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Comment: Re:Spectrum is measured in Hz? (Score 1) 91

by MattskEE (#48943725) Attached to: US Wireless Spectrum Auction Raises $44.9 Billion

Nope, reread your link. Channel capacity (at a given signal to noise ratio) is proportional to bandwidth alone. 1.000GHz to 1.065GHz is as good as 20.000GHz to 20.065GHz.

But as you say higher frequencies often have worse propagation characteristics, especially through buildings, which reduces channel capacity by reducing the signal to noise ratio.

Comment: Re:TWT based (Score 1) 54

by MattskEE (#48880641) Attached to: TWEETHER Project Promises 10Gbps MmW 92-95GHz Based Wireless Broadband

To get tens of watts from solid state in W-band yes you need either spatial or corporate (or both) combining of individual chips. So the amp ends up being of similar size to a mm-wave TWT but you don't need an expensive and large HV power supply or water cooling. Chip level output powers in GaAs I think have been done up to about 500mW, and 1-2W in GaN.

GaN for mm-wave still has some yield and reliability problems (pick at least one depending on supplier), and performance is not yet up to the ideal levels. But that's the same thing that GaN went through at lower frequencies, and mm-wave GaN is improving.

Comment: Re:TWT based (Score 2) 54

by MattskEE (#48879835) Attached to: TWEETHER Project Promises 10Gbps MmW 92-95GHz Based Wireless Broadband

Solid state GaAs is slowly catching up to TWTAs at this frequency. They're not common but it is possible to buy a 30 watt solid state amplifier, probably for the same price you can get a TWTA that has a little bit more power. GaN still has lots of problems at this frequency but it's improving and will likely be competitive with tubes within 5-10 years.

But yes it seems like it would be much easier to do this at Ka band where solid state amps are now a better value than tubes for communication applications.

Comment: Re:Physics doesn't work like that. (Score 2) 54

by MattskEE (#48879743) Attached to: TWEETHER Project Promises 10Gbps MmW 92-95GHz Based Wireless Broadband

In addition to penetrating solids the range is challenging (or expensive anyway) just because of limited transmit power levels. Power is important because that gives you your range, your cell phone and home wireless router transmit up to about 1 watt. A 1 watt output solid-state power amplifier at this frequency would cost $5-10k, or at least that was the case about a year ago. This project seems to propose using travelling wave vacuum tube technology which provides lots of drive power (50-100 watts) but at a high price (over $100-250k).

Comment: Re:kW or kWh? (Score 1) 245

by MattskEE (#48756419) Attached to: Bill Gates Endorses Water From Human Waste

What's wrong with kWh? For industrial processes that's a common energy unit.

It may confuse you but it doesn't confuse other people. In fact it makes more sense to most people since they have some frame of reference for how much energy a kWh but they don't have an intuitive frame of reference for Joules.

Comment: Re:even better (Score 5, Informative) 133

by MattskEE (#48639121) Attached to: Tesla About To Start Battery-Swap Pilot Program

Do you know how many solar panels it takes to charge an electric car? You're basically looking at a football field's worth, each.

Ah, to be young and full of made up numbers. Let's do the math.

The large Tesla battery is 85kWh. A solar cell typically has an efficiency of 10-20%, so with about 5kWh/m^2/day of typical solar radiation (check PVWatts for specifics in your town you can produce about 0.5-1kWh/m^2 per day.

If we assume 15% charging losses it will take 100kWh to charge a Tesla battery, which will require 100 to 200 square meters to produce in one day. A football field has about 5300 square meters, so we could expect one football field of tightly packed solar panels to charge around 26 to 53 Tesla's per day.

Comment: Re:wimpy talk (Score 5, Interesting) 187

by MattskEE (#48606605) Attached to: Graphene: Fast, Strong, Cheap, and Impossible To Use

Graphene in addition to the engineering challenges does have some very fundamental scientific challenges as well.

The most important challenge is its lack of a bandgap meaning that graphene transistors cannot be turned off. That drawback means that while it may have a ~500GHz cutoff frequency on par with silicon and below the InP records it will not modulate current in an energy-efficient way, and while it can create some forms of logic the lack of a bandgap limits its power amplifying frequency to a measly 50GHz, well below the competing technologies. Contrast that with Northrop Grumman's recent 1000GHz amplifier, which is admittedly not a great amplifier since it is run very near its cutoff frequency it has 1dB or less gain per stage, but it works which is still quite impressive.

So far the various methods that can give graphene a bandgap also take away the extremely fast electron transport properties that made graphene so interesting for electronics in the first place. Some of us working on competing technologies wonder why hundreds of millions of dollars have been spent on graphene transistor development without solving the fundamental bandgap problem - of course we just want that money directed to our own research, but some of us try to be realistic about the capabilities of what we are developing ;-)

I'm sure graphene will be useful for some things but so far there are still some fundamental problems that need to be solved before using it for high-speed electronics for wireless applications or digital logic. We'll see how it does.

Comment: Re:Usability Nightmare (Score 1) 63

by MattskEE (#48288897) Attached to: LG's 0.7mm Smartphone Bezel Is World's Narrowest

Cynical much? One phone does not need to be all things to all people in order to be successful. Not all of us need cases on our smartphones: in my 4.5 years of smartphone usage and two smartphones I have yet to damage my uncased phones in any way.

Since you need a case on your smartphone you should buy a different one, others of us enjoy the beautiful design of a tiny bezel. But I hope to keep my phone at least another 1-2 years so I'm not in the market currently.

Comment: Re:We use stuff like this (Score 1) 81

by MattskEE (#48287887) Attached to: Integrated Circuit Amplifier Breaches Terahertz Barrier

Why does the 3D printing matter? Some people do make ultra high frequency waveguide with 3D printing - in the case I'm familiar with they "printed" it on a stereolithgraphy machine out of a polymer, then gold plated all of the surfaces. It may have some applications for complex waveguide circuits which are not possible to make by other methods in a given size constraint. However, getting the plating thickness just right on such a small scale when you have to plate the inside of the long and super narrow waveguide tubes is difficult and conventional machining techniques are often faster and cheaper, and can have higher material quality than a printed or plated material.

The point of the Northrop Grumman work is that the circuit is integrated on a chip, so the waveguide interconnect will be relatively simple and simple objects can generally be made better, faster, and cheaper, by conventional techniques.

Comment: Re:For Starters (Score 1) 320

by MattskEE (#48247889) Attached to: What Will It Take To Make Automated Vehicles Legal In the US?

If that is the rationale, then the car needs to be 100% automated, under all circumstances, with all liability going to whoever made the damned thing.

I don't see why that would be necessary. Effectively you are saying that insurance over the lifetime of the vehicle should be factored into the purchase price instead of allowing people to buy insurance policies. That's not a bad idea but I don't think that it should be a requirement.

Instead this can be treated like any product: you buy an insurance policy to cover damages and go after the manufacturer in cases of negligent manufacturing or design flaws.

Comment: Re:Sounds wasteful and stupid ... (Score 1) 61

by MattskEE (#48247821) Attached to: Haier Plans To Embed Area Wireless Chargers In Home Appliances

They claim to use far-field power transmission (i.e. radiated power) rather than near field inductive coupling. The transformer analogy only works for near-field transmission but it tends to be difficult to get range. Far-field will be radiating power all over the place.

Comment: Re:Sounds wasteful and stupid ... (Score 1) 61

by MattskEE (#48247349) Attached to: Haier Plans To Embed Area Wireless Chargers In Home Appliances

If power is transmitted using near-field methods such as the direct inductive coupling used in RFID, most cell phone wireless chargers, and electric toothbrush chargers then the power transmission is coupled directly to the recipient device, and if the device is removed and the transmitter is still running then very little power is radiated away. This is potentially quite efficient. If you use far-field transmission then power is being radiated away whether a device is there to receive it or not. In order for it to be efficient you need high antenna gains to focus the power into a narrow beam the size of your receiver antenna aperture and beamforming to actively steer it. Otherwise the antenna is just spraying a broad beam of power in the general direction of the receiver like your sprinkler analogy.

They say it's using far-field transmission of power:

WattUp's RF transmission, which operates at 5.7MHz and 5.8MHz, is referred to in the industry as "far-field" wireless charging. Energous is not the first company to come up with the idea.

At such low frequencies it would be very hard for them to implement high gain antennas and beam forming. Also at such low frequencies I wonder how it can really be far field since the receiver will be well within a quarter wavelength of the transmitter.

More information is needed to fully answer the question, but this sounds like a convenience feature rather than an efficient one.

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