Helping hands

New standards for hand phantoms are being developed that will assist with the design of more efficient mobile phones.

The impact of the hand on the total energy loss from a mobile telephone has been identified as being more important than the user’s head, especially as phones become smaller. To assist with optimising the antenna system design, Mauro Pelosi and Gert Pedersen from Aalborg University in Denmark are working towards standardising a hand phantom that emulates how a human handles a phone.

Testing times

When we use a mobile phone, between 50 and 90% of the radiated power is lost by dissipation in the body as heat. To understand and test this further, anthropomorphic body phantoms, similar to crash test dummies, are used in electromagnetic measurements to emulate the effect of the user on the radiation and vice versa. The first Over The Air (OTA) tests took place a decade ago with a phantom head and torso, but today most compliance measurements are still done without a hand phantom. As it has become clear that the hand should not be neglected, it has recently been under study as part of the standardisation process carried out by the cooperating bodies CTIA (Cellular Telecommunications and Internet Association), 3GPP (3rd Generation Partnership Project) and the European COST2100 Action on Pervasive Mobile and Ambient Wireless Communications. The CTIA hand in particular has become the de facto phantom, and soon a standardised version will be released and guidelines defined.

Gripping research

A hand phantom designed to study a particular ‘grip’ on a mobile phone. The team from Aalborg University form part of the COST2100 group which is particularly active in proposing scientific background for the upcoming standard on OTA test methods for multi-antenna systems. They are conducting parametric investigations on hand grip, geometry, size and composition to derive guidelines for the definition of hand phantoms that represent typical ways of handling a phone. In their most recent work they have focused on the composition of the hand phantom’s material which can be, for example, an empty shell filled with a hand tissue equivalent liquid or a carbon loaded silicone monoblock. “Our study suggests that small tolerances in the material of hand phantoms have a small impact, and the most important factors remain the way a mobile phone is held and the relative position of the index finger with respect to the antenna,” said Dr Mauro Pelosi, a researcher in the Antenna, Propagation and Radio Networking group at Aalborg University.

Before using a specific and complicated hand phantom, it has been necessary for the team to conduct an extensive grip study to collect statistics on the handling of mobile phones in both talk and data/browsing modes. They aim to extend their findings to small terminals with multiple antenna systems, as in the future users will increasingly request services requiring high throughput. The focus will shift from talk mode to data mode and the influence of the human hand will continue to play an important role.

Designs of the future

The team is also active in providing innovative antenna solutions for small terminals and in radio propagation for the systems involving small terminals. “We are currently conducting measurement campaigns with a large number of users and phones to obtain the real-life influence of the hand including the spread among users”, said Pelosi. “One of the main focuses is the study of highly efficient antenna systems for the upcoming LTE standards including tuneable antennas and OTA test setup.”

In the future, the team expects that different approaches to antenna design will be needed. “The proliferation of standards to be covered by the antenna system in a mobile phone is bounded by a trade-off between impedance bandwidth, efficiency, and size,” explained Pelosi. “As we cannot compromise both size and efficiency, the solution will come from the use of tuneable narrowband antenna systems. The addition of context aware radio capabilities to the mobile will, together with wisely placed and controlled antennas, allow a more efficient utilisation of the resources.”

The Letter presenting the results on which this article is based can be found on the IET Digital Library. For further reading, please visit www.es.aau.dk/sections/antennas_propagation_and_radio_networking_apnet/