The Economist October 9th 2021 Science&technology 77
dicted,trpv1turnedouttobeheatsensi
tive. When thetemperature rises above
43°C,thechannelthroughitopens,per
mitting ionsofcalcium andsodiumto
pass. That chemical signal stimulatesa
nerveimpulsewhichtellsthebrainabout
thetemperaturechange.
trpv1turnedouttobeoneofseveral
temperaturesensitiveionchannels,some
ofwhichregisterheat,andsomecold.It
was one ofthe coldsensitive varieties,
trpm8, which was discovered simulta
neouslybyDrJuliusandDrPatapoutian.
DrPatapoutianthenwentontolookat
thesensationoftouch.Molecularbiology
havingadvancedintheinterim,hewas
abletoworkwithwholeproteins—or,rath
er,thegenesforwholeproteins.Heidenti
fied 72 proteins,expressedina mechani
callysensitivecellline,thatlookedlikepo
tentialtouchsensitiveion channels.He
testedthemoneata time,bysilencingthe
genesthatencodethemandpokingthere
sultingcells.Thefirst 71 silencingshadno
effect.Butthe72ndprovedtobeofthepro
teinhewaslookingfor.Hecalledthatpro
teinpiezo1.
Innature,piezo1isfoundnotinsens
oryneurons,butratherinorganslikethe
bladderwherepressuresensitivityisim
portant.ButDrPatapoutiandiscovereda
similarchannel,piezo2, whichis,indeed,
foundinnerveendings.Itisthisthatisre
sponsiblefortouchandproprioception.
Fascinatingwork,then.Andimportant.
Itisthroughthesenses,andthesenses
alone,thatpeopleareabletoperceivethe
world.Buttosometheawardcameasa
surprise.Ina yearofcovid,theyhadbeen
expectingthehonourstogoelsewhere—
perhapstotheinventorsofmrnavaccine
technology.LikeGod,however,thevarious
Nobelprizecommitteesworkinmysteri
ouswaystheirwonderstoperform.n
Thethermoelectriceffect
Cool thinking
R
efrigerators and airconditioners
are old and clunky technology, and rep
resent a field ripe for disruption. They con
sume a lot of electricity. And they generally
rely on chemicals called hydrofluorocar
bons which, if they leak into the atmo
sphere, have a potent greenhousewarm
ing effect. Buildings’ centralheating sys
tems, meanwhile, are often powered by
methane in the form of natural gas, which
releases carbon dioxide, another green
house gas, when it is burned, and also has a
tendency to leak from the pipes that deliv
er it—which is unfortunate, because meth
ane, too, is a greenhouse gas, and one
much more potent than CO 2.
One potential way of getting around all
this might be to exploit what is known as
the thermoelectric effect, a means of carry
ing heat from place to place as an electric
current. Thermoelectric circuits can be
used either to cool things down, or to heat
them up. And a firm called Phononic,
based in Durham, North Carolina, has de
veloped a chip which does just that.
The thermoelectric effect was disco
vered in 1834 by Jean Charles Peltier, a
French physicist. It happens in an electri
cal circuit that includes two materials of
different conductivity. A flow of electrons
from the more conductive to the less con
ductive causes cooling. A flow in the other
direction causes heating.
The reason for this is that electrons are
able to vibrate more freely when pushed
into a conductive material. They thereby
transfer energy to their surroundings,
warming them. When shunted into a less
conductive one, electrons’ vibrations are
constrained, and they absorb energy from
their surroundings, cooling those sur
roundings down. An array of thermoelec
tric circuits built with all the highconduc
tivity materials facing in one direction and
all the low conductivity ones in the other
can thus move heat in either direction, by
switching the polarity of the current. For
reasons buried in the mathematics of
quantum physics, the heat thus flowing
does so in discrete packages, called pho
nons. Hence the name of the firm.
The thermoelectric effect works best
whentheconductorsinvolvedareactually
semiconductors,withbismuthandtinbe
ingcommonchoices.Fancycamerascon
tainsimplecoolingchipswhichusethese,
as do some scientific instruments. But
Phononic’sboss,TonyAtti,thinksthatis
smallbeer.UsingthegoodofficesofFabri
net,a chipmakerinThailand,hehasstart
edmakingmoresophisticatedversionsat
highvolume,usingthesetoftoolsand
techniquesnormallyemployedtoetchin
formationprocessingcircuitsontowafers
madeofsilicon.Inthiscase,though,the
wafersaremadeofbismuth.
Theresultsare,admittedly,stilla long
wayfromsomethingthat couldheat or
coola building.Buttheyarealreadyfind
inglucrativeemploymentinapplications
wherespaceisata premium.Atthemo
ment,thefastestgrowingmarketiscool
ingtheinfraredlasersusedtofireinforma
tionencodingphotonsthroughfibreop
ticcables,forthelongdistancetransmis
sionof data. They are also beingused,
though,inthe 5 gmobilephonebasesta
tionsnowstartingtoblanketstreetcor
ners,tokeepthebatteriesofelectricvehi
cles at optimal operating temperatures,
andascomponentsoftheopticalfrequen
cyradarlikesystemsknownaslidar, that
helpguideautonomousvehicles.
The crucial question from Mr Atti’s
pointofviewiswhethersemiconductor
basedthermoelectronicscanbreakoutof
these niches and become more main
stream,in thewaythatsemiconductor
basedelectronicsandlightinghavedone.
Inparticular,hewouldliketoincorporate
heatpumpingchipsintobuildings,topro
videthemwithintegralthermoregulation.
In theircurrent form, thermoelectric
chipsareunlikelytoreplaceconventional
airconditioningandcentralheating be
causetheycannotmoveheatoverthedis
tancesrequiredtopumpitinandoutofa
buildinginbulk.Buttheycouldnonethe
lessbeusedasregulators.Insteadofturn
inga bigairconditioningsystemonoroff,
tolowerorraisethetemperaturebythe
smallamountsrequiredtomaintaincom
fort, with all the cost that entails, thermo
electric chips might tweak matters by mov
ing heat around locally.
Phononic has already run trials of such
localtemperaturetweaking chips in Sin
gapore, in partnership with Temasek, that
country’s staterun investment fund. In
2019 spGroup, Singapore’s utility compa
ny, installed eight of the firm’s heat pumps,
which comprise an array of chips pointed
down at people, pumping heat out of the
air above them, on the boardwalk on
Clarke Quay in the city. Phononic claims
the devices lowered the temperature in
their vicinity by up to 10°C and, as a bonus,
consequentlyreduced humidity by 15%. If
that can bescaledup, it would certainly be
a cool result.n
A new approach to carrying heat aroundasanelectriccurrent
Hot vibes
Thermoelectric circuit
Source:Phononic
Copper
conductors
Semiconductors
Heat
flow
Heatabsorbed→
(coldside)
→ Heat
emitted
(hot side)
→
→
→
→
Electrical
Moreconductive current
Lessconductive
Electrical
insulator
Electrical
insulator
→ → → → → →
+