The latest in a long line of weird computers runs
calculations on nothing more than air.
The complicated nest of channels and valves made by Minsoung
Rhee and Mark Burns at the University of Michigan, Ann Arbor,
processes binary signals by sucking air out of tubes to represent a
0, or letting it back in to represent a 1.
Video: Processor puffing
A chain of such 1s and 0s flows through the processor's
channels, with pneumatic valves controlling the flow of the signals
between channels.
Valve computer
Each pneumatic valve is operated by changing the air pressure in
a small chamber below the air channel, separated from the circuit
by a flexible impermeable membrane. When the lower chamber is
filled with air the membrane pushes upwards and closes the valve,
preventing the binary signal flowing across one of the processor's
junctions.
Sucking out the air from the chamber reopens the valve by
forcing the membrane downwards, letting the signal move across the
junction.
The two researchers used the valve-controlled channels to
produce a variety of logic gates, flip-flops and shift registers,
which they linked together to create a working 8-bit
microprocessor. That means that the longest discrete pieces of data
it can handle are eight binary digits long, like the processors
used in 1980s consoles such as the Nintendo Entertainment
System.
It's even possible to watch the pneumatic components in action,
because the valve membranes reflect light strongly whenever they
are forced downwards (see movie).
Lab helper
But the air processor is far from just being a computational
curiosity, say Rhee and Burns: it has the potential to improve the
"lab-on-a-chip" devices tipped to automate complex chemistry tasks
and improve disease testing, DNA profiling and other lab jobs.
These pocket-scale microfluidic devices are yet to be much
practical use, say the Michigan team, perhaps because they
typically require a large number of bulky and expensive off-chip
components to control their operation.
Using logic circuits is one way to bring most of those controls
onto the lab-on-a-chip itself and reduce running costs. But because
many microfluidic systems have no electronic components, adding
standard electronic valves to the device would require a new
fabrication process, says Burns.
"Many microfluidic systems use pneumatic valves to control
liquid flow, so adding the pneumatic control circuits should be
relatively simple and inexpensive," he says.
Although the device still requires an off-chip vacuum source to
operate, the volume of the microprocessor is so small that the
required vacuum can be generated by a hand pump.
Versatile approach
Andrew de Mello, a microfluidics expert at Imperial College
London, UK, thinks that the simplified method of operation could
lead to useful microfluidic devices for developing countries.
"The fact that you can generate that vacuum from a hand pump
means these devices are low power, and suited for remote
locations," he says.
However, the device is unlikely to have applications beyond its
use in microfluidics – the "air" or "vacuum" signals are very
sluggish compared with the lightning-quick flow of electrons
through a standard circuit.
"Shrinking the device would mean that the signals would travel
shorter distances and thus operate at higher 'clock speeds'," says
Burns.
Journal reference:
Lab on a Chip, DOI: 10.1039/b904354c