Nonvolatile 1-bit Intelligent Reflective Metasurface for RF Wave Manipulation and Control

© 2025. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to use any copyrighted component of this work in other works must be obtained from the IEEE. Link to publisher version with DOI: 10.1109/TAP.2025.3544663. Non-volatile 1-bit Intelligent Reflective Metasurface for RF Wave Manipulation and Control Xiaoyu Xiao, Zirui Zhang, Yize Li, Yifan Mao and Zhirun Hu, Member, IEEE Abstract—Semiconductor switches have played a crucial role in electronically reconfigurable circuits and systems. However, their power consumption, especially static power dissipation is still a major challenge. As the number of switches increases in modern wireless communication and sensing systems, such as reconfigurable antenna arrays and large intelligent reflective surfaces for 5G wireless communications and microwave holography,static power consumption becomes enormous, resulting in low system power efficiency and requiring thermal dissipation management, which not only hinders their applications but also increases operational costs. To address this issue, non-volatile switches enabled reconfigurable 6 × 6 metasurface with zero static power consumption is demonstrated. We also report the fabrication and characterization of the non-volatile switch that shows promising performance for high endurance. By controlling the switch states on the metasurface, the reflected electromagnetic wave can be effectively manipulated without any static power supply. Index Terms—Memristive switch, nonvolatile switch, reconfigurable metasurface, static power supply, zero static power. I. INTRODUCTION WIRELESS communication systems in today’s technological era require intelligent wireless connections for the increasing functionality and frequency bands of mobile devices and cloud-based IoT applications [1], [2], [3]. The desirability of dynamic reconfigurability in radio frequency (RF) devices and circuits is crucial to facilitate enhanced functionalities and optimize performance in the realm of wireless communications. Reconfigurable antenna and metasurface have been widely studied due to their reconfigurability, which enables the deployment of multifunctional and compact IoT systems. These reconfigurable components utilize techniques such as microelectromechanical systems (MEMS) [4], PIN diodes [5], [6], varactors [7], and photoconductive elements [8] or materials such as ferrites [9], liquid crystals [10], or tunable resistive materials like vanadium dioxide (VO2) [11] to control their operational functionalities, such as resonant frequency, beam steering, bandwidth, polarization and radiation patterns. However, except for MEMS, their dependence This work was supported in part by U.K. Engineering and Physical Research Council under Grant EPN010345, in part by the European Partnership on Metrology (EPM) 23IND10 OnMicro project which has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme (Funder ID: 10.13039/100019599) and by the Participating States. (Corresponding author: Zhirun Hu.) The authors are with the Department of Electrical and Electronic Engineering, University of Manchester, M13 9PL Manchester, U.K. (e-mail: [email protected]; [email protected]; [email protected]; [email protected]; z.hu@manchester. ac.uk). on a continuous power supply to preserve their states increases their power consumption and restricts their applicability in low-power, autonomous applications [7], [12]. On the other hand, MEMS usually require a higher voltage to switch on/off hence control circuits are needed which dissipate static power. Furthermore, MEMS are expensive for most RF/microwave applications [13], [14], [15], [16]. Recently, the concept of non-volatile switches, also known as memristive switches, has been reported [17]. The beauty of this type of switches is that they do not require a DC holding voltage (hence zero static power consumption), which can significantly increase the energy efficiency for wireless reconfigurable systems. Non-volatile RF switches with Metal-Insulator-Metal (MIM) structures have been investigated [17], [18], [19]. In [20], nonvolatile chip RFID tags were developed, while a frequency switchable antenna on flexible substrate [21] and pattern reconfigurable antenna [22] using a non-volatile switch as a reflector/director have been reported. A non-volatile TiO2−x switch integrated with antenna array was proposed [23]. But it has relatively higher ON-resistance (240 Ω), which hinders its RF applications. Efforts have also been made to fabricate 2D material non-volatile RF switches [24], [25], [26], [27]. However, there are few reports on non-volatile switches for reconfigurable metasurface applications so far. In this work, we have designed, fabricated, and characterized a non-volatile 1-bit coded reconfigurable 6 × 6 metasurface. The rest of this article are organized as follows. We first present nonvolatile switch design, fabrication, and characterization in Section II. Nonvolatile reconfigurable metasurface design, and numerical simulation are given in Section III. Subsequently, measurement results of the nonvolatile metasurface are presented and discussed in Section IV, followed by the conclusions in Section VI. II. NONVOLATILE SWITCH DESIGN, FABRICATION AND CHARACTERIZATION A nonvolatile switch can change between two different states by setting bias voltage. The beauty of such a switch is that it does not dissipate static power once it is switched in either ONor OFF-state whereas all solid-state switches (such as transistors and diodes) consume DC power to sustain on-state. Although each solid-state switch may only consume a few milliwatts static power, deployment of nonvolatile switches has a huge advantage for large phase arrays and large intelligent reflective surfaces, where hundreds and thousands switch elements are needed. System efficiency can be greatly improved if non-volatile switches are used. From an energy IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 73, NO. 4, APRIL 2025 2 efficiency point of view, non-volatile switches are highly desirable for any electrical tunable and reconfigurable systems. A. Non-volatile switch fabrication In this work, the non-volatile switch was designed to work in Sand Cbands. Nafion was chosen as the electrolyte. The on resistance Ron should be as small as possible so to reduce the insertion lose. The non-volatile switch fabrication process is illustrated in Fig.1. It uses DuPontTM Kapton RHN(125µm) as substrate , which undergoes sequential ultrasonic cleaning in acetone, deionized water, and isopropanol for 5 minutes each. The process starts with evaporative deposition of a 200 nm thick silver layer using a nickel shadow mask as the active electrode. This is followed by spin-coating a uniform Nafion layer at 3000 RPM for 60 seconds and air-drying at 120 °C for 2 min. At last, a 200 nm thick gold layer is deposited on top, serving as an inert electrode to prevent any switching effects that may arise from interfacial metal oxide formation [21]. The Ag/Nafion/Au structure is depicted in Fig. 2, with a FIB-SEM cross-section in Fig. 3, showing the Nafion layer’s thickness of 70 nm. Fig. 1: Fabrication process of Nafion non-volatile switch. Fig. 2: An Ag/Nafion/Au switch. B. Nonvolatile Nafion switch characterization The switching process is achieved by utilizing an electric field of appropriate voltage to create a conductive connection between the two electrodes through the Nafion electrolyte, whereas the dissolution of this connection occurs through the application of an electric field with an opposite polarity, shown in Fig. 4. When the positive voltage is applied to Ag electrode, Fig. 3: Cross-section FIB-SEM view of the device. Fig. 4: Cross-sectional diagram of the Nafion non-volatile switch and its operation mechanism. and negative to Au, with a proper amount of applied voltage, metallic filament will be formed between the two electrodes through the Nafion. There is no need for voltage to sustain the metal channel hence no static power is needed to maintain the on-state. The metallic filament channel will be dissolved by applying a reverse pulse. The DC performance of the non-volatile switch is evaluated on a probe station (Research Instruments) using the Keithley 4200 semiconductor characterization analyzer under ambient circumstances. A current compliance of 11 mA was established to reduce the risk of device damage without impairing its nonvolatility. Fig. 5(a) illustrates the currentvoltage (I−V) characteristics of the nonvolatile switch (also known as memristive switch) over five cycles. It shows that when the applied bias voltage increases to around 2 V, the current rapidly increases and the switch turns to ON-state. Each cycle demonstrates various turn-on voltages, from 0.5 V to 2 V. It should be noticed that the switching of all types of non-volatile switches is a statistical process. This is related to the fact that conductive filament growth depends a lot on the local conditions. Since the local conditions change from cycle to cycle, it is natural to expect certain level of variations in the switching voltages and resistances of the onand off-states [28]. Low on-state resistance is essential for non-volatile RF applications with minimal insertion loss. To switch off the device, a negatively biased voltage pulse of 8 V was used, as shown in Fig. 5(b), illustrating the device having changed from a low-impedance state (LRS, on) to a high-impedance state (HRS, off). It is worth mentioning that Nafion nonvolatile switches can’t be turned off using continuous voltage but through voltage pulse [21]. The pulse width of 10 ms was used to turn the device off, as shown in Fig.5(b). The detailed switching speed capability of the device will be discussed in the following section. The HRS IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 73, NO. 4, APRIL 2025 3 (a) (b) (c) (d) Fig. 5: DC characteristics of the Nafion non-volatile switch. (a) I–V characteristics of typical switching on effect. (b) I – V characteristic of switching off (using voltage pulse). (c) Time-dependent retention measurements of the switch at room temperature. (d) Endurance of the switch with 40 manual DC switching cycles. and LRS resistances of the non-volatile switch were measured (Keithley 4200s Semiconductor Characterization Analyzer). The measurements are taken every 6 s for 107seconds at room temperature. 0.01 V were applied to the switch during the measurement. The retentions of both ONand OFF-states of the device are shown in Fig.5(c), revealing that the switch can sustain its performance long after it’s switched on/off stably. An exponential extrapolation of the data (dashed lines) suggests that the device will retain for at least 10 years [29]. The durability of the device has also been measured by cycling between on and off for 100 cycles manually shown in Fig. 5(d). From both retention and durance measurements, it can be found that the on/off ratio is greater than 103and the onresistance is around 12-13 Ω. The RF properties of the switch have also been investigated experimentally. The de-embedding method was used [29]. The intrinsic components of the non-volatile switch, such as the on, off-resistance (Ron,Roff ), and off-capacitance (Coff ) were extracted based on the simplified equivalent circuit model, as shown in Fig. 6(b), from measured data: Ron = 6.6 Ω,Roff = 1.2 MΩand Coff = 0.36 pF. The FOM = 1/(2 πRon Coff ) of the switch is 66 GHz. The insertion losses of on-state and off-state are depicted in Fig. 6(c) and (d), respectively. The switch has insertion loss less than 0.55 dB at the on-state. The schematic diagram of switch speed measurement setup is depicted in Fig. 7. The measurement setup involves monitoring the voltage across the resistor connected in series with the switch. The source voltage was provided by Agilent 33210A Function Generator and IRF520 MOSFET switching circuit. In Fig. 8, the applied voltage pulse has a duration of 6 ms for turning on the device and 10 ms for turning off. The duration was chosen to be much longer than the time it takes to turn the device on or off. The resistance of RMeasurement in Fig. 7 was carefully chosen to match the initial states of the switch. The turn-on waveforms is presented in Fig. 8(a). The (a) (b) (c) (d) Fig. 6: (a) Top view of the fabricated non-volatile switch with microstrip line. (b) Equivalent circuit of the switch. Measured (de-embedded) |S21|in (c) the on-state, and (d) off-state of the switch. Fig. 7: Switch speed measurement setup. (a) (b) Fig. 8: Measured voltage waveform. (a) Turn-on. (b) Turn-off. (a) (b) Fig. 9: (a) The unit cell of the proposed metasurface, in which a non-volatile switch is embedded for tuning the reflection phase. (b) The respective planes of incidence and metasurface. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 73, NO. 4, APRIL 2025 4 (a) (b) (c) (d) Fig. 10: Angular stability of the proposed unit cell with TE and TM incident modes. (a) Reflection magnitudes with different obliquely incident waves (TE mode). (b) Phase differences with obliquely incident wave (TE mode). (c) Reflection magnitudes with different obliquely incident waves (TM mode). (d) Phase differences with different obliquely incident waves (TM mode). 50 kΩseries resistor prevents the test system from entering the current limiting, even if the switch is momentarily opened. Nevertheless, once the system input voltage attains 3-9 V, the switch turns on with a rise time 0.34 µs to 0.13µs (10% to 90% Vs), indicating the higher the switch on voltage the shorter the turn on time.The turn off waveforms are depicted in Fig. 8 (b). A 10 Ωseries resistor limits the current and safeguards the system. As the amplitude of switch off voltage rises, the turn-off time also becomes shorter. When the voltage changes from -9V to -20V, the switching time changes from 24.8 µs to 5.6 µs, also showing that the turn off time depends on the applied voltage. III. NON-VOLATILE RECONFIGURABLE METASURFACE DESIGN TABLE I: Dimensions of the proposed metasurface. Parameter mm Parameter mm P25.2 G1.1 B0.1 Ux8.8 L1.6 Uy19.9 W6.9 U3.6 The unit cell of the proposed reconfigurable intelligent metasurface (RIM), consisting of 6 × 6 patches and 36 nonvolatile switches on FR-4 substrate with ground plate, is shown in Fig. 9(a). The on-state of the switch can be regarded as a pure resistor, whereas the off-state can be seen as a resistor in parallel with a capacitor as shown in the equivalent circuit model in Fig. 6(b). Two narrow strips placed along the patches are DC bias lines to control the switch on/off. Table 1 lists all the geometric parameters for the metasurface. In the CST simulation, the states of the non-volatile switch were modeled by its equivalent circuit. The resistance and capacitance of on-state (code: 1) are 6.6 Ωand 0 F, and of off-state (code: (a) (b) (c) (d) Fig. 11: Surface current density distributions at 4.45 GHz on the top layer of the metasurface for a normally incident wave (θ= 0°) (a) On-state (TE mode). (b) Off-state (TE mode). (c) On-state (TM mode). (d) Off-state (TM mode). 0) 1.2 MΩand 0.36 pF, respectively. The TEM wave is incident on the unit cell at the angles as indicated in Fig. 10. Periodic boundary conditions were assumed, meaning that the simulation was performed on infinitely large periodic structure. The unit cell has two states which are controlled by a nonvolatile switch. The reflection magnitude and phase difference of the proposed unit cell for different incident angles are illustrated in Fig. 10. To evaluate the angular stability, the reflection phases between onand off-states versus incident angles are simulated under TE and TM mode incident waves at incident angles of 0°, 15°, 30°, 45°, 60° and 75° respectively from 4 GHz to 5 GHz, as illustrated in Fig. 10. At the desired frequency 4.45 GHz, the unit cell has a reflection magnitude greater than -2 dB, and the phase difference can be maintained form 160° to 200° when incident wave angle varies between 0° and 45° for both TE and TM modes. Fig. 11 displays the surface current density distributions at 4.45 GHz on the metasurface for the normally incident wave, with distinct behaviors observed across different states and modes. In the on-state (Fig. 11(a) and (c)), there is a significant difference in current densities between TE and TM modes, with TE mode showing notably higher current density than TM mode. This highlights the polarization sensitive characteristics of the metasurface, attributed to the structural asymmetry of the device. In the off-state (Fig. 11(b) and (d)), TE mode currents predominantly distribute over larger metal patches, whereas TM mode currents concentrate on smaller patches. These observations underscore the nuanced electromagnetic properties of the metasurface, reflecting its sophisticated response to varying operational states and wave modes. The non-volatile 1-bit coded reconfigurable metasurface IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 73, NO. 4, APRIL 2025 5 Fig. 12: Simulated 2D and 3D reflected far-field scattering patterns of a non-volatile 1-bit coded reconfigurable metasurface with different coding sequences at 4.45 GHz, evaluated under incident angles of 0° and 30° for TM and TE polarized waves. (a) Coding sequence ‘001001’ (TM mode). (b) Coding sequence ‘111111’ (TM mode). (c) Coding sequence ‘101101’(TE mode). (d) Coding sequence ‘111111’ (TE mode). (e) Coding sequence ‘101101’ (TM mode). (f) Coding sequence ‘001001’ (TM mode). (g) Coding ‘010010’ (TE mode). (h) Coding ‘001001’ (TE mode). consists of a 6 × 6 array of elements that can be programmed into different coding sequences, where ”0” and ”1” represent the off-state and on-state, respectively. Fig. 12 illustrates the simulated 2D and 3D reflected far-field patterns for various coding sequences under normal and 30° incidence considering both TM and TE modes. In Fig. 12, the 2D orthographic projection is utilized to illustrate the far-field radiation pattern as a colormap. The transformation formulas are u=sinθcosϕ and v=sinϕsinθ. The simulated 2D and 3D reflected farfield patterns under different coding sequences with 0° incident wave show distinct responses, as seen in Fig. 12 (a)-(d). The results for the TM mode incident wave are depicted in Fig. 12(a) and (b), and for the TE mode incident wave in Fig. 12(c)-(d). Under a normally incident wave with a coding sequence of ‘001001’ with TM mode and coding sequence of ’101101’ with TE mode, the main reflected beams are directed into two directions, as shown in Fig. 12(a) and (c). When the coding sequence is ‘111111’, regardless of whether it is TM or TE mode, the electromagnetic waves are mainly reflected directly to where they come although having different sidelobe patterns, as depicted in Fig. 12(b) and (d). Fig. 12(e)- (h) illustrate the corresponding reflection waves for the 30° incident wave with TE and TM modes for different coding sequences. The simulation results show that the primarily reflected beam in TM mode exhibits a pronounced angular difference, the reflected wave can be steered from -21° to 32° IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 73, NO. 4, APRIL 2025 6 from coding sequence ‘101101’ to ‘001001’. For the TE mode, the beam achieves an angular deflection from 26 ° to 35 ° from coding sequence ‘010010’ to ‘001001’. This highlights the coded metasurface’s capability for beam manipulation for both TE and TM incident waves. IV. NONVOLATILE RECONFIGURABLE METASURFACE EXPERIMENTAL RESULTS AND DISCUSSIONS The fabricated reconfigurable metasurface is depicted in Fig. 13(a). To ensure the implementation of far-field plane wave excitation on the metasurface, a critical distance between the metasurface and the antennas has been established. This separation is determined to exceed 2 meters, a calculation based on the equation d= (2D2)/λ, where D represents the metasurface’s maximum dimension. To establish a baseline for reflection amplitude and phase, comparative measurements have been performed with a metal sheet, identical in size to the metasurface, serving as a reference standard. The metasurface was measured in the anechoic chamber using the apparatus depicted in Fig. 13(b) and (c). Two linearly polarized horn antennas (Aaronia AG, PowerLOG 70180) with a frequency range of 700 MHz – 18 GHz were used as transmitter and receiver, respectively. Fig. 13(b) shows the angle indicator, which is made by using plastic wires directly placed below the holder that holds the metasurface and is covered by absorbers during the measurement. Seen in Fig. 13(c), the receiving antenna is manually rotated to align with the wires. It is made sure that the distance between the antenna and metasurface is constant. The received signal is recorded every 5°. The transmitting antenna is placed at a fixed transmission angle. A VNA (N9918A vector network analyzer) is connected outside the chamber through a coaxial cable and time gating function of the VNA is used. Fig. 14(a) and (b) illustrate the measured reflected far-field patterns at 4.45 GHz for different coding sequences under normally incident waves with TM and TE modes. It can be seen that the primary beam is reflected directly along the incident path, resembling the behaviour of a metallic surface when the coding sequence is ‘111111’. In contrast, with coding sequence ‘001001’, the normally incident TM wave is predominantly reflected in two distinct directions. Similarly, for coding sequence ‘101010’, the normally incident TE wave is also reflected in mainly two directions but with much reduced magnitude. This manipulation forms a fundamental aspect of wave-chaotic operations, which involves the propagation of electromagnetic waves through intricate structures, resulting in intricate and unpredictable wave patterns, which provide a unique approach for enhancing the efficiency and resilience of information transmission and radar detection. For a TM incident wave at a 30° incident angle, the main beam is reflected at angles of -21° for the coding sequences ”101010”, whereas 32° for ”001001”, as shown in Fig. 14(c). However, when the incident wave is in TE mode, the main beam is reflected at angles of 26 ° for the coding sequence ”001001” and 35 ° for ”010010”, seen in Fig. 14(d), respectively, resulting in a deflection angle of 9 °. These experimental results are in reasonably good agreement with the simulated (a) (b) (c) (d) Fig. 13: (a) Photo of fabricated metasurface and (b), (c) measurement setup in the anechoic chamber and (d) VAN in the screen room outside the anechoic chamber. (a) (b) (c) (d) Fig. 14: Simulated and measured reflected far-field patterns of the non-volatile 1-bit coded reconfigurable metasurface at 4.45 GHz for TE and TM modes with 0° and 30 °incident angles. (a) TM polarization at normal incidence with coding sequences ’111111’ (black) and ’001001’ (blue). (b) TE polarization at normal incidence with coding sequences ’111111’ (black) and ’101101’ (red). (c) TM polarization at 30° incidence with coding sequences ’101101’ (black) and ’001001’ (red). (d) TE polarization at 30° incidence with coding sequences ’010010’ (purple) and ’001001’ (black). IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 73, NO. 4, APRIL 2025 7 TABLE II: Comparison of different works Ref. Number of Switches Static Power Supply (Assuming Half Working) (W) Bias Voltage (V) Switch fabrication process Pricing for single switch Switch Type [30] 20 ×20 5.80 1.33 Complicated 4.47$ MADP-00090714020x [31] 8 ×8×2 0.93 1.4 Complicated 2.36$ MADP-00090714020W [32] 10 ×16 4 1.10 Complicated 0.37$ BAR50-02V [33] 16 ×32 3.70 1.33 Complicated 4.47$ MADP-00090714020x [34] 3 ×3×2 1.08 0.95 Complicated 0.38$ Infineon BAR63-03W This work 6 ×6 0 1.70 Simple Not available in market Non-volatile RF Switch ones, demonstrating the non-volatile switch enabled coded metasurface’s capability to achieve dynamic beam steering for both TE and TM incident modes. These results demonstrate the metasurface’s capability to achieve precise and dynamic beam steering with different polarization incident waves. Thus, the beam steering performance of non-volatile reconfigurable metasurface is validated. These beams are controllable through the coding sequence, in addition to wireless communications, the ability of non-volatile reconfigurable metasurface to control and manipulate the reflected wave fronts can be also very useful for wireless sensing, radar cross section (RCS) reduction and microwave holography. It is found that the limitation of beam steering angle is due to small number of the array, more accurate beam reflection angle can be achieved by a larger dimension of metasurface [35]. In Table 2, we compare the non-volatile reconfigurable metasurface with those published works in recent years. The distinguishing feature of the switches used in this work is that they consume no static power, which is particularly useful for today’s wireless reconfigurable systems which need to be energy efficient so to contribute to net zero. For instance, whether it is large intelligent reflective surfaces or large reconfigurable antenna arrays, they require a large number of switching devices such as pin-diodes. If non-volatile switches are deployed, we are a step closer to achieving green communication. V. CONCLUSION In this paper, we have designed, fabricated, and characterized a zero-static power non-volatile RF reconfigurable metasurface. The measured DC characteristics of the switch have proved the non-volatility of the device. The reconfigurability has been experimentally demonstrated by embedding the switches into properly designed metasurface for electromagnetic wave manipulation. 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Xiaoyu Xiao received the B.Eng. degree in electronics from Chengdu University of Information Technology, Chengdu, China, and the M.Sc. degree (Hons.) from the Department of Electrical and Electronic Engineering, The University of Manchester, Manchester, U.K., in 2020, where he is currently pursuing the Ph.D. degree in wireless communication and intelligent reflecting surface technology. His research interests include non-volatile RF switches, graphene/2-D materials RF, and fifthgeneration wireless communications. Zirui Zhang received the B.Eng. degree (Hons.) from the Department of Electrical and Electronic Engineering, The University of Manchester, Manchester, U.K. He is currently a member of the Sensors and Electronics group in the Department of Electrical and Electronic Engineering. His research interests encompass antennas, metasurface, reconfigurable RF devices, graphene/2-D materials, and memristive devices. Yize Li received the M.Eng. degree (Hons.) from the Department of Electrical and Electronic Engineering, The University of Manchester, Manchester, U.K., in 2020, and the Ph.D. degree in the same department in 2025. His research interests encompass transparent antennas, reconfigurable RF devices, metamaterials, electromagnetic absorbers, graphene/2-D materials for RF applications, and fifth-generation (5G) wireless communications systems. Yifan Mao received the B.Eng. degree in communication engineering from Hangzhou Dianzi University, in 2019, M.Sc. degree (Hons.) from the Department of Electrical and ElectronicEngineering, The University of Manchester,Manchester, U.K., in 2020, where he is currentlypursuing the Ph.D. degree from wireless communication, intelligent reflecting surface technology, Department of Electrical and Electronic Engineering. Hisresearch interests include large intelligent surfaces,array signal processing, and sixth-generationwireless communications. Zhirun Hu (Member, IEEE) received the B.Eng. degree in telecommunication engineering from Nanjing University of Posts and Telecommunications, Nanjing, China, the master’s degree in business administration, and the Ph.D. degree in electrical and electronic engineering from the Queen’s University of Belfast, U.K.,He has published more than 250 peer-reviewed journals and conference papers. His current research interests include graphene/2D materials for RF, mmWave and THz communications and sensing applications, wearable electronics, RF, mmWave and THz device, and circuit and antenna design, realization, and characterization.