LABORATORY OF METAMATERIALS AND SENSORS

Funtions: Fundamental and applied research in the field of metamaterials, sensors, and other related areas. Responsibilities: Conducting scientific research, developing technologies, and implementing the application of research outcomes in areas defined by the group’s designated functions. Providing advanced training of human resources in disciplines authorized by the Institute and consistent with the designated functions of the Laboratory. Management of human resources, assets, and materials in compliance with the prevailing regulations of the State and the Institute. Carrying out other tasks assigned by the Director of the Institute. Primary Research Areas: Flexible control of the interaction mechanisms between electromagnetic fields and advanced material structures under various extreme conditions: narrowband/broadband perfect electromagnetic wave absorption at ultra-miniaturized scales (U-MPAs); narrowband transmission via the phenomenon of near-field Electromagnetically Induced Transparency (N-EIT); bound states in the continuum (BIC) for electromagnetic wave confinement; and geometry-induced tunable electromagnetic responses for reconfigurability. Expertise in: design and fabrication technologies; optimization, analysis, and data-screening technologies based on machine learning (AI); and integration of devices and sensors into advanced technological systems related to metamaterials. Establishing a strong research group through the close collaboration of highly experienced groups, all of whom are experts in pioneering new research directions in metamaterials and sensing. Development of MS-IoTs infrastructure integrating wireless multi-sensor networks with metamaterials, enabling real-time environmental monitoring with high accuracy under extreme conditions. Infrastructure for wireless energy management, transmission, and storage integrated with metamaterials (MM-WPTs, MM-TPVs) for low- to medium-power devices. Multispectral camouflage technology (S-MPAs): electromagnetic wave absorption in the radar frequency range combined with low infrared emission for defense and security applications. Multispectral camouflage technology (S-MPAs): electromagnetic wave absorption in the radar frequency range combined with low infrared emission for defense and security applications.

Contact Details of the Head of the Laboratory -  Full name and academic title: Professor Nguyen Thanh Tung -  Office address: Room 321, Building A2, Institute of Materials Science, Vietnam Academy of Science and Technology -  Tel.: 0912 994 444 -  Email: tungnt@ims.(*)  -   note: replace (*) = vast.ac.vn

LIST OF MEMBERS AND COLLABORATORS

KEY ACHIEVEMENTS

1. Breakthrough Results in Fundamental Research

1.1. Broadband Absorbing Metamaterial Structures

Figure 1. (a) Schematic illustration of the metasurface (MS) of the broadband absorbing metamaterial structure, (b) unit cell, and (c) absorption spectra under both TE and TM modes.

The absorption of electromagnetic waves over a broadband frequency range with polarization insensitivity and angle independence is highly desirable for modern technological applications. Many metamaterial-based structures have been proposed to address these requirements; however, such designs are often multilayered and complex, or rely on special materials or external electrical components, such as resistors. In this paper, we present a metasurface structure fabricated in a simple manner using standard printed circuit board technology, yet capable of achieving high absorption above 90% over a broadband frequency range from 12.35 to 14.65 GHz, as illustrated in Fig. 1(a). The metasurface (MS) consists of unit cells composed of four symmetrical sub-structures assembled by metallic bar patterns, which generate broadband absorption through planar resistive-like interactions within the pattern without employing actual resistor components. Analytical, simulation, and experimental results demonstrate that the metasurface is also polarization-insensitive and maintains absorption above 90% at incident angles up to 45°. The proposed metasurface plays a fundamental role in absorber design and can be extended for absorber development at different frequency bands. Furthermore, enhanced absorption performance may be achieved through design refinements and improved fabrication techniques, paving the way for the integration of metamaterials into both civilian and military applications.

1.2. Tuning the properties of metamaterials exhibiting negative permeability and negative refractive index via external perturbations.

The research group has investigated and designed a metamaterial structure integrated with graphene to control negative refractive index characteristics in the terahertz frequency range. By varying the chemical potential of graphene from 0.0 to 1.0 eV, we demonstrated flexible control of negative refractive index properties, enabling a convenient transition between a transmission mode, in which electromagnetic waves can propagate within the frequency range where the material exhibits a negative refractive index (at 0.0 eV), and a reflection mode (at 0.8 eV), achieved through the integration of a graphene disk-array structure at room temperature, as illustrated in Fig. 1(b). The tunability of carrier density in graphene allows for the realization of the desired electromagnetic interactions between the metamaterial structure and electromagnetic waves in the THz regime. In addition, we studied the effect of temperature variation on the metamaterial under applied external voltage. Through extended simulations using the finite integration technique (FIT), we identified the capability of tuning the negative-index frequency region in the proposed metamaterial design. Our findings open promising opportunities for the application and development of multifunctional terahertz electronic devices.

1.3. Tuning the absorption and polarization properties of metamaterials through external voltage application.

Over the past year, research on metamaterials has been directed toward tunable, intelligent, and multifunctional devices. Specifically, studies have focused on implementing functionality that enables switching between absorption and polarization conversion (PC) states in metamaterial (MM) structures through the integration of varactor diodes, as illustrated in Fig. 3. In this configuration, varactor diodes are incorporated into the resonant structure of the MM and are tuned by external voltage to allow switching between absorption capability and polarization conversion. The proposed MM structure, referred to as the integrated MM, features an optimized unit cell as shown in Fig. 1(c), and has been experimentally characterized using the vector network analyzer (VNA) system installed at the Institute. The dependence of the co-polarized and cross-polarized reflection coefficients (PCR) and the total absorption of the hybrid MM on the applied bias voltage (from –19 V to 0 V) is presented in Fig. 1(c). PCR gradually increases as the magnitude of the bias voltage decreases, reaching nearly 90% at V = –19 V, as shown in Fig. 1(c). This demonstrates the crucial role of varactor diodes in enabling switching between absorption and PC states. The experimentally measured PCR values reached 81.5% (at 3.5 GHz) and 85.2% (at 3.6 GHz) at bias voltages of 0 V and –4 V, respectively. Potential applications of this research include frequency filters, sensors, telecommunications, and satellite technologies.

1.4. Enhancing the transmission efficiency of magnetically induced waves in two-dimensional inhomogeneous negative-permeability metamaterial structures.

In this study, we investigate the transmission of magneto-inductive waves (MIWs) in metamaterial structures with negative permeability. The inhomogeneous metamaterial slab consists of a 9 × 9 array of unit cells fabricated using a five-turn spiral structure on an FR-4 substrate, as shown in Fig. 1(d). Capacitors with values of 40 pF or 50 pF are attached to control the resonant frequency of each unit cell. The unit cells loaded with 50 pF capacitors resonate at 18 MHz, while those loaded with 40 pF capacitors resonate at 20 MHz. The higher-frequency resonating cells form a resonant cavity capable of localizing the magnetic field into a region much smaller than the wavelength of the magneto-inductive wave. Owing to the strong magnetic field confinement of the resonant cavity, magneto-inductive waves propagate much more efficiently in the inhomogeneous metamaterial structure compared to its homogeneous counterpart. Furthermore, we also explore the development of wireless power transfer methods based on magnetic resonance effects in conductive environments, employing metamaterials to enhance transmission efficiency.

In addition to the prominent studies mentioned above, other research directions are also being pursued, such as metamaterials exhibiting electromagnetically induced transparency (EIT), graphene-integrated metamaterials for broadband absorption enhancement, and origami-inspired metamaterial structures for controlling electromagnetic wave absorption properties.

2. Research and development of practical technologies

2.1. The features and technical specifications of the H₂ gas sensing device are summarized as follows:

• Measurement range: 0-100%LEL
• Resolution: 1%LEL
• Error: <5%LEL
• Capable of continuous on-site measurement and alarm; updates every 1 s with a 7-segment LED display.
• Power supply 5V-200mA
• Connectivity: PC interface and integration with alarm network system through RS485.
• Designed for operation in environments with temperature and humidity ranges of 0–50 °C and 0–95% RH.

2.2. A system for monitoring and controlling CO₂ concentration (using the fabricated sensor) based on IoT technology, implemented in an edible mushroom cultivation facility.

• IoT system for monitoring and controlling CO₂ parameters in mushroom cultivation.:
• Continuous 24/7 monitoring and control of CO₂ concentration with the fabricated gas sensor (range: 0–10,000 ppm; standard deviation: 50 ppm).
• Response time / data update: < 2 minutes
• On/off control of external devices via 4 ports (fan, humidifier, lighting, etc.), with programmable operating modes.
• Operating power supply: 220 VAC

Figure 2. Illustration of the environmental monitoring system (gas, temperature, and humidity sensors) integrated with metamaterials in a real-world environment.

REPRESENTATIVE PUBLICATIONS

[1] Hai Anh Nguyen, Thanh Son Pham, Bui Son Tung, Bui Xuan Khuyen, Dac Tuyen Le, Hai Yen Vu, Dinh Lam Vu, Nguyen Thi Hien,“Metamaterials based on hyperbolic-graphene composite: A pathway from positive to negative refractive index at terahertz”, Computational Materials Science 248, 113574 (2025).

[2] Nguyen Ngoc Linh, Le Thi Hong Hiep, Nguyen Khanh Viet, Huu Nguyen Bui, Hai Anh Nguyen, Bui Son Tung, Bui Xuan Khuyen, Thanh Son Pham and Vu Dinh Lam, “Patterned ground shielding for wireless power transfer system based on 1D metamaterial array in conductive media”, Physica Scripta, 100, 6 (2025).

[3] Bui Xuan Khuyen, Pham Duy Tan ,Bui Son Tung, Nguyen Phon Hai, ,Pham Dinh Tuan ,Do Xuan Phong, Do Khanh Tung, Nguyen Hai Anh, Ho Truong Giang, Nguyen Phuc Vinh, Nguyen Thanh Tung, Vu Dinh Lam, Liangyao Chen and YoungPak Lee, “Numerical Optimization of Metamaterial-Enhanced Infrared Emitters for Ultra-Low Power Consumption”, Photonics, 12(6), 583 (2025)

[4] Bui Xuan Khuyen, Nguyen Van Ngoc, Dinh Ngoc Dung, Nguyen Phon Hai, Nguyen Thanh Tung, Bui Son Tung, Vu Dinh Lam, Ho Truong Giang, Pham Duy Tan, Liangyao Chen, “Dual-band infrared metamaterial perfect absorber for narrow-band thermal emitters”, Journal of Physics D: Applied Physics, 57, 28 (2024)

[5] H. A. Nguyen, B. S.Tung, X. C. Nguyen, V. D. Lam, T. H. Nguyen, B. X. Khuyen, “Tunable dynamic metamaterial for negative refraction”, Journal of Physics and Chemistry of Solids, 186, 111804 (2024).

[6] Tran Van Huynh, Vu Dinh Lam, Bui Xuan Khuyen, Bui Son Tung, Nguyen Thanh Tung, “Controlling THz Absorption Properties of Metamaterials Based on Graphene”, Journal of Electronic Materials 52, 5719-5276 (2023).

[7] Le Thi Hong Hiep, Thanh Son Pham, Bui Xuan Khuyen, Bui Son Tung, Quang Minh Ngo, Nguyen Thi Hien, Nguyen Thai Minh and Vu Dinh Lam, “Enhanced transmission efficiency of magneto-inductive wave propagating in non-homogeneous 2-D magnetic metamaterial array”, Physica Scripta, 97, 2 (2022).

[8] Duong Thi Ha, Dinh Ngoc Dzung, Nguyen Van Ngoc, Bui Son Tung, Thanh Son Pham, YoungPak Lee, Liang Yao Chen, Bui Xuan Khuyen, Vu Dinh Lam, “Switching between perfect absorption and polarization conversion, based on hybrid metamaterial in the GHz and THz bands”, J. Phys. D: Appl. Phys. 54, 234003 (2021).

[9] Hoang Thi Hien, Do Thi Anh Thu, Pham Quang Ngan, Giang Hong Thai, Do Thanh Trung, Man Minh Tan, Ho Truong Giang, “High NH3 sensing performance of NiO/PPy hybird nanostructures”, Sensors and Actuators B, 340, 129986 (2021).

[10] Do Thi Anh Thu, Vu Thai Ha, Ho Truong Giang, Pham Quang Ngan, Giang Hong Thai, Le Anh Thi, Man Minh Tan, Tran Dai Lam, “Bi2S3 Nanowires: First-Principles Phonon Dynamics and Their Photocatalytic Environmental Remediation”, The Journal of Physical Chemistry C, 125 4086-4091 (2021).

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