Reducing the environmental impact of the billion or more phones that are sold each year.
If you want to get all hair-shirted about it, the green mantra of 'reduce, reuse, repurpose, recycle' doesn't leave much slack for buying things because you want them, because they are fashionable, or because you would feel left behind without them. But the mobile phone industry is based on getting new customers and keeping existing ones by creating new handsets that enable new services.
Subsidies, which hide the cost of the handset in the monthly fees, and free handset upgrades to retain customers, further divorce people from the reality of their phone use - that a lot of sophisticated electronics is being produced and then discarded after a relatively short period of time to sustain an industry's growth.
Gus Desbarats, chairman of product and user interaction design consultancy TheAlloy, has been working on mobile phones since the mid 1980s - the Orbitel 902 is one of his designs. He says the subsidy issue is very real: "Because the handset is free there's no perception of its value, so the criteria for getting rid of it are much lower.
"There is a certain amount you can do to reduce churn but the key problem is that network operators have a huge incentive to increase the sophistication of these interaction devices."
How big is the issue? Analysts such as ABI Research and IDC agree that although mobile phone sales have been hit by the global recession, around 290 million handsets were sold in the three months to the end of September. Sales for the year are expected to reach around 1.1bn units. That's a lot of new handsets. The ITU offers a different slant - it predicts that by the end of the year there will be 67 mobile phones for every 100 people on the planet - or two between three of us. And this is in a down year.
Why does it matter? Because it takes energy and resources to produce such sophisticated devices, it takes energy and resources to run them, and it takes energy and resources to dispose of them responsibly. Electronics manufacturing has also had a long-term relationship with some pretty unpleasant chemicals, and is still adapting to requirements to do without the most environmentally unfriendly of them.
Simple things first
What can be done? Most of the major handset makers are now making serious efforts to reduce the environmental impact of the manufacture, use and recycling of their phones. According to Desbarats, many companies are doing without the PVC and flame-retardant bromide materials that are now seen as environmentally suspect. But finding replacements for them is not easy.
"The problem is that the mobile phone is a hard design problem," he says. "The case material must have a high flow [to get into all the nooks and crannies of a modern case design], it must support thin walls, keep to tight tolerances, and survive high wear."
Surprisingly, Desbarats sings the praises of Nokia's increasing use of stainless steel in its cases: "Good old stainless steel is one of the neatest case materials out there. It is almost infinitely recyclable."
Companies are developing recycled and even bio-based plastics, but the key is ensuring absolutely consistent performance in a challenging design environment: "You can't compromise on that no matter how much you want to."
There can also be problems guaranteeing the availability of enough of these new materials with sufficient consistency: "It's one of the biggest problems with recycled materials."
He doesn't hold out much hope for the use of bio-plastics, such as those being developed based on soya, in handsets either.
"There was a lot of hype about it but as the designs got closer to launch it turned out they're not going to happen just yet."
There are other positive things that can be done. Smaller handsets use less material. Packaging can be reduced, and manuals supplied electronically. Single chip phones can simplify circuit boards, as can printing part of the circuitry on the case. OLED and e-Ink displays can cut power con-sumption, and so allow smaller batteries.
Desbarats also expects a lot of green innovation to come from servicing demand in the developing world: "The developing world is a huge market for the mobile phone because of the lack of infrastructure, so some of the most interesting stuff in recyclables is being done for that market."
Mobile phone chargers have been demonised for the amount of power they use in standby. According to Arcadio Leon, marketing director in the power management group of Analog Devices, the key improvement being made in chargers is to shift them from linear designs to more efficient switching designs. This can boost efficiency from around 60 per cent to 70 per cent for a linear charger to more like 90 per cent for the switching designs, he says.
Leon also argues that the ITU's recent decision to endorse a standard mobile phone charger from 2012, and the Chinese government's decision to do the same for its market, should boost efficiency and reduce waste as consumers keep their charger despite changing their handsets. Meanwhile Professor Sanowar Khan, of the school of engineering and mathematical sciences at City University London, claims to have developed a charger design with zero standby current - but can't say more because he hopes to patent it.
There are more subtle things that can be done to manage power consumption in handsets. Analog Devices is promoting point-of-load regulators, which can be quicker to implement than using system-wide power management ICs.
The company is offering standalone switching and linear regulators, and is using the same intellectual property to produce what it calls micro power management units (PMU), for example to handle the power for a camera subsystem. Each of these devices has an On/Off signal so that its start-up can be sequenced either by the handset's main processors or by a microPMU triggered by that processor: "That way you can have localised power control with a local device handling the sequencing."
Specialisation is key
Analog Devices' approach is to offload work from the main processor. The company has developed an LED backlight controller that has built-in ambient light sensing: "In many phones this is supported by the processor, so you're trying to implement a power-saving technique using a power-hungry processor. We've seen 60 to 70 per cent savings on LED driving with this."
The LED driver also does gamma correction - adapting the output of the backlight to what is being displayed, which can be an effective energy saver during video playback.
The company is taking a similar approach with a keyboard controller, which offloads the job of scanning a QWERTY keyboard matrix from the main processor. "The typical current we draw is 55µA. Using a fast processor that could be 60mA for 80ms at a time."
These localised approaches to handset power control may also simplify board design by reducing the number of tracks that have to go back to a central processor.
Graphics processor company nVidia is also arguing the energy efficiency advantages of specialisation in handsets, although in its case it is talking about major processing functions such as video encoding and decoding in top-end smartphones. Its Tegra handset chips include multiple processing cores, each optimised for a task such as 3D graphics or audio playback. Each core can be switched on and off as needed, to avoid standby leakage, and the company also uses techniques such as gated clocks and adjustable clock speeds to further reduce power needs.
Mike Rayfield, general manager of nVidia's mobile business, says that mobile phone battery capacities range between 1200 and 1800mAh, "and I am not counting on batteries saving the day anytime soon".
Against this budget, Rayfield says it can take 20mW to 30mW to do audio playback on a Tegra, and 200mW to 300mW to do 720p HD video playback.
"We think these are four to ten times more power-efficient [playback schemes] than anything else we have seen," he says.
More efficient designs can reduce the environmental impact of new handsets, especially at the high end, but to return to the green mantra of 'reduce, reuse, repurpose, recycle', making better use of what we already have may have a greater impact.
Many mobile phone companies are now offering incentives for customers to bring back their old phones for recycling. And a number of independent companies will buy unwanted handsets for cash, so that they can refurbish them and sell them on. According to Desbarats, there's also a pretty effective recycling scheme in the 'informal economy', as stolen handsets make their way to the developing world for resale.
None of these approaches, though, may be as effective as a scheme that used to exist in the UK.
"Go right back to the days of phone rental at BT," says Desbarats. "Many years ago, BT ran an ecosystem for recovery that was much more complete than what is available now."
Desbarats is also keen that people do more to repurpose phones. He points out that it's the cases of mobile phones that tend to wear out first, rather than the electronics. Re-casing phones, rather than discarding them, could give those sophisticated circuit boards they contain a new lease of life. He has even considered setting up a business to sell high-end handsets using high-technology case materials and engineering - with repurposed electronics.
Perhaps we should all go back to basics, and follow the example of billionaire retailer Sir Philip Green. According to an interview in The Times newspaper, his favourite gadget is a basic Nokia 6310 handset design that he has used for years. He does rather blot his environmental copy-book, though by revealing he has two of them in use and a dozen more for back-up. Even for the rich, it seems, it is not easy being green.