 THE word “smart” is ubiquitous these days. If you believe the hype, smart farms will all employ sensors to report soil conditions, crop growth or the health of livestock. Smart cities will monitor the levels of pollution and noise on every street corner. And smart goods in warehouses will tell robots where to store them, and how. Getting this to work, however, requires figuring out how to get thousands of sensors to transmit data reliably across hundreds of metres. On September 15th, at a computing conference held in Miami, Shyam Gollakota and his colleagues at the University of Washington are due to unveil a gadget that can do exactly that—and with only a fraction of the power required by the best devices currently available.
Dr Gollakota’s invention uses a technology called “LoRa” (from “long range”). Like Wi-Fi, this allows computers to talk to each other with radio waves. Unlike Wi-Fi, though, LoRa is not easily blocked by walls, furniture and other obstacles. That is partly because LoRa uses lower-frequency radio waves than Wi-Fi (900MHz rather than 2.4GHz). Such waves pass through objects more easily. More importantly, LoRa devices make use of a technique called “chirp spread modulation”. That means the frequency of the carrier wave—the basic radio wave, which is then deliberately deformed in order to carry data—rises and falls in a sawtooth pattern. That makes even faint LoRa signals easy to distinguish from background noise, which fluctuates randomly. Generating that carrier wave requires a lot of power. But modulating it, in order to impress data upon it, can be done by a chip that consumes almost no power at all. Conventional LoRa transmitters do both jobs. Dr Gollakota proposes to separate them. In his take on the system, a central transmitter, hooked up to a big battery or to the mains, broadcasts the carrier wave, while the task of impregnating it with data is done by a chip on the sensor. It accomplishes that by choosing to earth its tiny aerial, or not, millions of times every second. When the aerial is earthed, part of the carrier wave will be absorbed. When it is not, it will be reflected. If one of those cases is deemed to stand for “1” while the other represents “0”, the chip can relay data back to a receiver with the whole process controlled by three tiny, and thus very frugal, electronic switches. Dr Gollakota reckons that such chips can be made for less than 20 cents apiece. The signals they generate can be detected at ranges of hundreds of metres. Yet with a power consumption of just 20 millionths of a watt, a standard watch battery should keep them going a decade or more. In fact, it might be possible to power them from ambient energy: Dr Gollakota and his colleagues have experimented with running the chips from the electricity generated when light strikes a small photodiode. Like other LoRa devices, the chips are slow, transmitting data at about the speed of an old-fashioned dial-up modem. But most smart sensors will produce just a trickle of data in any case. The researchers are keeping quiet, for the time being, about the orders they have received. But early applications could be medical. The team have incorporated the chips into contact lenses and a skin patch. In hospitals, the chips could help track everything from patient gurneys to syringes and stethoscopes. Last year, Dr Gollakota unveiled variants of the chips that use ordinary Wi-Fi, too. These, he says, are in the process of making their way into disposable drug-delivery devices that notify patients via their phones when their medication is running low. That seems like a smart start. This article appeared in the Science and technology section of the print edition of The Ecomomist under the headline "Cheap and cheerful" Source: The Ecomomist
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In the fifth video in the Bare Essentials of Soil Mechanics series, Professor John Burland explains how important water pressure in the voids between soil particles is in determining the soil's strength. John describes how major disasters can take place if geotechnical engineers don't take into account water pressure in soils. To reinforce the importance of taking water pressure into account, Professor Burland cites the Abervan disaster in which an unstable manmade soil mound above the village of Abervan engulfed a school, killing 116 children and 28 adults.
In the first of two demonstrations, Professor Burland shows how important water pressure is at the contact point between two soil particles. The conclusion is that water pressure reduces the shearing force between particles, reducing overall soil strength. In the second demonstration, Professor Burland uses the example of building sandcastles at the beach to show how a small amount of water can increase soil strength. He explains this phenomenon by introducing the concept of surface tension. Learning outcomes This video will help learners answer questions such as:
About the Bare Essentials of Soil Mechanics Series This video is part of the Bare Essentials of Soil Mechanics series, funded by the Ove Arup Foundation, in which Professor John Burland draws on his many years of practice in geotechnical engineering and teaching to provide listeners with what he regards to be the key knowledge that geotechnical engineers need to understand about soil mechanics in engineering practice. Prof Burland is based at Imperial College London and has worked on hundreds of interesting projects, the most famous of which was stabilising the Leaning Tower of Pisa. More engineering teaching resources available on www.expeditionworkshed.org This work is licensed under the Creative Commons Attribution-NonCommercial 3.0 Unported License. Credits
Bare Essentials of Soil Mechanics - The Effect of Particle Size and Shape on Soil Strength14/2/2017 In the fourth video in the Bare Essentials of Soil Mechanics series, Professor John Burland demonstrates how soil grading (the range of particle sizes in a soil) and soil shape affect a soil's ability to resist load. In this video Professor Burland uses his base friction model, introduced in video 3 to model how changes to a soil affect its ability to resist the weight of a foundation pressing down on it. He compares the strength of a well-graded soil with a uniformly graded soil and demonstrates that a well-graded soil has greater ability to resist load.
Using the same model Professor Burland demonstrates the effect of particle shape on soil strength by comparing the behaviour of a soil made of round particles with the behaviour of a soil made of circular particles. The conclusion is the more angular the soil particles, the stronger the soil. More engineering teaching resources available on www.expeditionworkshed.org Learning outcomes This video will help learners answer questions such as:
About the Bare Essentials of Soil Mechanics Series This video is part of the Bare Essentials of Soil Mechanics series, funded by the Ove Arup Foundation, in which Professor John Burland draws on his many years of practice in geotechnical engineering and teaching to provide listeners with what he regards to be the key knowledge that geotechnical engineers need to understand about soil mechanics in engineering practice. Prof Burland is based at Imperial College London and has worked on hundreds of interesting projects, the most famous of which was stabilising the Leaning Tower of Pisa. This work is licensed under the Creative Commons Attribution-NonCommercial 3.0 Unported License. Credits Written and presented by: Prof John Burland, Imperial College, London. Concept design: http://www.thinkup.org/ Graphic design: http://thomasmatthews.com/ Direction/Production: http://www.ariesfilms.com/ Source: Expedition Workshed - www.expeditionworkshed.org In the third video in the Bare Essentials of Soil Mechanics series, Professor John Burland demonstrates how deposition under gravity of soil particles, in lakes and rivers, affects how soils behave. Prof Burland is based at Imperial College London and has worked on hundreds of interesting projects, the most famous of which was stabilising the Leaning Tower of Pisa.
In this video Prof Burland uses an ingenious model to show in slow-motion how soils are laid down in rivers and lakes. He uses his model to show how soils laid down under gravity form column structures within their mass, which makes these soils stronger vertically than horizontally. Prof Burland then goes on to illustrate how gravity effects the strength of soil at different depths. His experiment shows that the more load a foundation carries, the further it will push into the soil before it reaches equilibrium. The conclusion is that soil strength increases with depth. Learning outcomes This video will help learners answer questions such as:
About the Bare Essentials of Soil Mechanics Series This video is part of the Bare Essentials of Soil Mechanics series, funded by the Ove Arup Foundation, in which Professor John Burland draws on his many years of practice in geotechnical engineering and teaching to provide listeners with what he regards to be the key knowledge that geotechnical engineers need to understand about soil mechanics in engineering practice. More engineering teaching resources available on www.expeditionworkshed.org This work is licensed under the Creative Commons Attribution-NonCommercial 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/b... Credits Written and presented by: Prof John Burland, Imperial College, London. Concept design: http://www.thinkup.org/ Graphic design:http://thomasmatthews.com/ Direction/Production: http://www.ariesfilms.com/ Source: Expedition Workshed - www.expeditionworkshed.org In the second video in the Bare Essentials of Soil Mechanics series, Professor John Burland describes that soils are made up of individual particles - this is fact is fundamental to the understanding of soil behaviour. Prof Burland is based at Imperial College London and has worked on hundreds of interesting projects, the most famous of which was stabilising the Leaning Tower of Pisa.
In this video Prof Burland demonstrates how all soils, be they gravel, sand, or silt are made up of individual particles. Even clay, which is stiff to handle, can be dried out and when put under an electron microscope, can be seen to be made of particles. Using a simple demonstration, Prof Burland shows how a soil's ability to resist loads is generated by shearing resistance at the particle contacts. Learning outcomes This video will help learners answer questions such as:
About the Bare Essentials of Soil Mechanics Series This video is part of the Bare Essentials of Soil Mechanics series, funded by the Ove Arup Foundation, in which Professor John Burland draws on his many years of practice in geotechnical engineering and teaching to provide listeners with what he regards to be the key knowledge that geotechnical engineers need to understand about soil mechanics in engineering practice. More engineering teaching resources available on www.expeditionworkshed.org This work is licensed under the Creative Commons Attribution-NonCommercial 3.0 Unported License. Credits Written and presented by: Prof John Burland, Imperial College, London. Concept design: http://www.thinkup.org/ Graphic design: http://thomasmatthews.com/ Direction/Production: http://www.ariesfilms.com/ Source: Expedition Workshed - www.expeditionworkshed.org World-leading geotechnical engineer Professor John Burland introduces viewers to the world of soil mechanics. This is the first in the Bare Essentials of Soil Mechanics series: the key things a civil engineer needs to created to understand about soil mechanics. Prof. Burland is based at Imperial College London and has worked on hundreds of interesting projects, the most famous of which was stabilising the Leaning Tower of Pisa. In this video, Prof Burland invites us to spare a thought for the long-forgotten geotechnical engineer whose responsibility it was to stop the tunnels from falling on our heads or to prevent the skyscrapers from sinking into the ground. He goes on to describe soil mechanics as the branch of science that studies the mechanical behaviour of soils as they apply to the design of civil engineering structures.
Learning outcomes This video will help learners answer questions such as:
About the Bare Essentials of Soil Mechanics Series This video is part of the Bare Essentials of Soil Mechanics series, funded by the Ove Arup Foundation, in which Professor John Burland draws on his many years of practice in geotechnical engineering and teaching to provide listeners with what he regards to be the key knowledge that geotechnical engineers need to understand about soil mechanics in engineering practice. More engineering teaching resources available on www.expeditionworkshed.org This work is licensed under the Creative Commons Attribution-NonCommercial 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/b... Credits
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