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This paper presents a comparative study on three types of slim coil structures used as a three-dimensional (3-D) receiver in a wireless power transfer system with a planar transmitter coil. The mutual coupling values and their variations between the receiver structures and the transmitter coil are compared under different distances and angular orientations with respect to the transmitter coil. The merits of performance are related to the consistency of the mutual coupling values under different orientations in a range of distances from the transmitter coil. The practical results show that slim 3-D receiver coil structures can be compatible with a planar transmitter coil with reasonably high-mutual coupling.
This study presents a new design of a wearable orthosis of elbow joint with a bimuscular pneumatic servo-drive (PSD) with control based on the recording of bioelectric signals (BESs). The authors analyzed the impact of the induced brain activity and the muscular tension within the head of the participant on the BESs that can be used to control the PSD of the elbow joint orthosis. To control the elbow joint orthosis, a distributed control system (DCS) was developed, which contains two control layers: a master layer connected to the device for recording the BES and a direct layer contained in a wireless manner with the controller of the PSD. A kinematic-dynamic model of the elbow joint orthosis, patterned after the biological model of human biceps–triceps, was used in the programming of the PSD controller. A biomimetic dynamic model of the pneumatic muscle actuator (PMA) was used, in which the contraction force results from the adopted exponential static model of the pneumatic muscle (PM). The use of direct visual feedback (DVF) makes it possible for the participant to focus on the movement of the orthosis taking into account the motoric functions of the elbow.
This chapter introduces two emerging green communication techniques, i.e., wireless-powered and ambient backscatter communications, which have been receiving a lot of attention recently due to their outstanding energy efficiency. The chapter then presents technical challenges in developing green communication networks and review solutions based on game theory to address these issues. Finally, the chapter introduces an application of Stackelberg game model to address the energy and communication efficiency for an RF-powered cognitive radio network with ambient backscatter communications.
The characteristic transfer parameters of inductive power transfer systems highly depend on the relative position of the coils to each other. While translational offset has been investigated in the past, the effect of rotatory offset on the transfer parameters is widely unclear. This paper contains simulation results of an inductive power transfer system with a rotatory offset in three axes and shows the possible improvements in the coupling coefficient. As a result, rotation angles can be used as control parameters and thereby increase the system efficiency. Alternatively, the allowed misalignment area of the secondary coil can be increased while maintaining the functionality and same dimensions.
Now-a-days, far-field wireless power transfer/energy harvesting is underutilized due to the unavailability of proper methodology to design efficient system for maximum radio frequency (RF) power utilization. For efficient utilization of far-field RF energy an array/grid of rectenna, i.e. rectenna panel is required to generate the power from wireless signal. To minimize the engineering design phase period (design trials), this paper mathematically derives and summarizes the approach required for optimum rectenna panel design based on power available in the environment, RF transmit source capability, receiver power requirement and the design cost. For maximum power interception through a rectenna panel, its design parameters such as -panel size, number of rectenna, rectenna arrangement pattern, and rectenna spacing has been optimized in our work. Based on the optimization required, we have proposed the compact grid pattern with heterogeneous rectenna spacing. It has been proved theoretically in this paper that if a hexagonal shape panel is designed by placement of rectenna at vertices of equilateral triangle (with side length governed by antenna aperture) then, it is capable of intercepting maximum RF energy available at its location with the least number of rectenna.
The paper presents the results of studies on the effect of transistor DC operating conditions on GaN power amplifiers’ (PAs) power efficiency and linearity improved by digital predistortion (DPD). The single-ended 10 W (ISM2.45 GHz) and 150 W (3.4/3.6 GHz) GaN HEMT PAs excited by wideband LTE20 E-TM1.1 signal were tested. To check the applicability of the small-signal approach for designing of LTE signals’ PAs, the 150 W PA using transistor model extracted from S-parameters measured at the properly selected operating points was designed. The conventional DPD based on the indirect learning architecture and the memory polynomial model of PA non-linearity was implemented. The results of the research show that in case of class A and B PAs operating up to several dozen watts, an additional improvement in adjacent channel leakage ratio (ACLR) of the order of a few dB only by an increase in the quiescent drain current of PA transistor can be achieved. However, a noticeable ACLR improvement with a coincident increase in power-added efficiency (PAE) can be obtained by choosing the compromise DC operating point and using DPD. In the case of high-PAs, the linearity and efficiency are strongly dependent on the load of a transistor, thus the role of DPD is significantly increased.
A flexible and adaptive energy-efficient high-speed wireless hub is developed in polymer foil as a Hybrid System-in-Foil (HySiF) using Chip-Film Patch (CFP) technology. In this matter, the SiGe BiCMOS silicon chips (2.39 × 1.65 mm2) are thinned down to 45 μm and are embedded face-up inside a two-polymer CFP carrier. The active pads of the embedded silicon chips inside foil are extended to the surface of the foil to interconnect to the antenna on the foil. The integrated hybrid system has a signal transmission at 5–6 GHz frequency band. The overall thickness of the system is below 100 μm and its bendability is down to 4 mm radius of curvature. The designed and fabricated PA silicon chips operate at 50 mA with a 1.5 V supply voltage. Therefore, in addition to the high lateral thermal resistance of the thinned chip, self-heating loop inside polymer due to the low thermal conductivity of the embedding polymer raises the system temperature. Consequently, the thermal behavior and RF performance of the PA chip under different conditions are investigated. Moreover, the antenna with the required carrier frequency is simulated, fabricated, and measured on top of the polymer foil as a stand-alone system in the flexible CFP.
This paper presents a fully digital transmitter chain from baseband to antenna, including a modulator, two truly digital (i.e. fully switched) microwave power amplifiers and a transmit/receive switch. Both, amplifier and switch monolithic microwave integrated circuits were implemented in a GaN HEMT process. The novel amplifier design provides greatly reduced complexity, needing only three voltage sources. Measurements were conducted using 5, 20, and 100 MHz wide baseband signals. Carrier frequencies cover the 900 and 2000 MHz bands. For the 5 MHz BB signal an ACLR of over 52 dB is reached, fulfilling the 3GPP specs for base station use while still maintaining a final-stage drain efficiency of 46% at 6.5 dB peak to average power ratio. Full-scale output power at 30 V supply voltage was measured to exceed 3 W at 80% drain efficiency. Further features of this digital amplifier approach include small form factor and frequency agility, making it an ideal candidate for software defined radio.
Advances in material science and semiconductor technology have enabled a variety of inventions to be implemented in electronic systems and devices used in the medical, telecommunications, and consumer electronics sectors. In this paper, a wireless charging system is described as a wearable body heater that uses a chair as a transmitter (Tx). This system incorporates the widely accepted Qi wireless charging standard. Alignment conditions of a linear three-element coil arrangement and a 3 × 3 coil matrix array are investigated using voltage induced in a coil as a performance indicator. The efficiency obtained is demonstrated to be up to 80% for a voltage of over 6.5 Volts and a power transfer of over 5 Watts. Our results and proposed approach can be useful for many applications. This is because the wireless charging system described herein can help design seating areas for the elderly and disabled, commercial systems, consumer electronics, medical devices, electronic textiles (e-textiles), and other electronic systems and devices.
More mobile devices such as mobile phones and robots are wirelessly charged for convenience, simplicity, and safety, and it would be desirable to achieve three-dimensional (3D) wireless charging with high spatial freedom and long range. This paper proposes a 3D wireless charging cube with three orthogonal coils and supporting magnetic cores to enhance the magnetic flux outside the cube. The proposed system is simulated by Ansoft Maxwell and implemented by a downsized prototype. Both simulation and experimental results show that the magnetic cores can strengthen the magnitude of B-field outside the cube. The final prototype demonstrates that the power transfer distance outside the cube for getting the same induced electromotive force in the receiver coil is extended approximately by 50 mm using magnetic cores with a permeability of 2800. It is found that the magnitude of B-field outside the cube can be increased by increasing the width and the permeability of the magnetic cores. The measured results show that when the permeability of the magnetic cores is fixed, the induced electromotive force in the receiver coil at a point 300 mm away from the center of the cube is increased by about 2V when the width of the magnetic cores is increased from 50 to 100 mm. The increase in the induced electromotive force at an extended point implies a greater potential of wireless power transfer capability to the power pickup.
This work describes the design of a rectenna array exploiting orthogonal, closely-spaced UHF monopoles for orientation-independent RF energy harvesting to energize a passive tag, designed for UWB localization, with wake-up radio (WUR) capabilities. To reach this goal, different RF networks are studied to simultaneously realize RF decoupling of the antenna elements and matching of the radiating elements to the non-linear network of rectifiers. The design is performed for a wide power range of the RF incoming signals that need to be exploited for both energizing the passive tag and for providing energy autonomy to a WUR sub-system, used to minimize the long-term power consumption during tag standby operations. Two meandered cross-polarized monopoles, located in close proximity, and thus highly coupled, are adopted for orientation-insensitive operations. The combining RF network is reactive and includes an unbalanced power divider to draw a fraction of the harvested energy to a secondary way for WUR operations. The performance of the harvester is first optimized by EM/non-linear co-design of the whole system over an interval of low RF power levels. The system has been realized and experimentally validated: the superior results obtained, in terms of both dc voltage and power, with respect to a standard single-monopole rectenna, justify the deployment of the presented tag for the energy autonomy of future generation radio-frequency identification tags for indoor localization.
Wireless power transmission (WPT) systems with moveable mechanical parts have been acquired more and more attention during the past decade. However, due to the moveable feature of transmitting coil and receiving coil, misalignment issue lead to extra power loss, decrease in efficiency, increase in control complexity, and unwanted performance degradation of the whole system. Moreover, it happened frequently than those traditional planar coils systems. The motivation for this paper is trying to have a deep understanding of quantitative relationship between ball-shaped coils mutual inductance and misalignment. Based upon that, engineers would know more detail of the coils position and mutual inductance. So, optimized design might be achieved. On considering that, this paper presents a WPT system with a ball-shaped coil for robot joints. A mutual inductance calculation based on filament method aimed at ball-shaped coil is proposed. Based on these, nine different ball-shaped coil solutions are calculated. Then, model with a minimized change rate of mutual inductance against the angular misalignment is chosen as the optimized design. Circuit analysis of the WPT system with the series–series resonant topology is conducted to choose a proper working frequency and load. Finally, an experimental platform is established. It demonstrates the feasibility of the proposed calculation method and the feasibility of the WPT prototype.
The pulse radiating characteristic of a wrapped bow-tie antenna (WBA) and wrapped resistively loaded bow-tie antenna (WRLBA) is presented for impulse radar applications in this paper. The numerical analysis of the WRLBA is performed by comparing that of the WBA. The wrapped antennas are realized on a flexible substrate. The antennas are fed by an impedance tapered balun, which has an overall transmission loss of −1.4 dB over the balun length. The characteristics of the resistive loading to the wrapped antenna, such as reflection coefficient, reflected pulse in the time domain, voltage standing wave ratio, and input impedance, are experimentally investigated and compared with simulated results. The fidelity factor of the radiated electric field on the boresight direction for the WBA and WRLBA is calculated as 0.82 and 0.96, respectively. The wireless communication ability is evaluated by the transmission coefficient, group delay, boresight gain, and received waveform. The calculated fidelity factor of the received waveform for the WBA and WRLBA is 0.79 and 0.85, respectively. The average and variations of the group delay of both wrapped antennas are observed to be around 2.5 ns and less than 1.5 ns, respectively.
This article experimentally explores the use of ferrite cores to miniaturize the receivers used for inductive wireless power transmission. A variety of receivers were designed and fabricated using cylindrical ferrite cores, ranging in total size from 47 to 687 mm3. The receivers were tested with a commercially available transmitter operating under the Rezence (Air Fuel Alliance) standard at 6.78 MHz. Experiments measured performance of the receivers in terms of their maximum power draw and efficiency as functions of the receiver load and transmission distance. Experimental results showed that ferrite-core receivers could draw multiple watts of power with end-to-end efficiencies in excess of 50%. While the efficiencies are less than a commercially planar coil receiver, the ferrite-core receivers offer a >50% reduction in mass and >90% reduction in footprint. As a result, the receiver power densities reach up to 17.6 W/cm3, which is a 25× improvement over previously reported work. This effort confirms the viability of ferrite-core receivers for size- and weight-constrained applications.
This article examines China’s efforts to restore cable telegraph rights from the establishment of the Republic of China to the end of World War II. Challenging the conventional dichotomy of “Chinese” and “Western” actors in rights recovery issues, this article explores the intricate power relations between foreign cable companies, international interests groups and various political factions in China. It analyses China’s reclaim of cable sovereignty in three phases, each characterised by a particular controversy—the intra-clique struggle of the Communications Clique during the early Republic and the warlord era; the rivalry between the Nationalist Party, military and the state during the Nanjing decade; and the direct Sino-Japanese conflict during wartime. The article presents the argument that for the various interest groups, ideologies such as imperialism and nationalism served as rhetoric in their respective pursuits. It was the daily political tensions that played a crucial role in shaping how cable policies were devised.
This work presents a novel efficient and compact size coupled resonator system for wireless power transfer (WPT) based on compact half-ring resonators defected ground structure (HRRs-DGS). The proposed design is capable of supplying low power electronic devices. The suggested system is based on coupled resonators of DGS. An HRR-DGS band-stop filter is designed and proposed, and when two HRRs-DGS are coupled back-to-back, it transfers to a band-pass filter leading to a compact and highly efficient WPT system working at 3.4 GHz. The measured efficiency of the proposed coupled HRRs-DGS system is around 94% at a transmission distance of 12 mm which is filled with foam for stable measurements. The proposed design is suitable for charging electronic devices such as wireless sensor nodes at 3.4 GHz. Simulation and experimental results have shown acceptable agreement.
In this paper, we present a novel dual-band wearable compact flexible antenna for body-centric wireless communications (BCWCs). The design is based on a modified planar dipole with parasitic elements, meandered lines, and a rectangular reflector embedded into a hydrophobic rubber-textile multilayer substrate in order to get both good antenna performance and mechanical properties. The antenna's structure is analyzed and optimized in free space (FS), on a numerical and an experimental homogeneous flat phantom. The overall dimensions of the antenna are 50 mm × 40 mm × 4.6 mm and a prototype mass of 11 g, which makes it suitable for practical applications in BCWCs. The built prototype resonated at 2.47 GHz with a |S11|−26.90 dB and at 5.42 GHz with a |S11|−24.60 dB in the FS. The measured bandwidths are 500 MHz (2.2–2.7 GHz) and 1000 MHz (4.65–5.75 GHz) at lower and higher bands, respectively. The antenna exhibits a measured maximum gain of 1.17 dBi at 2.66 GHz and a radiation efficiency of 28.44% in FS. The 10 g average maximum specific absorption rate is 0.165 W/kg at 2.70 GHz and 0.520 W/kg at 5.24 GHz when the antenna is placed on the numerical phantom at net input power 0.1 W.
This paper discusses some significant design issues that are faced in resonant inductive system for wireless power transfer ‘on the move’. The targeted system adopts a single AC source to power a sequence of transmitting (Tx) coils, placed along the Rx path, whose geometry is optimized to minimize the variations of coupling for every possible Rx position. To retain a constant coupling coefficient, two nearby Tx coils are series-connected and simultaneously activated, establishing a path without any theoretical bound on its length, by a suitable switching network. This work analyzes the effects of asynchronous switching times, which are rigorously accounted for and minimized by a proper design of the compensating circuit elements, minimizing both the voltage spikes and the over currents on the coils, while keeping the system at resonance. A prototype operating at 6.78 MHz is built and experimental validations are carried out to verify the feasibility of a constant coupling link without experiencing the mentioned effects, but the adopted procedure is general and independent on its size or frequency.
Near-field communication (NFC) readers, ubiquitously embedded in smartphones and other infrastructures can wirelessly deliver mW-level power to NFC tags. Our previous work NFC-wireless identification and sensing platform (WISP) proves that the generated NFC signal from an NFC enabled phone can power a tag (NFC-WISP) with display and sensing capabilities in addition to identification. However, accurately aligning and placing the NFC tag's antenna to ensure the high power delivery efficiency and communication performance is very challenging for the users. In addition, the performance of the NFC tag is not only range and alignment sensitive but also is a function of its run-time load impedance. This makes the execution of power-hungry tasks on an NFC tag (like the NFC-WISP) very challenging. Therefore, we explore a low-cost tag antenna design to achieve higher power delivered to the load (PDL) by utilizing two different antenna configurations (2-coil/3-coil). The two types of antenna configurations can be used to dynamically adapt to the requirements of varied range, alignment and load impedance in real-time, therefore, we achieve continuous high PDL and reliable communication. With the proposed method, we can, for example, turn a semi-passive NFC-WISP into a passive display tag in which an embedded 2.7″ E-ink screen can be updated robustly by a tapped NFC reader (e.g. an NFC-enable cell-phone) over a 3 seconds and within 1.5cm range.
Wireless sensor networks are an increasingly popular tool for monitoring various environmental parameters. They can also be used for monitoring the electromagnetic spectrum. Wireless sensors, due to their small size, typically have simplified radio receivers with reduced sensitivity and use small antennas. As a result, their effective performance area is similarly limited. This is especially important in urban areas where there are various kinds of adverse propagation phenomena related to area coverage. The aim of this paper is to present the phenomena in the wireless sensor networks and propose criteria and methods to optimize their deployment to ensure maximizing the probability of detection of emissions, minimization of unmonitored areas, and to provide the necessary hardware redundancy in the priority areas. Influence of detection parameters, number of sensors and range constraints between sensors on received outcomes are also presented.