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why using higher freq?

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As frequency increases the size of the inductor required to get the same power goes down, and it's exponential, the frequency still has to be kept very low to avoid interfering with radio frequencies as because they're designed to intentionally transmit a lot of power at those frequencies that means you can detect it at... drastically greater distance. The FCC is probably very closely monitoring the developmental and commercial release of this type of product because of the very difficult line it treads from being a great way to transmit power without wires over short distances and as noise producer for the already crowded airwaves.

Even if the frequencies are much different from what other systems are design for interaction is still going to occur, and that interaction will be noise.
 
Because higher frequencies require smaller reactances (L and C). Look at the difference between a line-frequency (50/60 CPS) transformer compared to a RF transformer. Smaller L = smaller size.
 
Because higher frequencies require smaller reactances (L and C). Look at the difference between a line-frequency (50/60 CPS) transformer compared to a RF transformer. Smaller L = smaller size.
Carbonzit, you are somewhat confusing reactance with inductance. Reactance is the impedance of an inductor or capacitor which varies with frequency. Thus the reason for being able to use a smaller inductance at higher frequency is that, since inductive reactance is proportional to frequency, for a given reactance the size of the inductor goes down with frequency.
 
Carbonzit, you are somewhat confusing reactance with inductance. Reactance is the impedance of an inductor or capacitor which varies with frequency. Thus the reason for being able to use a smaller inductance at higher frequency is that, since inductive reactance is proportional to frequency, for a given reactance the size of the inductor goes down with frequency.

Well, let's just say that that's what I was trying to say, and leave it at that!
 
Ok thanks a bunch for all inputs,

Now another question is coming.
I took a look on wireless power transmitter demonstration hold by MIT students, They have used very high frequencies to for their device (the transmitter inductor or antenna I mean), What's the reason of using such high freq?
https://web.mit.edu/newsoffice/2007/wireless-0607.html


Thanks like always.
 
What higher frequency? The only reference in the article is to MHz range frequencies.. There is a massive difference between 1Mhz and 999Mhz, so the range listed is vague at best. The idea for wireless power transfer is to transfer power over a distance with as few other objects in the area interacting. Keep in mind in the Mhz range ANY conductive object with a length that is at harmonic equivalent to the wavelength of the oscillator frequency will receive power in direct relation to the harmonic it's naturally resonant at and that of the transmitter. Higher transmits better, but in the case of wireless power this is BAD because a power transmitter of sufficient energy at higher frequencies will naturally broadcast, oftene into other devices, such that sufficient power can be delivered at higher frequencies to electrically fry other devices not designed for it.

Also keep mind the study of human anatomy has never been done with any wireless power setups and that there are a multitude of naturally resonant structures in the human body.
 
What higher frequency? The only reference in the article is to MHz range frequencies.. There is a massive difference between 1Mhz and 999Mhz, so the range listed is vague at best. The idea for wireless power transfer is to transfer power over a distance with as few other objects in the area interacting. Keep in mind in the Mhz range ANY conductive object with a length that is at harmonic equivalent to the wavelength of the oscillator frequency will receive power in direct relation to the harmonic it's naturally resonant at and that of the transmitter. Higher transmits better, but in the case of wireless power this is BAD because a power transmitter of sufficient energy at higher frequencies will naturally broadcast, oftene into other devices, such that sufficient power can be delivered at higher frequencies to electrically fry other devices not designed for it.

Also keep mind the study of human anatomy has never been done with any wireless power setups and that there are a multitude of naturally resonant structures in the human body.

Thanks for your input sir.

https://www.electro-tech-online.com/custompdfs/2011/05/463_WiTricity.pdf
The above say that the freq is 10Mhz In the said case, Now the question is why they do not use 60Hz of the mains for the system? It seems that they have used a switching power supply to increase the freq, The output of a wireless is an inductor or an inductor-capacitor tank circuit, Now please tell me why higher freq is needed or a such output in a wireless power transmitter?

Thanks
 
zesla, your question has already been answered in this thread, and the materials linked in it. If you do not understand why, then you need to research more until you do as simply stating why hasn't taught you what you need to know.

10mhz can never be used in wireless power transmitting because it's in the RF band that is legally restricted to very controlled levels. Due to the power levels being used as well it can never occur in a large scale application because if even off band high power transmitters will swamp out normal telecommunications.

All these tests were done in Faraday cages (metal lined rooms)
 
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You know, I'm kind of curious too. See, I understand why a higher frequency is needed than the mere 60Hz of US mains, that's a no-brainer. But SMPS use higher frequencies for the same reason, and many engineers find it perfectly acceptable to remain in the 40kHz-200kHz range. You can build very powerful SMPS with frequencies far lower than 1MHz. So why jump to that order of magnitude at all? Once you go below the ~150kHz used for AM radio that part of the spectrum is almost empty, until you get to 80kHz or so. That's plenty of room. For short range wireless power for small devices like cell phones, 100kHz should be perfectly acceptable.
 
30–300 kHz is for Navigation, time signals, AM longwave broadcasting, RFID, amateur radio
I think there are some spots where data/voice is never sent out. 10.7mhz, 445khz, 160khz.
 
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