The Economist - UK (2022-04-02)

72 Science & technology The Economist April 2nd 2022

voltaic sensors are used to measure levels

of illumination, temperature, air pollution

and even (of particular interest at the mo­

ment) airborne pathogens. Automatic sys­

tems  fed  these  data  can  then  adjust  light­

ing,  heating,  ventilation  and  air­condi­

tioning levels appropriately. 

Photovoltaic sensors can also track pro­

ducts on assembly lines and monitor qual­

ity  during  manufacture.  They  offer  eyes

and  ears  in  sterile  chambers  and  provide

early  warning  of  shortages  or  leaks.  They

generate  vast  quantities  of  data  as  well,

which  can  be  used  to  maximise  efficien­

cy—though firms that employ them in this

way tend to be secretive about the details.

A study published in 2019 on the industrial

applications of all sensor types in Germa­

ny,  Switzerland  and  Austria  by  ey,  a  con­

sultancy, estimated the combined boost to

revenue  from  their  extensive  deployment

could be as high as 34%, depending on the

sector involved.

Obviously, photovoltaic harvesting has

restrictions, for it is suitable only in places

where the lights are usually on. That works

for  offices  and  those  parts  of  factories

where people operate. But for many indus­

trial  applications,  especially  those  being

carried  out  in  the  dark,  a  more  useful

source  of  scavenged  energy  is  heat.  The

trick  of  turning  this  into  electricity  was

discovered two centuries ago, and has been

improving ever since. It usually involves a

device  called  a  thermocouple,  made  of

sheets  of  two  appropriate  materials  laid

face  to  face.  When  one  side  is  hotter  than

the  other,  electrons  move  between  the

sheets, generating a current.

Turning up the heat

One  firm  which  makes  energy­harvesters

that  work  this  way  is  Perpetua  Power,  in

Oregon.  Its  devices  are  designed  for  inac­

cessible  locations  where  battery  replace­

ment would be impractical. Perpetua’s sen­

sors have been installed on oils wells in the

freezing conditions of Alaska and the des­

ert heat of California, to measure the pres­

sure at the well heads. They have, as well,

been fitted to steam­flow gauges under the

streets of New York, to make sure custom­

ers are billed correctly for their use of the

city’s district­heating system.

abb, a Swedish­Swiss firm, also makes

temperature  sensors  that  rely  on  thermo­

electric harvesting. Customers in the food

industry  use  it  to  ensure  ovens  are  suffi­

ciently  hot,  while  owners  of  industrial

plants can check their cooling systems are

working properly. And thermal harvesters

can  even  be  embedded  in  the  concrete

foundationsofbuildings,oraffixedtoin­

ternal  beams,  to  flag  up  structural  weak­

nesses and mechanical problems. 

Another field in which energy­scaveng­

ing  sensors  are  being  deployed  is  trans­

port.  It  is  here  that  vibrations  and  move­

ment  come  into  their  own.  Perpetuum,a

firm  spun  out  of  the  University  of  South­

ampton, in Britain, in 2004, and boughtin

2021  by  Hitachi  Rail,  designs  sensorspo­

wered  by  piezoelectricity.  This  is  a phe­

nomenon  whereby  certain  materialsgen­

erate  current  when  stressed  or  deformed.

Perpetuum’s  products  monitor  the  condi­

tion of railway rolling stock—an abundant

source  of  vibration.  Sensors  installed in

wheels,  gearboxes  and  motors  are  ableto

assess  those  components’  health  by  look­

ing  out  for  thermal  and  vibrationaltell­

tales of mechanical defects. They canalso

watch  the  condition  of  the  track.  Several

countries’  railway  networks  make  useof

them  to  varying  degrees,  including  those

of America, Australia and India.

Shake, rattle and roll

ReVibe Energy, a Swedish firm, has similar

aims.  Its  sensors,  which  rely  on  electro­

magnetic induction rather than piezoelec­

tricity  to  convert  vibrations  into  energy,

can be fixed to carriage wheels to monitor

their  position  as  well  as  the  stresseson

their  bearings.  ReVibe’s  technology  isbe­

ing  applied  to  mining  as  well,  to  lookout

for unusual patterns of movement inma­

chines involved in the crushing and trans­

port of aggregates.

There  is  also  one  further  source of

movement,  which  might  be  exploitedto

run sensors. This is the human body itself,

which it is becoming increasingly fashion­

able to adorn with sensors. A plausibleway

to convert body­movement into electricity

is  to  employ  devices  called  triboelectric

nanogenerators  (tengs).  These  convert

friction  into  electricity  using  a  method

that goes back at least as far as the Ancient

Greeks,  namely  rubbing  together  twoso­

called  triboelectric  materials  (amber,the

Greek word for which is elektron, andwool

were  once  popular)  to  create  a  static

charge.  tengs  turn  this  party  trick  intoa

useful  resource  by  conducting  the  charge

so generated away as a current.

tengs,  invented  a  mere  decade ago,

might plausibly be incorporated intosen­

sors attached to human bodies or clothing.

Bodies  are  continuous  generators  ofmo­

tion,  whether  from  breathing,  gesticulat­

ing or running for a bus. The flexibilityof

many  triboelectric  materials  makes  them

ideal  for  sewing  into  fabrics,  wherethey

could harvest the body’s movement inor­

der  to  power  sensors  that  monitoredvital

statistics such as breathing and pulserate

during  exercise.  Such  sensors  mightalso

do  well  in  the  hands  of  clever  marketing

types,  with  the  phrase  “batteries  notin­

cluded” being not a warning but a boast.n

Anti-anti-tankweapons

The best defence is

a good offence

R

ussian tankshave  been  having  a  tor­

rid  time  during  the  invasion  of  Uk­

raine.  According  to  Oryx,  an  open­source

intelligence blog, at least 153 of them have

been  destroyed  so  far,  along  with  312 ar­

moured  vehicles.  (The  figures  for  the  Uk­

rainian side are 26 and 57 respectively.)

Many  of  these  have  been  blown  up  by

cheap  anti­tank  guided  missiles  (atgms)

carried  by  Ukrainian  infantry.  Western

countries have shipped thousands of such

weapons to Ukraine, ranging from Ameri­

can  Javelins  via  Swedish­designed  nlaws

to  German­made  Panzerfaust­3s.  The  war

has been a powerful demonstration of the

threat  they  pose  to  modern  armour,  says

Jon Hawkes, a land­warfare guru at Jane’s, a

British  military  intelligence  firm.  Some

Russian tank drivers have resorted to weld­

ing scrap­metal cages to their vehicles in a

dubious effort to add extra protection.

It  is  ironic  that  atgms  have  proved  so

effective, since Russia—and the Soviet Un­

ion  before  it—was  a  pioneer  of  so­called

“active  protection  systems”  (apss)  de­

signed  specifically  to  defeat  them.  Unlike

armour, which is intended to limit damage

to a vehicle if it is hit, apss are there to stop

missiles striking in the first place. Armies

around the world are experimenting with,

and  deploying,  them.  The  war  in  Ukraine

will add urgency to that task.

apss come in two varieties, dubbed

“soft­kill”and“hard­kill”.Soft­killsystems

How to protect tanks against cheap,

deadly missiles

As yesow,soshallyereap

CorrectionIn “Dealing with degradation” (March

26th) we said that devices connecting to Starlink

terminals via Wi-Fi can download 150 megabytes of

data a second. The correct figure is 150 megabits, an

eighth of that rate. Sorry.