PROS AND CONS REACTION TO OCTOBER 27 EDITORIAL ABOUT HYDROGEN FUEL CELLS Dear Editor: All the excitement over hydrogen fuel cells is really neat, but think about this:
A terrorist wants to blow up a major building. He pulls his manure-laden pick-up truck over to the nearest fuel-cell pitstop and presto, he has upped his energy density by who knows how much.
In addition, although hydrogen is a "renewable" resource, just exactly how is it going to be renewed? Most systems rely on either chemical or catalytic separators, and the chemicals used are really toxic, or the catalysts age over time, and are rare besides. Electrolysis won't work, because it takes more energy to separate the hydrogen from water than the hydrogen returns. Therefore, some external source is required to supply the missing energy. And I haven't seen the equations that describe how this works.
Add in the issues with heat generation (which is a pollutant without chemicals), weight of the generators and tankage, and the issues of controlling the escape of hydrogen in closed spaces (think underground parking garages), and you have some real obstacles to overcome.
Worse, I haven't seen anyone addressing the developments required to simplify the production of hydrogen.
I'm not anti-technology or anti-advancement, but I would just like to know why the oil companies think this is a good idea. They don't stand to make anything off of a nearly free resource (as hydrogen is touted in some areas). Les Howell Staff Technologist Teradyne Inc.
Dear Editor: I've been reading Electronic Design for many decades. With me, your magazine consistently rated between excellent and delightful. This is why it bothers me that, in your October 27 Editorial, you (and many others too) have fallen prey to the incessant drumbeat of false advertising.
Please bear with my somewhat pedantic explanation for my reasoning:
Hydrogen, in sharp contrast to natural gas, oil, wood, etc., is not a primary energy source. It only exists as a man-made product. Further, a hydrogen fuel cell is an energy storage device. And just like any other energy storage, such as a battery, it gives back but a fraction of the energy needed to manufacture it in the first place.
No doubt, the hydrogen fuel cell has excellent, special applications. The U.S. space program used 2 + O2 fuel cells throughout. It is also quite dangerous: Remember Apollo 13? I for one do not care to sit in my car over a 1000-psi hydrogen bottle. After an accident, for instance, the hydrogen burns with an invisible, extremely high-temperature flame. Nor do I care to let this thing be handled by an ordinary neighborhood mechanic.
I've read about hydrogen being cracked aboard a car, stationary generator, etc., from other fuel. Now this is a scam, if I ever saw one. The hydrocarbon fuel has to be cracked, because your run-of-the-mill fuel cell cannot handle carbon. Remember, liquid or gas fuels are generally hydrocarbons. Fully half of their energy derives from the carbon portion, and it gets thrown away! So, before hydrogen is used in the fuel cell:
100%
Original fuel
45%
After cracking (5% to run the cracker)
36%
After fuel cell (80% efficient)
Good diesel engines regularly get there, and big power stations are in the mid-40% range. What's more, cracking pollutes. So where is the advantage?
Because of all these drawbacks, you might conclude, I am categorically against the hydrogen fuel cell. But let me emphatically state: I can hardly wait for a methanol-fueled laptop, cell phone, as well as all the sundry small appliances. In these applications, the efficiency does not matter as much as continuous operation. Undoubtedly, the methanol fuel cell would represent a notable advance over present-day batteries, just as today's lithium units have it all over yesterday's leaky zinc-carbon ones!
Finally, we must all understand that research is necessary and good, and nobody in his/her right mind refuses federal grants, when given. Levente Letso AT&T Bell Labs (retired)
RESPONSE TO OCTOBER 27 DESIGN SOLUTION ON GROUNDING MIXED-SIGNAL CIRCUITS PROPERLY Dear Editor: A good article but perhaps a bit empirical on the antenna theory. For example, the author states:
"Radiation is, therefore, a function of the loop area outlined by the current path. It doesn't matter whether one or both of these conductors is a piece of wire, a pc-board trace, or a plane." This is not necessarily the case. A pc-board trace placed above a ground plane creates an antenna having twice the "current area" (length × current), as compared to the same trace driven against another trace. The radiation from the "ground plane" antenna is 6 dB higher, given the same antenna current. The radiation resistance is 4× for the ground plane case. This is due to the "image" antenna within the ground plane. For an electrically short trace, the vias are the real antenna.
Another generalization implies that the radiation is proportional to the loop area. It is not stated whether the resulting electric field or the resulting radiated energy is proportional to the loop area. Given a square, or a circular small loop antenna (<1/10 wavelength circumference), the radiated power is proportional to the area.
However, given a very rectangular loop antenna, such as a microstrip trace above a ground plane, the electric field will be proportional to the via height and not the horizontal trace length. This is due to radiation from the horizontal trace being largely canceled by the magnetic-field cancellation from the ground plane. The vias, being far apart, do not exhibit such high magnetic-field cancellation and radiate rather well as two very short dipoles.
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