344 research outputs found
RF energy harvesters for wireless sensors, state of the art, future prospects and challenges: a review
The power consumption of portable gadgets, implantable medical devices (IMDs) and wireless sensor nodes (WSNs) has reduced significantly with the ongoing progression in low-power electronics and the swift advancement in nano and microfabrication. Energy harvesting techniques that extract and convert ambient energy into electrical power have been favored to operate such low-power devices as an alternative to batteries. Due to the expanded availability of radio frequency (RF) energy residue in the surroundings, radio frequency energy harvesters (RFEHs) for low-power devices have garnered notable attention in recent times. This work establishes a review study of RFEHs developed for the utilization of low-power devices. From the modest single band to the complex multiband circuitry, the work reviews state of the art of required circuitry for RFEH that contains a receiving antenna, impedance matching circuit, and an AC-DC rectifier. Furthermore, the advantages and disadvantages associated with various circuit architectures are comprehensively discussed. Moreover, the reported receiving antenna, impedance matching circuit, and an AC-DC rectifier are also compared to draw conclusions towards their implementations in RFEHs for sensors and biomedical devices applications
A parasitic patch loaded staircase shaped UWB MIMO antenna having notch band for WBAN applications
A staircase-shaped quasi-fractal antenna is presented to meet the requirements of compact electronics operating in UWB or E-UWB spectrum. A conventional broadband monopole antenna is converted into UWB antenna utilizing three iterations of fractal patches. The resultant antenna offers wide impedance bandwidth ranges 2.3–17.8 GHz, having a notch band at 6.1–7.2 GHz. Afterwards, a two-port MIMO antenna is created by placing the second element orthogonally with an edge-to-edge distance of 8.5 mm, that is λ/15 where λ corresponds to free space wavelength at the lowest cut-off frequency. Hereafter, a meandered line-shaped stub is inserted to reduce the mutual coupling between closely spaced MIMO elements to less than −25 dB. As the intended application of the proposed work is On-body, Specific Absorption Rate (SAR) analyses are carried out at 2.4, 5.8 and 8 GHz, showing an acceptable range for both 1-g and 10-g averaged tissues standards. Moreover, various parameters of the MIMO antenna are studied, and a comparison is made between simulated and measured results as well as those of the state of the art
Accurate quantum transport modelling and epitaxial structure design of high-speed and high-power In0.53Ga0.47As/AlAs double-barrier resonant tunnelling diodes for 300-GHz oscillator sources
Terahertz (THz) wave technology is envisioned as an appealing and conceivable solution in the context of several potential high-impact applications, including sixth generation (6G) and beyond consumer-oriented ultra-broadband multi-gigabit wireless data-links, as well as highresolution imaging, radar, and spectroscopy apparatuses employable in biomedicine, industrial processes, security/defence, and material science. Despite the technological challenges posed by the THz gap, recent scientific advancements suggest the practical viability of THz systems. However, the development of transmitters (Tx) and receivers (Rx) based on compact semiconductor devices operating at THz frequencies is urgently demanded to meet the performance requirements calling from emerging THz applications.
Although several are the promising candidates, including high-speed III-V transistors and photo-diodes, resonant tunnelling diode (RTD) technology offers a compact and high performance option in many practical scenarios. However, the main weakness of the technology is currently represented by the low output power capability of RTD THz Tx, which is mainly caused by the underdeveloped and non-optimal device, as well as circuit, design implementation approaches. Indeed, indium phosphide (InP) RTD devices can nowadays deliver only up to around 1 mW of radio-frequency (RF) power at around 300 GHz. In the context of THz wireless data-links, this severely impacts the Tx performance, limiting communication distance and data transfer capabilities which, at the current time, are of the order of few tens of gigabit per second below around 1 m.
However, recent research studies suggest that several milliwatt of output power are required to achieve bit-rate capabilities of several tens of gigabits per second and beyond, and to reach several metres of communication distance in common operating conditions. Currently, the shortterm target is set to 5−10 mW of output power at around 300 GHz carrier waves, which would allow bit-rates in excess of 100 Gb/s, as well as wireless communications well above 5 m distance, in first-stage short-range scenarios. In order to reach it, maximisation of the RTD highfrequency RF power capability is of utmost importance. Despite that, reliable epitaxial structure design approaches, as well as accurate physical-based numerical simulation tools, aimed at RF power maximisation in the 300 GHz-band are lacking at the current time.
This work aims at proposing practical solutions to address the aforementioned issues. First, a physical-based simulation methodology was developed to accurately and reliably simulate the static current-voltage (IV ) characteristic of indium gallium arsenide/aluminium arsenide (In-GaAs/AlAs) double-barrier RTD devices. The approach relies on the non-equilibrium Green’s function (NEGF) formalism implemented in Silvaco Atlas technology computer-aided design (TCAD) simulation package, requires low computational budget, and allows to correctly model In0.53Ga0.47As/AlAs RTD devices, which are pseudomorphically-grown on lattice-matched to InP substrates, and are commonly employed in oscillators working at around 300 GHz. By selecting the appropriate physical models, and by retrieving the correct materials parameters, together with a suitable discretisation of the associated heterostructure spatial domain through finite-elements, it is shown, by comparing simulation data with experimental results, that the developed numerical approach can reliably compute several quantities of interest that characterise the DC IV curve negative differential resistance (NDR) region, including peak current, peak voltage, and voltage swing, all of which are key parameters in RTD oscillator design.
The demonstrated simulation approach was then used to study the impact of epitaxial structure design parameters, including those characterising the double-barrier quantum well, as well as emitter and collector regions, on the electrical properties of the RTD device. In particular, a comprehensive simulation analysis was conducted, and the retrieved output trends discussed based on the heterostructure band diagram, transmission coefficient energy spectrum, charge distribution, and DC current-density voltage (JV) curve. General design guidelines aimed at enhancing the RTD device maximum RF power gain capability are then deduced and discussed.
To validate the proposed epitaxial design approach, an In0.53Ga0.47As/AlAs double-barrier RTD epitaxial structure providing several milliwatt of RF power was designed by employing the developed simulation methodology, and experimentally-investigated through the microfabrication of RTD devices and subsequent high-frequency characterisation up to 110 GHz. The analysis, which included fabrication optimisation, reveals an expected RF power performance of up to around 5 mW and 10 mW at 300 GHz for 25 μm2 and 49 μm2-large RTD devices, respectively, which is up to five times higher compared to the current state-of-the-art. Finally, in order to prove the practical employability of the proposed RTDs in oscillator circuits realised employing low-cost photo-lithography, both coplanar waveguide and microstrip inductive stubs are designed through a full three-dimensional electromagnetic simulation analysis.
In summary, this work makes and important contribution to the rapidly evolving field of THz RTD technology, and demonstrates the practical feasibility of 300-GHz high-power RTD devices realisation, which will underpin the future development of Tx systems capable of the power levels required in the forthcoming THz applications
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Design and analysis of metamaterial based microstrip patch antennas for wireless applications.
Doctoral Degree. University of KwaZulu-Natal, Durban.Due to the tremendous growth of wireless communication applications, there is an enormous demand for more compact antennas with high speed, wider coverage, high gain, and multi-band properties. The microstrip patch antennas (MPAs) and multiple-input multiple-output (MIMO) antennas with high gain and multi-band properties are suitable to fulfil these requirements. MPAs have been found to possess unique qualities such as light weight, low profile, easy fabrication, and integration. However, the low gain, narrow bandwidth, and mutual coupling in the MIMO antennas limit the performance of MIMO systems. Several techniques have been studied and implemented over the years, but they are not without limitations. The utilization of artificial materials such as metamaterials has proven to be efficient in overcoming the limitations of MPAs.
Due to the advancement in modern technology, it is necessary to study and use recently developed metamaterial structures. Metamaterials (MeTMs) are artificially engineered materials with electromagnetic properties that are not found in nature. MeTMs are used due to their electric and magnetic properties. The goal of this thesis is to design and investigate a novel metamaterial structure which can be integrated into the microstrip patch antennas for improving their performance. The design, simulation, and measurement of the metamaterial is carried out on the Computer Simulation Technology (CST) studio suite, Advance Design Systems (ADS) software, MATLAB, and the Rohde and Schwarz network analyzer etc.
In this thesis, a novel I-shaped metamaterial (ISMeTM) structure is proposed, designed, and investigated. The proposed novel ISMeTM unit cell structure in this work has a characteristic shape that distinguishes it from earlier multi-band MeTMs in the literature. The structure's unit cell is designed to have an overall compact size of 10 mm × 10 mm. The structure generates transmission coefficients at 6.31 GHz, 7.79 GHz, 9.98 GHz, 10.82 GHz, 11.86 GHz, 13.36 GHz, and 15. 5 GHz. These frequency bands are ideal for multi-band satellite communication systems, C, X, and Ku-bands, and radar applications etc.
The performance of the MPA is improved in this work, by integrating a novel square split ring resonator (SSRR) metamaterial. The performance of the proposed antenna is investigated and analyzed. The SSRR is designed to have a dimension of 25 x 21.4 x 1.6 mm2 which is the same dimension as the radiating patch of the MPA. The SSRR is etched over the antenna, and it operates at single operating frequency of 5.8 GHz with improved gain from 4.04 to 5.3 dBi.
Further, the MPA with improved parameters for multiband wireless systems is designed, analyzed, fabricated, and measured. The proposed design utilizes the ISMeTM array as superstrate with the area of 70 x 70 mm2. The superstrate is etched over a rectangular MPA exhibiting multi-band properties. This antenna resonates at 6.31, 9.65, 11.45 GHz with increased bandwidth at 240 MHz, 850 MHz, and 1010 MHz. The overall gain of the antenna increases by 74.18%. The antenna is fabricated and measured. The simulated results and the measured results are found to be in good agreement.
The mutual coupling and low gain problems in MIMO patch antennas is also addressed in this thesis. A 3 x 5-unit cell array of the ISMeTM is used as a superstrate over a two port MIMO patch antenna. The two port MIMO antenna with the superstrate provides triple-band operation and operates over three resonance frequencies at 6.31, 9.09, and 11.41 GHz. A mutual coupling reduction of 26 dB, 33 dB, and 22 dB for the first band, second band and third band, respectively is attained.
In this thesis, a novel I-shaped metamaterial structure is introduced, which produces multiband operation. The presented metamaterial is suitable for various multiband wireless communication applications. The integration of a square split ring resonator metamaterial enhances the performance of the antenna. Using the I-shaped metamaterial a high gain multiband microstrip antenna is designed. The I-shaped metamaterial array is utilized to improve the performance of the MIMO antenna. Various antenna parameters confirm that the presented MIMO antenna is suitable for multiband wireless communications
Programmable Microwave Devices (PMDs) based on Liquid Metal
This thesis presents microwaves device which we term a programmable microwave device (PMD). This thesis presents building block elements (BBEs)/PMDs which can realize functional and parametric reconfiguration. This thesis also discusses how to implement Gallium-based liquid metal in a reconfigurable circuit/antenna. Two works were finished and presented in this thesis. The first work presented a BBE and a PMD that can realize the functional reconfiguration. The proposed BBE/PMD can alter its function between non radiating (resonator/filter) mode and radiating (antenna) mode. The proposed BBE/ PMD realizes functional reconfiguration with the aid of liquid metal (LM). The proposed single BBE operates in resonator mode when the fluidic channels are filled with liquid metal. Whereas it operates in antenna mode when the fluidic channels are emptied of liquid metal. When several BBEs are cascaded, they form a PMD. A PMD can realize filter mode operation when the fluidic channels are filled with liquid metal or antenna mode operation when liquid metal is withdrawn. In this work, an easy approach of 2D-shaping LM was also introduced. This approach allows 2D-shaped LM for being used in realizing reconfiguration. When operating in the antenna mode the proposed PMDs provides a measured peak realized gain of 7.23 dBi and a simulated total efficiency of 84%. When operating in the filter mode the proposed PMDs provides a band pass response and exhibits a maximum insertion loss of 1.9 dB, within the passband. The filters have a 10 dB return loss bandwidth of 340 MHz ranges from 2.28 GHz to 2.62 GHz. The second work presents an operating frequency reconfigurable antenna mode BBE, which realizes a wide operating frequency reconfiguring range with the aid of liquid metal. The capability of LM could have a significant impact on reconfigure capability of the proposed PMD. We firstly designed and manufactured a hardwired version of operating frequency reconfigurable antenna mode BBE. After we verified the measurement results of hardwired antenna mode BBE, we 3D-printed the fluidic channels using Polylactic acid (PLA). LM can be filled into the 3D-printed fluidic channels with a changeable length which tunes the operating frequency of the antenna mode BBE. The measurement results of the operating frequency reconfigurable antenna mode BBE agree with the simulation results, verifying the capability of this antenna mode BBE
1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface
A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance
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