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The resonance of the bridge wasn't involved at all. For resonance, the wind would have to match the resonant frequency of the bridge.

No, the argument is that the bridge was self-resonant . Self-resonance isn't just for electronics; when you strike a bell or tuning fork and it resonates at a specific frequency, you're experiencing self-resonance.

Nice try, but the fact that the aircraft are all moving in relationship to each other plus the fact that the interconnect signals are only traveling between them as fast as the radar signals they receive means trying to triangulate with timing differences would be close to impossible.

The reason GPS works is the satellites are synced to an atomic clock source to a billionth of a second accuracy, along with dynamic orbital-correction information to give the exact distance to the satellite. Even with the new "atomic clock on a chip" to give distances, their spacial locations would be unknown. http://www.nist.gov/public_aff...

Newer planes use a phase-array antenna system to give azimuth (direction) to the signal source. With multiple planes receiving directional information and sharing that information between themselves, a location can be determined. As with your timing approach, the more receivers and wider the separation, the better the accuracy. http://www.microwaves101.com/e...

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The idea sounds great. But when you think realistically, you will know there is always a tradeoff. If you look at the paper and ideas by ignoring all the marketing messages, you can see there are flaws and it cannot apply to MIMO solutions.

Basically, the idea is to place the 1 Rx antenna between two Tx antennas so that the signals from two Tx antennas are out of phases at the Rx antenna position. Yes, it works for the purpose that you want the Rx antenna receives no signal from Tx antennas. However, this also changes the antenna beam pattern which will reduce the coverage for the reception of the signal by half. The placement of 2 Tx antennas is the same as have a Uniform Linear Array (ULA) with 2 antennas with some inter-element distances. For example, if you place the antennas with lambda/2 away (where lambda is the wavelength), you will receive very weak signal at the broadside angle. In the other word, you trade the reception quality at broadside angle for the null-out effect at your Rx antenna.

Just look at the image here and you can choose the null wherever you like

Actually, you have two degrees of freedom here to choose any position/angles you want to have the weakest signals (null-out effect). 1) by changing the phase difference between two Tx antennas. For example, making them 180 degree out of phase, the null will happen at the middle between two antennas. In this case, you trade your reception along the direction perpendicular to your antenna array with the so-call single duplex. 2) by changing the inter-distance between two antennas. For example, you can make the distance with lambda*3/4 away to create the 180 degree out of phase. The drawback is the same. You trade the reception at certain area with this null-out at certain position.

People can argue, you can increase the inter-distance more, so that more grating lobes can be observed. Because there are multiple paths, eventually, the whole space can be covered. Yes, you are right. But how far away two antennas should be separated? It definitely depends on the environment. You can make it adaptive. So a dedicated engineer needs stand at the access point to change the antenna separations per request. And if you place the antennas so far away, is that really practical to have such systems?

So, they are just using one mode of the ULA to achieve the signal cancellation at the receiver point. But since they are twisting the antenna patterns, if you add more antennas trying to achieve 3x3 or 4x4, you are doomed. Because the degree of freedom has been used to cancel the signal at receivers, you have no more degree of freedoms for more spatial streams. So, yes, they can increase the capacity by two fold (in some area of coverage), but not beyond as in MIMO solution!

I believe there is an use case. But we should know the tradeoff and whether it is suitable for real deployment.

The modulation frequency is not what defines the skin depth. The 217 Hz modulation frequency is irrelevant. The lowest relevant frequency is the 850 MHz (in US and Canada) signal frequency.
Read Microwaves101 on skin depth.
Or read the wiki page which is a bit simpler but not as complete.
The fact that the signal frequency and the modulation frequency is what counts isn't directly told here, but if you read it you may find it appear as bright as daylight.

it seems entirely possible that it was affected by the heat ahone generates in a 50 minute phone call [...] they should redo the experiment, actually do something where the antenna is seperate from the phone body and next to the brain.

The problem would then be that the microwaves themselves will generate heat in the brain, leading to some metabolic perturbation.

Supposing our body does not contain "rectifying" biological structures (an "organic diode") able to work at nanosecond time constants, can we please stop discovering dielectric heating and investigate whether the heating itself affects our brain?

You are correct 60GHz seems to be an O2 absorption frequency, see this chart:

http://www.microwaves101.com/encyclopedia/images/mmwavechart.gif

It looks like 4 dB/km attenuation in the dry and 15 dB/km in the rain.

-molo

Jane Q, you've got some good points but it's still a bit mixed up. IAAME (I am a microwave engineer)

1/ A rectenna the size of New Mexico would actually be very inefficient. Narrow beams are the best way to efficiently transmit microwave signals.

2/ Correct, microwaves are not ionising radiation. Microwaves just heat you up and cook you from the inside out, they don't cause mutations and cancer like the other sort of radiation.

3/ Correct, 100 mW from the transmitter is not necessarily 50 mW at the target.... unless the target is close enough of course :) But microwave propagation follows an inverse square law, so double the separation and exposure drops to one fourth.

4/ Radiation from cellphones and from WiFi are both in the microwave bands. Low bands, sure, but definitely microwaves.

5/ 50 mW might sound big but it's nothing. Check out Microwaves101 for more about exposure levels: http://microwaves101.com/encyclopedia/biological.cfm

For what it's worth, I think this SPSS is a crock. Too expensive, maintenance sucks, and there are too many other options that are lower risk and lower cost.

You can read about Padmasree Warrior on the Cisco web site. There is a link to a biography of her. (PDF)

Quoting from that biography: "Warrior joined Cisco in 2007." She is not the source of Cisco's problems; those problems were huge long before 2007. Ms. Warrior left Motorola on December 4, 2007. It is not correct to imply that she had a strong connection with Cisco. She was there less than a year.

Another quote: "Prior to that, she was the CTO at Motorola, where she led a team of 26,000 engineers and directed Motorola Labs, with an annual R&D budget of $3.7 billion."

Quote from another source: "Did Motorola do the right thing and retire the head of Thoughtbeam when they shuttered the operation? Nope, in a Dilbert moment they promoted Thoughtbeam's leader Padmasree Warrior to Chief Technology Officer of the entire Motorola company"

Maybe Ms. Warrior helped create Motorola's problems. Motorola has been on a loooong, slow downward slide.

When Intel's 8600 was released the vice-president of technology at the company where I worked was very unhappy. The architecture is poor, as anyone who has programmed in assembly language knows. For a time there was a hope that the 68000 would take over the market. But Motorola's management wasn't able to take advantage of that temporary superiority.

Motorola's Semiconductor Products Sector is now Freescale Semiconductor.

Other people also think Motorola's management is amazingly weak. For example, Carl Icahn said this: "It is essential to the future of Motorola that its directors realize that the BOARD, especially at this precarious time, is NOT A COUNTRY CLUB OR A FRATERNITY, and that truly "qualified" people whose interests are truly aligned with Stockholders, are needed..."

You said, "I personally think the best person for the role would be a non-partisan, non-corporate figure." That's what I think, also.

Sorry to nit pick, but at 60Hz, I get a skin depth of about 6 Meters.
http://www.microwaves101.com/encyclopedia/calsdepth.cfm

I think we can discard worrying about skin depth...

Even if you are incredibly generous with the numbers, the overall efficiency of this system would be very low. 80% Efficiency for the power amplifier in the transmitting satellite would be extremely good, and doesn't take into account all of the other losses that will take place in the satellite, such as generating and amplifying the RF signal and antenna and sidelobe losses. So in other words, 80% would be basically ideal with today's technology (Amplifier efficiency). Now take into account the losses on the ground. Converting that RF power at several GHz back into 60Hz AC is going to cost power, I'm honestly guessing here because I've never looked at any such system, but in power electronics the bigger the change in voltage and/or frequency means worse efficiency, and the RF signal would probably be converted back down to DC then, transmitted over power lines as 60Hz AC. So I'm going to be generous and say we might be able to get 85% at the receiving station.

So we're at 80%(transmit) * 85%(transit) * 85%(receive) = 57.8% efficiency. Almost half of the electrical power collected by the orbiting station is lost before it gets to the power lines.

Now also take into account the fact that satellites are *very* expensive to build and launch, incredibly difficult to perform maintenance on, you have the expense of maintaining the satellite's orbit and software, and the expense of building and manning a ground station. Based on all of these factors I would be very, very surprised if orbiting solar stations are going to be viable options without some major advances. Maybe if we get the whole space elevator thing worked out so satellite launches are cheaper, but I'm not holding my breath.

For non-PC items, check out http://www.microwaves101.com/content/microwavemortuary.cfm

It has mainly microwave devices, but it's nice to see some variety - like the snake.

Hence, you put a slim, shielded tube over the distance you want to transfer. At each end of the tube is a transmitter/receiver. With further research it might even be possible to bend these tubes, so they go around corners etc. This would solve all the problems identified.


This tube has a name and has been in existance for many years. It's called a waveguide.
http://en.wikipedia.org/wiki/Waveguide
http://www.microwaves101.com/encyclopedia/waveguide.cfm

Drawings of some waveguides are here;
http://www.uniquesys.com/products/passive/waveguides/s111_2.html?gclid=COyF1u6coo8CFSI4YAod20h_aQ

You can buy eliptical waveguide here for frequencies up to about 22 GHZ.
http://antennasystems.com/ewassy.html
and rectangular waveguide up to 40 GHZ here.
http://www.antennasystems.com/waveguide.html