Notes by Akshat Jiwan Sharma

  In radio engineering it's well known that interference reduces the strength of the signal.  With respect to interference we talk about things like constructive and destructive interference. In constructive interference signals are in phase and reinforce each other.  In destructive interference signals are out of phase and cancel each other.  But when we talk in terms of energy, when we consider electromagnetic waves as propagating energy sources a different question arises How does interference affect the energy of the wave,if it does at all?  Now it's quite obvious that unlike signals that can lose information energy can't be "lost". However energy can be transformed as well as transferred.  In that case does the transfer of energy happens within the wave or between the interfering waves.  Or to put it another way does the wave that carries energy lose it to another in case of destructive interference and gain it from another in case of constructive...

 They do contribute positively to some extent but on the whole the effect is negative. If you consider a p-n junction semiconductor typically used in solar cells you will find that room temperature is sufficient to "activate" the junction by making electrons available in the conduction band. In fact room temperature (27c) is usually the temperature at which you obtain the peak power and results described in the data sheet. This is the "lab" temperature. If the temperature were 0K then there would be no conduction electrons to produce electricity. So appropriate amount of heat is necessary to generate electricity from p-n junction. As the operating temperature of the cells increase more electrons will be available in the conduction band and hence it will increase the conductivity. Infact semiconductor conductivity increases exponentially with temperature. https://fog.ccsf.edu/~wkaufmyn/ENGN45/Course%20Handouts/15_ElectricalProps/06_TemperatureConductivitySemiConducto...

Bluetooth is a form of wireless communication. In wireless connections the component responsible for establishing the physical layer (the part over which actual data exchange takes place) is the antenna. The distance to which the signal can travel depends upon The construction of the antenna. Its geometry,the materials it's made of. The conditions in which it operates The placement of the antenna. Whether the signal it generates has to pass through obstacles or there is a clear line of sight. Now the thing about antennas is that they are reciprocal. This means that If an antenna is a good transmitter (whatever parameters you choose to define good) it will also be a good receiver(on the same parameters). But even when you use similar antennas the operating conditions of the transmitter and receiver can be different leading to a dismilliar performance between two devices. Now coming to your question. It's not so much whether the transmitter or the receiver that decides the distan...

  #engineering #energy  If you were to look across semiconductor manufacturing technology a few common steps would stand out. Growth of semiconductor boule (crystal). Post processing steps that cut the boule into wafers, polish those wafers etc. Doping of wafers as well as deposition of active components on wafer,which will differ from application to application. Silicon, the most popular semiconductor material, is grown into a boule from the liquid phase. The dopants are mixed in the melt and the big crystal that is formed after the process is finished is chopped into multiple thin small wafers. Crystallization from liquid phase is quite popular in semiconductor metallurgy but crystal growth does not have to take place from the liquid phase. Yes it is the most popular way to grow silicon crystals but it is not the only way. More and more fabrication technologies are preferring growth from the vapor phase. Why? Vapors/gas can be controlled more easily. It can lead to higher pu...

  #engineering #heat It takes energy to do anything. It takes energy to move, to write,to watch, to read. Similarly it takes energy to make something. Without energy nothing  can be done and nothing can be made. Heat of formation is that energy which is required to make a product out of its constituents.  In  chemistry we usually deal with what are known as chemical reactions. In a reaction, reactants combine with each other in different ways to form products.  The difference in energy of formation of products and reactants is called heat of reaction. A reaction may release energy such as the one which involves combustion of fuels . In such a reaction the fuel is burned in oxygen to create new products. Since energy is given off as heat and light in a  combustion reaction the heat of formation of products is lower than the heat of formation of reactants.This means that the products are much more energetically favorable than reactants.  The elements whi...

 Despite being a liquid, water is considered to have a tensile strength.Tensile strength of water depends upon its purity. Pure water can have tensile strength as large as 140Mpa where as impurities in the form of dissolved air & particulate matter can reduce this value to as small as 100 kpa.  https://pubs.rsc.org/en/content/articlehtml/2015/lc/c5lc00048c It is known that in bulk water when the pressure exceeds tensile strength, vapor cavities form but what happens in capillary bridges when pressure exceeds the tensile strength is not fully explored in literature.  [Model for capillary bridge collapse] Capillary bridges form when water forms a thin film connecting two solid bodies. These bridges are on a mm scale length. When an extension force is applied to either or both of the bodies liquid film starts thinning out and eventually breaks.  Compare necking in capillary Bridge with hydrodynamic stretching. In hydrodynamic streching bulk water moves through a sma...

  #engineering #energy  Of All the energy that we receive from the sun every day barely 1% of it is used by the pants. This energy is captured in the form of edible food as well as biomass. When we talk about biofuels most of the discussion is centered around ethanol. How can we convert the energy stored in edible food to usable  fuels. Ethanol works but it suffers from two major disadvantages 1. Ethanol production must compete with food for human consumption. Are we going to eat sugars or turn it into fuel? 2. It captures a very small portion of energy while disregarding all the waste biomass that is available for free.  There have been attempts at extracting energy from waste biomass by  converting it into ethanol in what is known as 2g ethanol but the process has been rather complicated and the results have been only average. On the otherhand using biomass for direct combustion has produced better energy conversion but its only been useful for large power pla...

  #ageofcarbon  In a major breakthrough all carbon based electronics were printed using a 2d aerosol printer. Carbon nanotube as channel,graphene as electrodes and nanocellulose as dielectric. All of these materials were formulated into an ink before printing. Fully recyclable.  https://pratt.duke.edu/about/news/recyclable-printed-electronics  A flexible 32 bit microprocessor has already been  printed on a plastic sheet using indium’’gallium’ zinc oxide technology. While this is the most feature complete implementation at present, carbon nanotube / graphene based devices are expected to become more prominent in flexible/2d printed electronics. Especially as they simplify the material requirements.  https://www.nature.com/articles/s41586-021-03625-w In another development researchers created OLED by pyrolysis of human hair to create emissive carbon quantum dots. Blue light was emitted from the device.  https://www.ledinside.com/news/2020/6/humanhair_ole...

 The pressure at the bubble wall cannot exceed the bulk modulus of the film. The pressure generated depends upon film thickness. From numerous experiments it is known the thickness of bubble wall varies between 1 nanometer to 1000 nanometers https://www.researchgate.net/publication/252733803_Measuring_soap_bubble_thickness_with_color_matching The pressure developed at the bubble wall is largely independent of the bubble radius and depends only on the bubble wall thickness. This is because it is the outer liquid film of the bubble that fractures releasing all the volumetric strain stored. To understand why let us first understand how a bubble forms.  A bubble is a gas liquid system. A gas core surrounded by liquid film. To start with there are bubble nuclei which act as seeds from which a larger bubble grows. When gas content increases it displaces the liquid volume that would have been in its place otherwise.It happens until a very thin film of liquid remains surrounding the g...

  #engineering #carbon In between conducting graphite and insulating diamond elemental carbon offers vast opportunities for creating tunable bandgap semiconductors that can be applied to any application that you can think of. High voltage rectification, high efficiency solar energy conversion to electricity, solid state white light emitting diodes, transparent conducting oxides, metallic contacts, transistors, integrated photonic circuits ,nano antennas and more.  You are limited only by your imagination.  All carbon organic semiconductors offer some advantages which simply can't be matched by any material synthetic or natural.  1. Tunable band gap up to 5 ev 2. Ability to form molecular PN junctions with hetero atom bonding  3. Cheap raw materials that can be acquired from any general store. No supply chain issues.  4. Availability of precursors in all three forms of matter (solid,liquid and gas) to allow for different growth techniques.  5. Alternat...

Pure silicon for white light led is not a suitable emissive material. The band gap of silicon corresponds to emission in the infra red and red regions of light. For the light to be white the emission centers must radiate higher energy wavelengths. Greens and blues. This is not possible with silicon alone. But because silicon is such an abundant material that is already widely used in electronic industry and as such has a great deal of tooling created around it , there is immense interest in making silicon based white light emitting(wle) diodes work. While silicon alone is insufficient for wle its compounds can work. Silicon carbide has already shown its ability to emit in blue, green and yellow regions(infact it was the first led ever made). Now research is being conducted into silicon oxycarbide which has shown some promising initial results. The paper "White light emission from amorphous silicon oxycarbide a-SiCxOy thin films: Role of composition and postdeposition annealing...

  Unlike fracture which is breakage or failure of a material system at one point comminution involves continual breakage until specific size is reached. Material fracture studies are usually applied to structural engineering problems. Fracture mechanics gives engineers a number beyond which a material will fail to perform its role and consequently result in failure of the component. In comminution however it is required to break the material into particles of desired size.This seems simple enough but the process is barely efficient why? [Losses Kinetic, acoustic, thermal ,wear resistance due to debris, no leverage] Firstly the amount of losses in a mill performing comminution are significant and unavoidable these machines make a lot of noise leading to acoustic losses, they vibrate ,generate heat. Many mills especially the ones which rely on impact with the different materials like hammer, ball, vibratory loose even more energy in kinetic collisions  Balls, hammers collide wit...

  Phosphors are a class of materials that absorb shorter wavelengths of light and emit longer wavelengths. They do this very very fast. Phosphors have allowed for a more compact led package. In phosphor based leds The active layer emits high energy wavelength. Some of this energy is absorbed by phosphor coating that converts it into low energy wavelengths. Thus result is that the overall energy radiating from the led package appears to be white. Mixture of blue, green, yellow, red. Before phosphors it was a common practice to use single colored LEDs. To produce white light then it was necessary to use atleast three LEDs. This was expensive,inefficient and a major reason why it took so long for leds to succeed even though they were discovered in early 1900s way before the invention of modern semiconductors. Phosphors have been revolutionary and yet there is a great deal of research being done to replace them why? One reason is that they loose energy. The overall efficiency of the le...

Bulk modulus relates the change of volume to change in pressure  B=(v/dv)*dp dp=B*dv/v https://www.theleeco.com/support-resources/engineering-tools/fluid-mechanics-for-liquids/bulk-modulus/ Because the initial volume of the bubble remains constant greater the change in volume of the bubble greater the pressure developed at the wall.  Bubble is basically a liquid film enclosing gas within it. When it bursts it's actually the liquid film that fractures. The amount of pressure developed at this time depends upon the volumetric strain stored within the film.  At the time of formation of the bubble the liquid film has to stretch. It's volume increases as it expands. This expansion is stored in the film as volumetric strain. So more the expansion of bubble ,more the strain that will be developed and thus greater the pressure at the time of collapse.  However there are limitations. Maximum strain that can be sustained by the liquid film depends upon intermolecular forces.Fo...

Gas discharge lamps were pretty efficient. Sodium vapor lamp remains the most efficient artificial lighting source even to this day. But efficiency is not everything. And they did suffer a few problems 1. Even though conceptually simple,they were complicated to manufacture. The housing needed a way to handle materials in gas phase. Usually glass was used which is fragile to handle so many of these lighting devices had to be protected during their entire operation. The device required components such as ballasts to regulate energy flow. Compare this to LEDs that are shipped in plastic encapsulation and can be arranged in any pattern. Since it runs on dc it can be integrated with both portable devices that run on battery and in homes with mains voltage. 2. With the success of LED some of the semiconductor engineering technology that was used for manufacturing chips could now be used for LEDs . Today light is completely a semiconductor device and it benefits from any improvement that happ...

 TADF is a phenomenon that allows excited electrons that would otherwise dissipate energy as heat to emit light in visible frequencies. When electrical energy is applied to materials a distribution of singlet and triplet electrons are created. Singlet electrons can fluoresce triplets can't. In TADF triplets can absorb surrounding heat and transition to singlet leading to an emission. Now a few things are clear from this 1. In a TADF material there will be two sets of emission. First from the normal singlet electrons and then from the triplets that converted to singlet. 2. There will be a delay in the second emission. Because it takes some time for triplet electrons to absorb energy and transition to a state where emission is possible. This time is in nanosecond range so it can still be called fluorescence. But because of the slight delay its called delayed fluorescence. 3. The frequency of the delayed fluorescence can either be the same as normal singlet fluorescence or it can be s...

  The basic concepts are still the same. TADF is still fluorescence. Energy absorption,charge separation recombination and emission are occuring just like they do normally. But TADF materials allow emissive entities to absorb thermal energy from surroundings and change state before emission. Why is this relevant? Fluorescent emission happens when the excited state electron has the opposite spin quantum number as the ground state electron.The system of electrons is paired having net spin 0. In this case a smooth transition occurs between excited and ground state leading to an emission. But in practice things rarely go smooth. As many as 75% of electrons can change their spin state when electrically excited and become what are known as triplets (system of electrons with same spin). These triplets are forbidden to return to ground and loose energy as heat (phosphorescent glow might also occur but its too slow and at too low an intensity to be useful in lighting applications). This is ...

  Bubble collapse is actually 2 things 1.Rupture/spalling of the outer water film leading to shockwaves inside gas. 2. Implosion/compression of the inner gas leading to sonoluminescence  To calculate the pressure at the bubble wall we can plug in numbers in the expression for bulk modulus  K=v*dp/dv dp is the change in pressure  dv is the change in volume  v is the initial volume At 1% change in volume with K=2.22*10^9 pa for water 2.22*10^9=V*dp/(1.01v-v) 2.22*10^9*.01=dp 2.2*10^7 pa or 22 Mpa To calculate the velocity at which the film ruptres we need to derive an expression that relates stress at fracture to known parameters like volume and mass.  Work done to fracture the film,W=F*d*a/a Where a is the area d is the distance , f is the force applied and w is the work done.  This can be rewritten as  W=stress*volume The work done will be equal to kinetic energy acquired by the ruptured film .5mv2=stress*volume V=√2*stress*volume/m Rewriting this...

 A lighting device is basically a transducer converting the input energy into light. A candle is a lighting device that converts chemical energy to light. An led is a lighting device that converts electrical energy to light. The basic emission principle is the interaction of energy and matter. In an led when electrical energy interacts with semiconductor matter , electrons absorb that energy. The amount of energy they can absorb and hence radiate is limited by their band gap (an intrinsic property which can be engineered to some extent). When they relax they release the absorbed energy as light. In a candle when the soot vapor gains enough heat it starts glowing orange/red. Any material when it absorbs energy starts emitting it. Now the question arises if both an led and a candle simply emit light why use one and not the other? Here the question is of efficiency. For every input joule of energy we want to maximize the output light. Heat is wasteful. And mostly so is non visible spe...

  75 Terrawatts of energy is used daily by the plants for photosynthesis. Even though this is a big number its just .1% of total energy received from the sun daily,166 petawatts. But still this is more than 4 times the annual consumption of energy by humans, 16 terrawatts. Plants mostly absorb from red and blue portions of the solar spectrum (cyanobacteria can photosynthesize from IR) Antenna complex within the leaves of the plant are responsible for extracting energy from the sunlight. These molecular nanoantennas work on the principle of resonance energy transfer. In simple terms each section of antenna extracts energy from a particular wavelength of light and pass on the rest. Other sections of antenna the extract energy from the portion of light they accept and pass on the rest. Although these molecules are called "antenna complex" they are actually organic semiconductors.  They absorb only those frequencies of light that fall within their band gap. The proof can be found...

 A single element has a well defined emission spectrum. Most elements emit strongly in a band of frequencies that cover portions of visible light. Since electromagnetic colors are additive, if you combine these emissions the resultant light will appear to be some shade of white. Warm white,cool white etc. In that sense single element white light emission is possible But practically it is a massive engineering challenge to emit white light from a single element. Why? Well because each emission frequency corresponds to a specific energy input. To be able to emit different frequencies from a single element we will have to apply different input energies to the emitter. How are we going to do that? As an example consider sodium vapor lamp. It is the most efficient artificial lighting device ever created. Even more efficient than LEDs. You might have seen it on highways and parking lots where it emits a characteristic yellow light. Have you ever asked yourself why yellow? Its because yel...

#manufacturing #semiconductors Semiconducting materials are the driving force behind IT and electronics industry. Silicon carbide is one of the oldest known semiconducting materials around. Silicon carbide's synthesis is quite easy in theory. All you need to do is heat up silica and carbon to very high temperatures. Because both silica and carbon are abundant materials and people have been synthesizing silicon carbide since 1800's. Infact the first led was made out of silicon carbide.  Making a semiconductor grade single crystal out of silicon carbide is challenging. Both from the perspective of energy required as well as the time it takes to grow the crystal. The most widely used technique today vaporizes the silicon and carbon containing constituents and have them deposit layer by layer on the growth surface,usually a silicon wafer.  For those interested in learning about manufacturing semiconductor grade silicon carbide heres a book which covers not only the synthesis of cr...

 Absolutely. Concentrated solar power (CSP) can be used to synthesize new materials especially those which are formed at high temperatures. It can be used for sintering,melting,vapor deposition processes. In short any manufacturing process or step that uses heat can benefit from CSP. We are talking about temperatures that easily cross 1500C with a concentrating lens and some designs even crossing 2000 degrees celcius. CSP lens is just about as efficient, when all variables are factored in, as an industrial laser. And because sun is a broadband energy source,as opposed to an industrial laser which usually radiates at only one wavelength CSP has an added advantage of activating surface under treatment. There's a greater chance for the material to absorb high energy solar wavelengths better than laser where it has to work with only one wavelength,usually lower energy. This leads to an improved energy efficiency. Although this idea is not new it has gained importance due to the current...

 #science #innovation The importance of revival of electrostatics as a science Why aren't more industries and colleges paying more attention to this seemingly forgotten branch of physics? Despite being of importance in material science ,energy (through generators and motors) and fundamental research electrostatics as a discipline has been languishing in educational institutions as well as in industries. Electrostatics is taught only as primary level science with no courses available for higher levels of study. Recent studies have proven that old machines such as wimshurst generators can be used to generate HVDC directly for transmission or as a source of plasma. Heres a paper describing it as a circuit of capacitors http://www.lajpe.org/march14/12_LAJPE_857_Horacio_Munguia.pdf Currently only a single organization exists to promote the interests of people studying electrostatics. https://electrostatics.org/ This needs to change. We must make more such associations especially in Afri...