iPhone 4 sensitivity to fingers explained by a Ph.D. in electromagnetics

Invisible Shield for Apple iPhone 4!“The technical explanation for the variation in signal strength found when closing the iPhone’s case gaps with one’s fingers is, that the antennas are being “loaded”. The loading from fingers, a material with a high relative permittivity of ~50 at 2 GHz, changes the input impedance and resonant frequency of the antenna resulting in loss,” Positronic_Matrix writes over on REDDIT’s Apple forum.

“If I had to take an educated guess, I suspect pressing one’s fingers across the gap increases the gap capacitance and changes the feed input impedance and electrical length of the antenna,” Positronic_Matrix explains. “It is analogous to holding on to a piano wire with two fingers while it is being struck. Its resonant frequency will shift and its quality factor will drop, resulting in a sound that is off key and muffled.”

“A solution often employed in the field is to preload an antenna. Preloading is including a large permittivity in the design, so when a human puts it close to their body, there isn’t a significant change. The down side of this is that it often reduces bandwidth and efficiency,” Positronic_Matrix explains. “So you can either have a great antenna that takes a hit when your fingers are near it or have one that is not quite as good but never changes. Isn’t it like Apple to choose the former and like the masses to cry for the latter? (wink)”

Positronic_Matrix explains, “Note that if the antennas were designed to be inside the case as opposed to being part of it, they would likely have a loss somewhere between the best (unloaded) and worst (loaded) performance of the existing antenna. It’s all an engineering tradeoff.”

“The best solution is to not touch the antennas at the gap (Steve is right) or to buy a phone cover that keeps your high-permittivity sausages away from the RF sensitive areas,” Positronic_Matrix writes. “Apple made the trade off for you and in my opinion it is a novel and good one, provided it can survive the bad PR generated by the griping gap grippers.”

Full thread here.

MacDailyNews Take: Now we know what Gray Powell was supposed to be testing. wink

Apple can correct the bad PR they are now receiving by simply doing the right thing: Free “bumpers” with all iPhone 4 purchases, as opposed to ripping people off to the tune of US$29 for a 29-cent piece of colored rubber. For more of our thoughts on this issue, please read our Take here.


  1. NO DOUBT….

    Apple needs to QUICKLY climb down from what is coming across as arrogance (Steve…you have to admit that’s what ‘Don’t grip it like that sounds like)

    and offer a FREE rubber case to all purchasers of the new phone OR a subsidized discount on a range of already inexpensive cases. $29..I have basically every product Apple makes…but I will NOT buy the new phone unless and until Apple takes steps to correct this problem…Yes…it’s an engineering tradeoff…who gives a damn? Fix it.

  2. I’ve had my iPhone 4 since Wednesday — with no case — and this has been a NON ISSUE for me. You have to hold it in such an awkward way for this to happen, that it would just never happen in regular use. Apple designed this right.

  3. I like his take. After reading the article below, I’ve decided I don’t want a bumper. I want a clear thin plastic ring that just barely covers the antennas on my iPhone 4.


    As soon as someone comes out with that thin clear plastic solution, I’ll buy it. I’m thinking of something so thin that you’d want to replace the ‘ring’ after dropping your phone on cement a few times. They should come in packs of 3 or something, since it’s so thin they market it as disposable. Switch it out every 6 months.

    Anyone else think that would be the perfect? Solves this little ‘death grip’ issue and also gives a little protection to our beautiful stainless steel phones. Plus you don’t end up hiding the beautiful design of this phone.

  4. When Sony was king of the hill and sold the most expensive pro gear in the world, customers regularly complained that they should supply cases for their expensive high end gear for free, when they charged a hefty price for these essential and “necessary” accessories too. It never happened.

    If Apple would supply some sort of free hand band, there would ( bet?) be whiners that would complain that it’s too this or too that.

    before exercising the word “arrogance” so often “to see how it fits’ go check a real dictionary ( not wikipedea) and realize that it’s arrogance, usually only to the ignorant and really common sense if the facts are as stated, despite a possible disagreement.

    You want a cover get one of your choice. It won’t change the facts, but might help the problem.

  5. @breeze
    No, I won’t stop complaining about this. Not until I can use my phone like I’ve always used my phone (3G and 3GS included), without having to watch where I put my hands & fingers. It’s ridiculous that the most sensitive spot on the case is the one place where people normally hold it. Now if the sensitive spot were, say, along the top edge, I could understand that one. In my location, holding it “normally” results in no data and/or stuttering speech, and sometimes total loss of signal. If I hold it normally while using an app (not Safari or email or anything else that needs data, cause it won’t go), after a minute or 2 I see “No Service”. Means that I can’t get any calls while using an app is what it means.

    Yeah, I’m complaining.

  6. How many people actually grip the phone the way it is in the vidoes while they’re actually talking? I’d say none.

    I’m left handed, and hold the phone exactly the way it’s demonstrated to show bad reception when I’m dialing, or sometimes surfing the web. But the minute I bring the phone to my ear to actually, you know, talk, it’s virtually impossible to hold it with your palm covering the lower left corner.

    And to the people crying “I won’t buy it until they fix this,” I say great. Shorter lines for the rest of us.

  7. As I wrote in another thread Apple can simply not inform every single iPhone 4 purchaser in the whole world that they need scotch tape or a bumper case for the phone to work as it should be.

    At the bare minimum this information needs to be attached to a free case which in turn needs to be attached to the iPhone 4 itself in the box sold, this is the cheapest way to fix this problem IMO with regards to damage control.

  8. I suspect most iPone owners wont want a rubber baby buggy bumper around their iPhone but would prefer a more elegant case.

    For those that use their iPhones naked then they have a choice, As the article points out, to either have a great antenna or a poor antenna. A rubber baby buggy bumper will give you a poor antenna.

    At least the design tradeoff Apple chose left more choices for the consumer.

  9. Hmmm, this is really a mixed bag, some people are experiencing a problem others, not. I`d like to see the actual numbers of people with problems after a week, besides hearing from the basement dwelling professional ihaters who claim to have this problem yet have never owned an Apple product in their lives (and boy have they been a vocal bunch).
    I`ve got a month to monitor this until it`s released in Canada, if this is a bad initial batch and the issue is resolved I`m getting one, if not I`m holding on to my current model.

  10. Look, if “some attenuation of antenna performance” is “a fact of life for every wireless phone” then what kind of a magic is hidden in “one of many available cases” since using them solves the problem?

    Do they want to say that “iPhone 4 in a case” is not one of “wireless phones” any more since “some attenuation of antenna performance” just stops happening?

    This is just BS.

  11. Yes…I have an iPod Sock…I’m not kidding

    and I’ve had the hockey puck mouse and imacs, mac pros, macbook pros, mac minis, Xserves, even an apple camera and a newton…remember those?

    I have a first gen iPod, 2nd, 3rd, and two iPhones.

    and I own a LOT of stock.

    honestly…Apple needs to address this with something more than a dismissive comment.

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