Guest Post by Trinity Nick
7 June 2010 – The Apple iPhone 4 is unveiled. A smartphone that seems very promising and enthralling with all its novel features like the Retina Display, the upgraded camera, the FaceTime video calling, the external antennae, the glass panels on the back & the front and the exquisite sleek form factor.
15 June 2010 – Pre-orders for the iconic gadget kick-off.
24 June 2010 – iPhone 4 hits stores. Sales figures struck about 1.5 million!
Post 24 June 2010 – The web is flooded with iPhone 4 signal reception issues. When held in the hand, the device magically, or rather tragically, lost bars that indicate signal strength. From 5 bars, they dropped to 3, then 2, then one and then none.
16 July 2010 – Apple holds a press conference to speak about the iPhone 4 issue.
The iPhone 4 Antenna Design
Apple tried something that was never done before by any other mobile phone maker. The iPhone 4 has a metal band running all around its rim. This metal band is not just a structural element, but is also the antenna of the device. The metal strip has 3 slits in it – 2 on either lower sides and one on the top. The metal rim on the left hand side (when the phone is facing you), is the antenna for Bluetooth, GPS and WiFi. The rim on the right hand side, handles calls and mobile data (UMTS and GSM). This design along with the glass back, were supposed to enhance signal strength, thus dropping fewer number of calls and offering better reception.
When users hold the phone in their hand, their palm tends to cover the lower side of the antenna, bridging the gap between the 2 antennae, on the left hand side. As soon as this happens, the signal strength bars displayed on the screen start collapsing one by one, sometimes leaving none of them standing. Apple is a company that has carved a great niche for itself in the field of consumer-products like laptops, MP3 players (iPods) and smartphones. Their technology is considered supreme in the market. And hence any issue, whether major or minor, with their products will be made a mountain even if it is a mole-hill. The reception issue of the iPhone 4, thus earned the name “grip of death” in the blogosphere.
What Apple had to say…
Initially, Apple dismissed the issue saying that many mobile phones in the market suffer from this problem and users should avoid holding the device that way (covering the lower left side of the phone). They also advised using bumper cases made of rubber, that would sit around the phone, preventing direct contact of the antennae with the hand. This work-around did help reduce the dropping of signal.
There was rumor that Apple had discovered a problem with the formula that was used to calculate the number of signal bars to be displayed on the screen. Apparently, the number of bars being displayed did not actually indicate the real signal strength. There were reports that Apple would be providing a software fix for resolving this issue.
On 16 July 2010, a press conference was held at the company’s head quarters at California, where CEO Steve Jobs announced that iPhone 4 users will be offered free cases to get rid of the reception problem. He also mentioned that only a small percentage of iPhone 4 users, (0.55%) have been reported to have the reception issue, and that the problem has been blown out of proportion by the media. Moreover, all rumours about a software patch were put to rest, as there is going to be none. Apple is adamant that the signal strength issue is not exclusive to the iPhone 4. Mr. Jobs explained that many Nokia mobile phones ship with a sticker on their back saying “don’t touch here”. The reception issue was demoed with a Blackberry Bold 9700 phone during the conference, as well.
What some antenna design experts had to say…
Many experts are of the opinion that the antenna design of the Apple iPhone 4, is the culprit of the signal strength problem. Blogs by Spencer Webb (engineer and president of AntennaSys) and Simon Byrnand (blog in talk3g.co.uk) have been referred to for the following:-
Some years ago, antennas on mobile phones were located on the top. They could be pulled out for better signal reception. Over the years, these long antennas were shrunk to stubs, that jutted out from the top of the phone. As time passed by, these stubs were reduced to small bumps, on the top of the device. These bumps were then replaced by embedded antennas, where they were completely integrated within the body of the cell phone. However, with such a design, where the antenna is placed on the top of the mobile phone, very close to the head, the amount of radiations absorbed by the head tissues were more.
The FCC (Federal Communications Commission) in the US imposed strict limits on the amount of radio frequency energy that can be absorbed by the human body when using mobile phones. This energy limit has been termed as Specific Absorption Rate (SAR) and it has been fixed at 1.6 watts per kilogram. Mobile phones with radio frequency energy levels at or below this limit are considered safe for being legally sold in the US.
In-order to meet these requirements, the mobile phone makers came out with a new design where the antenna is embedded at the lower end of the device, farthest away from the head. Almost all mobile handsets being sold today have adopted this design. However, none of these manufacturers seemed to have thought that the lower end is the place where the phone will be touched by the hand.
Now with the iPhone 4, this antenna has been brought totally outside where it directly comes in touch with the hand.
A mobile phone antenna is a metallic strip which picks up radio waves from the air, meant for the mobile phone. The antenna is designed with precise dimensions to match the frequency of the radio waves that it has to pick up. Hence the antenna resonates at a particular frequency, which corresponds to the frequency of the radio waves. Spencer Webb explains 2 effects that come into play when the hand is held over the antenna on the mobile phone. These are detuning and attenuation.
In layman terms, detuning is the change caused in the resonant frequency of the antenna, due to contact with the hand. The human hand can be considered to be a bag of salt water. Hence it is a dielectric. As such, it can be polarized, or it can concentrate an electric field. When it touches the antennas, it loads them with this field and causes a decrease in their resonant frequency. This reduces the amount of energy that can be squirted into them. Webb takes the example of tapping an empty wine glass with a fork. The glass will resonate at a particular frequency. However, if the glass is filled with some wine, the resonant frequency will change, when it is tapped with the fork. In this case, the frequency will increase. It is the same with all mobile phone antennas. The touching of the hand alters their resonant frequencies.
Using a bumper case separates the direct contact of the hand with the antenna. Thus, the reception problem is reduced to a large extent. One thing to note here is that, the rubber bumper is a dielectric too. However, the electric field concentrated by it, is much less compared to that concentrated by the hand. Hence, the bumper too does load the antenna, but to a much lower extent than the hand. Dielectrics have something called as dielectric constant. This is a number which expresses the amount of electrostatic lines of flux the dielectric can concentrate. For the hand, this constant is about 20. It can vary from person to person depending on each one’s diet, BMI, sweaty or dry hands, weather and plenty more factors. For the rubber bumper, the dielectric constant is 3.3. This indicates that the bumper concentrates a lower electric field than the hand.
Attenuation is the loss of radio signals due to absorption. The human body is a dielectric, but not a non-conductor. It can conduct electricity but not as effectively as conductors. Hence the human body can be called a lossy-conductor. There will be loss of energy due to absorption by the body tissues. This energy absorbed is partially converted into heat, which can damage the tissues. And that’s exactly why the FCC has imposed the SAR levels on mobile phones. Coming back to attenuation, contact of the hand with the antenna can cause loss of signal being radiated into space by the antenna. While this is true for almost all mobile phones having their antenna at their lower end, the problem is more pronounced in the iPhone 4 which has its antennas on the outside, where there is direct contact with the hand.
Does Apple admit to a design flaw?
Yes. But indirectly. During the press conference held on 16 July, CEO Steve Jobs said, “I’m not saying we didn’t make a mistake, we didn’t know that it would have these issues.”
As for now the bumper cases save the day.
This is a guest post by Trinity Nick from the UK. A technical-geek, she reviews laptops and mobile phones that are released in the UK market.