The objective of this dissertation is to develop task scheduling guidelines and algorithms for wireless sensor nodes that harvest energy from ambient environment and use supercapacitor based storage systems to buffer the harvested energy. This dissertation makes five contributions. First, a physics based equivalent circuit model for supercapacitors is developed. The variable leakage resistance (VLR) model takes into account three mechanisms of supercapacitors: voltage dependency of capacitance, charge redistribution, and self-discharge. Second, the effects of time and supercapacitor initial state on supercapacitor voltage change and energy loss during charge redistribution are investigated. Third, the task scheduling problem in supercapacitor based environmentally powered wireless sensor nodes is studied qualitatively. The impacts of supercapacitor state and energy harvesting on task scheduling are examined. Task scheduling rules are developed. Fourth, the task scheduling problem in supercapacitor based environmentally powered wireless sensor nodes is studied quantitatively. The modified earliest deadline first (MEDF) algorithm is developed to schedule nonpreemptable tasks without precedence constraints. Finally, the modified first in first out (MFIFO) algorithm is proposed to schedule nonpreemptable tasks with precedence constraints. The MEDF and MFIFO algorithms take into account energy constraints of tasks in addition to timing constraints. The MEDF and MFIFO algorithms improve the energy performance and maintain the timing performance of the earliest deadline first (EDF) and first in first out (FIFO) algorithms, respectively.

In the present thesis, I have proposed methodology of two stages Dickson charge pump, which is capable of harvesting energy at 2.45 GHz RF signal to power any low powered device. Presented design uses a simple and inexpensive circuit consisting of four microstrip patch antennas, some zero-bias Schottky diodes, Wilkinson power divider and a few passive components. Circuit was fabricated on a 60 mils RO4350B substrate (=3.66), with 1.4 mils copper conductor. Demonstration showed the charge pump provides a good performance, as it drives the low powered devices with as low as 10dBm input power at 1m away from the energy source. Thesis paper will present design techniques illustrated with data obtained on prototype circuits. The objective is to wirelessly gather energy from one RF source and convert it into usable DC power that is further applied to a set of low power electronic devices. Radio Frequency Identification (RFID) tag system could also be improved using this method. RF-to-DC conversion is accomplished by designing and characterizing an element commonly known as a Rectenna, which consists of an antenna and an associated rectification circuitry. The rectenna is fully characterized in this dissertation and is used for charging low powered devices.

A wireless sensor system is proposed for a targeted deployment in civil infrastructures (namely bridges) to help mitigate the growing problem of deterioration of civil infrastructures. The sensor motes are self-powered via a novel magnetic shape memory alloy (MSMA) energy harvesting material and a low-frequency, low-power rectifier multiplier (RM). Experimental characterizations of the MSMA device and the RM are presented. A study on practical implementation of a strain gauge sensor and its application in the proposed sensor system are undertaken and a low-power successive approximation register analog-to-digital converter (SAR ADC) is presented. The SAR ADC was fabricated and laboratory characterizations show the proposed low-voltage topology is a viable candidate for deployment in the proposed sensor system. Additionally, a wireless transmitter is proposed to transmit the SAR ADC output using on-off keying (OOK) modulation with an impulse radio ultra-wideband (IR-UWB) transmitter (TX). The RM and SAR ADC were fabricated in ON 0.5 micrometer CMOS process. An alternative transmitter architecture is also presented for use in the 3-10GHz UWB band. Unlike the IR-UWB TX described for the proposed wireless sensor system, the presented transmitter is designed to transfer large amounts of information with little concern for power consumption. This second method of data transmission divides the 3-10GHz spectrum into 528MHz sub-bands and "hops" between these sub-bands during data transmission. The data is sent over these multiple channels for short distances (?3-10m) at data rates over a few hundred million bits per second (Mbps). An UWB TX is presented for implementation in mode-I (3.1-4.6GHz) UWB which utilizes multi-band orthogonal frequency division multiplexing (MB-OFDM) to encode the information. The TX was designed and fabricated using UMC 0.13 micrometer CMOS technology. Measurement results and theoretical system level budgeting are presented for the proposed UWB TX.

The fifth generation (5G) wireless communications technology will be a paradigm shift which does not only provide an explosive increment on the achievable data rate per cell, but also ideally decreases the costs and energy consumption per data link. The engineering requirements of 5G standard can be intuitively interpreted as highly enhanced spectral efficiency and energy efficiency. This thesis focuses on the practical implementation issues of the massive multiple-input multiple-output (MIMO) and energy harvesting systems. To begin with, massive MIMO, as one of the key technologies of 5G systems, can provide enormous enhancement in spectral efficiency. For a practical massive MIMO system, hybrid processing (precoding/combining), by restricting the number of RF chains to far less than the number of antenna elements, can significantly reduce the implementation cost compared to the full-complexity radio frequency (RF) chain configuration. This thesis designs the hybrid RF and baseband precoders/combiners for multi-stream transmission in the point-to-point (P2P) massive MIMO systems, by directly decomposing the pre-designed digital precoder/combiner of a large dimension. The performance of the matrix decomposition based hybrid processing (MD-HP) scheme is near-optimal compared to the singular value decomposition (SVD) based full-complexity processing. In addition, the downlink communication of a massive multiuser MIMO (MU-MIMO) system is also investigated, and a low-complexity hybrid block diagonalization (Hy-BD) scheme is developed to approach the performance of the traditional BD method. We aim to harvest the large array gain through the phase-only RF precoding and combining and then BD processing is performed on the equivalent baseband channel in the massive MU-MIMO scenario. The MD-HP and Hy-BD schemes are examined in both the large Rayleigh fading channels and millimeter wave channels. On the other hand, energy harvesting is an increasingly attractive and renewable source of power for wireless communications devices, which contributes to the enhancement of the system energy efficiency. This thesis also designs the energy cooperation assisted energy harvesting communication between a practical transmitter and receiver, whose hardware circuits consume non-zero power when active. The energy cooperation save-then-transmit (EC-ST) scheme aims to obtain the optimal active time ratio and energy cooperation power for the maximum throughput under additive white Gaussian channels and the minimum outage probability under block Rayleigh fading channels. / Graduate

The master´s thesis project was performed in collaboration with the design and engineering company Eker Design from Fredrikstad in Norway, who is designing and developing flip cover NFC keyboards for smartphones. The new product idea is the full-sized NFC desktop keyboard for public institutions to offer to pupils, students or business people for instance. The thesis project is examining how such a product can be designed and should be designed in order to fit into its market and environment to meet the target group´s interest in order to be successful. With a human-centered design approach the project work was starting by the user and the market. The work consisted of analyzing and emphasizing with the market which mainly included the users, the competitors and the trends within a market analysis and a survey research. From the findings and insights of the research phase a design strategy and a business model for the new keyboard was created and communicated via a design brief. Different ideas and concepts were created, tested and presented via concept sketches along with mock-ups. The final concepts were evaluated via a concept evaluation in relation to the requirements of the business and user value. The final concept was developed and designed via the CAD software SolidWorks and the rendering software Keyshot. The design and development phase was focusing on functionality, usability, materials, surfaces, textures and the mechanical and technical solutions for the design. The result of this thesis project is named TRANSIT and is presenting how a collapsible desktop keyboard which is offering a NFC connection could look like and work to offer to people in public places such as libraries or universities and be as well be suitable for people to use at home. The TRANSIT keyboard is a simple and robust concept of a full-sized tactile keyboard which is offering a NFC connection as well as a Bluetooth connection for devices which do not support NFC yet. The design is aimed for smartphones and tablets and is offering a support which consists of an automated stand and a back plate which angle is adjustable step-less. The design allows to collapse stand, keyboard and back plate into a compact package which makes it easy to store and transport. Furthermore the design is providing a charging option for the smart device via energy harvesting or cable and has therefore internal batteries.   The project is ending with the final presentation of the physical model in scale 1:1. / Detta examensarbete genomfördes i samarbete med design och ingenjörsföretaget Eker design från Fredriksstad i Norge, som designar och utvecklar flipcover NFC tangentbord till smartphones. Den nya produktidén är ett fullstort stationärt NFC tangentbord för offentliga institutioner, tänkt att användas av till exempel elever, studenter eller affärsmänniskor. Detta examensarbete undersöker hur ovan nämnda produkt kan och bör designas för att passa dess målmarknad och möta målgruppens intresse för att bli framgångsrik. Med en Human-centered design approach, började projektet med att utgå från användaren och marknaden. Arbetet bestod i att analysera och empatisera med marknaden som huvudsakligen bestod av användare och konkurrenterna, samt att undersöka trender genom en marknadsundersökning. Med utgångspunkt från de insikter som uppkom genom projektets utforskningsfas, skapades en design strategi och en affärsmodell för det nya tangentbordet i form av en design brief. Olika idéer och koncept skapades, testades och presenterades via koncept skisser och mock-ups. Det slutgiltiga konceptet utvecklades och designades med hjälp av CAD programvaran SolidWorks och renderingsprogrammet Keyshot. Design och utvecklingsfasen fokuserade på funktionalitet, användbarhet, material, ytor, texturer och mekaniska och tekniska lösningar för designen. Den slutgiltiga produkten heter TRANSIT och visar på hur ett hopfällbart stationärt tangentbord som erbjuder en NFC-anslutning skulle kunna se ut och fungera för människor som arbetar på olika platser i det publika rummet, som på bibliotek eller universitet. Men även för privat användning i hem. TRANSIT tangentbordet är ett enkelt och robust koncept av ett fullstort taktilt tangentbord som erbjuder en NFC-koppling såväl som Bluetooth for enheter som ännu inte stöder NFC. Designen, som är riktad mot smartphones och tablets, har ett ställ som består av ett automatiskt stöd och en bakplatta med steglös justering. Designen gör att tangentbordet, stödet och bakplattan går att fälla ihop till ett kompakt paket som är enkelt att transportera och förvara. Dessutom erbjuds möjligheter att ladda smart-enheter via energi-skördning eller kabel då enheten har inbyggda batterier. Projektet avslutades med en slutpresentation av en fysisk modell i skala 1:1.

Nowadays with the world oil price soaring, the energy issue is becoming a significant topic and the possibility of harvesting ambient energy receiving much attention. In this dissertation, the main topic surrounds improving the piezoelectric energy harvesting device in several aspects and the final objective is to integrate it with low power consumption device, for example a wireless sensor network (WSN) node to extend the battery lifetime and further supply the energy to device directly. Based on the high mechanical quality factor of the structure, the output power of the piezoelectric energy harvesting device will decrease rapidly when the exciting frequency is out of the resonant frequency range. The tunable resonant frequency technique is proposed to broaden the resonant frequency range and increase the output power effectively. Then this technique is successfully combined with a WSN module to transmit the RF signal. To broaden resonant frequency another method is proposed, based on a bistable vibrating cantilever beam and a switching-type interface circuit (SSHI). It's a new and interesting concept to combine these two techniques. The magnets are used to make mechanical behavior non-linear and increase the output power at non-resonance. The SSHI technique through zero-velocity detection can work well when system is driven in non-linear system. The experimental and simulation results through work-cycles discussion show good performance of combining these two techniques. In the interface circuit design, synchronized switching harvesting on an inductor (SSHI) have been verified a successful technique to increase output power in low-coupling system. In order to make use of the SSHI technique in the real application, the velocity control self-powered SSHI (V-SSHI) system is proposed. Unlike the conventional peak detector technique, the zero-velocity detection is used to make the switching time more accurate. The energy flow is separated into three paths to construct the V-SSHI and the experimental results show good performance. When the system is not low-coupled, the SSHI technique will damp vibration.This technique is called SSDI (synchronized switching damping on an inductor). Based on the self-powered technique and zero-velocity detection used in the V-SSHI, these techniques are further applied in structural damping to construct a self-powered SSDI (SP-SSDI). The major advantage is that it is only necessary to sacrifice a small amount of damping performance to make the system fully self-powered. The theoretical analysis and experiment results of time domain comparison and frequency response testing show the limit and performance of the SP-SSDI technique. The SP-SSDI system is a like a feedback loop system and when the displacement is over the limit the SP-SSDI will effectively damp the vibration.

Damping in a multitude of engineering applications has a variable threshold requirement based on the input excitation given to the system. In most applications the desired system response is known but the input to the system is a time dependent function with fluctuating amplitudes and frequencies. Therefore for optimal performance the damping characteristics of a given system must be able to adapt to increase or decrease the amount of energy being absorbed by the system. In most mechanical systems (including vehicles) damping is achieved through a viscous medium; such as hydraulic oil. Although the oil is capable of absorbing the unwanted energy in the system, its passive nature limits its ability to achieve an optimal amount of damping given the excitation. To achieve the requisite functionality of variable damping; a multitude of solutions have been implemented, proposed, and evaluated at both commercial and academic research levels. These solutions have met the variable damping requirements but have significant cant drawbacks associated with them. To address the shortcomings associated with the aforementioned variable damping solutions, a hybrid design consisting of a conventional hydraulic damper and a linear motor topology was fused together to produce a hybrid variable damper. In this hybrid design, the oil in the system acts as bias and the linear motor topology allows for variability in the amount of damping being provided to the system. This hybrid design allows for the requisite variable damping requirement to be achieved. In addition to the hybrid design being able to achieve variable damping, it has the capacity to act as a generator and also provide fail-safe operation due to the viscous bias. Through analytical, FEM analysis and experimental modeling the hybrid damper has been characterized and with a high level of agreement between the various results. This work has also shown that the design is capable of achieving variable damping with the capacity to recover energy from the system.

Fundamental research to implement the printed autonomous wireless sensor platform is studied in three aspects: fabrication method, material selection, and novel applications for autonomous sensing/communication. Additive fabrication processes, such as inkjet printing technology and electroless electroplating, are discussed and the additively created metal layers are characterized. Fundamentals for material characterization utilizing resonators are presented and electrical properties of flexible low-cost substrates like synthetic Teslin paper and Poly(methyl methacrylate) (PMMA) are characterized. Widely used flexible substrates for printing, such as Liquid Crystal Polymer (LCP) and Kapton (polyimide), are summarized and tabulated as well. Novel antenna-based applications for efficient and autonomous operation of wireless sensor system, such as an antenna on Artificial Magnetic Conductor (AMC) for wearable applications, an active beacon oscillator for Wireless Power Transfer (WPT), and a multiband RF energy harvester, are designed and their performances are experimentally verified. The printed RFID-enabled sensor topologies with/without RFID chip are discussed as a new sensor platform for autonomous wireless operation. Fully inkjet-printed via topology for system miniaturization and integration is proposed for the first time. Challenges, circuit modeling and experimental data are presented. Future and remaining work to implement the novel low-cost autonomous wireless sensor platform are also discussed.

Rechargeable batteries are found in almost every battery powered application. Be it portable, stationary or motive applications, these batteries go hand in hand with battery charging systems. With energy harvesting being targeted in this day and age, high energy density and longer lasting batteries with efficient charging systems are being developed by companies and original equipment manufacturers. Whatever the application may be, rechargeable batteries, which deliver power to a load or system, have to be replenished or recharged once their energy is depleted. Battery charging systems must perform this replenishment by using very fast and efficient methods to extend battery life and to increase periods between charges. In this regard, they have to be versatile, efficient and user programmable to increase their applications in numerous battery powered systems. This is to reduce the cost of using different battery chargers for different types of battery powered applications and also to provide the convenience of rare battery replacement and extend the periods between charges. This thesis proposes a user programmable charging system that can charge a Lithium ion battery from three different input sources, i.e. a wall outlet, a universal serial bus (USB) and an energy harvesting system. The proposed charging system consists of three main building blocks, i.e. a pulse charger, a step down DC to DC converter and a switching network system, to extend the number of applications it can be used for. The switching network system is to allow charging of a battery via an energy harvesting system, while the step down converter is used to provide an initial supply voltage to kick start the energy harvesting system. The pulse charger enables the battery to be charged from a wall outlet or a USB network. It can also be reconfigured to charge a Nickel Metal Hydride battery. The final design is implemented on an IBM 0.18µm process. Experimental results verify the concept of the proposed charging system. The pulse charger is able to be reconfigured as a trickle charger and a constant current charger to charge a Li-ion battery and a Nickel Metal Hydride battery, respectively. The step down converter has a maximum efficiency of 90% at an input voltage of 3V and the charging of the battery via an energy harvesting system is also verified.

Zugl.: Zürich, Techn. Hochsch., Diss., 2009