Wednesday, March 27

Scientific Greek: the prefixes ‘pico-’, ‘piezo-’ and ‘pyro-’

The prefix ‘pico-’ means ‘one-trillionth’ (one million-millionth, or a ‘ten to the twelfth’, part), symbolised by ‘p’. ‘Piezo-’ (from the Greek verb meaning ‘to press, squeeze’) means ‘subjected to pressure’. ‘Pyro-’ means connected with fire -- as in words like ‘pyrotechnics’ and ‘pyromaniac’.

In his article ‘Power Play’ (27 March 2002, http://www.technologyreview.com/articles/wo_cameron032702.asp), David Cameron describes a new ‘bare-bones’ wireless experiment that is nearly ‘ready to hit the airwaves’. At the Wireless Research Center in Berkeley, California, Prof. Jan Rabaey and his group -- funded by industry and the government -- have been working to create ‘picoradio’. This is a network of wireless nodes that ‘run advanced information systems, use an absolute bare minimum of energy, and cost next to nothing.’ No batteries will be needed, because the nodes (the size of shirt buttons) can extract all the energy they need from their surroundings. The prototype of a wireless network demonstrating picoradio’s low-energy protocol is due for completion in April, and the group intend to build a fully operational network prototype by December.

Each node will contain one or more sensors for measuring temperature, pressure, motion, light, sound or the like; a microprocessor; an interface to communicate with other nodes; and a power component, either solar cells or a piezoelectric polymer that can convert vibrations from the environment into electricity. One possible application, according to Rabaey, is climate control for large buildings. As Cameron explains, to operate on such low power, each node communicates only with one adjacent to it, which in turn signals the next, forming what Rabaey calls a ‘multi-hop network’. The network could be used for other jobs that use radio-frequency identification technologies, like tracking items or people in a contained space.

Piezoelectric polymers, i.e. cheap pressure sensors, have many applications. One such polymer is polyvinylidiene fluoride (PVDF), used in e.g. basketball players’ shoes that light up when the wearers land on their feet after a hard rebound. Piezoelectric film converts the pressure into a voltage that is then picked up and activates the LEDs on the heels of the shoes. Other current applications include pressure sensors in robotic hands, micro-actuators, displacement detection, active vibration control, force and pressure gauges, microphones, hydrophones, ultrasonic transmitter-receivers, impact localisation, non-destructive testing, toys, disk drives, ultrasonic imaging equipment and accelerometers. (Sources: http://www.stanford.edu/~puppy/desk/polymer.htm and http://www.piezotech.fr/appli.html.)

Pyroelectric sensors, on the other hand, detect humans’ and animals’ movements by sensing infra-red emissivity (http://www.acroname.com/robotics/parts/R3-PYRO1.html). The word ‘pyroelectric’ is applied to certain crystals that, on being heated, become electrically polar, i.e. exhibit positive and negative electricity at opposite ends (the effects being reversed while cooling). It is also applied to the effect exhibited by such crystals and to devices employing it. (Source: OED.)

Pyrolysis is ‘decomposition of a substance by the action of heat; loosely, any chemical change produced by heating’ (OED). Pyrolytic boron nitride (PBN), for example, is (I read at http://www.matweb.com/SpecificMaterial.asp?bassnum=CADV10), ‘an anisotropic, high-temperature ceramic’ that shows a unique combination of high electrical resistance and good thermal conductivity. It is non-toxic, non-porous and ‘exceptionally pure by virtue of the synthesis process (high temperature/low pressure chemical vapor deposition)’. PBN is widely used the semiconductor, electronics, metallurgical, thin-film and pharmaceutical industries. (Information provided by Advanced Ceramics Corporation.)