Thermoelectric microconverter for energy harvesting systems

This paper presents a solution for energy microgeneration through energy harvesting by taking advantage of temperature differences that are converted into electrical energy using the Seebeck effect. A thermoelectric microconverter for energy scavenging systems that can supply low-power electronics was fabricated using thin films of bismuth and antimony tellurides. Thin films of n-type bismuth (Bi2Te3) and p-type antimony (Sb2Te3) tellurides were obtained by thermal coevaporation with thermoelectric figures of merit (ZT) at room temperature of 0.84 and 0.5 and power factors (PF × 10−3 [W · K−1 · m−2]) of 4.87 and 2.81, respectively. The films were patterned by photolithography and wet-etching techniques. The goal for this thermoelectric microconverter is to supply individual electroencephalogram (EEG) modules composed by an electrode, processing electronics, and an antenna, where the power consumption ranges from hundredths of microwatts to a few milliwatts. Moreover, these wireless EEG modules allow patients to maintain their mobility while simultaneously having their electrical brain activity monitored.Portuguese Foundation for Science and Technology - Project FCT/PTDC/EEA-ENE/66855/200

Thermoelectric generator and solid-state battery for stand-alone microsystems

This paper presents a thermoelectric (TE) generator and a solid-state battery for powering microsystems. Prototypes of TE generators were fabricated and characterized. The TE generator is a planar microstructure based on thin films of n-type bismuth telluride (Bi2Te3) and p-type antimony telluride (Sb2Te3), which were deposited using co-evaporation. The measurements on selected samples of Bi2Te3 and Sb2Te3 thin films indicated a Seebeck coefficient in the range of 90–250 μV K−1 and an in-plane electrical resistivity in the range of 7–17 μÄ m. The measurements also showed TE figures-of-merit, ZT, at room temperatures (T = 300 K) of 0.97 and 0.56, for thin films of Bi2Te3 and Sb2Te3, respectively (equivalent to a power factor, PF, of 4.87 mW K−2 m−1 and 2.81 mW K−2 m−1). The solid-state battery is based on thin films of: an anode of tin dioxide (SnO2), an electrolyte of lithium phosphorus oxynitride (LixPOyNz, known as LiPON) and a cathode of lithium cobaltate (LiCoO2, known as LiCO), which were deposited using the reactive RF (radio-frequency) sputtering. The deposition and characterization results of these thin-films layers are also reported in this paper.This work was fully supported by FCT/PTDC/EEA-ENE/66855/2006 project

Термоэлектрический контроль металлов геодезических скважин

Достоверное измерение термоэдс при контроле металлов и сплавов требует выполнения специальной методики измерения. К сожалению, эти требования не выполняются в коммерчески доступном оборудовании, и поэтому полученные данные часто содержат систематические ошибки. Описываются решения, позволяющие получать более достоверные данные величины термоэлектродвижущей силы.A reliable measurement of the thermopower in the testing of metals and alloys requires special analytical techniques. Unfortunately, these requirements are not met in commercially available equipment and, therefore, the resulted data often contains systematic errors. This scientific work describes a solution that allows obtaining more reliable data through decent evaluation of the thermopower

Robust Control Architecture for Waste Heat Harvesting with Non-Inverting Buck-Boost Converter

Thermoelectric generators (TEG) can be used to harvest wasted heat. TEGs are characterized by a wide output voltage range and a considerable output resistance leading to a maximum power point dependent on the working temperature. Non-Inverting Buck-Boost converter is used to manage, from one side, the wide voltage range, and from the other a battery. This article investigates a robust control architecture to recover the maximum energy from the exhaust's heat avoiding instability issues and maximizing converter efficiency

Wearable Human Motion and Heat Energy Harvesting System with Power Management

A combined human motion and heat energy harvesting system are under investigation. Main parts of the developed human motion energy harvester are flat, spiral-shaped inductors. Voltage pulses in such flat inductors can be induced during the motion of a permanent magnet along its surface. Due to the flat structure, inductors can be completely integrated into the parts of the clothes, and it is not necessary to allocate extra place for movement of the magnet as in usual electromagnetic harvesters. Prototypes of the clothing with integrated proposed electromagnetic human motion energy harvester are created and tested. Voltage of generated impulses is shown to be high enough to be effectively rectified with commercially available diodes and ready to be stored; however, efficiency depends on properties of controlling circuit. In order to increase the sustainability of the energy source and its stability, an option for combining a motion energy harvester with a human body heat energy harvester is also considered. Thermoelectric generator that harvests electricity from waste heat of human body is presented, and generated voltage and power are compared at different activity levels and ambient temperatures. Power generated with thermoelectric generator located on lower leg reached up to 35 mW with peak voltages reaching 2 V at certain conditions. A possible power management set-up and its efficiency are discussed

Application of thermal energy harvesting from photovoltaic panels

This paper describes a newly developed system for harvesting thermoelectric energy from photovoltaic panels. This system helps to power monitoring systems for photovoltaic panels (PVs) in locations where there is no energy source using waste thermal energy from PVs exposed to the sun’s rays. In the study described here, the thermal energy from a PV panel was captured and transferred to a thermoelectric generator (TEG). A temperature gradient was created by reducing the temperature using an aluminium heat sink in ambient weather conditions. This temperature gradient was used to generate electricity via two TEGs. In field tests carried out in April, in Aksaray province in central Turkey, the maximum temperature gradient due to solar radiation was measured as 21.08 °C. The harvested energy was increased to a usable level of 4.1 V using a DC-to-DC converter and stored in a li-ion rechargeable battery. The maximum charge current level of the battery was 147 µA. The maximum harvested energy was 458.64 mW, and a stable level of around 350 mW was achieved. The experimental operation of the prototype system was carried out in stable weather conditions; however, weather and climatic conditions greatly affect levels of energy harvested as a result of changing temperature gradients. The energy obtained with the prototype may reduce the battery maintenance costs of PV monitoring systems and lead to the development of new such systems which cannot presently be used due to a lack of energy

First vs second order magnetocaloric material for thermomagnetic energy conversion

International audienceWe estimate the power and efficiency of a thermal energy harvesting thermodynamic Brayton cycle using a first and second order magnetocaloric materials as active substance. The thermodynamic cycle was computed using a simple thermal exchange model and an equation of state deduced from a phenomenological Landau model. For the first and second order materials, narrow and high frequency cycles are optimum and give similar performances. Considering technological issues hindering the increase of frequency, we introduced a more detailed approach where we take into account the time needed to switch the material between two heat reservoirs. We show that the first order material equation of state leads thermodynamic cycle shape keeping it closer to the optimum cycle. Conditions to improve the performance of second order materials are discussed. In addition, we infer key remarks for prototype design regarding the power density and efficiency reachable in different configurations

The deposition of Bi2Te3 and Sb2Te3 thermoelectric thin-films by thermal co-evaporation and applications in energy harvesting

First Published 2012Bismuth, antimony and tellurium compounds (Bi/Sb/Te) are known as the best thermoelectric materials for room temperature operation. Despite thermoelectric devices with these materials being used for many years in macro-scale dimensions (millimetres sized devices), only few attempts were done to reduce these devices to the micro-scale (micrometers sized devices). The deposition of thermoelectric films was reported before using techniques like electrochemical deposition (ECD), metal-organic chemical vapour deposition (MOCVD), pulsed laser deposition (PLD), sputtering and thermal evaporation [1-8]. Each technique has its vantages and disadvantages, and a summary can be found in the table 5.1. In this table, CVD and ECD present opposite characteristics: While CVD films present high figure of merit (ZT), but a low deposition rate and expensive and complicated equipment is required (specific gases are needed for the deposition), ECD is a simple process, allowing high deposition rates (tens of μm can be achieved) but resultant films present low ZT. However, ECD allows the creation of structures during the deposition process, using the LIGA process (from German “Lithographie, Galvanoformung, Abformung”, meaning Lithography, Electroplating and Molding). In this chapter, the deposition of Bi2Te3 and Sb2Te3 thin films by thermal co-evaporation is described.FCT/PTDC/EEA-ENE/66855/200

All-solid-state batteries : an overview for bio applications

Batteries are crucial for most of bio applications. Batteries based on a liquid or polymer electrolyte needs a weight protective packaging which decreases their energy density and increases their size. This paper aims to identify, on the one hand, the efforts performed in thin-film batteries until now, and on the other hand, to provide an overview about the future perspectives in integration of batteries with flexible electronic circuits and energy harvesting systems. The overview highlights the need for an on-going investigation that aims to replace metallic lithium anode of batteries through different approaches. Other materials, namely silicon or germanium, seem promising when combined with nanostructures. Three dimensional and integrated batteries will increase its volumetric capacity.This work was financial supported by FCT funds with the project PTDC/EEAELC/114713/2009, with second author scholarship SFRH/BD/78217/2011 and strategic project from Algoritmi Centre FCOMP-01-0124-FEDER-022674