Mitigating the Problem with Tape/Gloves

I originally tested the iPhone 4 in a number of different positions in the hand, and in a bumper case, and generated the signal strength drops reported in our previous article.

Signal Attenuation Comparison in dB - Lower is Better
  Cupping Tightly Holding Naturally On an Open Palm Holding Naturally Inside Case
iPhone 4 24.6 19.8 9.2 7.2
iPhone 3GS 14.3 1.9 0.2 3.2
HTC Nexus One 17.7 10.7 6.7 7.7

After getting those numbers, my first thoughts were that two dominant effects were responsible for the iPhone 4 signal drop being measured. The first was detuning due to capacitance added by the hand making galvanic contact with the stainless steel, and possibly even coupling the two discrete antennas together. The second was simply attenuation due to our meatbag extremities (read: hands) being not perfectly transparent to RF at 850 MHz and 1.8 GHz. I made some Star Trek references that some of you caught about us being bags of mostly water - it’s true, and it’s something Apple has emphasized heavily in its letter - that all phones drop signal when your hand is in between the path to the base station antenna. The real question was how much of that 24 dBm drop was due to galvanic contact with your capacitive hands (detuning), and how much was due to your hands being mostly water, and so close to the radiative surface.

Almost immediately after the issue was identified, many took it upon themselves to apply adhesive insulative tape to the troublesome area. Others suggested testing with rubber gloves on to see how much the issue changed. I set out to test both.

Allow me to introduce you to my friend Kapton tape.

No, it isn’t a gold iPhone 4, nor have I dipped the stainless steel band in gold (you have no idea how many people have asked) - it’s the native amber color of the world’s most awesome tape. I managed to find a roll of 1-mil thick Kapton tape that is exactly the right width of the iPhone 4’s stainless steel band. It’s miraculous really how exact the match is, without any cutting or tweaking, it just fits.

What makes Kapton the most conclusive choice of tape here ever (and not your grandpa’s electrical tape or duct tape) is that it’s the industry standard for flexible printed circuits. In fact, it’s what’s used to insulate just about every flex PCB antenna around. The tape obviously has a huge impedance, so when I hold it, I’m insulated completely from the stainless steel band.

I wrapped the tape all the way around the phone - not just the lower left trouble corner - to guarantee complete insulation. Of course, it’s impossible to use the phone like a phone this way since you cover the dock connector, speakers, and microphones, but just for testing. The other thing the tape simulates is how the iPhone 4’s antenna would behave with a thick 1-mil (25.4 µm) coating. To test, I cupped the phone just like I did to cause the 24 dBm drop before.

I also took an ordinary natural latex glove (yes, really) and held the iPhone, this time without any Kapton tape wrapped around the phone. Nothing special here, just a laboratory glove and cupping the phone.

The results speak for themselves.

Signal Attenuation Comparison from Cupping Tightly in dB - Lower is Better
  Bare Phone 1 mil Kapton Tape Coating Applied Natual Latex Rubber Glove on Hand
iPhone 4 24.6 16.6 14.7
iPhone 3GS 14.3 N/A N/A
HTC Nexus One 17.7 N/A N/A

Instead of a 24.6 dB drop from cupping the phone tightly without a case, with bare skin, we see a 16.6 dB drop with tape all the way around, and a 14.7 dB drop wearing a rubber glove. Insulating the stainless steel completely from the hand completely results in 9 dB less of signal drop. The remaining 16 dB is then due to the hand being so close to the phone.

The takeaway is that the best coatings Apple could possibly apply would bring the drop down to 15 or 16 dB - in league with the Nexus One’s worst case drop, and almost in league with the iPhone 3GS worst case drop. It’s hard to argue that bringing the signal drop down to levels other phones have been selling with for a year now isn’t a problem solved type solution.

However, adding tape won’t completely eliminate the drop in received signal, nor does it mitigate the problem nearly as much as getting a case. In fact, if you’re really concerned about dropping signal on any phone, you should get a case anyways. It demonstrably reduces the signal attenuation added by having your hand so close to the radiative surface of the antenna.

Oxide on Stainless

I talked with a number of materials science wizards, and picked their brains about the possibility of applying a nonconductive coating to the iPhone 4’s stainless steel antenna bands.

The response I got back was that stainless steel is difficult to coat by very nature of it being “stainless.” The metal unsurprisingly develops a dull oxide which itself is a poor conductor, but forms a protective layer that resists tarnishing and corrosion. This same layer that makes the metal stainless makes it difficult to coat. Some grades of stainless are apparently much easier to coat than others, but nearly all grades would require abrasion or chemical etching, followed by vapor deposition of the coating.

It’s not impossible to coat though, and if rumors that new iPhones built in recent weeks are rolling out with coatings turn out to be true, it’s obviously being done. But coating the stainless steel bands is obviously something Apple had to have considered.


I originally thought my Kapton tape was 5-mils thick, turns out it's 1-mil thick Kapton Polyimide, with adhesive for a total of about 2-mils of thickness. It's P-221 Permacel branded tape billed as the "ultimate" in electrical insulation.

Total Silent Recall?

Gizmodo reported (and iFixit followed up) on some users claiming that newer iPhone 4s had a different coating on their stainless steel band that mitigated the signal attenuation issue caused by tightly holding the phone. In theory, with the right coating, Apple could deliver the same sort of results we just showed using the Kapton tape. To date we haven’t been able to get our hands on one of these iPhone 4s with improved coating.

We found an iPhone 4 produced in week 28 of 2010 (digits 4 & 5 from the left of the iPhone 4’s serial number indicate production week) and took a multimeter to it. There was no measurable difference in resistance between it and our older iPhone 4s. In other words, the band was just as conductive. While this doesn’t rule out the possibility of Apple changing the manufacturing process on the phone, I wouldn’t waste time trying to hunt down a phone manufactured on a specific date just yet.

Proximity Sensor

Until two days ago neither one of us had experienced the proximity sensor issue with the iPhone 4. The proximity sensor on the iPhone detects if your face is close to the screen, like it would be during a phone call. If it does so, the iPhone turns off its screen to avoid any accidental input and save power. The proximity sensor issue manifests itself by the phone incorrectly assuming that you aren’t holding the phone up to your head and turning the screen back on. This happens in the middle of a call and often results in your cheek doing things on your phone without your knowledge.

Two days ago I was on a phone call when the proximity sensor all of the sudden decided that my face was no longer near the phone. My cheek then navigated into my contact list and tried to FaceTime with another contact while I was on the phone. I didn’t find out until the iPhone complained that a FaceTime connection couldn’t be established (due to the contact my cheek was trying to FaceTime with not having an iPhone).

I’m on the phone quite a bit and so far this was the first and only time the proximity sensor bug cropped up. We’re still looking into it but so far we can’t tell what the root cause is or if it’s helped by iOS 4.1.

Better at the Low End, Mixed Feelings Everywhere Else Final Words
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  • mac11 - Friday, July 16, 2010 - link

    Glad I had the patience to read thru this long article. It's logical, unbiased, THOROUGH, and grammatical(meakes it more pleasant to read). After reading 1,000 article titles, and over 100 articles referring to the Apple antenna issue / non-issue, I finally come to a rather complete understanding of the matter. I feel at ease now knowing what needs to be known.

    My conclusion: iPhone 4 antenna has greater extended sensitivities, but more susceptible to interference from hand grips than 3GS or Nexus One. And the call can be dropped due to this deeper interference if your starting signal was weak enough to start with. And the re-formulated signal strength bars gives much more truthful representation of your area signal strength.

    Thank you AnadTech.. kudos, and my respecta to your great journalism.
  • a different user name - Friday, July 16, 2010 - link

    How are they showing signal power dB dBm instead of bars on iPhone 4?
  • jmlev - Friday, July 16, 2010 - link

    How do I switch from bars to a -db reading on my iPhone4, like you show in the pictures?
  • gypsy1962 - Friday, July 16, 2010 - link

    Guys, as usual, 1st class commentary! I highly applaud your technical and analytical skills, a skill-set sorely missing in much of the commentary flowing around the net these days...
  • marraco - Friday, July 16, 2010 - link

    The olders bars jus were a hoax to cheat buyers into thinkin than the device got better signal than competing products.
    Again the same history. Marketing propaganda.
    Now also Apply blames the buyer over a design flaw, pretending that the signal is lost because the owner grab the device in wrong way.

    This is from a company that pretends to charge high prices for “better” quality.
  • betanerd - Friday, July 16, 2010 - link

    When you referred to the "signal reporting lie that started with the 3g". Are you referring to When it was released people complained about poor signal. Then Apple released an "update" that supposedly fixed it. I remember something of the sort happening. Perhaps the pr/updates have all be to make owners feel better till the next itteration. 3g complaint: bad signal-->update disproportionate(signal readout inflation) bar formula. ip4 complaint: signal drops/bad signal -->update more proportionate bar formula(your signal isn't really that good) + bigger, easy to read, confidence(ala enzyte) inspiring bars. Has/can anyone checked older releases to see if this is the case. If so it may make the argument/lawsuit stronger. Not that I wish any ill will towards Apple.

    +Some have mentioned a possible problem with they way the micro sims are cut. Where the contacts touch the metal sim tray which touches the metal antenna band. Any truth to that?

    +Perhaps placebo effect Have any reports come in about different serial numbers? Such as 8___=death grip susceptible, 7____=not susceptible? from Mac rumors it may have been debunked but, i was from a sample of 1.

    + Have any owners that say they have no problems come forward to have their phones tested or recored the testing by death grip and multimeter?

    I'm not sure how much it matters...Free cases till Sept30!
  • Hxx - Friday, July 16, 2010 - link

    apple announced that they will give a free protective case
  • v12v12 - Friday, July 16, 2010 - link

    I love it... watching the illogical, the brainwashed and zombified consumer-cattle actually try and defend a company (irregardless of if it's "Apple" or not) that's been factually proven over many, many years to actively and purposefully defraud consumers with falsified and heavily padded performance (G4/5 anyone?) data. Documented and legally proven accounts of advertising and marketing fraud (search it yourself if you're gullible enough to ask) to further profits. Settling many justified lawsuits out of court (Creative for 100MIL?!) as to not have to admit “wrong doing,” or face the laws they’ve broken…
    __This company is well known (factually documented) for using strong-arm tactics to control vendors AND even their own consumer base... Yes "Apple" tells you it's YOU that has the problem, even if it's them. Blah blah, this isn't a bash, for these shady practices apply to many other competing companies as well.

    So here's your insanity; you the consumer-cattle (pleb) are required by law to pay in full, up front for this device. They are required to render to you a FULLY WORKING device for which you paid. You find out that the device is bugged/not working 100% AS ADVERTISED (there's a law for that also) and now you're looking for retribution, but are told "sorry, there's no problem." It's YOUR problem I guess? Mean while what's going on behind the scenes are nothing but meetings on how to keep the "problem" internalized, until they can find a 'solution'..." in the meantime you are left with little recourse to solving this issue until Apple tells you??? Ever tried to return an iPhone, you'd think you were trying to return a bomb from the vehement response from the "geniuses" at the Apple store... So what now, yep just sit there and WAIT for Apple to tell you what or if there's a problem (regardless if Anand/Gadget/someone else proves it) at all... Then more waiting on a "solution," but all the while WHO is reimbursing you for your time, hassle, lack of service, AND interest on your money they now have possession of...

    Why is it that as the consumer, you/we have to go through all these hoops, lies, tricks and turmoil over a device that's been PAID FOR IN FULL? Turn the logic around and apply the same habitual shenanigans to consumer behavior, and Apple will send you a court summons to get "their" money asap! Heck they might refuse service to you based on your shoddy track-record. "Oh you say my check/CC didn't clear... sorry it's cleared, there's something wrong with your machines kthxbye..." "What, you want me to send you extra money b/c the 1st installment didn't fully cash out? Sorry I'll get you the money when I get it..." "Oh you want the money right now, and extra for your troubles... yeah umm, I'll let ya know when I get the rest (I still say it's your machines in error), but for now, here's $5 to tide you over..."

    Would this bull-shat work if the tables were turned, hell fscking NO it wouldn't work... so who in their right mind expects to get what they've been told they'll get? This crap is just laughable... year after year, product "upgrade" after upgrade; you are still getting hustled by Apple/Vzn/big-business and there's naves out there so fanatical and brainwashed into defending these overt, mega greed based institutions. Lol INSANITY… But there’s relief in knowing no matter how factual, logical, common-sense based your diatribe is, SOME cattle just won’t ever get it. They’ll keep buying, supporting these businesses that want nothing but to rip you off and leave you with whatever you get; “working” or not… Slave mentality to the MAX… lmfao (Though I do wish Anand/Tom etc would stop with the hand slapping and stick these criminals in the FIRE they deserve.)
  • SunSamurai - Friday, July 16, 2010 - link


    Show us on the doll where apple touched you.
  • Levictus - Saturday, July 17, 2010 - link

    Do you get paid to defend Apple from criticism or something? Because you seem a little too obsessed with arguing with people who criticize Apple. I mean if you like their products or are into Steve Jobs, good for you. You need to understand that there are people who have other interests in life than Apple's products and marketing.

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