Bristol University researchers have proven the iPhone’s antenna problem affect most mobile phones
No smartphone can escape the “death grip”, according to a study published by a team at the University of Bristol. The results indicate a massive reduction in reception sensitivity when mobile phones are held in certain ways.
The research stems from problems that initially arose with the Apple iPhone 4 last year. Users reported problems in reception when the phone was gripped in their hands and, at one point, it looked like Apple might have to recall units. The company claimed at the time that it was not purely an Apple problem but that it affected all phones. Some phones failed to show any signal degradation in normal use because of differences in antenna placement within the design – but the new research shows that all phones can be affected.
Disclosed by a rule of thumb
The Bristol team is ultimately searching for a solution to the problem but first had to duplicate the conditions that gave rise to the reduced reception. This was achieved by operating a “prototype” phone in hands-free mode, by physically holding the phone in different ways, and by using a simulated thumb to fine-tune the results.
The “phantom thumb” was devised to simulate the dielectric properties of skin.
The paper, published in the IEEE journal: Antennas and Wireless Propagation – Letters, builds on previous research by the university’s Centre for Communications Research (CCR) that analysed multi-antenna, or multiple-input multiple-output (MIMO) wireless devices. These are used in the latest cellular radio networks and local area network Wi-Fi products.
The new research rigorously investigated the effects of obstructing the antenna of an unnamed phone prototype. The researchers noted changes in the signal levels caused by obstruction of the signal, various position and using the phone while in motion.
The results indicated that a 100-fold reduction in the sensitivity of the device could occur when gripped in the hand, or when the phantom thumb was held against the phone. The contact did not actually affect the shape of the phone’s radiation pattern but dramatically degraded the electrical match between the antenna and the electronic circuitry.
Managing the problem
Further tests showed that even a gap created by the plastic casing between the antenna surface and the phantom thumb had no real effect. Apple’s stop-gap solution to the problem was to offer a free “bumper”, a thick rubber band that wrapped round the rim of the phone. As the name implies, the bumper was originally designed to protect the iPhone from damage if it was dropped. The thickness of the rubber created sufficient space between the antenna and the user’s fingers and restored the phone’s performance.
Mark Beach, professor of radio systems engineering at Bristol University, concluded that the “antenna position and user grip on smartphones may lead to obstruction of radio signal paths and antenna detuning”.
So, having proved that the death grip appears to be a universal phenomenon, the research is now turning to examine how the effects can be reduced or eliminated. Automated re-tuning of the antenna elements could provide an answer to maintaining the efficiency but the CCR team has yet to complete its new line of research.