CO2 Carbon Dioxide
GHGs Greenhouse Gases
MEMS Microelectromechanical systems
VLSI Very-large-scale integration
Table of Contents
Renewable energy resources are in greater demand then ever due to the major problem facing human kind regarding energy shortage, over population and the growing rate of industrial activity. As of the end of 2017 the current world population accounted for ≃7.5 Billion people (Worldometers 2018). Taking this figure into account as well as the astonishing rate of growth of the human population, it is as important as ever too explore other renewable energy harvesting avenues, apart from wind, wave, solar, hydro electrical, biomass and geothermal which can combat in the aid for the worlds energy demand. As well as the energy shortage and over population issue there is also the issue of environmental concerns, such as climate change which comes from the burning of our fossil fuel resource. The over reliability of burning fossil fuels as a means of producing energy is resulting in the depletion of this resource, and there for will mean that energy for everyday needs will have to be sought out from other sources. A research paper carried out by Shahriar Shafiee and Erkan Topal titled “When will fossil fuel reserves be diminished?” estimates the reserves of oil, coal and gas calculated depletion time is around 35, 107 and 37 years, respectively, by their proposed method. The paper also examined the world consumption to reserves ratio based on 2006 figures, in which the reserves of oil, coal and gas lasted a further 40, 200 and 70 years, respectively (Shafiee and Topal 2009). The figures from this research paper show that the rate at which we burn fossil fuels in the production of energy is not sustainable. Due to this revelation research into energy harvesting methods, apart from the methods already in practice, needs to be further examined in order to break dependence from fossil fuels while still maintain global energy security. The use of renewable energy harvesting devices also tackles the environmental challenges such as climate change and carbon dioxide (CO2) emissions.
The environmental impacts of the human energy demand are growing and already reached record heights for local, regional, and global environmental impacts, such as pollution to the air, oceans and lakes. Due to increasing costs of energy and decreasing fossil fuel supply, protecting the environment and harnessing sustainable forms of power are of the highest priority in the modern society. Countries throughout the world are seeking out ways in which they can combat this issue, which will contribute to the energy demand without adding to the environmental impact caused already. In addition to the growing population, another major cause of environmental issues such as pollution is the developments in industry. Developments in the industrial sector since the beginning of the industrial revolution have played a significant bearing on the pollution rates of Green House Gases (GHG) in the atmosphere. The rates of GHG in the air is the main contributor to climate change in the modern world.
Harvesting Energy provides the best possible techniques for approaching the global energy problem that does not require depleting natural resources Energy harvesting technology or renewable technology, which generate energy from the use of natural replenished resources, has expanded substantially in the past decade. The general global idea of renewable energy has shifted significantly. Twenty years ago, people widely acknowledged the potential of renewable energy, but large-scale deployment still had to be demonstrated. Now twenty years on, continuing technology advances and rapid deployment of many renewable energy technologies—particularly in the electricity sector—have amply demonstrated their potential.(The first decade:2004-2014 2014). Now in present time, the presumption of renewable technologies is that they are our main tool in adapting to climate change, as they provide energy security. Other benefits offered from renewable technologies include, reliability and resilience, improved public health, inexhaustible energy and added bonus of offer economic benefits such as jobs and profit to investors. From this information it is clear that continues investment and resources need to be implemented in the present and future design of renewable technologies, as well as the discovery of new or updated renewable energy technology.
Below is a list of aims and objectives which will be achieved in the undertaking of this project.
- To gain knowledge of the operating systems used within different technologies available to capture energy generated by human traffic and vehicles.
- To gain knowledge of the different technologies available in this field and to determine the best practice of each product and its power output rate.
- To research current installations of each individual product and determine its performance in the given location.
- To design a proposed tool that will examine the feasibility of each individual product and rate its performance.
- To compare the results of each product against each other to determine most efficient technology available.
- To propose locations suitable to the installation of the most suitable technology.
- To calculate the effectiveness of the product in the chosen location by determining its overall contribution to the total energy demand of the given location.
- To evaluate results and give a conclusion of overall performance of human energy harvesting technology.
This section outlines the approach the author will implement throughout the duration of this project and a brief overview of each subsequent chapter.
The approach to this work was as follows:
- Perform a literature review to establish sufficient knowledge on the technology of human energy harvesting, that covered areas of the use for the technology, the mechanics of the technology, the resources used by the technology and possible installation locations suitable to the technology.
Chapter 2: Provides an overview of Energy Harvesting floor tiles. The reasoning for the technology and the main factors associated with the production of energy from this renewable technology are examined. A greater in-depth analysis of the mechanics of the technology is then overviewed, which examines the different transduction methods incorporated in each available technology to produce energy from the vibration of the energy harvesting floor tiles. Resources the technology need to produce energy are then examined. Finally, locations suitable to the application of the technology are then discussed.
Chapter 3: Initiates the investigation into the current technologies available. A case study is carried out on each major commercial technology to determine its best practice. The case study will include where each product is best suited to being installed, the power available from each product, and cost and installation price for each available product.
Chapter 4: Feasibility of each product is calculated through a design tool proposal. Results of each product are then compared against each other. The feasibility study will evaluate based on cost, power produced and human/vehicle traffic needed per tile to produce suitable power
Chapter 5: Propose locations that the technology could play a significant role in the energy demand based on the results achieved from the previous chapter. Determine best practice technology most suitable to each location and evaluate the overall performance of the given technology installed in that location.
Chapter 6: Provides a discussion based on the main points discovered in each chapter of this project.
Chapter 7: Concludes the project, evaluating the projects overall performance based on the initial aims and objectives set out for this project. Recommendations for further improvement of the project are then outlined, to aid further development of this topic.
As outlined in Chapter 1. a literature review was carried out to act as a basis for which all relevant information used throughout this thesis was gathered and compiled to further the understanding of the thesis based topic, harvesting energy from the movement of pedestrians and vehicles. In order to get a better understanding for the thesis an extensive area of topics was covered which have a significant impact on the project. These researched areas were then divided into 5 different topics which lists as follows: 1) Reasoning for technolog, 2) Energy Generation, 3) Mechanics of the technology and 4) Application of the technology. From the experience gained from each researched area, a greater knowledge would be obtained for the overall potential existing from the use of human energy harvesting technologies in the everyday environment. The researched areas revealed a substantial amount of literature relevant to each topic as well as the overall topic of the thesis.
2.1.1 Reasoning for technology
With the availability of many types of human powered energy harvesting methods, the combination of applying the right applications to pair with the right locations of human energy sources is equally as important as the method of harvesting energy itself. As the power source is the human body, any power harvested would be logical to be used for improving quality of life. Hence this section looks at applications within the health and medical sector which helps aid the user through pervasive health monitoring.
Applications for Human Energy Harvesting are commonly split into two sections : Energy Harvesting inside the body or Implantable devices and Energy Harvesting outside the body or referred to as On Body Monitoring or even called Body Sensor Networks. Both sections present different challenges but share a common goal in improving pervasive health monitoring and quality of life. Both types of application also share a common theme of data transfer method, wireless data transfer technology. However, this research only focusses on external application of energy harvesting.
The need for wireless data transfer for implantable devices is clear as it is medically unsatisfactory and unsafe to have physical wires pass through under the skin. The wires could potentially cause medical complications to the patient and in severe cases, lead to fatalities. A second argument is the convenience that wireless data transfer brings into the application. Hence, an ideal situation that human energy harvesting brings is an application that enables health monitoring in a fit-and-forget package.
Kinetic energy is the energy an object possesses due to the motion of that object. This energy can be defined as work required to accelerate a body of from rest to a certain velocity. This kinetic energy within the body will remain constant unless the velocity of the object is changes due to an external force. The general formula for kinetic energy is given as:
The use of the piezoelectric concept can be seen by Christopher A. Howell, who carried out a performance measurement of four different concept ideas for “Heel Strike Units”, in which a small electric transducer that uses piezoelectric elements was placed on the heel of a shoe. The piezoelectric material used, Lead Zirconate Titanate (PZT5A), converted the mechanical force acting on the heel of the shoe into electrical energy. (Howells 2009).
The idea behind the mechanics of an electrostatic generators is a variable capacitor. The mechanical vibrations experienced drive the variable capacitance capacitor. The value of variable capacitance has freedom to then then oscillate between a max and min value. Mechanical energy is converted into electrical energy when a capacitor is constrained. The charge on the capacitor will transfer to the intended load or a connected storage device for later use as the capacitance level decreases (Zhu 2009). Electrostatic transducers are widely used in the detection of ultrasonic waves in air, and can also be incorporated in the generation process of these airwaves (Pizarro et al. 1999).
Electrostatic transducers can be split into three categories, In-plane Overlap, as shown in Fig c, In-plane Gap Closing, as shown in Fig h, and Out-of-plane Gap closing as shown in Fig k. Both In-plane Overlap and Out-of-plane Gap Closing deviates the overlap area that is between the fixed electrode fingers. Out-of-Plane Gap Closing deviates the distance between electrode plates as shown below (Zhu 2009)
Figure w. Basic components of electrostatic transducers (Zhu 2009).
An electrostatic transducer circuit is shown in Figure q. The Vin for the given circuit may be a storage device such as a capacitor or a rechargeable battery. The circuit contains a variable capacitor (
Cv). Cpar is the parasitic capacitance associated with the variable capacitor structure and any interconnections, which limits the maximum voltage. CL is the storage capacitor or any kind of load.
Figure q Electrostatic transducer circuit (Zhu 2009).
The Equation (f) used to calculate voltage at a max value for the given circuit is:
The Equation (5) used to calculate the max. energy available from the given circuit is:
A disadvantage of an electrostatic transducer compared to that of a piezoelectric transducer is that this process requires an initial voltage. Due to this reason, it is difficult to class this mechanism of energy harvesting from kinetic movement as supplying its own 100% power supply. This mechanism is however an efficient source to supply power to a battery which can then be used to supply voltage to a given load. Electrostatic transducers can be easily incorporated into transducer generating systems by mechanical means. With the ease of implementing this form of system, it is commonly used in Very-large-scale integration (VLSI) systems without major complications (Zhu 2009).
A project carried out by Sandeep Arya et al (Arya et al. 2016). attempted to test the performance of an electrostatic generator in a MEMS (Microelectromechanical systems) based cantilever device used to detect ultrasonic signal generation. The conclusion from this project was that the simulated, fabricated and testing of this generator was a success. The experimental output time took less than that of the simulated result they previously carried out. P.D. Mitcheson et al (Mitcheson et al. 2004). analysed, simulated and tested a micro engineered power generator. The device was suitable for application in sensors to be worn on the human body, which were motion-driven. The device was based on electrostatic generation, and was successful for low frequency operation. Although this project was successful for low frequency operations, it shows the potential available from electrostatic generators powered by kinetic energy from human motion.
“In a sentence, an electromagnetic transducer for a vibrational energy harvester has a magnet attached to the mass of the transducer or generator and will be able to produce a voltage with a coil attached to the system as the magnet moves”(Yew 2015).
Faraday’s law of electromagnetic induction states that an electric current will be induced in any closed circuit when the magnetic flux through a surface bounded by the conductor changes. This applies whether the field itself changes in strength or the conductor is moved through it. The induced voltage, also known as electromotive force (emf [V]), can be written as:
where [Wb] is the magnetic flux. The direction of the emf is given by Lenz’s law.
In electromagnetic generators, permanent magnets are used to produce a magnetic field and
coils are used as the conductor. In the simple case of a coil with N turns and length [m]
moving through a perpendicular magnetic field of constant strength, the emf across the coil is
where B [T] is the flux density going through the coil and [m·s-1] is the velocity of the
relative motion. It is seen that the emf is proportional to the moving velocity when the coil is
moving through the magnetic field. In addition, increasing the length and the number of turns
increases the emf, but increases the coil resistance. Thus more power will be wasted through the coil.
Figure 2.5 Circuit representation of an electromagnetic generator with a resistive load.
(Reproduced from )
The circuit representation of an electromagnetic generator with a resistive load is shown in
Figure 2.5. The relationship between the current through the load and the induced emf is given
where [Ω] and [H] are the resistance and inductance of the coil, respectively. Table
2.4lists some reported electromagnetic generators with their main characteristics.
Magnetostrictive energy tranducers can be considered a new concept when examined next to other energy generaters or transducers. Magnetostrictive energy tranducers work on a procedure of magnetization, which causes the material in the transducer to change its shape. While this change is occurring, the magnetic flux density of the material changes. It is this change in magnetic flux density that causes the generation of an induced voltage.
The most popular magnetostrictive materials (MsM) used in energy transducers are an amorphous metallic glass Metglas 2605SC and a crystalline alloy Terfenol-D. Wang  evaluated the Metglas 2605SC and was able to list several advantages of this method of transduction. Firstly, it was stated that the Metglas material was capable of being annealed under a strong transverse magnetic field in its width direction hence improving the magnetomechanical coupling coefficient to > 0.9 as well as the ability to reduce the footprint of this transducer in this situation.
However, several challenges of this method of transduction were also noted. As a coil is needed within the transducer system, it complicates things when trying to integrate with MEMS and certain types of magnetostrictive materials may need bias magnets within their system too.
There have also been findings of researchers combining piezoelectric materials and magnetostrictive materials together in a single transducer to evaluate if it is a better option. Dai , evaluated a vibration energy harvester that combined magnetostrictive material with piezoelectric material in a Terfenol-D/PZT/Terfenol-D sandwich and the 37
prototype achieved a load power of 1.055mW at 51Hz. Lafont  on the other hand combined two sheets of PZT-5 piezoelectric material with a sheet of Terfenol-D magnetostrictive material. Using a magnetic field that rises to 0.3T, causing the magnetostrictive material to change its shape and in turn, channel that change onto the piezoelectric material which produced a maximum of 214V and generated 95 μJ of energy. This shows by smartly combining piezoelectric materials which require mechanical strain to generate electrical power with magnetostrictive materials, the designs of the energy harvesters could be improved to eliminate the need for a pick up coil in pure magnetostrictive transducers
The concept of a hybrid energy harvester is one that contains two or more different energy harvesting mechanisms, such as the mechanisms described above. This type of energy harvester aims to capture the majority of available energy by incorporating different mechanisms into its design which is best suited to the application it is being used for. A research paper was carried out by Yang et al. (Yang et al. 2010) which investigated the design of an energy harvester integrated with both electromagnetic and piezoelectric mechanisms. The energy harvester was designed with a piezoelectric cantilever, substrate of two-layer coils and permanent magnets. The power density measured from the prototype was 790
µWcm3given by the piezoelectric elements and 0.85
µWcm3from the electromagnetic components. Other hybrid designs attempt to capture energy from different sources such as solar and vibration both incorporated into the design of the energy harvester, and convert it into electrical energy (Khameneifar 2011).
Piezoelecric generators have the simplist structure amoung the three transducers and they can produce appropriate voltage for electricl devices. However, the mechanical properties of the piezoelectric material may limit overall performance and lifespan of the generator. Although piezoelectric thin film can be intergrated into a MEMS fabrication process, the piezoelectric coupling is greatly reduced. Therefore, the potential for th intergration with microelectronics is less than that for electrcstatic micro-generators.
2.3.6 Comparisons of Generating mechanics
Figure t. Table Comparing the different kinetic generating mechanics (Zhu 2009).
Renewable energy technology is based on the idea of using earth’s natural resources as a means in which energy is created, rather then relaying on the burning of fossil fuels, ultimately leading to their depletion over time. Earth’s natural resources such as heat and light from the sun, and the motion of water and wind can be captured using renewable technology and transferring it into electrical energy. The power generated from each renewable source varies, depending on the resource it relies on. Each different technology has its own set of benefits and challenges that must be accounted for in its design. For example, wind is a resource that varies in its dependency as the wind speed is constantly changing as well as wind direction. Without the use of these natural resources we would not be able to capture the energy available, and thus, transfer it towards a useful source such as electrical energy or heat.
All of the resources mentioned above, are Earths natural resources. However, the technology under examination in this project realise on a differ resource to aid in the production of electrical energy, which is that of human power. Human power, or movement can be classed as a source that is suitable to harvest if the correct method to do so is in place. The human body can be considered a store for energy. The problem being that the majority of this energy becomes wasted energy that is of no use. Human energy harvesting technology was designed in the hopes of capturing this energy and turning it into a useful source that benefits the user or organisation (Yew 2015)
The main human power sources that this technology was designed for was that of Human traffic, which accounts for kinetic energy from pedestrians for both interior and exterior designs, and vehicle traffic, which accounts for the kinetic energy from cars, vans, and trucks as they drive over the installed tiles. Kinetic energy can be harvested from the two modes mentioned above from several different methods which have been developed and installed in everyday use such as Pavegen, Waynergy Floors, Power leap (PZT), Innowattech and Soundpower. As mention before, the different technologies will be further examined in Chapter 3. The novelty of this technology is that is uses humans, the main contributors to the environmental issues we face today, and harnesses their available energy from everyday activities. It is important to note that roughly half the world’s population now live cities, or urban areas. To date his technology has, for the majority of the time been installed in cities or urban areas as this will experience the most human traffic and vehicle traffic, and therefore produce the most potential energy (Abdalla et al. 2017).
Walking is human activity that requires internal energy, sourced from food that is eaten, to produce movement of the human body. The energy released from the movement of the human body in the action of walking has the potential to be harvested and transfer into to a useable source such as electrical energy. Antaki et al. (Antaki et al. 1995) developed a battery charging system that was installed on the heel of a boot. This device was capable of producing different power rates depending on the user and their weight. The figure r. below demonstrates the results generated from the model and its power capabilities.
Figure r. Model midsole generator: Measured power vs. theoretical power output (Antaki et al. 1995)
Another research paper carried out on harvesting energy from the sole of a shoe compared different devices. The devices with the most potential generated roughly about 0.8 W of energy. The goal of the project was to scavenge energy to be used for mobile and wireless electronic devices (Paradiso and Starner 2005).
A research carried out to model the energy harvesting potential in an educational building using piezoelectric materials was undertaken at the Macquarie University in Sydney, Australia. The paper examined the frequency of pedestrian mobility, from which they developed a model of covering a total of 3.1% of the floor area of the college that would generally see the highest pedestrian frequency and pave it with piezoelectric energy harvesting tiles. The results of the proposed model indicated that an estimated 1.1 MW h/year could be generated. They also indicated that with a possible improvement in the energy conversion efficiency of the piezoelectric material the model would be capable of further capturing 9.9 MW h/year. This new figure generated would be capable of producing roughly 0.5% of the annual energy need of the building (Li and Strezov 2014).
Traffic on roads has significantly increased worldwide over the last 30 years. In many highly populated areas, the emissions given off from vehicles have become the dominant air pollutant source. Pollutants released from vehicle traffic can be severely harming to the environment, with such pollutants as carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx) released during the process of driving (Zhang and Batterman 2013).
Figure o. Central Statistics Office (CSO): Vehicles licensed for the first time December and Year 2017 (Vehicles licensed for the first time december and year 2017 (summary) 2018)
The above figure highlights the increase in cars licensed for the first time in 2017, which also shows the rate of growth of cars over each year. While it is difficult to calculate the total number of cars on the roads in Ireland this figure demonstrates the growth of cars and the potential field in which energy could be generated. Although vehicles add considerably to the pollution in the atmosphere, if it was possible to capture wasted energy released from vehicles while driving it could be transferred to potential electrical energy.
Using the same principal as harvesting kinetic energy from human movement, the potential kinetic energy from vehicles could also be harvested and used as a potential benefit. The technology developed to harness energy from vehicle movement utilises the weight of the vehicle acting down, and from the method of a transducer transfer’s that energy to a beneficial form such as electrical energy.
A review carried out by Lukai Guo and Qing Lu for the Department of Civil and Environmental Engineering University of South Florida shows the potential energy creation if the entire Florida roadway was covered by a proposed energy harvesting system. The calculations showed that if the entire roadway was covered by a thermoelectric type pipe system, the generated electrical energy would be roughly 55 GWh per day. In contrast, if the roadway system was covered in a piezoelectric type system it would roughly generate 4.04 MWh of electrical energy per day (Guo and Lu 2017).
Hiba Najini et al. also carried out a paper to represent the potential energy from vehicles as they drove over speed bumps. This method integrated the concept of compressed air. With a traffic rate of 500 vehicles per hour, and accounting for various vehicle speeds it calculated that at a speed of 100, 80, and 120 km/ph the energy yielded was roughly 255, 137, and 469kWh, respectively (Najini and Muthukumaraswamy 2017).
The electrical energy created from the harvesting of energy from human movement can be used directly to power appliances or can be stored for later use. The storage of this power takes place in batteries. Batteries are a device that can store electrical energy by chemical means. When a small chemical reaction takes place within the battery, energy can then be released through the form of electricity. The mechanics of a battery is that hen this chemical reaction takes place; it transfers the electrons within the battery from its anode to its cathode. This transfer occurs across electrolyte material (Hamlen et al. 2002).
Batteries can also be recharged, which has the opposite effect on the battery as it restores the electrical energy. The electrical energy restored is then transferred back into the chemical bonds. Batteries capable of recharging their power are most commonly Lithium-ion batteries. In today’s world batteries are used in a number of different applications from both small scale to large scale uses, such as batteries for mobile phones as shown in Fig (Baguley 2013) to the new Tesla Mega battery in Australia, Fig. The biggest application for batteries is to supply power to low power consuming portable devices (Balouchi 2013).
Figure x. Lithium ion batteries which supply power to most mobile devices
Figure x. The world’s largest lithium-ion battery: Tesla Mega battery in Australia
Non-rechargeable batteries are usually manufactured from battery chemistries such as Alkaline, Lithium or even Zinc-Air. Primary batteries usually possess a higher energy density (2880 J/cm3) compared to secondary batteries and have relatively stable voltage output hence are widely used to power electronics. However, due to the relatively short life span and single use capacity, a replacement is needed once the power generating chemistry in the battery runs out. This proves to be a problem environmentally in how to dispose of the batteries as the chemicals from many batteries are toxic. Secondary batteries do not eliminate this issue completely but help alleviate it by being able to be recharged after running out of power. Common rechargeable battery chemistries are Nickel-cadmium (Ni/Cd), Nickel-metal Hydride (Ni/MH) and Lithium-ion. The power density of these batteries is lower (1080 J/cm3) than of primary batteries but they will last a lot longer in the long run. Secondary batteries generally have higher up-front costs than of primary batteries but are more cost effective in the long term.
Theory of kinetic energy harvesting
Kinetic energy is the energy an object possesses due to the motion of that object. This energy can be defined as work required to accelerate a body of from rest to a certain velocity. This kinetic energy within the body will remain constant unless the velocity of the object is changes due to an external force. The general formula for kinetic energy is given as:
Kinetic energy is a critical part of the design process of vibration energy harvesting floor tiles as it is the science behind the basis of this technology. The energy required, which is kinetic energy from humans, is the power supply for which energy harvesting tiles require to produce electricity. a transduction mechanismto generate electrical energy from motion and the generatorwill require a mechanical system that couples environmentaldisplacements to the transduction mechanism. The design ofthe mechanical system should maximize the coupling betweenthe kinetic energy source and the transduction mechanismand will depend entirely upon the characteristics of theenvironmental motion. Vibration energy is best suited toinertial generators with the mechanical component attachedto an inertial frame which acts as the fixed reference.
The inertial frame transmits the vibrations to a suspended inertial mass producing a relative displacement between them. Such a system will possess a resonant frequency which can be designed to match the characteristic frequency of the application environment. This approach magnifies the environmental vibration amplitude by the quality factor of the resonant system and this is discussed further in the following section.
The transductionmechanism itself can generate electricity by exploiting the mechanical strain or relative displacement occurring within the system. The strain effect utilizes the deformation within the mechanical system and typically employs active materials (e.g., piezoelectric). In the case of relative displacement, either the velocity or position can be coupled to a transduction mechanism. Velocity is typically associated with electromagnetic transduction whist relative position is associated with electrostatic transduction. Each transduction mechanism exhibits different damping= characteristics and this should be taken into consideration while modelling the generators. Themechanical system can be increased in complexity, for example, by including a hydraulic system to magnify amplitudes or forces, or couple linear displacements into rotary generators.
The Mechanics of the Technology
Vibration is ubiquitous in our everyday environment. The vibration caused by the nature of the wind, earthquake, tsunami and so on is with great energy that we are still unable to effectively control and use. As a matter of fact, the vibration of the industrial motor, the vibration of the vehicle on the road, and some other small vibration contain the micro energy we can use. Table 1 shows the classification of vibration sources in different environments.
If we choose an appropriate way, the energy produced by these tiny vibrations can be converted into electrical energy for storage and use. We look through lots of documents and find that the technique of collecting weak vibration energy by electromagnetic energy harvester has been developed maturely. Then it will introduce the research status of electromagnetic energy harvester
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