Surface micromachined MEMS variable capacitor with two-cavity for energy harvesting

In this research, a novel MEMS variable capacitor with two capacitive cavities for energy harvesting was developed that use the wasted energy associated with undesirable mechanical vibrations to power microelectronic sensors and actuators widely found in structures and systems surrounding us. The harvested power, though very small, can have a profound effect on the usage of microsensors. First, the self-powered sensors will no longer require regular battery maintenance. Second, the self-powered chip is a liberating technology. On a circuit board, it can simplify the connection. On a commercial jet, the sensors can greatly simplify cabling. The design, fabrication, modeling and complete set of characterization of MEMS variable capacitors with two-cavity are presented in details in this thesis. The MEMS variable capacitors are unique in its two-cavity design and use of electroplated nickel as the main structural material. The device consists of 2x2 mm² movable capacitive proof mass plates with a thickness of 30 [mu]m suspended between two fixed electrodes forming two vertical capacitors. When the capacitance increases for one cavity, it decreases for the other. This allows using both up and down directions to generate energy. The suspended movable plates are supported by four serpentine springs with a thickness of 3-5 [mu]m that are attached to the address lines on a silicon substrate only at the anchors' points which is made of electroplated nickel. The serpentine suspension beams are made with a width, thickness and total length (four serpentine turns) of 15 [mu]m, 5 [mu]m and 1485 [mu]m. Five gold stoppers with height of 2-4 [mu]m were electroplated on the fixed plates to prevent snap-down of the movable plates by overwhelming electrostatic force. SiO2 and Si3N4 thin layers were patterned on the fixed plates to insulate the stoppers and enhance the dielectric property of capacitive cavities. The MEMS variable capacitor with two-cavity has been designed and modeled using MEMS CAD tool and COMSOL Multi-PhysIncludes bibliographical references (pages 108-118)

Chapter Managing Heat Transfer Issues in Thermoelectric Microgenerators

This chapter deals with heat transfer challenges in the microdomain. It focuses on practical issues regarding this matter when attempting the fabrication of small footprint thermoelectric generators (μTEGs). Thermoelectric devices are designed to bridge a heat source (e.g. hot surface) and a heat sink (e.g. ambient) assuring that a significant fraction of the available temperature difference is captured across the active thermoelectric materials. Coexistence of those contrasted temperatures in small devices is challenging. It requires careful decisions about the geometry and the intrinsic thermal properties of the materials involved. The geometrical challenges lead to micromachined architectures, which silicon technologies provide in a controlled way, but leading to fragile structures, too. In addition, extracting heat from small systems is problematic because of the high thermal resistance associated to heat exchanged by natural convection between the surrounding air and small bare surfaces. Forced convection or the application of a cold finger clearly shows the usefulness of assembling a heat exchanger in a way that is effective and compliant with the mechanical constraints of micromachined devices. Simulations and characterization of fabricated structures illustrate the effectiveness of this element integration and its impact on the trade-off between electrical and thermal behavior of the active materials in device performance

Urubu: energy scavenging in wireless sensor networks

For the past years wireless sensor networks (WSNs) have been coined as one of the most promising technologies for supporting a wide range of applications. However, outside the research community, few are the people who know what they are and what they can offer. Even fewer are the ones that have seen these networks used in real world applications. The main obstacle for the proliferation of these networks is energy, or the lack of it. Even though renewable energy sources are always present in the networks environment, designing devices that can efficiently scavenge that energy in order to sustain the operation of these networks is still an open challenge. Energy scavenging, along with energy efficiency and energy conservation, are the current available means to sustain the operation of these networks, and can all be framed within the broader concept of “Energetic Sustainability”. A comprehensive study of the several issues related to the energetic sustainability of WSNs is presented in this thesis, with a special focus in today’s applicable energy harvesting techniques and devices, and in the energy consumption of commercially available WSN hardware platforms. This work allows the understanding of the different energy concepts involving WSNs and the evaluation of the presented energy harvesting techniques for sustaining wireless sensor nodes. This survey is supported by a novel experimental analysis of the energy consumption of the most widespread commercially available WSN hardware platforms.Há já alguns anos que as redes de sensores sem fios (do Inglês Wireless Sensor Networks - WSNs) têm sido apontadas como uma das mais promissoras tecnologias de suporte a uma vasta gama de aplicações. No entanto, fora da comunidade científica, poucas são as pessoas que sabem o que elas são e o que têm para oferecer. Ainda menos são aquelas que já viram a sua utilização em aplicações do dia-a-dia. O principal obstáculo para a proliferação destas redes é a energia, ou a falta dela. Apesar da existência de fontes de energia renováveis no local de operação destas redes, continua a ser um desafio construir dispositivos capazes de aproveitar eficientemente essa energia para suportar a operação permanente das mesmas. A colheita de energia juntamente com a eficiência energética e a conservação de energia, são os meios disponíveis actualmente que permitem a operação permanente destas redes e podem ser todos englobados no conceito mais amplo de “Sustentabilidade Energética”. Esta tese apresenta um estudo extensivo das várias questões relacionadas com a sustentabilidade energética das redes de sensores sem fios, com especial foco nas tecnologias e dispositivos explorados actualmente na colheita de energia e no consumo energético de algumas plataformas comercias de redes de sensores sem fios. Este trabalho permite compreender os diferentes conceitos energéticos relacionados com as redes de sensores sem fios e avaliar a capacidade das tecnologias apresentadas em suportar a operação permanente das redes sem fios. Este estudo é suportado por uma inovadora análise experimental do consumo energético de algumas das mais difundidas plataformas comerciais de redes de sensores sem fios

Remote Powering and Communication of Implantable Biosensors Through Inductive Link

Nowadays there is an increasing interest in the field of implantable biosensors. The possibility of real-time monitoring of the human body from inside paves the way to a large number of applications and offers wide opportunities for the future. Within this scenario, the i-IronIC project aims to develop an implantable, low cost, health-care device for real-time monitoring of human metabolites. The contribution of this research work to the i-IronIC project consists of the design and realization of a complete platform to provide power, data communication and remote control to the implantable biosensor. High wearability of the transmitting unit, low invasivity of the implanted electronics, integration of the power management module within the sensor, and a reliable communication protocol with portable devices are the key points of this platform. The power is transmitted to the implanted sensor by exploiting an inductive link. Simulations have been performed to check the effects of several variables on the link performance. These simulations have finally confirmed the possibility to operate in the low megahertz range, where tissue absorption is minimum, even if a miniaturized receiving inductor is used. A wearable patch has been designed to transmit power through the body tissues by driving an external inductor. The same inductive link is used to achieve bidirectional data communication with the implanted device. The patch, named IronIC, is powered by lithium-ion polymer batteries and can be remotely controlled by means of a dedicated Android application running on smartphones and tablets. Long-range communication between the patch and portable devices is performed by means of Bluetooth protocol. Different typologies of receiving inductors have been designed to minimize the size of the implantable device and reduce the discomfort of the patience. Multi-layer, printed spiral inductors and microfabricated spiral inductors have been designed, fabricated and tested. Both the approaches involve a sensibly smaller size, as compared to classic “pancake” inductors used for remote powering. Furthermore, the second solution enables the realization of the receiving inductor directly on the silicon substrate hosting the sensor, thus involving a further miniaturization of the implanted device. An integrated power module has been designed and fabricated in 0.18 μm CMOS technology to perform power management and data communication with the external patch. The circuit, to be merged with the sensor readout circuit, consists of an half-wave voltage rectifier, a low-dropout regulator, an amplitude demodulator and a load modulator. The module receives the power from the implanted inductor and provides a stable voltage to the sensor readout circuit. Finally, the amplitude demodulator and the load modulator enable short-range communication with the patch

Development and efficiency optimizing of the human body energy converters

Nowadays it is known that the human body is continuous source of many types of energy and the devices used for collecting energy taken from the environment also have the required capabilities for the collection of the energy produced by the Human body (HB), but very limited and with very low efficiency. Low power and high yield converters are particularly needed in these cases of collecting energy from human activity and its movements due to the small amount of energy generated this way. But this situation can be improved. Enhancing or focusing the human movements by using mechanical amplifiers applied to the piezoelectric element. By doing so the input of energy in the element increases. As such increasing its output, therefore producing more energy

Power Approaches for Implantable Medical Devices.

Implantable medical devices have been implemented to provide treatment and to assess in vivo physiological information in humans as well as animal models for medical diagnosis and prognosis, therapeutic applications and biological science studies. The advances of micro/nanotechnology dovetailed with novel biomaterials have further enhanced biocompatibility, sensitivity, longevity and reliability in newly-emerged low-cost and compact devices. Close-loop systems with both sensing and treatment functions have also been developed to provide point-of-care and personalized medicine. Nevertheless, one of the remaining challenges is whether power can be supplied sufficiently and continuously for the operation of the entire system. This issue is becoming more and more critical to the increasing need of power for wireless communication in implanted devices towards the future healthcare infrastructure, namely mobile health (m-Health). In this review paper, methodologies to transfer and harvest energy in implantable medical devices are introduced and discussed to highlight the uses and significances of various potential power sources

Piezoelectric Energy Harvesting: Enhancing Power Output by Device Optimisation and Circuit Techniques

Energy harvesting; that is, harvesting small amounts of energy from environmental sources such as solar, air flow or vibrations using small-scale (≈1cm 3 ) devices, offers the prospect of powering portable electronic devices such as GPS receivers and mobile phones, and sensing devices used in remote applications: wireless sensor nodes, without the use of batteries. Numerous studies have shown that power densities of energy harvesting devices can be hundreds of µW; however the literature also reveals that power requirements of many electronic devices are in the mW range. Therefore, a key challenge for the successful deployment of energy harvesting technology remains, in many cases, the provision of adequate power. This thesis aims to address this challenge by investigating two methods of enhancing the power output of a piezoelectric-based vibration energy harvesting device. Cont/d

Micro-fabrication and characterization of highly doped silicon-germanium based thermoelectric generators

Over the last decades of research on sustainable energy, thermoelectric generation has been identified as a potential energy harvesting solution for a wide range of applications. Nowadays, the commercial thermoelectric technology is almost entirely based on tellurium alloys, it mainly addresses room temperature applications and it is not compatible with MEMS and CMOS processing. In this work, silicon-germanium based micro-devices have been designed, developed and characterized with the aim of addressing the heat recovery needs of the automotive industry. The micro-scale of the fabricated devices, together with the full compatibility with silicon micro-processing, also profiles an interesting potential for application in the autonomous sensor field. Most importantly, the configuration and the fabrication processes of such silicon-based generators constitute a platform to transfer the results of decades of promising material investigations and engineering into practical micro-scaled thermoelectric generators. The room temperature characterization of the manufactured micro-generators revealed power factors up to 13.9x10-3 µW/(cm2K2) and maximum output power density up to 24.7 µW/cm2. In such temperature range, the micro-devices manufactured in this work are still not as performing as the state-of-the-art bismuth-telluride based technology. However, at around 300 C, the developed micro-modules are predicted to produce a maximum power output of 1.2-1.5mW under 10 C temperature gradient, which corresponds to 35-45% of the room temperature performance of the only commercial bismuth telluride based micro-devices. The results show that silicon-germanium micro-modules could potentially compete with the state-of-the-art commercial micro-devices, being better performing at higher temperature, but also offering the advantage of being a sustainable MEMS and CMOS compatible option for autonomous sensors integration