Wi-Fi Frequency Bands Research Articles

Quad-Band Rectifier Circuit Design for IoT Applications

In this work, a novel quad-band rectifier circuit is introduced for RF energy harvesting and Internet of Things (IoT) applications. The proposed rectifier operates in the Wi-Fi frequency band and can supply low-power sensors and systems used in IoT services. The circuit operates at 2.4, 3.5, 5, and 5.8 GHz. The proposed RF-to-DC rectifier is designed based on Delon theory and Greinacher topology on an RT/Duroid 5880 substrate. The results show that our proposed circuit can harvest RF energy from the environment, providing maximum power conversion efficiency (PCE) greater than 81% when the output load is 0.511 kΩ and the input power is 12 dBm. In this work, we provide a comprehensive design framework for an affordable RF-to-DC rectifier. Our circuit performs better than similar designs in the literature. This rectifier could be integrated into an IoT node to harvest RF energy, thereby proving a green energy source. The IoT node can operate at various frequencies.

Warm Rydberg atom-based quadrature amplitude-modulated receiver

Rydberg atoms exhibit both remarkable sensitivity to electromagnetic fields making them promising candidates for revolutionizing field sensors and, unlike conventional antennas, they neither disturb the measured field nor necessitate extensive calibration procedures. In this study, we propose a receiver design for data-modulated signal reception near the 2.4 GHz Wi-Fi frequency band, harnessing the capabilities of warm Rydberg atoms. Our focus lies on exploring various quadrature amplitude modulations and transmission frequencies through heterodyne detection. We offer a comprehensive characterization of our setup, encompassing the atomic response frequency range, attainable electric field amplitudes, and sensitivity, which we estimate to be equal to 0.50 µV cm−1 Hz−0.5. Additionally, we delve into analyzing communication errors using Voronoi diagrams and evaluating the communication channel capacity across different modulation schemes. We find that the maximum achievable capacity for a single communication channel equals 19.3 Mbps and can be achieved using the QAM4 scheme.

Compact, Broadband and High Gain Uniplanar Quasi-Yagi Microstrip Antenna for End-Fire Radiation

This paper describes a uniplanar, compact, broadband, and high gain quasi-Yagi microstrip antenna to achieve radiation in the end-fire direction. The major elements of the proposed antenna include one element of each: reflector, ground plane (acts as another reflector), driven, and director. The concept of microstrip and Yagi-Uda antennas are coupled to lower the inter-element spacing, thus reducing the antenna dimensions along the boom length significantly. U-shaped reflector elements are used to reduce the lateral dimension of the antenna. The antenna's directivity is enhanced in the lower and upper-frequency bands with the help of reflectors and directors, respectively. A compact size of (0.52 × 0.22 × 0.009) has been achieved along with an impedance bandwidth of 46.5% for |S 11| < −10 dB and a peak gain of 6 dBi (with 1 dB variations) over the entire bandwidth. The novelty of the proposed uniplanar quasi-yagi MSA is proved by comparing the Figure of Merit (FoM) with the reported work. The proposed antenna is fabricated, and the measured results are in good agreement with the simulated results. The proposed uniplanar quasi-Yagi antenna is ideal for wireless applications that required end-fire radiation in 2G, 3G, 4G, Wi-Fi frequency bands, and portable direction-finding devices.

Target driven design of electromagnetic metamaterial for dual-band Wi-Fi energy harvester

With the development of Internet of things (IoT), there have a large amount of interconnected devices communicates with each other through electromagnetic (EM) waves sent by Wi-Fi router. It is promising to harvest Wi-Fi energy realizing wireless power transmission for sensors or microelectronic devices. However, the energy is hardly to be harvested effectively due to the complexity and disorder of EM waves. To address such issue, we propose an EM metamaterial based on parametric equation as dual-band Wi-Fi energy harvester operating at 2.45 GHz and 5.8 GHz. By adjusting these equation parameters, the prototype can achieve almost an arbitrary shape, avoiding the problem of local optimal solutions. Through the co-simulation of MATLAB and CST Studio Suite software, we design a genetic algorithm (GA) to optimize the proposed structure so that it can harvest energy at Wi-Fi frequency bands. The optimized metamaterial exhibits electric dipole resonance and magnetic dipole resonance simultaneously at 2.45 GHz and 5.8 GHz, and the maximum harvesting efficiency is 96.9% and 95% at normal incidence, respectively. In particular, the metamaterial has the characteristics of polarization insensitive, ultra-wide band and wide-angle harvesting. It is expected to integrate with small electronic devices to realize the function of remote energy conversion, self-powered, and maintenance-free in the era of advanced wireless networks.

Wi-Fi inside an airplane

In this work, we present results for measurements of personal exposure to Radiofrequency electromagnetic Fields (RF-EMF) from 2.4 GHz Wi-Fi and 5.8 GHz Wi-Fi frequency bands while travelling by airplane. The flight was taken by a researcher of this work, it departed from Barajas Adolfo Suarez Airport in Madrid (Spain) and arrived in Benito Juárez International Airport (Mexico City – Mexico), on the 20th of June 2021. The measurements were carried out using two EME SPY 140 personal exposimeters. Results indicate that exposure levels change at any moment. Values are variable when the researcher is inside the airplane prior to takeoff or landing, when the airplane is airborne and when the Wi-Fi is in use or not. The average value registered during the whole flight was 123 μW/m2 with a 95 percentile of 273 μW/m2 in 2.4 GHz Wi-Fi frequency band, and the average value was 87.1 μW/m2 with a 95 percentile of 184 μW/m2 in 5.8 GHz Wi-Fi frequency band.

Frequency Integration of Dual-band Hexagonal Metamaterial Resonator antenna for Wi-Fi and 5G Wireless Communication

Abstract The integration of 5G mm-wave and Wi-Fi frequency bands becomes significant for upcoming 5G wireless applications for providing a large frequency ratio. This work presents a frequency reconfigurable hexagonal metamaterial resonator (HMR) antenna for Wi-Fi and a 5G mm-wave frequency band. A PIN diode is utilized to link up a microstrip patch antenna (MPA) with HMR to achieve integration of the Wi-Fi frequency band. The resonant frequency of the proposed antenna is 5 GHz (Wi-Fi) and 27.87 GHz with peak gain 2.33 dB and 7.12 dB, respectively. The operating bandwidth of the proposed antenna is 800 MHz (4.5-5.3 GHz) and 1020 MHz (27.35-28.37 GHz). The rogers RT5880 substrate with thickness 0.508 mm, dielectric constant 2.2, and loss tangent 0.009 has been used for designing the antenna. The overall size of the antenna is 30×23×0.508 mm3.

A Dual-Band Antenna Design for 2.4 and 5 GHz Wi-Fi Applications

In these days, with the improvement of wireless and mobile communication, Wi-Fi technology is everywhere in life. When wireless communication standards are examined, it is observed that 2.4 GHz (2.4-2.4835 GHz) and 5 GHz (5.15-5.825 GHz) frequency bands are used as the Wi-Fi frequency band. Therefore, in this paper, a microstrip Wi-Fi antenna design with dual band performance at 2.4 GHz and 5 GHz frequencies has been achieved. Thanks to the choice of microstrip antenna. It will be ensured that the proposed antenna has the advantageous features of microstrip antennas compared to other antennas. The feed of the antenna will realize with a microstrip line. FR-4 substrate is used as dielectric material with a thickness of 0.8 mm. Thanks to the preferred materials and cheap production cost, fabrication of the antenna is considered. The CST Studio Suite is preferred by the world's largest technology and engineering companies, as it provides a market advantage over the products by providing a shorter development period and lower cost. The design stages of the antenna have been carried out using CST Studio Suite. Also, important parameters of the antenna have been examined and optimized bandwidth, input impedance, resonance frequency, reflection coefficient, return loss, etc. As a result, dual-band Wi-Fi antenna design has been determined with wide bandwidth and high gain.

Flexible and Wearable Hybrid RF and Solar Energy Harvesting System

In this article, we demonstrate a flexible and wearable hybrid radio frequency (RF) and solar energy harvesting system for powering wearable electronic devices. The system consists of a flexible transparent antenna, a flexible transparent rectifying circuit, and an amorphous silicon solar cell. By utilizing transparent stacked structure, the rectenna and the solar cell can provide more hybrid output power to accommodate more application scenarios. The flexible transparent antenna shows two impedance matching bandwidths of 3.5–3.578 and 4.79–5.09 GHz, covering n78/n79 fifth-generation (5G) communication frequency band and 5-GHz WiFi frequency band. At the frequency of 3.5 GHz, the flexible transparent rectifying circuit achieves a high RF-to-dc conversion efficiency of 54.67% at 13 dBm RF input power. In the room with a light intensity of 210 lux, compared with a single solar cell, the hybrid energy harvesting system can obtain an additional 35.6%–769.5% output power when the RF source power is varied from 4 to 10 dBm. These results demonstrate that the proposed flexible and wearable RF-solar energy harvester can provide reliable electric power supply, which can be a potential candidate for powering wearable electronic devices, distributed sensors and IOT devices.

An ultra‐wideband polarization insensitive frequency selective surface for shielding applications

A dual layer polarization-insensitive frequency selective surface (FSS) with ultra-wideband response for electromagnetic shielding is presented in this article. In the proposed configuration, a single layer FR4 dielectric substrate is used in which the top metallic layer comprises of combined square and circle loop and the bottom metallic layer comprises of combined swastika shape and circle loop. The proposed FSS exhibits a 13.5 GHz ultra-wide stop band response from 2.3 to 15.8 GHz. The proposed FSS has a fractional bandwidth of 148%, and the structure is polarization insensitive for the incident angles up to 450 in both TE and TM modes. The performance of the simulated structure is compared with the fabricated structure and the measured results are in tune with the simulated results. It can be used for shielding applications of Wi-Fi frequency bands 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, 6 GHz, X band microwave link communication, and aircraft mobile satellite services.

AIR-FI: Leaking Data from Air-Gapped Computers Using Wi-Fi Frequencies

This paper presents a new attack allowing attackers to exfiltrate data from isolated, air-gapped computers via Wi-Fi frequencies. We show that malware in a compromised air-gapped computer can generate signals in the Wi-Fi frequency bands. The signals are generated through the memory buses - no special hardware is required. Sensitive data can be modulated and secretly exfiltrated on top of the signals. We show that nearby Wi-Fi-capable devices (e.g., smartphones, laptops, and IoT devices) can intercept these signals, decode them, and send them to the attacker over the Internet. We utilized the physical layer information exposed by the Wi-Fi chips to extract the signals. We further implemented the transmitter and receiver and discussed design considerations and implementation details. We evaluated this covert channel in terms of bandwidth and distance and presented a set of countermeasures. Our evaluation shows that data can be exfiltrated from air-gapped computers to nearby Wi-Fi receivers located meters away at bit rates of 16&#x00A0;b/sec.

Train-mounted Broadband Monopole Antenna for 5G Communication

As a convenient and efficient public transport system, high speed railway (HSR) was rapidly deployed in China. Since the fifth generation (5G) mobile communication system is commercially applied, it is necessary for mobile terminals antennas to cover multiple operating bands to be compatible with various communication systems. Here a HSR-mounted broadband and high-gain monopole antenna is proposed. By using the meander technology and introducing the tapered structure, the proposed antenna operates over a bandwidth of 694-960 MHz and 1350-5975 MHz (VSWR&lt;1.8), which covers both 2G-5G mobile communication and WiFi frequency bands. The dimensions of the proposed antenna are 400 mm × 330 mm × 78 mm. The measured average gain is 6.11 dBi over the entire bandwidth.

Beam-Steerable Transponder Based on Antenna Array and Phased Modulators

This letter presents a novel concept of beam-steerable transponder based on antenna array and phased modulators. The steerability of the beam is achieved by optimally delaying the modulated reflected signal at each antenna element (i.e., changing the phase in frequency domain) with load modulation technique. In this manner, the reflected backscattered signal power can be maximized at one particular direction. The approach makes transponder to collect ambient waves from any direction and further modulate and redirect it to any other direction. The results obtained through experimentation proves the feasibility of omnidirectional transponder and pave way for future lower power smart devices. The transponder functions in the Wi-Fi frequency band of 2.4 GHz.

The Novel CPW 2.4 GHz Antenna with Parallel Hybrid Electromagnetic Solar for IoT Energy Harvesting and Wireless Sensors

The design and implementation's novelty simultaneously utilizes the antenna's frequency, polarization, and feed structure to maximize the harvested RF energy and become a microstrip communication circuit for wireless sensor or communication systems in IoT devices. In addition, the optimization of the parallel circuit configuration has a voltage doubler model with an integrated parallel system and thin-film solar cells. Implementation of the antenna structure has two-line feeds in one antenna. Usage both feeds have the same function as CPW circular polarization. Another advantage is that there is no miss-configuration when installing the port exchanges when using both output ports simultaneously. The 2-port antenna has an area of 1/2 per port (where accessible wavelengths work well at the 2.4 GHz frequency). It has been shown to achieve a relatively narrow bandwidth of 86.5 percent covering WiFi frequency band networks and IoT communications. It does not require additional filters and analog matching circuits that cause power loss in the transmission process in parallel voltage doubler circuits. Integrating a reflector on the CPW antenna with two ports for placement of thin-film solar cells provides antenna gain of up to 8.2 dB. It provides a wide beam range with directional radiation. Using a multi-stage parallel to increase voltage output and integrated with a thin-film solar cell converter proves efficient in the 2.4 GHz frequency band. When the transmission power density is -16.15 dBm with a tolerance of 0.023, the novel energy harvester configuration circuit can produce an output voltage of 54 mV dc without adding solar cell energy. And Integrated thin-film solar cell a light beam of 300 lux in the radiation beam area of -16.15 dBm, the energy obtained has a value of 1,74467V. It also shows that the implementation of this configuration can produce an optimal dc output voltage in the actual indoor and outdoor ambient settings. The optimization of antenna implementation and the communication process with Multiple signal classifications improves the configuration of antennas that are close to each other and have identical phase outputs. It is instrumental and efficient when applied to IoT devices.

Isolation improvement of compact LTE MIMO terminal using combination of neutralisation line and modified ground structure

A multi-wideband MIMO antenna is presented for LTE MIMO terminals. The proposed antenna covers LTE700, GSM1800, GSM1900, UMTS, LTE2500, and Wi-Fi frequency bands. The multi-antenna elements are placed at the top two corners of printed circuit board (PCB) in the mirror image position. Each antenna element consists of a driven element and a shorted radiating element. To make the compact antenna structure, radiating element is meandered, folded, and shorted to the ground through copper wire. The size of each radiator is 15 × 25 × 4 mm3. Further, a combination of neutralisation line and modified ground structure is designed and deployed between radiating elements to reduce the mutual coupling between them. According to the measurement results of the fabricated antenna prototype, the isolation between two antenna ports is better than -12 dB over the operating frequency band. The simulated and measured results are found in close agreement. Moreover, to investigate the performance of the proposed antenna on the real application platform, mobile environment and user proximity analyses are carried out. Besides, total radiated power (TRP), channel capacity loss (CCL) and specifi c absorption rate (SAR) to peak location spacing ratio (SPLSR) are calculated and found well below the limit of Federal Communication Commission (FCC) standard.

Effect of Dielectric Substrate Parameters Which Dimensions of Lens and Distance From Antenna on The Gain Enhancement of Microstrip Antenna with Metamaterial

In this study, it was aimed to determine the effect of dielectric substrate parameters which dimensions of lens and distance from antenna used as lens layer in front of antenna on antenna gain for the 2.45 GHz Wifi frequency band and calculate the effect of dielectric substrate on increasing the gain of classical microstrip antenna by using metamaterial lens layer (Square split ring resonator). For this purpose, a conventional microstrip antenna with a center resonant frequency of 2.45 GHz was first designed with the help of an electromagnetic simulation program. Then, the dielectric lens layer's size and distance from the antenna parameters were optimized and a maximum gain of 16% was obtained. In addition, it was determined that the dielectric lens layer size had more effect on increase of gain than the distance between antenna and lens layers. Then, the dielectric lens layer, 5λ / 16 antenna size and λ / 4 antenna distance which selected randomly, was designed and placed as a lens in front of the antenna (without using metamaterial). It was observed that the dielectric lens layer had an effect of antenna gain of about 7% for the single layer and 22% for the double layer. A square split ring resonator-shaped metamaterial lens layer with the same parameters as the resulting dielectric lens layer was then designed and placed in front of the conventional microstrip patch antenna for the 2.45 GHz Wifi frequency. It was observed that the lens layer with metamaterial increased the gain of the antenna by about 22% by placing it in single layer and 87% by placing it in double layer in front of the conventional microstrip amenna.

Broadband and high gain multilayer multiresonator elliptical microstrip antenna

In this study, a low cost, broadband and high gain multilayer multiresonator microstrip antenna (MSA) is designed. It consists of one metallic fed patch at the bottom layer and two circular patches (1B2 T) are printed on the bottom side of the top FR4 substrate layer, which is air suspended. Two configurations with the bottom patch of circular and elliptical shapes are compared. The elliptical 1B2 T MSA provides better bandwidth (BW), i.e. 53.4% with peak gain of 9.8 dBi. The antenna design parameters are selected to provide maximum BW with uniform gain. The elliptical 1B2 T MSA is further enclosed in a metallic cavity, which improves the BW, gain and front to back (F/B) ratio of the antenna. The elliptical 1B2 T MSA with cavity enclosure is fabricated and tested. Experimental results are in agreement with simulated ones. The elliptical 1B2 T MSA with cavity provides 55.7% BW with peak gain of 12.1 dBi and F/B of >18 dB. The proposed antenna can be used in GPS, 2G, 3G, 4G and Wi-Fi frequency bands applications.

Failed handoffs in collaborative Wi-Fi networks

Cognitive radio networks enable a more efficient use of the radioelectric spectrum through dynamic access. Decentralized cognitive radio networks have gained popularity due to their advantages over centralized networks. The purpose of this article is to propose the collaboration between secondary users for cognitive Wi-Fi networks, in the form of two multi-criteria decision-making algorithms known as TOPSIS and VIKOR and assess their performance in terms of the number of failed handoffs. The comparative analysis is established under four different scenarios, according to the service class and the traffic level, within the Wi-Fi frequency band. The results show the performance evaluation obtained through simulations and experimental measurements, where the VIKOR algorithm has a better performance in terms of failed handoffs under different scenarios and collaboration levels.

Radio Frequency Energy Harvesting System Making Use of 180° Hybrid Couplers and Multiple Antennas to Improve the DC Output Voltage

This paper introduces the implementation and experimental results obtained with a radio frequency energy harvester system. A radio frequency combining power circuit based on the characteristic of the 180o hybrid coupler to combine energy is proposed here to be used in radio frequency energy harvesting schemes. Through experimental validations, this proposal demonstrates to offer important advantages compared with other radio frequency energy harvesters found in the literature, including a harvesting voltage enhanced, ease implementation, since is not require any modification in the hybrid coupler,and multi-band function using wideband antennas. The system is designed to harvest energy in the GSM, UMTS, and Wi-Fi frequency bands. The validation of the proposed system using four receiving antennas showed a direct current harvested voltage of 301 mV at 2.5 GHz for an input power of -7 dBm. In addition,the terms of accumulated voltage gain and cumulative efficiency are introduced to evaluate the performance of the proposed combining circuit in radio frequency harvesting schemes.

Mechatronics and Remote Driving Control of the Drive-by-Wire for a Go Kart.

This research mainly aims at the construction of the novel acceleration pedal, the brake pedal and the steering system by mechanical designs and mechatronics technologies, an approach of which is rarely seen in Taiwan. Three highlights can be addressed: 1. The original steering parts were removed with the fault tolerance design being implemented so that the basic steering function can still remain in case of the function failure of the control system. 2. A larger steering angle of the front wheels in response to a specific rotated angle of the steering wheel is devised when cornering or parking at low speed in interest of drivability, while a smaller one is designed at high speed in favor of driving stability. 3. The operating patterns of the throttle, brake, and steering wheel can be customized in accordance with various driving environments and drivers’ requirements using the self-developed software. The implementation of a steer-by-wire system in the remote driving control for a go kart is described in this study. The mechatronic system is designed in order to support the conversion from human driving to autonomous driving for the go kart in the future. The go kart, using machine vision, is wirelessly controlled in the WiFi frequency bands. The steer-by-wire system was initially modeled as a standalone system for one wheel and subsequently developed into its complete form, including front wheel steering components, acceleration components, brake components, a microcontroller, drive circuit and digital to analog converter. The control output section delivers the commands to the subsystem controllers, relays and converters. The remote driving control of the go kart is activated when proper commands are sent by the vehicle control unit (VCU). All simulation and experiment results demonstrated that the control strategies of duel motors and the VCU control were successfully optimized. The feasibility study and performance evaluation of Taiwan’s go karts will be conducted as an extension of this study in the near future.

A Triple-Band High-Gain Multibeam Ambient RF Energy Harvesting System Utilizing Hybrid Combining

Overcoming the challenge of battery recharging and replacement in industry Internet-of-Things (IoT) applications is considered by proposing the design of a triple-band high-gain multibeam ambient radio frequency (RF) energy harvesting system utilizing hybrid combining. The novelty of the design is that it simultaneously exploits frequency, space, and polarization to maximize the harvested RF energy. Wideband hybrid combining is proposed, which enables the harvesting of energy at low RF power densities while maintaining the wide frequency and space coverage necessary for ambient RF energy harvesting. The antenna design consisting of 16-ports has an average area per port of 0.3λ × 0.3λ (where λ is the freespace wavelength at 1.8 GHz) and is demonstrated to achieve a wide relative bandwidth of 38.5% covering the GSM-1800, UMTS-2100, and WiFi frequency bands. Hybrid combining of the 16-port antenna provides multiple antenna beams each with up to 11 dBi antenna gain and these provide broad beam coverage. The design for the rectifiers, using multistub impedance matching, is also provided and these are shown to be efficient over the frequency bands of interest. Measurements in an anechoic chamber demonstrate that the proposed energy harvesting system can provide an output dc voltage of more than 755 mV, an output dc power of more than -6.4 dBm and RF-to-dc efficiencies greater than 40% when the power density is more than 1400 μW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . It is also shown that the proposed system can provide output dc power of 80 μW and 7.3 μW in real outdoor and indoor ambient environments, respectively.