LIG metasurface with an r value of 9.66 shows significant advantages over reported shielding switches. Mechanistically, conductive pathways in the LIG strips allow electrons to accelerate, prolonging their motion and efficiently converting incident electromagnetic energy into electron kinetic energy. This induces intense secondary radiation that suppresses transmitted waves in the “On” state. Conversely, when the electric field is perpendicular to the strips, electron response is limited, secondary radiation diminishes, and wave transmission dominates (“Off” state).
- Electromagnetic Encryption and Encoding
Using the LIG metasurface as a modular unit, researchers constructed a 3 × 5 coding array capable of representing all alphanumeric characters (0–9, A–Z). Moreover, a larger number of data points (such as color, transparency, depth, etc.) can be encoded in a single surface through different orientation of units from 0° to 90°, thus enabling, for instance, the encoding of a colored QR code storing substantial amounts of information.
Especially in the process of encoding and decoding, the following factors jointly determine the final results: (1) the wavelength and direction of incident waves, (2) the arrangement design of the encoded surface, (3) the distance between the surface and the scanning probe, and (4) the corresponding information detected from the electromagnetic strength. Therefore, a one-to-one mapping of incident wave-encoded surface-decoded information can be established, thereby enabling the as-prepared metasurface to be applied in electromagnetic encryption and decryption of critical information.
This work was published in National Science Review (NSR). Ph.D. candidates Pengfei Chen and Xinrui Yang are the co-first authors. Dr. Zhe Wang, Prof. Haoran Zu, and Prof. Daping He are the corresponding authors.