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Comment: Re:Why Fy? (Score 1) 255

by MattskEE (#47754605) Attached to: How many devices are connected to your home Wi-Fi?

I actually thought his maglight comparison was an excellent layperson analogy. In a crowded room I would be less unconcerned, although there may be several emitters, anything that is a reasonable distance away from you has been attenuated greatly by the spreading of the signal and spread out over a much larger portion of your body. I have not read the scientific literature but I would guess that the main area of interest for RF safety is the cell phone in your pocket since you could conceivably absorb a large portion of that phone's transmitting power over a fairly small volume of your body.

This does not apply to megawatt radars, or kilowatt microwave ovens, but to single watt phones/wifi there's not much to be concerned about.

Comment: Re:Why Fy? (Score 1) 255

by MattskEE (#47754577) Attached to: How many devices are connected to your home Wi-Fi?

Sorry for the late response that you probably won't see. I could calculate some numbers, although getting an exact value is tricky because while with skin depth and antenna aperture you could relatively easily estimate the volume over which the RF power is dissipated into heat, I lack the background to calculate the rate at which heat will be conducted away and spread out. I'm sure that regulatory agencies have done this calculation.

You should really do some reading on the subject such as: http://www.durham.ca/departmen... (this is for Canada but from a quick google it seems informative, I'm sure there are similar US-specific references).

Anyway to give you an idea of a reasonable worst case, a typical phone or router will give off 1 watt maximum. Let's say for the sake of argument that you absorb all of that as a worst case (which you won't). Is that a lot? Not really. At about 4000 J/kg-degreesC for water it will take 160 seconds to heat one shot glass (40mL) of water by 1 degree C. During that time heat will be conducted away so you will likely see much less than a single degree temperature rise, which is safe.

If you want more detail there is ample scientific literature on the subject, but this back of the envelope calculation based on reasonable worse case conditions seems to show that the danger from RF emitters that are code compliant is negligible.

Comment: Re:Feedback loops (Score 2) 271

by MattskEE (#47753143) Attached to: Numerous Methane Leaks Found On Atlantic Sea Floor

This is something where engineers know things that climate scientists apparently don't.

If the positive feedback was so strong, that the system was unstable (right half plane as it were) the earth would already be Venus. Doesn't stop climatologists talking out of the butts and proposing just such strong positive feed-backs.

TL;DR; Don't ask a climatologist a control systems question and expect a reasonable answer.

Real engineers know that reality is rarely a linear system represented only by poles and zeros. And they also know that complex systems can have multiple locally stable points, and that even stable systems may "ring" when perturbed with potentially catastrophic consequences.

Consider the humble electronic oscillator which most certainly has a right half plane zero, does its output rise over time until it blows up the universe (aka turns into Venus)? No it doesn't. And to describe the magnitude of the oscillation generally requires the nonlinear transistor model which includes things like the maximum output current of the transistor, it is not a simple linear model like the one you propose.

Earth is quite complex and while an engineer could model it as a control system it would be much more complex than the one you have proposed.

TL;DR Engineers are just as capable of being incorrect as climate scientists are.

Comment: Re:Why Fy? (Score 4, Informative) 255

by MattskEE (#47723573) Attached to: How many devices are connected to your home Wi-Fi?

Now I would be extremely interested to hear why my comments would give you that impression?

None of the above reasons, only that you seem to be very concerned with low-level non-ionizing radio frequency fields which are not thought to be a health hazard.

If you want your visitors to leave phones at the door to enhance social interactions and if you don't want to use mobile devices indoors personally for the same reasons, that's perfectly okay though a bit unusual.

You get the crazy label though if you think that low level RF is a safety risk.

Comment: Summary misplaces emphasis on one point (Score 4, Informative) 166

Actually Mikey gives four reasons for the healthcare.gov problems, but the summary just focuses on the last one, probably because it sounds funny:

The original points (as summed up by me in a few words) were (1) Fragmentation of implementation, (2) Lack of monitoring of system, (3) Lack of experience by the companies building it, and (4) workplace culture clash.

Comment: Re:Why use wireless power? (Score 1) 138

by MattskEE (#47609537) Attached to: Harvesting Wi-Fi Backscatter To Power Internet of Things Sensors

Yes and if you read their paper an RF switch is used to adjust the terminating impedance of this antenna which perturbs the reflectivity. That RF switch will consume a finite energy and power. It is an active component and not a passive component. A passive component would not accomplish the modulation.

I think it sounds reasonable that a reflector like this might be able to use less energy per bit than a conventional high-efficiency transmitter, since the RF power is being provided elsewhere, this is effectively just a modulator inserted between (or to the side of) the transmitter and receiver. However the study authors do not perform any theoretical analysis or measurement in their paper to support this notion.

Comment: Re:Why use wireless power? (Score 1) 138

by MattskEE (#47607897) Attached to: Harvesting Wi-Fi Backscatter To Power Internet of Things Sensors

Although this device takes no internal power to cause the back scatter effect

That's incorrect, a switch always requires energy to change state, as well as a usually very small amount of power to maintain at least one of the two states. Quite a bit of a CPU's power dissipation comes from the energy consumed by CMOS switches switching from a one state to another.

It may well be that this is more power efficient than other methods of transmitting information but that has yet to be backed up by theory or demonstration.

Comment: Re:iFind (Score 4, Insightful) 138

by MattskEE (#47605221) Attached to: Harvesting Wi-Fi Backscatter To Power Internet of Things Sensors

It only works because it has a very low bitrate of 1kbps:

The UW’s Wi-Fi backscatter tag has communicated with a Wi-Fi device at rates of 1 kilobit per second with about 2 meters between the devices.

Although the authors claim that "The Wi-Fi Backscatter tags do not require any batteries and can harvest energy from ambient RF signals" they make no attempt to back up this claim with measured or estimated energy efficiency of this transmitter. The standard metric for high efficiency transceivers is joules per bit, because low bitrate communication always consumes less energy than high speed, but the only useful way to compare it to another high efficiency transmitter is to see if it can transmit a certain amount of data for less energy.

While I don't expect every paper to address every aspect of a technology, they should not then turn around and make baseless claims like "We believe that this new capability is critical for the commercial adoption of RF-powered Internet of Things." in a length 12 page paper that fails to address the one metric which would allow them to make such a claim.

Comment: Re:Headline trifecta (Score 1) 81

by MattskEE (#47577611) Attached to: Nevada Construction Project Could Be Tesla/Panasonic Gigafactory

Competition is also good for business because it increases the total size of the market, increases availability and reduces costs from 3rd party vendors (batteries, motor drives, charging stations, etc), and reduces costs of specialized labor (eventually) by growing the labor pool of engineers who design electric vehicles.

Having a big part of a small market is not a good way to go. I think Elon's goal (in addition to any altruism on his part) is to grow the entire market and ecosystem for electric vehicles while holding onto a decent (but perhaps smaller) market share.

Comment: Re:Lots of people criticize this for its obviousne (Score 1) 182

Probably because he doesn't live in China.

This is China we're talking about, with 1.3 billion people. I'm sure that people have already strapped filters onto fans, this one guy just happens to be getting some feel-good-DIY publicity because he's marketing his product. Kudos to him because it seems like a good thing that he's doing this, but I would be amazed if this is actually considered novel in China.

Comment: Re:Hmmm... (Score 1) 171

by MattskEE (#47571627) Attached to: Quiet Cooling With a Copper Foam Heatsink

I agree that this doesn't pass the sniff test. A foam has a low ratio of metal to air, it's the cross-sectional area of the copper that allow vertical conduction of the heat from the heat spreader plate. This has little copper area so conduction is limited. It's further worsened by the random nature of the strands so the heat is conducted laterally as well as vertically and so the conductive thermal resistance is increased because the heat needs to travel a longer path.

So while I'm not saying it doesn't work, I suspect that this foam is more of a gimmick than a properly optimized heatsinking solution.

Comment: Re:not likely (Score 1) 200

by MattskEE (#47537159) Attached to: Cable Companies: We're Afraid Netflix Will Demand Payment From ISPs

I get that the meteoric rise in online video streaming by customers puts pressure on ISPs because if affects the oversubsribe ratio that they can use (which is required to turn a profit) while still providing a good user experience.

But what I don't get is why you can possibly blame Netflix. Your customer requested 100GB from Netflix last month. Netflix supplied it based on your customer's request. If you think 100GB (or however much) data in one month is too much then throttle your customer, but do it fairly based on each customer's usage and don't play favorites with which companies you allow your customers access to. 100GB of Netflix traffic should be treated the same as 100GB of porn, or whatever else your customer is getting up to.

My university's residential internet connection started undergoing major strain several years ago, primarily due to online video. So they implemented traffic throttling. I don't remember the precise details, but it was along the lines of a daily 1GB of unthrottled data between 4PM-1AM after which speed was reduced , and no throttling from 1AM-4PM. This was a completely fair and balanced way of providing a pretty good user experience while limiting traffic during peak hours to avoid congesting the network.

Comment: Re:I disagree (Score 1) 390

by MattskEE (#47484441) Attached to: Verizon's Accidental Mea Culpa

How does settlement usually work for unbalanced connections? My thought is that since the Verizon customers request data from Netflix servers, and Level 3 delivers that data to the Verizon network, then if anybody paid settlement it should be Verizon.

But since this is an everybody-wins situation (Netflix pays level 3, Customers pay Verizon, all customers are happy when the pipes run smoothly) then settlement free peering makes sense.

Comment: Re:user error (Score 1) 710

by MattskEE (#47459927) Attached to: People Who Claim To Worry About Climate Change Don't Cut Energy Use

I don't believe we can change global climate.

Not with that attitude you can't!

But seriously, we are the most powerful race on the planet, we use over 30 billion barrels of oil per year (over 1.2 trillion gallons). Nobody knows exactly how much oil there is, but as a rough estimate from a layman it seems likely that we could estimate that in less than a thousand years we'll have probably burnt over a million years worth of natural carbon storage, i.e. it is being released over a thousand times faster than it was stored.

To me that it as least suggestive that we as a species could have an effect on atmospheric CO2 concentration and through that global climate and ocean acidity.

Too much of everything is just enough. -- Bob Wier

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