Harnessing energy for wearables: a review of radio frequency energy harvesting technologies

Wireless energy harvesting enables the conversion of ambient energy into electrical power for small wireless electronic devices. This technology offers numerous advantages, including availability, ease of implementation, wireless functionality, and cost-effectiveness. Radio frequency energy harvesting (RFEH) is a specific type of wireless energy harvesting that enables wireless power transfer by utilizing RF signals. RFEH holds immense potential for extending the lifespan of wireless sensors and wearable electronics that require low-power operation. However, despite significant advancements in RFEH technology for self-sustainable wearable devices, numerous challenges persist. This literature review focuses on three key areas: materials, antenna design, and power management, to delve into the research challenges of RFEH comprehensively. By providing an up-to-date review of research findings on RFEH, this review aims to shed light on the critical challenges, potential opportunities, and existing limitations. Moreover, it emphasizes the importance of further research and development in RFEH to advance its state-of-the-art and offer a vision for future trends in this technology

Antenas 3D para utilização em transmissão de energia sem fios

Mestrado em Engenharia Eletrónica e TelecomunicaçõesThe 3D printing has seen a very strong growth in the last five years, especially since began to appear solutions of this kind of technology at much lower prices and for common user. The design of freedom associated with the three-dimensional structures can create complex geometries that produce very specific characteristics of radiation for very demanding applications. Today, it is possible to do this without big budgets. In this dissertation the lens based solution is explored through 3D printing technology. Three antennas are presented, one microstrip coupled antenna without lens, the second with an extended hemispherical lens and the third with a spherical lens. The purpose of these antennas is to provide or capture power for passive sensor networks in space. These antennas operate in the K band, more specifically at 20 GHz. In these frequencies, the lenses become acceptable in size for many applications. With this dissertation it was concluded that the use of printed lenses in 3D printers is an interesting solution to increase the gain and to focus the electromagnetic field of an antenna. These characteristics allow to create small and compact antennas with a high gain that can perform a similar performance to others with higher cost and dimensions, such as reflectors, arrays, or horn antennas.A impressão em 3D tem assistido a um crescimento bastante acentuado nos últimos cinco anos, especialmente desde que começaram a aparecer soluções deste tipo de tecnologia a preços muito mais baixos e para o utilizador comum. A liberdade de desenho associada `as estruturas tridimensionais permite criar geometrias complexas que produzem características de radiação muito específicas para aplicações bastante exigentes. E, hoje em dia ´e possível fazer isto sem precisar de grandes orçamentos. Nesta dissertação ´e explorada a solução baseada em lentes, através da tecnologia de impressão 3D. São apresentadas três antenas, uma antena microstrip alimentada por acoplamento sem lente, a segunda com uma lente semiesférica estendida e a terceira com uma lente esférica. O objetivo destas antenas ´e fornecer ou captar potência para redes de sensores passivos no espaço. As antenas apresentadas funcionam na banda K, mais concretamente a 20 GHz. A estas frequências as lentes tornam-se aceitáveis em tamanho para muitas aplicações. Com esta dissertação concluiu-se que a utilização de lentes impressas em impressoras 3D ´e uma solução interessante para aumentar o ganho e focar o campo eletromagnético de uma antena. Estas características permitem criar antenas pequenas e compactas com um ganho elevado e que conseguem ter uma performance semelhante a outras de maior custo e dimensões, como por exemplo, as parabólicas, agregados, ou cornetas

Experimental Demonstration of Coexistence of Microwave Wireless Communication and Power Transfer Technologies for Battery-Free Sensor Network Systems

This paper describes experimental demonstrations of a wireless power transfer system equipped with a microwave band communication function. Battery charging using the system is described to evaluate the possibility of the coexistence of both wireless power transfer and communication functions in the C-band. A battery-free wireless sensor network system is demonstrated, and a high-power rectifier for the system is also designed and evaluated in the S-band. We have confirmed that microwave wireless power transfer can coexist with communication function

Integrated on-chip gallium arsenide schottky diode and antenna for application in proximity communication system

The objective of this research is to investigate the possibility of direct integration between III–V based materials of Schottky diode and planar antenna without any insertion of the matching circuit by applying direct connection through Coplanar Waveguide (CPW) structure. Gallium Arsenide (GaAs) and integrated onchip Schottky diode and antenna are considered as the promising material and device structure, to achieve such purposes. This kind of device structure should be able to function as wireless power supply as well as power detector. To achieve this objective, several basic components were studied. Firstly, the design, fabrication and characterization of individual Schottky diode and planar antenna were conducted in order to understand both Direct Current (DC) and Radio Frequency (RF) characteristics. RF signals were well detected and rectified by the fabricated Schottky diodes with the cut-off frequency of up to several tens GHz, and a stable DC output voltage was generated. The RF characteristics of planar dipole and meander antenna as a function of antenna dimension were investigated. Good return loss was obtained at the resonant frequency of the antenna. From the direct injection experiment, the conversion efficiency up to 80 % of 1 GHz signal to the diode was achieved. Then, the integrated device was evaluated by transmitting RF signal from a different planar antenna and also using a horn antenna placed at a certain distance. The irradiated signal was successfully received by the planar antenna and rectified by the integrated diode. The rectification achieved was due to enough power received by the antenna to turn on the diode (Schottky barrier height = 0.381 eV- Cr/Au metallization, turn on voltage = 0.8 V). The output voltage of several volts (V) was generated at the load which was connected in parallel to the diode. A maximum output voltage of around 0.6 V and 130 mV were generated at the load resistance for frequency of 2 GHz and 7 GHz, respectively. A closed-form equation for the conversion efficiency of the Schottky diode has been derived to analyse the diode for the high frequency rectenna. The measured results were in good agreement with calculated results with small discrepancy between them due to resistance blow up effect, effect of non-linear junction capacitance, effect of the finite forward voltage drop and the breakdown voltage of the diode. From these presented results, the proposed on-chip AlGaAs/GaAs HEMT Schottky diode and antenna seems to be a promising candidate to be used for application in proximity communication system as a wireless low power source as well as a highly sensitive RF detector device

Hybrid Power Divider and Combiner for Passive RFID Tag Wireless Energy Harvesting

This paper presents three- and five-ports radio frequency (R.F) hybrid power divider combiner (HPDC) designs with multiband characteristics operating at 2.4 GHz (ISM, IEEE 802.11b,g); 5.8 GHz (IEEE 802.11n, a and 802.11ac); and 6 GHz (IEEE 802.11ax) wireless standards for energy-efficient 5G-enabled passive Internet of Things (IoTs) sensors; energy harvesting (E.H); passive radio frequency identification (RFID) tags; multiple-input multiple-output (MIMO) antenna beamforming; and data communication applications spanning D.C to the 6-GHz frequency range. The presented HPDC designs operate at a centre-design frequency of 3 GHz on a Rogers RO4350 substrate. The designed novel HPDC demonstrates a good match between the ports, high isolation between the output ports, and equal power distribution between the output ports. Furthermore, the obtained return and isolation losses are less than -10 dB for the Wi-Fi 6E standards. The reported findings hold an excellent promise for R.F energy harvesting and utilisation, adaptive intelligent energy-efficient data communication, and seamless, ubiquitous satellite-cellular convergence connectivity applications

AN INTEGRATED ELECTROMAGNETIC MICRO-TURBO-GENERATOR SUPPORTED ON ENCAPSULATED MICROBALL BEARINGS

This dissertation presents the development of an integrated electromagnetic micro-turbo-generator supported on encapsulated microball bearings for electromechanical power conversion in MEMS (Microelectromechanical Systems) scale. The device is composed of a silicon turbine rotor with magnetic materials that is supported by microballs over a stator with planar, multi-turn, three-phase copper coils. The micro-turbo-generator design exhibits a novel integration of three key technologies and components, namely encapsulated microball bearings, incorporated thick magnetic materials, and wafer-thick stator coils. Encapsulated microball bearings provide a robust supporting mechanism that enables a simple operation and actuation scheme with high mechanical stability. The integration of thick magnetic materials allows for a high magnetic flux density within the stator. The wafer-thick coil design optimizes the flux linkage and decreases the internal impedance of the stator for a higher output power. Geometrical design and device parameters are optimized based on theoretical analysis and finite element simulations. A microfabrication process flow was designed using 15 optical masks and 110 process steps to fabricate the micro-turbo-generators, which demonstrates the complexity in device manufacturing. Two 10 pole devices with 2 and 3 turns per pole were fabricated. Single phase resistances of 46Ω and 220Ω were measured for the two stators, respectively. The device was actuated using pressurized nitrogen flowing through a silicon plumbing layer. A test setup was built to simultaneously measure the gas flow rate, pressure, rotor speed, and output voltage and power. Friction torques in the range of 5.5-33µNm were measured over a speed range of 0-16krpm (kilo rotations per minute) within the microball bearings using spin-down testing methodology. A maximum per-phase sinusoidal open circuit voltage of 0.1V was measured at 23krpm, and a maximum per-phase AC power of 10µW was delivered on a matched load at 10krpm, which are in full-agreement with the estimations based on theoretical analysis and simulations. The micro-turbo-generator presented in this work is capable of converting gas flow into electricity, and can potentially be coupled to a same-scale combustion engine to convert high-density hydrocarbon energy into electrical power to realize a high-density power source for portable electronic systems

Applications of the pressure effect on the electrical energy: Piezoelectric example

Geçmişten günümüze teknolojinin hızla gelişmesi, hızlı nüfus artışı ve buna bağlı üretim artışı gibi etkenlerle enerji ihtiyacı artmıştır. Bu ihtiyacı karşılamak amacıyla genelde fosil yakıtları kullanılmaktadır. Son yıllarda tüm ülkelerde; fosil yakıtların tükenecek olması ve bu yakıtlarının kullanımının doğaya zarar vermesi nedeniyle alternatif enerji kaynakları araştırmalarına ciddi kaynak aktarmaktadır. Doğaya zarar vermemeleri, gelecekte tükenmeyecek olmaları, çeşitli kaynakları (güneş, rüzgâr, su, jeotermal …) kullanmaları, her ülkeye uygun bir veya daha fazla alternatif olması yenilenebilir enerji kaynaklarına ilgiyi artmıştır. Bu çalışmada piezoelektrik malzemeler kullanılarak canlıların (temelde insan) hareketlerinin elektrik enerjisine çevrilmesi araştırılmıştır. Bu amaçla, enerji hasadı yapılabilen 1 m2 zemin oluşturulmuştur. Enerji hasadı zemini düşük maliyetli malzemeler kullanılarak tasarlanmıştır. Zemin tasarımında 0.33mm kalınlıkta piezodisk ve 1mm kalınlıkta piezodisk ayrı ayrı kullanılarak zemin tasarımı yapılarak analiz yapılmıştır. 0.33mm kalınlıktaki piezodiskler ile oluşturulan zemin için 28,58 $harcanmış ve 60 kg bir insanın 1 dakika yürümesi sonucunda maksimum 3,976 mW üretmiştir. 1mm kalınlıktaki piezodiskler ile oluşturulan zeminin için yaklaşık 50,16$ harcanmış ve 60 kg bir kişinin üzerinde 1dakika yürümesi sonucunda 4,029 mW üretmiştir. Deney sonucunda üretilen akımın çok küçük olması, zarar gören malzemelerin yenilenme maliyetleri, ilk kurulum ve işletme maliyetleri oldukça yüksektir. Zeminden üretilen enerjinin depolama maliyetinin; üretim maliyeti, iv malzeme ve işletme maliyetleri ile birleştiğinde ekonomik değeri olmadığı görülmüştür. Aynı zamanda üretilen enerji kullanılacak bir güce sahip değildir. Çok daha büyük alanda, çok daha fazla sayıda kişilerle (AVM girişleri, fabrika yemekhaneleri…) belli seviyede enerji elde edilebilir ancak verimli olmaktan uzak kalacaktır. Buradan hareketle piezoelektrik malzemelerle verimli bir temiz enerji sistemi kurarak işletmek çalışmadaki ve benzeri tasarımlarla mümkün olamamaktadır. Malzemenin endüstriyel alanda kullanılabilmesi için farklı tasarım çalışmalarının sürdürülmesi gerekmektedir. Tez çalışmasının, bu alanda kendinden sonraki çalışmalara kaynaklık edeceğine inanılmaktadır. Bu amaçla tüm tasarım adımları gösterilmiş, malzemeler tanıtılmış ve teknik bilgiler eksiksiz çalışmada yer almaktadır

Available Technologies and Commercial Devices to Harvest Energy by Human Trampling in Smart Flooring Systems: a Review

Technological innovation has increased the global demand for electrical power and energy. Accordingly, energy harvesting has become a research area of primary interest for the scientific community and companies because it constitutes a sustainable way to collect energy from various sources. In particular, kinetic energy generated from human walking or vehicle movements on smart energy floors represents a promising research topic. This paper aims to analyze the state-of-art of smart energy harvesting floors to determine the best solution to feed a lighting system and charging columns. In particular, the fundamentals of the main harvesting mechanisms applicable in this field (i.e., piezoelectric, electromagnetic, triboelectric, and relative hybrids) are discussed. Moreover, an overview of scientific works related to energy harvesting floors is presented, focusing on the architectures of the developed tiles, the transduction mechanism, and the output performances. Finally, a survey of the commercial energy harvesting floors proposed by companies and startups is reported. From the carried-out analysis, we concluded that the piezoelectric transduction mechanism represents the optimal solution for designing smart energy floors, given their compactness, high efficiency, and absence of moving parts