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


View All Comments

  • SunSamurai - Thursday, July 15, 2010 - link

    People like you are not missed. All you are is an apple basher. The phone has bugs that need to be worked out, calling broken is foolish and only shows your maturity and bias. Reply
  • trochevs - Thursday, July 15, 2010 - link

    Mr. Anand Lal Shimpi,

    I love your articles, because they are very accurate, fact based, and clearly separate fact from personal options. But I feel in this particular case you are letting your personal love for Apple to ignore the facts a bit here. I have big problem with following two sections:

    "We have consistently argued that the 4’s antenna is a design choice by Apple. As we’ve seen in our testing there are situations where the iPhone 4’s antenna makes things better (e.g. holding onto calls with very low signal strength) and other situations where the design makes them worse (e.g. holding it wrong in situations with low signal strength)."

    "The iPhone 4 is better at holding onto calls and data at very low signal levels. We’ve mentioned this one before but it’s worth reiterating. The new antenna does let me make calls and transmit data at very low signal strength. With the iOS 4.1 update I was able to make a call at -115dB on the 3GS, however the call did drop within a minute of starting it. By comparison I was able to have a much longer conversation without dropping the call at -120dB on the 4. By no means is this a scientific comparison, but anecdotally both Brian and I feel that the low signal strength performance of the iPhone 4 is better than the 3GS."

    First some facts that I have picked up while I study RF tech in order to get my M.S. in EE:
    1.The signal level is measured by the receiver circuits. Usually it is the voltage that regulate the Automatic Gain Loop that is used to maintain constant signal level at the input of detector circuit.
    As result any antenna gains would be clearly visible as improve signal level at all time.
    2.The antenna is passive device as result it have static efficiency and antenna gain does not depends on signal strength.

    I would like to point out to you inconsistency in your analysis:

    1. If you can maintain better call at -120dB with iPhone4, but you can't do the same with iPhone 3Gs proves that iPhone4 have better receiver/decoder circuit then iPhone 3Gs only.
    2.If the iPhone 4 antenna is better then 3Gs you are going to see better signal level on iPhone 4 in anywhere like places where the signal is strong and especially where the signal is weak. But all your test clearly shows that receiver in iPhone 4 has to work harder in order to compensate for bad antenna.

    To remind you: “My mother always taught me that honesty is the best policy ...

    So please be truthful to this statement and stop with the apologies on Apple's behalf. The only apology we need is one coming from Apple and it should be very short: “We made a mistake and we are going to fix it” that's it. Stop saying that iPhone 4's antenna is some kind of engineering compromise, because it is not. The antenna design is crap. Credits for the better operation of iPhone 4 in low signal are due to the base-band chip designer/manufacture. Please acknowledge that, they really deserve it, no Apple.
  • SunSamurai - Friday, July 16, 2010 - link

    The ntenna design is not crap. It simply need a revision to fullfill what it was aiming for. If it were crap then they would need to fully redesign it. They do not. Reply
  • leexgx - Friday, July 16, 2010 - link

    fast fix is just give out the bumper case and have it come with every iphone

    if i was going to get an iphone (and i am not) the first thing i would buy is the case or full case(protect the back and front) as it not that hard to shatter the screen or the back now

    most of my house all runs on Android based phones here from when posting(apart form my main phone thats HTC HD1 WIN 6.1 for business use but i am considering going all Android as text input is faster under my desire phone)
    T-mobile G1 thats been passed down (main issue bat is crap had to fit an 2000mha bat to make the phone usefull) ,
    upgrade to T-mobile HTC desire as my second phone HD1 main (bigger bat as default seems to last day and an half now),
    Orange - Sony X10 {big one} works well big screen and big cam on it (only bad thing is seems to be an finger smugs magnet on the screen)
    Orange Samsung Galaxy S (that looks more like an iphone with the middle button)
  • iwod - Thursday, July 15, 2010 - link

    I dont think anand is Pro Apple, it sounds more like you are Anti Apple.

    The Antenna is not broken. It may have faults and its problem. But it still does calls and data in most if not all situation. Well thanks to US which has poor coverage and signal from AT&T. You will be worse then others around the world.

    If i put how Motorola's design and tune their Antenna as Standard. Then pretty much 95% of all phone sold by Non Motos have problems. Or according to your wording, Broken.

    It doesn't come with a broken USB Port.

    Bluetooth is an Software problem.

    If you can not stand software problems, then dont even go on to internet. Because every single devices on earth have it. And you should complain about Windows Mobile first.
  • slickr - Friday, July 16, 2010 - link

    O please spare me the lecture.
    I have not expressed in any way that I'm anti Apple now have I, but when I see a bad device and Anandtech staff trying to defend Apple and say that users are wrong for "holding it wrong", its just the bars and not the antenna that is wrong, makes me sick.

    I have huge respect for this website, but right now some of that respect is shattered.

    You sir, can not comprehend the facts! If the antenna can't catch signal if you are holding it in a particular way that is considered broken. That's like Razor mouse not registering movements if you put your hand on it in a particular way. Yes it may work 80% of the time, but that does not change the fact it wont work 20% of the time.

    There are several reports of broken or in other words faulty USB port. In some instances on some iPhone 4 the USB makes an electrical surge when connected with a USB cable and it gets destroyed. This is firstly not safe for the health of the users and screws your iPhone 4, so you need to get it to service to repair the broken USB port.

    How do you know bluetooth problems are software? This is the Apple favoritism. It may or may not be software problem, but the fact is there is a problem with it.

    If you go buy Apple I don't care, its your personal opinion, but having a huge and well known website advertise Apple in these articles if beyond all credibility !!!
  • SunSamurai - Friday, July 16, 2010 - link

    Its not considered broken, because it still works. Try the dictionary before telling people to comprehend words ;) Reply
  • slickr - Saturday, July 17, 2010 - link

    It only works part time, so its broken.

    Take this for example: Your brand new $500 dollars TV all of a sudden stops working, than after placing it in a different position starts working again, than the problem occurs again and you move it again. No matter what you do it still keeps reoccurring and the only way to fix it is by buying additional stuff for it.

    I consider that broken and would never want to buy a TV from that manufacturer again, but it the case of Apple's iPhone 4 its being defended and promoted as user problem for "holding it wrong" Come on.

    And that is only one of the multiple problems Apple has with the iPhone!
  • anandreader - Sunday, July 18, 2010 - link

    It's broken for some people, not for others. I don't experience the problem because I avoid touching the antenna at the gap. I'm also right handed so that's easy for me. For a left-handed person, yeah it's going to be broken if they can't hold it the way they'd like to hold it.

    For me, the phone is better than any other cell phone I've had. When I'm in a strong signal area, the phone sounds like a landline phone - the voice on the other end is crisp and static free.

    Bottom line - the antenna is only an issue for some, not all, people. Your statement that the antenna is broken is overly broad.
  • slickr - Tuesday, July 20, 2010 - link

    You just proved my point, even if only 10 out of 10 million people are affected its broken. And it could also happen to you and any other in any case, just touch is in the spot and the antenna loose connection and whoala a problem.

    Plus iPhone 4 is crap in other areas too, I'd gladly take the Samsung or Nokia N900 any day over the iPhone!

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