March 1, 2011 at 2:00 PM ET
How users of some smart phones grip their gadgets can indeed lead to dropped calls — and, at least in a lab setting, placing an Apple-style plastic bumper between the antenna and thumb failed to fix the problem, according to new research on the so-called "grip of death" and potential fixes.
The antenna problem was widely reported among users of Apple's iPhone 4 last June, which prompted Mark Beach and colleagues at the University of Bristol's Center for Communications Research to revisit and update data collected in 2005 using a personal digital assistant with a new round of tests on a smart phone prototype.
In the new tests, the researchers investigated what happens when the thumb of a smart phone user directly obstructs a particular type of antenna. They compared their findings to results with the same phone and same antenna, but placed so that the antenna was not obstructed by the thumb.
"This is an emulation of the principal problem which was of interest in the summer of 2010, yes, and that was our motivation to re-open our log books and data," Beach told me in an email. But, he emphasized that "we did not use an iPhone 4 and we did not use the patented (and commercially secret) antennas we believe to be on the iPhone 4."
The team found that a thumb placed over the antenna "comprehensively disrupts the electrical characteristics of the antenna," Beach said.
"This means that its ability to transmit/receive signals is severely impaired — especially that the received signal strength tends to fall significantly and then tends to fluctuate more widely and so to be less reliable."
Overall, the thumb disruption led to a 100-fold reduction in sensitivity of the smart phone. This de-tuning of the antenna was found not to significantly alter the shape of the radiation pattern, but worsened the electrical match between the antenna and the electronic circuitry, according to the research.
In short, "signal strength is in general worse and more likely to drop below the threshold at which a connection to the network can be maintained," Beach said.
The grip of death appears to only be a problem, however, when the antenna is placed so that a user is likely to place their thumb over it. When the antenna is not directly obstructed, even when the thumb was nearby, call quality was "considerably better," he added.
"Thus, although some distance of thumb from antenna is needed, it does not have to be physically very large," Beach said.
The team tried to fix the problem by placing a thin layer of plastic between the antenna and the thumb – this is akin to the bumper Apple gave out to iPhone 4 users to address their antenna problems.
"There was no recovery in the electrical behavior of the antenna … its transmitting/receiving characteristics were not returned to their hands free state," Beach said, though he emphasized that this was under test scenarios.
Another potential fix the team is investigating is a technique called Virtual MIMO (multiple-input multiple-output) in which the number of antennas per phone is reduced, but are shared between users. The team is presenting results at a conference in Paris this week, and the research has been published in IEEE Antennas and Wireless Propagation Letters.
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