The so-called 'death grip' effect, in which a user's hand touching a smartphone antenna degrades its radio connections - a major issue for the iPhone 4 with its external antennae - is real and is a serious problem, according to British boffins researching the matter.
Furthermore they found that plastic insulation between hand and metal has no useful effect - so that "bumper" case may be a completely pointless addition.
The new boffinry comes from the Centre for Communications Research at Bristol uni. The centre's Professor Mark Beach is an expert in the engineering of MIMO (multiple input multiple output, aka multi-element or "smart") antennae, nowadays de rigueur in modern smartphones enabled for various kinds of cell and Wi-Fi networking.
The prof and his colleagues examined the performance of MIMO antennae in various circumstances: with the signal obstructed by a user's hand as one might see in any smartphone, then with the antenna actually in contact with a "thumb phantom" with the same dielectric properties as human skin. Finally performance was examined under the circumstances of handsfree operation, with no inconvenient flesh-sacks nearby.
According to a Bristol uni statement accompanying the research:
The results from the study indicate a 100-fold reduction in sensitivity of the device when held, or when the user’s thumb is mimicked by phantom material. This de-tuning of the antenna was found not to significantly alter the shape of the radiation pattern, but dramatically worsened the electrical match between the antenna and the electronic circuitry.
“Antenna position and user grip on smartphones may lead to obstruction of radio signal paths and antenna detuning," confirms Beach. It appears that you can perfectly well muck up the performance of any modern smartphone by enclosing it in your hand, but actually touching the antenna offers a further opportunity for trouble.
The famous 'death grip' or 'antennagate' brouhaha which emerged following the debut of the iPhone 4 - which is pretty hard to use without touching its antennae - has now largely died down. At the time, the only solution offered by Apple (other than software fixes) was to wrap the handset in a plastic insulating "bumper".
What do Beach and his colleagues have to say to that?
Well, according to the Bristol uni statement:
Further tests concluded that providing a gap between the antenna surface and the phantom thumb using a layer of plastic electrical insulator did not restore the matching and operational sensitivity of the phone for the antennas under evaluation. Thus, some phone covers in the market place may not improve the situation.
That said, the "bumper" advice from Apple may not have been totally wrong: the iPhone 4 also had an additional problem with a gap between two external antennae being bridged by a user's hand, something that hasn't been investigated here.
Meanwhile Beach and his crew are looking at ways around the issue. The prof says that the CCR at Bristol is working on “automated re-tuning of the antenna elements" which might change the technical landscape in future.
Full details on the research are available here for subscribers to the IEEE journal Antennas and Wireless Propagation Letters. ®