Wireless Energy transfer

Wireless Energy transfer:-

Briging AC up, here's another use. Last month or so, a team of engineers in MIT successfully powered up an electric bulb using wireless energy transfer. With matching coils for transmitter and receiver, they were able to transfer very high range magnetic energy and power up the desired device.

Reason for using magnetic energy is most of the world is electrically conducting to some degree but magnetically inert and magnetic energy being a convertable form can be readily used to generate electricity.

Just a thought to ponder upon

That's exactly how transformers have been working since years. The energy transfers between the primary and secondary windings through a magnetic field.
The MIT engineers were only able to do it wirelessly for a few meters or so. We can consider it as a wireless transformer with the core being air. Most probably they were using a high frequency alternating magnetic field.
The concept is still very inefficient because they might have spent a hell lot of energy generating that strong magnetic field than what is required to light a bulb through simple pair of conductors. Things will be promising when they are able to do such a thing more efficiently and hence transmit energy to greater lengths.

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one more funny question. If the MIT engineers use such a strong magnetic field then won't the transmitter attract metal objects towards it? It is like a strong electromagnet right? Won't the electronic devices around it malfunction? e.g. most CRT TVs show a distorted image when a small magnet is brought close to the picture tube.

a. MIT engineers did not use a large magnet to transmit energy. The fundamental is "quite close to" transformers, but not exactly like it. Just close.

b. Energy is transmitted by EM waves, and not just the magnetic field.

Here is the tinkering with another funny question part -

In Transformer the actual field that dies of for inverse squared for distance it is used. In case of EM waves and resonant high gain antennas, we can use something called as transfer modes (There are two kinds - transfer electric and transfer magnetic modes - Namely TE and TM. TE00 is the most basic mode used in/describes isotropc antenna EM pattern). The EM waves and antennas have properties that can make them "high gain" by these properties. So no need of a big magnet. No need to worry about getting things attaracted to the device.

Now the part that I mention also is that people at MIT actually used magnetic resonance, because most things are magnetically inert. Another such device is a CT scanner. People usually dont carry iron crutches close to the CT scanner but everything else is just as easily allowed in that room as in any other ward of hospital. Because even though that ONE piece of magnet packs field capable of the strength of 10 earths, it is in a world that is magnetically nuetral. Thats my understanding - please comment if you think otherwise...

AC funny question + answer:

AC funny question + answer:-

nobody answered it till now. let me answer it :-).
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Q) What really is a funny quiz question perhaps is - Current is defined as "Charge flowing through a conductor" in +2 physics books. Now in AC, typically an electron in power transmission wire moves merely 10 atoms far to a direction when it is called back to oscillate again back and forth. So question is if this electron never reached the bulb in my house, how come it glows?

Ans) Imagine there is a long pipe (the wire) that is completely filled with water (the electrons). Now what will happen if i push the water a little from one end of the pipe. The water on the other end of the pipe will immediately push forward. The reverse happens when i pull back the water. So even though the water molecules at one end of the pipe have not reached the other end, the molecules at the other end have moved back and forth. Thus energy transfer has taken place (i.e. moving of water molecules). I could use this energy to do some work, (e.g. turn a propeller).

This can also answer the 2nd funny question below
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Q) In case of Direct current, electrons move in a copper conductor at a speed of only 1/4mm per second. For such a slow speed it will take an electron several minutes to travel a few inches of wire between the battery and the bulb. How come then does the light bulb turn on instantaneously?

:-)

parabolic shape of rx antenna

parabolic shape of rx antenna......:-

For a rx. antenna it is necessary to accumulate signals in a greater extent ,so that the beam area under the major beam lobe as much as possible. in parabolic reflecting antennas a property of light is being used, the reflective property. as the antenna is parabolic in nature, when signals fall in the dish, the dish reflect the signal in a converging manner. at the center of the antenna a sensor (receiver) is placed and it get the signal with high intensity... so a high accuracy signal is being received.

But, in some cases yagi uda antenna is also used as rx. , because it is mainly an array of antenna(BSA or EFA), so its efficiency can be manipulated by adjusting the no. of array elements.........again, the size of an antenna should be optimized according to its efficiency.....

RF frequencies...are not ultra ultra ultra

RF frequencies...are not ultra ultra ultra........:-

1. i think rf freq.s are not ultra ultra ultra high freq. it can be named as super high freq.(SHF:3GHz-30GHz) and extremely high freq.(EHF:30GHz-300GHz)........
2. see the chart below:
3. ELF: extremely low frequency 3Hz to 30Hz (100'000km to 10'000 km)
4. SLF: superlow frequency 30Hz to 300Hz (10'000km to 1'000km)
5. ULF: ultralow frequency 300Hz to 3000Hz (1'000km to 100km)
6. VLF: very low frequency 3kHz to 30kHz (100km to 10km)
7. LF: low frequency 30kHz to 300kHz (10km to 1km)
8. MF: medium frequency 300kHz to 3000kHz (1km to 100m)
9. HF: high frequency 3MHz to 30MHz (100m to 10m)
10. VHF: very high frequency 30MHz to 300MHz (10m to 1m)
11. UHF: ultrahigh frequency 300MHz to 3000MHz (1m to 10cm)
12. SHF: superhigh frequency 3GHz to 30GHz (10cm to 1cm)
13. EHF: extremely high frequency 30GHz to 300GHz (1cm to 1mm)

mobility!!!:-

mobility!!!:-
it might seem confusing to claim electronmobility is greater than hole mobility. infact it is true as for a a undoped semiconductor e mobility is twice hole's... HOW

its just the way we define holes and electrons
hole is a vacancy of electron...

but the electrons which generate holes and what we call hole current are different from the electrons that constitute wha we call electron current...

hole current is hue to electron vacancies in valance band...

electron current is due to flow of electrons in conduction band...

so the mobility issue is therefore obvious... hope thats clear...

When we are talking about hole mobility we are not taking about positive ion mobility. So mass goes out of the window. Yes, the energy required to move a hole is much more than the electron, and that as has been vaguely pointed out in mails earlier is the leading cause of slow hole mobility, but physically, electron moves as a body, and hole moves as an empty space through the atomic structre with a pull against the move from all the atoms surrounding it.

Thats my thinking, that hole gets electric field exerted resistance from pull all around.

Displacement Current:-

Displacement Current:-

Lets define current first. Current is when charge passes through a plane. Plane can be anything from being in space or for that matter opposite plate of the capacitor!

1. If we think of displacement current in physical/pure physics way - When you start charging one plate of cap, the other starts to get opposite charge. Energy is being passed from one point to other (simply speaking...rate of transfer of evergy, leads to power, leads to = I^2*R, where R is 337 Ohm aprox. and I is displacement current by the way... will come to this later). It will only happen in transient state, the energy travels on the back of the entity called displacement current. It is not something that just exists in equations to satisfy some void.

2. Since there is no energy flow, no power delivered, no change of potential from one value to other, there is literally no one doing anything in static field. Hence displacement current is non-existing in this case. If you read through any antenna or EM energy book, you'd come across the same guy that carries energy ahead.

I would want to mention though, when you place a static charge in space, from the instance it was placed to the instance it exists, that period is of "Step transient". Something green's function in mathematics defines such phenomenon. So there is no such perfect static field thing in nature. So where ever you turn, you'll see displacement currents all around you... even in static fields... when they are propagating that is :)

Antenna design:-

Antenna design:-

First of your good reference can be Radio Frequency and Microwave Communication Circuits - Devendra Misra, if you are off to designing a complete transmission system. You need chapters 4, 5, and 10. The band you are talking about is not a "free" band though (I "THINK" it is not free for public - just a word of caution - be careful. 2.4 GHz is free, 5.5 GHz is free... try that ????)

You would already know this but Friis formula I think would be helpful for Antenna power calculations, but it would also be very important what your recevier system is going to be? The power amplifier you want, you can use most of GaAs/GaInAs based device. They would give you very good and cheap LoS kind of 1KM range. For my 5.5 GHz system I found it very useful. I also tried PHEMT EC2612 for Low Noise Amplifier on receiver end.

signal strength near oceans

signal strength near oceans:-

Since cellular towers are on land, minimal coverage is there towards seas. Rivers, usually have lots and lots of trees near them. Trees are blobs of water hanging in air, because leaf's contain a lot of water. Water being extremely bipolar in nature absorbs EM energy, and we end up with poor/minimal signal there. Satellite signal is good on the sea level usually very good, because satellite signal does not suffer any multipath or interference as it would in common cities. In clear sky atmosphere you receive good satellite signal strength but it is still worse than you would have in any vast plain field on land. Reason again is heavy evaporation causes signal loss...

use a frequency multiplier with VCO, PLL, comparator

use a frequency multiplier with VCO, PLL, comparator:-

The frequency multiplication is actually carried out quite cleverly in the phase-locked loop's feedback loop, by using a frequency divider on the output of the voltage controlled oscillator (VCO). This divided-down output is fed-back to the input comparator and compared to the reference frequency. Since the divided down frequency is smaller than the reference frequency, the comparator generates a voltage signal to the VCO, telling it to increase the output frequency. It continues to do this via the feedback loop, raising the VCO output frequency, until the divided-down frequency from the VCO output is equal to the reference frequency. At this point the comparator stabilizes and generates no more signals to the VCO, or only minor changes to maintain stability. The output frequency from the VCO will be stable at the input reference frequency multiplied by the value of the feedback divider.

Why use AC

Why use AC:-

First reason of supplying AC to houses is historic. When Edison's company was sending electricity to houses in beginning, it was all DC. Later machines were produced that could produce electricity in much more efficient way and suppy at cheaper cost. Reason was obvious - Edison's rivals could use turbines to produce power with utmost ease and they could transmit power exteremly efficiently as AC uses sine waves.

Starting from that, transformers, stepping up and down of power became possible with AC, reducing the losses even further. Then there are other inherent advantages of AC such as you dont un-necessarily charge something up if a power cable is falling on something, there are ways to reduces losses in AC even further that are not at all there in DC and so on.