Home Mobiles The Moving Parts In Your Mobile – Forbes

The Moving Parts In Your Mobile – Forbes

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Tiny slices of quartz crystal are vibrating in your phone as you read this.Getty

Since the valve replaced the relay, and the transistor the valve, we’ve become used to the idea that electronic devices don’t have moving parts in them. It’s part of what distinguishes electrical devices from electronic ones and in the 1960s it was fashionable to call this “Solid State”, because nothing moved. Indeed in terms of hard disks the SSD has replaced the old-fashioned mechanical one.

But phones, computers and other electronic devices do have moving parts in them. It’s just the move very, very little. There are two types of moving parts, crystals and MEMS.

The crystals in your phone or computer are the same as the ones in a quartz watch. They provide the clock speed for the processor. The MEMS are Micro Electro Mechanical Systems. That is microscopic moving parts etched out of silicon.

The beauty of quartz is that it can be made to resonate fantastically accurately. Quartz is grown as a large crystal and then cut into slices. The angle of that slice is one of the major contributing factors to the frequency. It’s typically around 40Mhz. A noisy electrical signal is put into the crystal but it vibrates to the tune of the one with which the crystal has sympathy.  Gary Ramsdale from AEL crystals which designs the devices explained to me that fractures can be introduced into the crystal slice so that it vibrates against itself to give a multiplication factor, but while this is very clever it’s a technique which is prone to unreliability and so most often the multiplication of the frequency is done in circuitry outside of the crystal. These things are small. AEL’s smallest package is 1.6 x 1 mm and the crystal is 0.6 x 0.6mm within it. Although they are unlikely to get smaller as there is a limit on the size of crystal which can be made to vibrate.

And it’s not just the processor which has a crystal, a small computer or phone might have separate devices for  wi-fi, bluetooth and zigbee or ethernet.

So that’s a lot of extra components in a device. And space is hugely precocious in a mobile phone. This is where MEMS comes in. The typical MEMS application in a phone is the sensor which can tell which way up a phone is. A set of balanced levers taken down to microscopic size measure how the phone is tilted. But MEMS can be used like a tiny tuning fork to create oscillations and so have the potential replace crystals. What more exciting is that MEMS are made out of silicon so in theory the oscillator could be built into the processor chip, something that would be impossible with quartz. Not only would this help reduce the component count and size of the phone internals, MEMS are lower power than quartz which matters at the milliwatt level they are used for.

There are also implications for two of the fastest growing areas of technology: 5G infrastructure and automotive. Both can be harsh environments and MEMS are less sensitive to shock and rapid temperature changes than quartz.

But that doesn’t mean MEMS will replace crystals. AEL Crystals’ Shaun Mellor told me that five years ago his company, which designs quartz components, was worried that time was up for quartz, and so started working with MEMS companies, but quartz has become so cheap, and MEMS have moved upmarket so now the company lives in both camps, and no longer forecasts the imminent demise of quartz, indeed the company makes the smallest watch crystal available, which gives rise to the thought that even non-mechanical watches rely upon a mechanical part.

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