BosonQuest

Learn Physics or Get Bored Trying

iPhone 4 versus duct tape

There has been an awful lot of talk lately about the iPhone 4’s antenna troubles. And indeed, from having used one for a few weeks, it does indeed behave badly if held in a particular manner in a weak signal area. But one rumour has been following this story around like a bad smell—the legendary Duct Tape “Solution”.

It seems obvious enough—two antennae next to each other, separated by an insulated gap; fine until you “bridge” the gap by having your hand in contact with both sides, causing a short-circuit. Hey presto: no signal. So a small square of insulating tape over the gap, and problem solved! Alas, no.

Most people have heard of a capacitor, though perhaps don’t know what one is or does. Quite simply, it is two conductive “plates” separated by a thin dielectric, or insulating, layer. So an antenna with a layer of tape being held by a person such that an area of skin is in contact with the tape is basically a large capacitor. When a voltage is applied across a capacitor, charge builds up on the two conducting plates over time. As the charge builds up, the capacitor starts to resist more and more current from flowing, eventually stopping the flow altogether. The amount of charge that can accumulate is called the capacitance, and this varies directly with the area of the conducting plates (area of hand covering antenna), and inversely with the thickness of the dielectric layer (tape).

In an alternating, or oscillating, current, both the voltage across a component and the current flowing through it resemble a sine-wave. If you divide the amplitude (height) of the voltage wave by the amplitude of the current wave across a component, you get a number that is called the impedance of the component. Note the similarity with the resistance of a component in a DC circuit, which you might recall from school is equal to the (constant) voltage divided by the (also constant) current. The impedance of a component in an alternating current is essentially how much it… well… impedes the flow of current.

What this is leading up to is the fact that, across a capacitor in an alternating current, the impedance varies inversely with both the capacitance and the alternating frequency of the signal, which for mobile phone radio waves is pretty high—around 400-1800 Mhz. So the impedance of a piece of tape separating a radio antenna and your hand is negligible. You may as well be touching the antenna directly.

Roughly speaking, in an alternating current, rather than charge flowing round a circuit, it oscillates back and forth. With a capacitor in the way, charge builds up on the plates just as in a DC circuit, but at high frequencies, it turns round and goes the other way too fast for enough charge to build up on the plates to impact the current.

The good news for people whose phones work with a bit of duct tape on the antenna is that your phone works without it too. Trust me. The bad news is that if you have gone around saying your phone is unusable without tape, then you are fooling yourself. And the really bad news for people who have published damning reviews of the iPhone 4 while suggesting that duct tape will fix it, is that you are lying to your readers. Plain as. This is not to say that the phone doesn’t have an antenna problem—it does—but if you say your tests showed improvement with duct tape, you cast serious doubt on the validity of your tests.

As for solutions, well, with a bumper, or other case, you are increasing the thickness of the dielectric layer in the “capacitor” between your hand and the antenna, dropping the capacitance way down, and to the point that its impedance is too great to cause the antenna detuning issue, even at radio frequencies. You can also minimise the capacitance by altering your grasp of the phone—lower the contact area and you lower the capacitance. So Apple’s well-published suggestions “not to hold it that way” or “use a case” are scientifically the best ways to reduce the problem. But as many have pointed out, a phone for which the natural grip is the wrong one (all phones have bad areas, most aren’t right where you want to put your hand), or for which you need to spend additional cash to get a decent performance is a poorly designed phone. Apple should really address this somehow; right now it seems that the best course would be the free case, and iPhone users putting up with the fact that our phones are awesome at pretty much everything… except being phones. Or return it, of couse.

If you read the rest of my blog here you will see that I am but an amateur physicist, so it’s fair to say I could have this wrong. But the level of physics in this material is not particularly high, and since there’s no real way that I can be setting up experiments in the areas I’m currently studying, I jumped at the chance to test this theory out for myself. And while the results were more qualitative than quantitative (since I lack the means), I have tested duct tape, electrical tape, Sellotape and the plastic overlays that came off the phone when I unboxed it. No difference was noticeable with any of these materials entirely covering the parts of the antenna that were in contact with my hand. If you want a more credible source for these findings, there are a number of posts worth reading at www.antennasys.com/antennasys-blog.

Ain’t science a bitch?

Update: thanks to the nice folk at Anandtech, it seems I’m right and wrong. High impedance tape does exist, and can be applied to the phone. Even with such tape, the impedance is not enough to completely isolate you from the antenna, though perhaps it could do so enough to bring the phone into line with others. I would guess the tape must be made from a material with an impressively low dielectric constant; I still believe that the DIY fixes involving bog-standard tape are spurious, and if you want the best performance in a weak signal, a case would be a good idea. But it’s nice to think that there is a potential solution out there—also nice to know I was on the right tracks.

July 14, 2010 Posted by | Science in the media, Tech | , , , | 8 Comments

The Darker Side of Science

I wrote this article a few months back; at least two people read it.  Since it was one of the motivations that kicked this off, I figured I’d pea-roast it here.  Note: It’s possible I was feeling a little tetchy at the time—a certain Director General of the BBC had recently published a plan to take my toys away.

—snip—

Science. I’m all for it. Without science, we may not today have discovered mp3 players, DVDs, or even the humble laser pointer with which to annoy cats.

But there is a darker side to science. Einstein; Oppenheimer; Feynman: had they known the consequences of their thirst for knowledge, would they have continued in their atom-splitting ways?

I am, of course, referring to the terrible blight that our society now lives with: background visual accompaniments to Horizon “science” documentaries. Being somewhat of the geek persuasion, and therefore having nothing better to do of a Friday evening (once I was sure that Lost was recording to irritate me another night), I sat back and queued up this week’s Horizon: “Is Everything We Know About The Universe Wrong?” (to which the answer is, of course, “no, I know for a fact that Mark Thompson is a <censored>”).

First of all, can we please stop accompanying every mention of the word “maths” or “calculated” with close-up footage of people scribbling pseudo-equations on black/whiteboards? Or at least get enough different shots so that a child—or even an arts graduate—can’t see the same scribble being used to represent cosmic expansion, particle energies and the narrator’s tax return?

Into the content itself, and we start out with some background about The Big Bang. And with every mention of The Big Bang, we see a fresh shot of the bulk of the programme’s budget literally going up in smoke via the joy of slow motion pyrotechnics. Of course, the budget only stretches to 20 or so actually unique explosions, so they cycle them such that none gets used more than, say, 4 or 5 times throughout the programme.

But wait! Someone’s spotted a problem with The Big Bang (pop) theory! It simply cannot explain what happened for the first few thousand millennia or so. What’s needed here are some reverse slow motion explosions. And since we have to throw out some of our calculations, how about close up shots of people literally erasing pseudo-equations with their felt pens!

So what are our scientists to do? What if there simply isn’t an explanation for the shortcomings of The Big Bang (pop) that lends itself to a palatable visual aid? Turns out we’re OK. Some physics dude came up with a model of the time immediately following The Big Bang (pop) called “Inflation”. Cue physics dude standing in a warehouse next to a giant flacid red balloon, itself attached to a gas pipe (I don’t blame it). Gas tap is turned, balloon… wait for it… inflates. Oh yes.

And of course they have several such balloons, many camera angles and a whole plethora of camera speeds to demonstrate how pretty pretty a slow-motion balloon is, just in case you get distracted by the science. And it turns out that some calculations (scribble) led to a graph (brief shot of bendy line) that some observations of background radiation between The Big Bang (pop) and the end of inflation (balloon) matched up with on at least 4 points on the bendy line (may have been more than 4, but the person drawing the dots on the bendy line only had so much time to do it in before the science got too scary). Though no-one yet knows why Inflation (balloon) stopped (still shot of balloon) before the Universe expanded too far (balloon being over-inflated and bursting in another demonstration of how slow motion balloons make it all safe).

But now we hear that something’s wrong with gravity (ooh—magnetic ball bearings on a wooden board; that’s new). Galaxies just aren’t the shape they’re supposed to be. I know this, because I saw a close-up of someone chalking a swirly line onto a blackboard. With science again stumped, the programme moved on to pondering whether it can all be fixed using Dark Matter, which is, like, invisible (ARGH! CAN’T SHOW INVISIBLE! RUN THE BALLOON!).

I must confess, I have no idea what happened after that; I turned the damn thing off and started writing this.

But all is not hopeless. The shambles that was Horizon brought back to mind the excellent Wonders of the Solar System, running on Beeb 2 Sundays (repeated Thursdays, available on iPlayer), presented by the altogether lovely Professor Brian Cox: D:Ream keyboardist, regular 6 Music Breakfast Show guest, and occasional member of the ATLAS project at the LHC (http://hasthelargehadroncolliderdestroyedtheworldyet.com/)*. This is what science documentaries should measure up to.

OK, in places the first episode strayed towards travelogue, as we see locals bathing in the Gangees at Varanasi, where Cox was waiting to witness a perfect total solar eclipse (lucky git!). But even in these scenes, we see him occasionally blu-tacking space-probe images of solar eclipses from other planets onto a red stone wall, while tourists wander past doing…well…touristy things. And all the while, he has the smile on his face that you will only ever see from someone who absolutely, bloody loves what (s)he gets to do for a living.

And OK, the programme occasionally falls into the ubiquitous trap of near any reality-based programme whereby we need to see what’s going to happen later, followed by something happening, followed by what just happened. But honestly, it was less guilty of that than most.

But overall, where it did cut to visual aid, it didn’t go half-measures. “This is sunset on Mars, as seen by the robotic rover, Spirit”. And not a balloon in sight. We even get to the bit where he has to do a bunch of sums to figure out the total power output by the sun. “That’s four, times pi, times…”. The sound fades, we get some desert shots, and not a single scribble! Back to Cox: “It’s four hundred, million, million, million, million watts. That is a million times the power consumption of the United States every year, radiated in one second. And we worked that out by using some water, a thermometer, a tin and an umbrella. And that’s why I love physics.”

And I dare you not to.

* It turns out he was also science-advisor for the Danny Boyle film Sunshine. Which I didn’t know when I tweeted about watching that after Wonders in a message that may have come across as, well, twattish. D’oh!

June 14, 2010 Posted by | Science in the media | , , , | Leave a comment