A POWER DISTRIBUTION SYSTEM BUILT FOR A VARIETY OF UNATTENDED ELECTRONICS

A power distribution system (PDS) delivers electrical power to a load safely and effectively in a pre-determined format. Here format refers to necessary voltages, current levels and time variation of either as required by the empowered system. This formatting is usually referred as "conditioning". The research reported in this dissertation presents a complete system focusing on low power energy harvesting, conditioning, storage and regulation. Energy harvesting is a process by which ambient energy present in the environment is captured and converted to electrical energy. In recent years, it has become a prominent research area in multiple disciplines. Several energy harvesting schemes have been exploited in the literature, including solar energy, mechanic energy, radio frequency (RF) energy, thermal energy, electromagnetic energy, biochemical energy, radioactive energy and so on. Different from the large scale energy generation, energy harvesting typically operates in milli-watts or even micro-watts power levels. Almost all energy harvesting schemes require stages of power conditioning and intermediate storage - batteries or capacitors that reservoir energy harvested from the environment. Most of the ambient energy fluctuates and is usually weak. The purpose of power conditioning is to adjust the format of the energy to be further used, and intermediate storage smoothes out the impact of the fluctuations on the power delivered to the load. This dissertation reports an end to end power distribution system that integrates different functional blocks including energy harvesting, power conditioning, energy storage, output regulation and system control. We studied and investigated different energy harvesting schemes and the dissertation places emphasis on radio frequency energy harvesting. This approach has proven to be a viable power source for low-power electronics. However, it is still challenging to obtain significant amounts of energy rapidly and efficiently from the ambient. Available RF power is usually very weak, leading to low voltage applied to the electronics. The power delivered to the PDS is hard to utilize or store. This dissertation presents a configuration including a wideband rectenna, a switched capacitor voltage boost converter and a thin film flexible battery cell that can be re-charged at an exceptionally low voltage. We demonstrate that the system is able to harvest energy from a commercially available hand-held communication device at an overall efficiency as high as 7.7 %. Besides the RF energy harvesting block, the whole PDS includes a solar energy harvesting block, a USB recharging block, a customer selection block, two battery arrays, a control block and an output block. The functions of each of the blocks have been tested and verified. The dissertation also studies and investigates several potential applications of this PDS. The applications we exploited include an ultra-low power tunable neural oscillator, wireless sensor networks (WSNs), medical prosthetics and small unmanned aerial vehicles (UAVs). We prove that it is viable to power these potential loads through energy harvesting from multiple sources

An ultra-low power voltage regulator system for wireless sensor networks powered by energy harvesting

A DC-DC converter is an important power management module as it converts one DC voltage level to another suitable for powering a desired electronic system. It also stabilizes the output voltage when fluctuations appear in the power supplies. For those wireless sensor networks (WSNs) powered by energy harvesting, the DC-DC converter is usually a linear regulator and it resides at the last stage of the whole energy harvesting system just before the empowering sensor node. Due to the low power densities of energy sources, one may have to limit the quiescent current of the linear regulator in the sub-uA regime. This severe restriction on quiescent current could greatly compromise other performance aspects, especially the transient response. This dissertation reports a voltage regulator system topology which utilizes the sensor node state information to achieve ultra-low power consumption. The regulator system is composed of two regulators with different current driving abilities and quiescent current consumptions. The key idea is to switch between the two regulators depending on the sensor state. Since the "right" regulator is used at the "right" time, the average quiescent current of the regulator system is minimized, and the trade-off between low quiescent current and fast transient response has been eliminated. In order to minimize the average quiescent current of the system, nano-ampere reference current design is studied, and the proposed reference current circuit is shown (theoretically and experimentally) to reduce the supply voltage dependence by 5X. The regulator system has been fabricated and tested using an ON Semiconductor 0.5 μm process. It has been verified through experiments that the proposed system reduces the quiescent current by 3X over the state-of-the-art in the literature; and, more importantly, it achieves low quiescent current, low dropout voltage, and fast transient response with small output voltage variation all at the same time. The thesis further presents data on the application of energy harvesting system deriving energies from various RF signals to power a commercial off-shelf wireless sensor node

Circuitos integrados com baixo consumo de potência para aplicações em captação de energia

Orientador : Prof. PhD. André Augusto MarianoCoorientador : Prof. Bernardo LeiteDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Elétrica. Defesa: Curitiba, 01/12/2016Inclui referências : f. 104-106Área de concentraçãoResumo: Neste trabalho apresenta-se uma arquitetura de sistema de captação de energia, com capacidade para fornecer alimentação a sensores e dispositivos ou para armazenar a energia em uma bateria ou capacitor. A arquitetura proposta é composta por um conversor RF para CC, um pré-elevador de tensão, um oscilador em anel, um elevador de tensão, um regulador de tensão e um circuito de referência de tensão e corrente. Considera-se que o conversor RF para CC forneça 200 mV para que na saída do elevador de tensão obtenha-se 1,2 V. O gerador de clock, na frequência de 3,25 MHz com duas fases, é alimentado com a tensão de 400 mV, para aumentar a eficiência do elevador de tensão. A tensão de saída do sistema é 1,0 V, entregue pelo regulador de tensão a partir de 1,2 V de entrada. Os circuitos são projetados usando tecnologia CMOS 130 nm. Simulações pós-leiaute mostram que o consumo total de corrente desses três blocos principais é de aproximadamente 130 ?A, permitindo alimentar uma carga de 2 ?A, com tensão de 1 V estável na saída. Dois circuitos foram enviados para serem fabricados: o primeiro contendo o oscilador em anel com o buffer e o elevador de tensão, e o segundo um regulador de tensão incrementado pela fonte de referência de tensão externa e corrente interna. Os resultados de medidas dos dois circuitos apresentaram resultados semelhantes aos das simulações. Palavras chave: captação de energia; regulador de tensão; elevador de tensão; oscilador em anel; microeletrônica; baixo consumo; baixa tensão.Abstract: In this work an architecture of energy harvesting is presented. The system provides power supply to sensors, devices and it is able to storage energy in a battery or capacitor. The proposed architecture consists of an RF-DC converter, a voltage pre-booster, a ring oscillator, a voltage booster, a voltage regulator and a voltage and current reference circuits. It is considered that the RF-DC converter provides 200 mV for the voltage booster to raise to 1.2 V. The clock generator operates at 3.25 MHz with two stages and powered with a voltage of 400 mV, to increase the efficiency of the voltage booster. The output voltage of the system is 1.0 V delivered by the voltage regulator from the input of 1.2 V. The circuits are designed using a 130 nm CMOS technology. Post-layout simulations have shown that the total current consumption of these three main blocks is approximately 130 ?A, allowing to sustain a load of 2 ?A, with a stable 1 V output voltage. Two circuits were fabricated: the first containing the ring oscillator with the buffer and the voltage elevator, the second, a voltage regulator, with internal and external voltage sources. The measurement results of the proposed circuits are similar to those from simulations. Keywords: energy harvesting; voltage regulator; charge pump; ring oscillator; DC/DC converter; microelectronic; low power; low voltage

Rf Energy Harvesting For Wireless Communication Systems: Statistical Models For Battery Recharging Time

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2014Thesis (M.Sc.) -- İstanbul Technical University, Instıtute of Science and Technology, 2014Yeni bir enerji kaynağı olarak nitelenebilecek olan enerji hasatlama sistemleri, enerji kullanan her cihazın çevrede bulunan mevcut enerji kaynaklarını kullanarak, enerji bakımından kendi kendine yetmesi olarak açıklanabilir. Özellikle düşük güç harcayan cihazlarla kullanıldığında enerji hasatlama bütünleyici bir çözüm olarak ortaya çıkmaktadır. Elektromanyetik frekans spektrumunun bir bölümü olan radyofrekans (RF) işaretleri de, haberleşme sistemleri için enerji hasatlama yapılabilecek enerji kaynaklarından biridir. Bu tezde, RF işaretinden enerji hasatlama konusu ele alınmakta ve RF işaretinden enerji hasatlama sistemlerinde pil şarj zamanının istatistiki olarak nitelenmesi üzerine bir çalışma yapılmaktadır.Energy harvesting systems contribute to energy requirements of low-power devices as renewable energy sources. Radio frequency (RF) signal energy can be used as an energy source for energy harvesting systems. The RF signal energy available in the medium is received by the antenna of RF energy harvesting system, and converted to DC signal energy to power the electrical device. In this thesis, RF energy harvesting is emphasized for providing energy to wireless communication devices. Moreover, the distributions of battery recharging time are characterized for various wireless channel models.Yüksek LisansM.Sc

Electromagnetic Energy Harvesting Surfaces

The concept of wireless power transfer (WPT) was successfully demonstrated in the early years of the 20th century. One promising application of using the WPT concept is the WPT transmission utilizing a large array of solar cells outside the earth's atmosphere to collect solar energy and then converts it to microwave power for transmission to earth using highly directive antennas. Space solar power SSP transmission concept may play an important role in the near future in harvesting clean and sustainable energy from space. The SSP concept calls for the large rectenna (i.e., antennas and rectifying circuitry) arrays farms that receive the microwave power that is transmitted from space and convert it into usable DC power. To obtain high power and high output voltage, the use of a large rectenna array is necessary, and hence the focus of this thesis is on improving the harvesting efficiency of rectenna systems. The two main figures of merit to evaluate a WPT rectenna system are the radiation to AC efficiency, and the radiation to DC efficiency. The latter combines the efficiencies of the electromagnetic energy collectors or antenna, and that of the rectifying circuitry. In the progress towards improving the efficiency of a rectenna array system, efforts were heavily focused on improving the AC to DC conversion efficiencies. However, in most previous works, efforts to improve the efficiency of the antennas were not pursued. The majority of rectennas were in fact designed using conventional antennas because of their wide use in modern communications technologies but not for their particular ability or suitability to efficiently harvest electromagnetic radiation. The first part of this thesis introduces, for the first time, the use of dielectric resonator antenna (DRA) in an array form as an energy harvester. A single DRA and a 1x3 array were used to build foundation profiles for using DRAs in an array form as an energy harvester. The proposed structures were designed and fabricated to maximize energy reception around 5.5 GHz. The size of the ground plane and coupling between dielectric resonator (DR) elements in an array were studied with special focus on the overall efficiency of the antenna structure for different incident polarizations. A 5x5 array was built and tested numerically and experimentally. Measurements showed that energy absorption efficiency as high as 67% can be achieved using an array of DRAs. Then an extension of this finding was carried out considering the DRA's fabrication challenges. A complementary DRAs structure consisting of DR blocks backed by cut grounds is proposed. It was shown through numerical simulations that the complementary DR blocks resonator can efficiently deliver the incident power carried by an electromagnetic wave to a load with an efficiency of 80%. The concept of using an electromagnetic energy harvesting surface (EHS) structure is introduced in the second part of this thesis. A design of an electromagnetic EHS inspired by an array of printed metallic dipolar elements is introduced. The unit cell of the EHS is based on two printed asymmetric off-center fed dipoles. As a proof of concept, a finite array of 9x3 unit cells was analyzed numerically and experimentally to work at 3 GHz. The array was first analyzed for maximizing radiation to AC absorption where each dipole was terminated by a resistor across its gap. An overall radiation to DC harvesting efficiency of 76% was obtained experimentally. The third part of this dissertation presents a design for a multi-polarization electromagnetic EHS inspired by a multi-layer unit cell of printed asymmetrical metallic dipolar elements. The harvesting array features two layers that collectively capture the incident energy from various incident angles. The harvester was first analyzed for maximizing the radiation to AC absorption at 3 GHz where each dipole was terminated by a resistor across its energy-collecting gap. As a proof of concept, a multi-layer array consisting of 3x3 asymmetrical dipolar elements of the multi-layer unit cell was fabricated and measured experimentally. The experimental results yielded an overall radiation to DC harvesting efficiency of 70%for multiple incident polarizations. Next, an EHS is introduced for receiving multiple polarizations while using only one metallization layer. The EHS unit cell is based on two cross-dipoles that enable capturing the energy from various angles of illuminations at an operating frequency of 3 GHz. The simulation results yielded a radiation to AC efficiency of 94% at multiple angles of polarization. For validation, a finite array of 7x7 unit cells was fabricated and tested experimentally. The experimental results of the EHS energy harvesting array show an overall radiation to DC harvesting efficiency of 74% at various polarization angles. A critical design feature of the proposed cross-dipole EHS array is that it allows direct matching to a rectifying circuitry at the dipoles plane. The thesis concludes by introducing an efficient dual-band EHS array using two stacked-layer of cross-dipole elements for efficient harvesting at two frequency bands for multiple polarizations. The proposed EHS array introduces the concept of stacked surfaces that can be directly integrated with the rectification circuitry. The multilayer EHS array allows direct matching to a rectifying circuitry such that DC power is collected at the elements' plane for each layer. The total achieved harvested DC power is the collective contribution of the rectified DC power from the EHS's layers. A finite multi-layer array of 7x7 unit cells was fabricated and tested experimentally. The experimental results of the dual-band EHS energy harvesting array show an overall radiation to DC harvesting efficiencies of 77% and 70%, respectively, at various polarization angles at the desired operating frequencies of 2.7 GHz and 3.4 GHz

Engineering thin films of magnetic alloys and semiconductor oxides at the nanoscale

The thesis aims to exploit properties of thin films for applications such as spintronics, UV detection and gas sensing. Nanoscale thin films devices have myriad advantages and compatibility with Si-based integrated circuits processes. Two distinct classes of material systems are investigated, namely ferromagnetic thin films and semiconductor oxides. To aid the designing of devices, the surface properties of the thin films were investigated by using electron and photon characterization techniques including Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), grazing incidence X-ray diffraction (GIXRD), and energy-dispersive X-ray spectroscopy (EDS). These are complemented by nanometer resolved local proximal probes such as atomic force microscopy (AFM), magnetic force microscopy (MFM), electric force microscopy (EFM), and scanning tunneling microscopy to elucidate the interplay between stoichiometry, morphology, chemical states, crystallization, magnetism, optical transparency, and electronic properties. Specifically, I studied the effect of annealing on the surface stoichiometry of the CoFeB/Cu system by in-situ AES and discovered that magnetic nanoparticles with controllable areal density can be produced. This is a good alternative for producing nanoparticles using a maskless process. Additionally, I studied the behavior of magnetic domain walls of the low coercivity alloy CoFeB patterned nanowires. MFM measurement with the in-plane magnetic field showed that, compared to their permalloy counterparts, CoFeB nanowires require a much smaller magnetization switching field , making them promising for low-power-consumption domain wall motion based devices. With oxides, I studied CuO nanoparticles on SnO2 based UV photodetectors (PDs), and discovered that they promote the responsivity by facilitating charge transfer with the formed nanoheterojunctions. I also demonstrated UV PDs with spectrally tunable photoresponse with the bandgap engineered ZnMgO. The bandgap of the alloyed ZnMgO thin films was tailored by varying the Mg contents and AES was demonstrated as a surface scientific approach to assess the alloying of ZnMgO. With gas sensors, I discovered the rf-sputtered anatase-TiO2 thin films for a selective and sensitive NO2 detection at room temperature, under UV illumination. The implementation of UV enhances the responsivity, response and recovery rate of the TiO2 sensor towards NO2 significantly. Evident from the high resolution XPS and AFM studies, the surface contamination and morphology of the thin films degrade the gas sensing response. I also demonstrated that surface additive metal nanoparticles on thin films can improve the response and the selectivity of oxide based sensors. I employed nanometer-scale scanning probe microscopy to study a novel gas senor scheme consisting of gallium nitride (GaN) nanowires with functionalizing oxides layer. The results suggested that AFM together with EFM is capable of discriminating low-conductive materials at the nanoscale, providing a nondestructive method to quantitatively relate sensing response to the surface morphology

Vibrational energy harvesting using piezoelectric ceramics and free-standing thick-film structures

This thesis presents a series of broad but systematic and consecutive investigations on the topic of piezoelectric energy harvesting. These include material fabrication and characterisation, harvester fabrication and material parameter selection, electric output and dynamic behaviour tests of energy harvesters, and the feasibility of utilising lead-free piezoelectric materials for energy harvesting. Three lead-based and one lead-free perovskite solid-solutions compositions have been researched individually and compared to each other. In the form of bulk ceramics the lead-free composition is considered capable of replacing the lead-based compositions for vibrational energy harvesting at room temperature. Typical properties of ε$_r$≈4700, $P$$_r$≈9 μC/cm$^2$, $d$$_3$$_3$≈500 pC/N, $k$$_p$≈0.51 have been achieved for the lead-free and lead-based compositions respectively. Vibrational energy harvesting based on a novel structure of piezoelectric/silver multi-layer free-standing thick-film unimorph and bimorph cantilevers have been investigated using two of the lead-based compositions. A planar shrinkage difference of 3-6% between the silver and piezoelectric layers is suggested in order to ensure successful fabrication. When tested under harmonic vibration conditions, a comparison of unimorph individual harvesters suggests that higher piezoelectric voltage and electromechanical coupling coefficients may be preferred when selecting materials. Further optimisations involving bimorph devices with tip proof mass have demonstrated maximum harvester outputs (root mean square) of about 9 μW and 2.8 V with approximately 14% bandwidth under resonant vibrations (I 00-150 Hz, 0.5 - I.Og). In addition, the cantilevers have utilised to harvest wind energy with a modified spinning configuration, exhibiting 3.4 V average open-circuit output voltage in optimum wind conditions