Notes by Akshat Jiwan Sharma

 Tunable visible light emitter using the 7 element framework  Objectives that should be achieved by the emitter are  1. No phosphors. It should be a direct emission. Electrical energy converted to light energy.  2. Electrically tunable. We should be able to modulate the color of the light by changing the voltage applied.  3. Our light source should be warm white by default.  4. It must not use complicated packaging. Should be rugged by default.  And finally it must be built with the 7 widely available elements (h,c,n,o,na,si,fe) The obvious answer is to make sic which has proven electroluminescent properties. However the large energy needed for its synthesis & comparatively lower efficiencies reduce its appeal. While the latest research on this subject has put forward new ideas of improving efficiencies chief among them being fabricating nanowires & engineering defects in the crystal ,the high energy required is still a problem.  One of th...

Well at present terabit speeds are available in fiber optic cables. But that is the total throughput of the cable. A fiber optic cable is made up of a number of "strands" that operate at much lower speeds. In fact these strands are simply outputs of ethernet cards. So now if you look at max ethernet speeds you'll get something like 1gb/10gb/40 gb etc. So the speeds on the strands are limited by the processing capability of on board electronics. If you go by wikipedia https://en.m.wikipedia.org/wiki/Fiber-optic_cable "Modern fiber cables can contain up to a thousand fibers in a single cable, with potential bandwidth in the terabytes per second" some rough math will tell you that each strand is doing a gigabit. Which is easy to achieve with common gigabit ethernet cards. A 1000 of them for a cable in the example given above. Now coming back to the topic. Terabit data through home wifi routers. It's certainly possible. The bottleneck is not physical medium. Wif...

  Water is an efficient refrigerant. Cloud cooling can cool water droplets to temperatures as low as  -70 degree Celsius. To effectively use water as a refrigerant we need to understand how it evaporates.  How does water evaporate? Water does not need to reach 100 degree Celsius before evaporation. Water is constantly evaporating in seas at temperatures between 0-35 degree Celsius. The reason for this is bubbles that are created at the surface of air water interface due to continual wave motion.  [Bubbles have been observed when water is stretched to pressures below its vapor pressure. This is about 3 kpa for 25C ] [Bubbles can also form when air is mixed with water as is the case in the seas where wind velocities are high] These bubbles implode leading to pressures as large as 2.1 GPA breaking the hydrogen bonds in water & causing it to vaporize.  https://akshatjiwannotes.blogspot.com/2024/10/what-is-maximum-wall-pressure-developed.html?m=1 Inherent advanta...

   If you want to test a prebuilt antenna (ex the one you may have bought) then there are a couple of ways Test antenna on each port separately. Insert coax into one port and measure the reception on the receiver. This will establish whether the ports are working individually. Take 2, 4 port antennas and use one for transmission and the other for reception to see if they work. In this setup you can try different arrangements: all 4 transmitting and 1 receiving , 2 Transmitting and 3 receiving ,4 transmitting and 4 receiving and so on. This test is more thorough and will let you test for all possible success and failure conditions. On the other hand If you're building such a system then you could 1. Test the array elements individually 2. Arrange them in the manner you want to feed them and do a continuity test. 3. If the elements work individually and they are continuous then they would work as arrays, but you can repeat the test cases defined above for a more thorough test. H...

   1. Single atom spectrum If we consider carbon as a single atom then it emits all over the visible light spectrum. There are emission lines in red,yellow,green,blue indigo & violet colors. With carbon there's a complete rainbow of colors. By applying corresponding energies(electrical,heat,mechanical it doesn't really matter what kind of energy)specific color lines would be obtainable in carbon.  2. Graphite vs diamond vs diamond like carbon Practically speaking however we don't really find one atom of carbon floating around displaying its vivid colors. Carbon atoms arrange themselves into a dark black graphitic form or a transparent diamond form. Already we have two extremes of optical properties in a single element.  But there's also diamond like carbon. In this form due to functionalization the bond angles of hetero atom-decorated carbon starts to look like that of sp3 diamond. Consequently its properties tend to shift towards diamond as well. It becomes opti...

  Generally there are three known ways in which a band gap can be created in carbon. 1. Via functionalization. However functionalization is a chemical reaction that changes the underlying material properties.  2. Creation of allotropes that have tunable band gaps like fullerenes & tetrahedral amorphous carbon(Tac or diamond like carbon).Fullerenes are hard to obtain in large quantities and Tac can't be patterned. Meaning it has to be first deposited & then post processing steps need to be applied. Unlike other forms of carbon(eg glassy) this introduces complexities in manufacturing.  3. Creating quantum dots.Quantum dots are few atom structures(a 2nm qd will only contain about 28 carbon atoms,possibly less) and therefore their energy levels are discretized and different from bulk crystal structures. For this reason they are also called artificial atoms.  While QDs offer a simple strategy to tune band gaps in any element/semiconducting compound its hard to act...

Generally speaking the device that transforms one form of signal (or energy) into another is called a transducer. If a router is equipped with an optical transducer it will be able to directly use fiber optic cable to convert light signal into an electrical signal. If not you'll need another device that takes fiber optic cable as input and gives out a signal over an ethernet cable that can be plugged into the router. Going into a bit more detail just like there are RJ45 interfaces for ethernet cables in routers fiber optic cables have special interfaces that handle light signals. These interfaces plug into specific cards on the motherboard of the device. Many companies build these cards with a PCIe or M.2 slot interface that you can place in a motherboard. For fiber channels the cards contain SFP slots. SFP stands for small form factor pluggable. As the name suggests these are pluggable(swappable) network interfaces for different physical layers. There is an ethernet SFP, there is ...

   One of the goals of 5G is to have low range but dense networks. Meaning each cell site will serve a small area but there will be a lot of cell sites. These sites are called small cells (Although small cells are not exclusive to 5G,they have have been proposed numerous times across cellular generations,but experts say that 5G with its mmwave will be best suited for small cell adoption) In this architecture traditional towers will be expensive and may even prove to be a hindrance in realizing the goal of small cells. (Incidentally facebook with its terragraph is looking to do something similar https://terragraph.com/) 5G operators want to turn anything into a cell site. Lighting poles, utility poles, advertisement panels, rooftops, subways, malls, stadiums. Basically they want a cell site anywhere they can hang their radio equipment. If you look at traditional towers today you'll find them dotted with antennas of various shapes and sizes. Most of these antennas aim to create ...

   The three essential components that make wifi work are The radios. These generate the carrier waves 2.4 ghz / 5ghz (or both in dual bands ) and encode the data on the wave according to the modulation scheme. The total speed of the network depends upon the kind of modulation used. The antennas that serve as the interface between transmitting and receiving devices. They are responsible for sending and receiving signals. Portable wifis have integrated antennas. Most home routers have external antennas where as carrier grade wifi may use custom antennas for long distance transmission.  The operating system that makes the network "intelligent". This is the software part that controls the operation of radios and ties together the networking layers into a coherent system that everyday users can work with. Now the actual operation includes many more details but this is the general principle of how wifi or any wireless system works. A hotspot is basically an internet access poi...

  In a previous post we had discussed how we can create mmwave & microwave frequency using a frequency comb.  https://akshatjiwannotes.blogspot.com/2024/11/making-broadband-generator-for.html But there are a few problems with the method described in that post. Mostly related to fabrication of photodiodes on the substrate & its arrangement into a photonic pattern.  New method for generation of high frequency AC for communication and computing systems in gigabose to terrabose range.  Instead of using for whispering galleries or frequency combs fabricated on chips we use a diffraction grating. The big advantage being :easy to fabricate ,easy to understand, simple operation, no complicated theory, works with uncollimated light source, stable reliable operation using passive components.  Photo detectors cavity resonators +diffraction grating :how it works Light shines on a diffraction grating and forms a diffraction pattern Photo diodes are placed on the patt...

I don't think that it was any single factor or idea but rather several different things coming together that has made wireless internet cheap and fast. There is more fiber connectivity today than any other time before. The way the internet is structured it still requires fixed line transport. But luckily that transport is extremely fast and extremely cheap both on the scale of passive components (like the cable) and on the scale of active components like the switches. Cheap consumer devices have enabled more people to get on the internet and help drive revenue for internet service providers who have in turn invested their profits to get even more people on to the network. Rural areas are lagging behind but there are positive developments on that front too with penetration of fiber as well as development of low cost access points. The application industry has done really well. Facebook,YouTube, amazon, flipkart have all built services that people want to use. Due to their efforts, t...

  Wood in plants serves a specific purpose. It is structured in a way that allows it to serve that purpose. What roles does wood need to fulfill in a plant? 1. Load bearing --To hold the weight of the plant 2. Defense --Against pathogens & against elements(water,air) 3. Transport of food ,water & minerals to growth sections/active elements of the plant.  #1 requires it to be really tough #2 requires it to be sealed #3 requires it to be well networked(or connected). For transportation to occur there needs to be transport pathways.  Botanically sections of wood are arranged into cells & tissues. These cells & tissues are the working /active elements of the wood & are responsible for its actual growth & sustenance. But we are interested in the big picture details. How wood forms & what is its final structure when it matures? To simplify matters in the mature portions of the wood the cells are all dead. A mature wood,which can be identified by its ...

  Thanks for asking this question. Any electromagnetic signal carrying any power, whether a few nanowatts or terrawatts, will travel to the end of the universe if it's unobstructed. EM waves don't lose energy or power in free space. It is only when EM waves interact with matter that they get reflected,refracted or absorbed. Any transfer of energy between wave and matter can take place only when they interact with each other. With that out of the way let us say that you shine a very high energy radiation, a terrahertz wave like visible light ,from a flashlight , on a 10 floor building would it be detected on the other side? Unlikely. That means that the wave has stopped propagating after a few meters. Some of it reflected, some transmitted ,other absorbed. Now increase the power of radiation 10 watts,100 watts,1000 watts and so on. With increased power more of the light will try to penetrate through the building but then rapidly lose its power and only faint signals will be visi...

  If you look at wireless deployments across the world you'll find that the big corporations dominate the market. They have the capital and wherewithal to provision and maintain the network. To be an internet service provider you need to be big. This is the nature of the industry. Thanks to capital investments made by big companies we enjoy seamless network connectivity almost everywhere. However there are two sides to every coin. An organization that would invest billions of dollars in laying down the infrastructure would most certainly want to maximize their return from the investment. And it follows that they would want to target people who can actually afford to pay their prices. The Internet has therefore seen maximum growth in urban areas. In the rural areas people don't have access to the network. This is a problem because internet connectivity can help raise awareness,skills as well as knowledge in the community which may be costly to acquire by traditional means,like s...

  Switching speeds determine how fast (or how densely)data can be encoded on a carrier wave .Carrier wave may be a very high frequency visible light but if the encoding speed is slow,like say turning a light on and off mechanically,data rates will be slow.  So the frequency of carrier waves only becomes a problem when we have encoding technologies that can exceed the frequency of the carrier.  On the other hand we need a large bandwidth for transporting huge amounts of data being generated. This is where visible light shines. Even though most of the telecom carriers use frequencies in the IR the property of glass fibers is such that it can carry broadband signals in both IR and in visible light. So high data densities are achieved simply be encoding multiple streams of information on a single fiber thread.  This is such a big advantage that comparatively slow data encoders(current state of the art ethernets being able to o/p at few gbs only) can be colliminated so th...

  “When I was small, 2GB of data was too much for a month, but nowadays even 2GB a day is not sufficient. Why is too much data being consumed for every task?” Your observation is correct. However this phenomenon is not limited to the internet. In just about every industry as the production and supply has become more efficient the consumption has grown to match it. Back in those days there were few video streaming websites,nothing like Instagram or facebook to get people to actively use the network. The Internet was limited to simple messaging and even the infrastructure that supported it was expensive. File sharing was big but was only used by people who were good with computers. For everyone else hard disks were passed around ;) A lot of things have happened since then Huge investment in fiber optic cables have made the internet cheaper for more people. So optimizing the amount of data sent over the wire is no longer a priority for Devs. Devices have become easier to use. Mobile p...

Because Stirling engines are external heat engines, meaning they don't require source of heat inside the engine (unlike IC engines) they have the potential to serve as a common research project with promise for application in a variety of industries Stirling engines as external heat engines can be used by nuclear, oil and gas and concentrated solar power generators to transform heat into work. Regardless of how you think energy should be generated in short, mid and long term Stirling engines are one area where different Industries can find common ground to collaborate. Besides in large infrastructure projects like electrical energy generation (more specifically as heat to mechanical energy transducers) stirling engines are useful to automotive, HVAC ,pumping  and cleaning industries. The industries that are focused on doing functional rather than structural work.  The groups focused on Stirling engine research can isolate themselves completely from the source of energy ,the ki...

What you want to do is called traffic shaping. With traffic shaping you can create rules that will help you prioritize a certain kind of traffic over others. The specific steps will depend upon the operating system of your router but in general this is what you need to do Figure out how you want to identify your IOS device on your router. The easiest way is to use the mac address . You can find out the Mac address of your device by going through the settings menu. Now use this mac address to assign a static IP address to the device. On openwrt (a linux os for routers) you can assign static IP address like so  https://docs.turris.cz/basics/luci/static-dhcp/static-dhcp/ Tell the router that the traffic coming from this IP address should be given priority over everything else. In openwrt you can use HTB or hierarchical token bucket to organize traffic into different "buckets" and prioritize one over the other. Here's a good explanation with diagrams and examples  https://wik...

The challange 1. Carbon is a very small atom. With an atomic number of 6, there are only 5 other atoms that are smaller than carbon. Compared to silicon with an atomic number of 14 the doping choices are minimal. Unlike silicon, elemental carbon can't be melt processed so existing tools & understanding about dopants (or more generally alloying) are out.  2. Carbon has a very rich chemistry. Elements like hydrogen & nitrogen that would become good candidates for doping actually form covalent bonds with carbon[1]. And instead of providing electron-hole pairs, the band gap continuously. Compare this with boron & phosphorus in silicon where they act more or less in their free atomic state. Sure with careful engineering maybe hydrogen & nitrogen can be made to fit inside carbon lattice (nitrogen happily sits inside diamond for example & it would be expected that it would act as a dopant in diamond like carbon as well)  3. The crystal arrangements of carbon that ...

  #engineering #magnets Magnets are critical to energy infrastructure today. They are used in generators (coal,hydroelectric,wind) ,motors in electric vehicles,mechanical pumps etc. Most magnets today use nickel,cobalt,neodymium, Strontium etc. These materials are hard to find, extract & purify. For a renewable energy future it is extremely important to make magnets from easily available materials. Latest research has shown that permanent magnets can be made from abundant materials : iron,carbon,silicon & nitrogen Iron nitride has already been demonstrated as the most powerful magnet ever synthesized but nitriding can be a little complicated. https://phys.org/news/2010-03-iron-nitrogen-compound-strongest-magnet.html https://magnairon.com/technology/niron-2/ Reasonably powerful magntes can be created with composites of iron,carbon and silicon. These elements are much easier to work with. https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.15.024012 https://www...

  The inability of telecom companies to live up to promised speeds is not unique to India. 4G speeds have been peaking at 50 Mbps all over the world https://www.opensignal.com/reports/2018/02/state-of-lte https://www.opensignal.com/sites/opensignal-com/files/data/reports/global/data-2019-05/the_state_of_mobile_experience_may_2019_0.pdf a far cry from the promised 1000 mbps. I must admit that I'm of the opinion that speed is overrated after a certain limit is reached but if you look at a modest last gen wifi machine you'll find that it easily achieves a gigabit. And it does it while being lighter,less power hungry and easier to provision and maintain. Now some experts will point out that the speed measurement is at fault. And that a base station has to serve several hundred users while maintaining coverage over large distances. It is true but then again many questions arise – the most important being Why has the industry not been able to reduce the base station prices? Why have ...

Mechanical work is good for systems where large power but imprecise operation is needed. There is not much precision in rotation of a fan or working of a pump but they consume a lot of energy. Electrical work on the other hand is invaluable where precision is needed on an electronic scale. LED, electronic circuits ,TVs, computers can't directly work on heat you need electrical energy for them. Similarly all modern communication systems are useless without electricity. it is for these systems we need to ensure a continuous sustainable electrical supply.But here too heat has a role to play  if you think about it most of the energy generated today is by steam turbines at around 40 to 60% efficiency. we can generate electrical energy from stored thermal energy that matches the efficiency of turbines and transport them through the grid via existing infrastructure. The only difference being the heat source that was chemical ,nuclear is now stored heat.  The systems( battery ,engine,...

Yes microwave ovens do in fact operate at 2.4 ghz, the same frequency as wifi and Bluetooth . But most wifi radios these days also operate at 5GHz which is not used by microwave ovens…..yet. A well designed microwave oven captures most of the EM energy inside the box to provide efficient heating and is not a good radiator. So the interference with wifi is minimal and only limited to the time when the oven is in operation and in close proximity to wifi signal. If we look at the term microwave more generally though, it is that frequency which covers the electromagnetic spectrum between 300 MHz to 300 ghz. In theory this is a very wide spectrum but in practice you're limited to only those frequencies for which you have decently priced generators available. 2.4 ghz,5 ghz,12 ghz , 24 ghz,60ghz etc etc. Fun fact cosmic microwave background radiation containing the information about early universe also(as the name suggests) falls within the microwave band. 

"Stretching it thin” It is one thing to complain about complexity and another when a concept can really express what is actually happening on material level. Take phase change of water, for example, from liquid to gas. Commonly known as evaporation what is happening here? Thermodynamics gives us a pressure temperature graph and leaves us to make sense of it. 100 degree Celsius at 1 atm and so on. But pressure temperature diagram can be wrong at worst and incomplete at best. Water evaporates when the hydrogen bonds holding the liquid together split. The force per unit area or pressure required to split the bonds decreases as water is doped with impurities like solid particles and gas molecules. These impurities act as nucleation sites of vapor bubbles leading to what is known as heterogeneous cavitation within water volume or on water surface where air infiltration is maximum.  The force used to split the bonds maybe thermodynamic as in heat or mechanical (hydrodynamic or acoustic)...

TV and radios are different from the internet. Now it's true that both the internet and TV can use fixed lines or broadcast towers or satellites but that's where the similarity ends. The internet is a globally connected network. Efforts are made to distribute the load on the servers by using content delivery networks (CDNs) and edge servers, to provide localized services, but the internet is still a one giant interconnected network. Because it is connected, bottlenecks for any particular service whether it be a global DNS or a local bank website affects all the users of that service equally. So for the internet to be fast it has to be fast all through its chain. That is tough. Moreover the internet is a platform on which the community can actively participate. Meaning the communication is bidirectional. Now on the other hand if you look at TV or radio they are broadcast services. Communication is unidirectional. You can watch a program but only passively. All of the available b...

Because traditional power plants have shaped the environment for electrical energy production and distribution it is cheaper to make them, cheaper to run them and easier to distribute power generated from them. On the other hand renewable energy resources shine in the areas that have precisely been untouched by the grid. Some dry desert, a high up mountain ,or some forgotten coast somewhere. In addition to the extremely high manufacturing cost of equipment, there is the added cost of installation ,transmission and generation only to compete with the massive advantage that the grid + power plants offer. This advantage is not going away anytime soon. The only way renewable energy could gain traction is if Renewable energy could create new markets for its consumption Renewable energy industry could research and come up with better materials to reduce the cost of infrastructure. Or some traditional power plant owner might invest in renewable energy as a means to augment their capacity Or m...

 WiFi router is an integrated communication device that works through the physical to the application layers. Whereas cloud technology (at least the part that we interact with) is the application layer. Hence all the functions of the wifi router can't be replicated on the part of the cloud we interact with. There needs to be a device that provides physical connectivity ,Mac networking,DHCP routing etc Having said that you can certainly have cloud based control panels that can let you control one or all of your deployed wifi devices. That would work. As long as you have on field devices to work at lower layers of communication. On a similar note all the higher application layer functions like captive portals can go through the cloud. In short, some functions can be deployed on the cloud. Some can't.