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RESEARCH ARTICLE
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Manipulation of Convection Using Infrared Light Emitted
from Human Hands
Hanrui Zhu, Zhen Luo, Lifu Zhang, Qingchen Shen, Runheng Yang, Weizheng Cheng,
Yingyue Zhang, Modi Jiang, Chunzhi Guo, Benwei Fu, Chengyi Song, Peng Tao,
Shun An,* Wen Shang,* and Tao Deng*
Control of convection plays an important role in heat transfer regulation,
bio/chemical sensing, phase separation, etc. Current convection controlling
systems generally depend on engineered energy sources to drive and
manipulate the convection, which brings additional energy consumption into
the system. Here the use of human hand as a natural and sustainable infrared
(IR) radiation source for the manipulation of liquid convection is
demonstrated. The fluid can sense the change of the relative position or the
shape of the hand with the formation of different convection patterns. Besides
the generation of static complex patterns, dynamic manipulation of
convections can also be realized via moving of hand or finger. The use of such
sustainable convections to control the movement of a floating “boat” is
further achieved. The use of human hands as the natural energy sources
provides a promising approach for the manipulation of liquid convection
without the need of extra external energy, which may be further utilized for
low-cost and intelligent bio/chemical sensing and separation.
1. Introduction
Convection commonly occurs in nature, such as in the
atmosphere,[1]in the ocean,[2–4]in ice shelves,[5]and around the
sun.[6,7]Convection most of the time leads to the energy exchange
and the mass transfer, and is widely used in many different
systems,[8–10]including motion systems[11,12 ]and heat transfer
systems.[13,14]Convection can also carry specific nanoparticles or
H. Zhu, Z. Luo, L. Zhang, Q. Shen, R. Yang, W. Cheng, Y. Zhang, M. Jiang,
B. Fu, C. Song, P. Tao, S. An, W. Shang, T. Deng
State Key Laboratory of Metal Matrix Composites
School of Materials Science and Engineering
Shanghai Jiao Tong University
Shanghai 200240, P. R. China
E-mail: anshun@sjtu.edu.cn;shangwen@sjtu.edu.cn;
dengtao@sjtu.edu.cn
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/advs.202307020
© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.
This is an open access article under the terms of the Creative Commons
Attribution License, which permits use, distribution and reproduction in
any medium, provided the original work is properly cited.
DOI: 10.1002/advs.202307020
targeting molecules for directional trans-
portation, which further broadens the
application of convection in bio/chemical
sensing systems[15,16]and separation
systems.[17]Generally, the formation
of the convection is the result of the
nonequilibrium state inside the liquid.[18,19]
One type of the nonequilibrium state
is the temperature gradient that is usu-
ally generated by engineered energy
sources, including the hot plate,[20,21]
the IR lasers,[22,23]the visible lamp,[24 ]
and the ultraviolet (UV) light source.[25]
The engineered energy sources for
generating and controlling the convec-
tion can be simply classified as contact
sources[26,27]and non-contact sources.[28–30 ]
The use of contact energy sources may
lead to the mechanical wear and fatigue,[31]
and the contamination of the fluid may
also happen through the direct-touching
operation. Therefore, non-contact energy sources, with the ad-
vantages of reduced mechanical wear and minimized contam-
ination of fluids, are gradually involved in many convection
systems.[32–34]The man-made non-contact energy sources, how-
ever, require the use of external energy for their proper operation,
which may limit their potential use. For example, Zhang et al. in-
vestigated an approach to manipulate the in-fiber nanoparticles
by inducing thermocapillary convection via a far-IR laser with the
L. Zhang
Department of Materials Science and Engineering
Rensselaer Polytechnic Institute
Troy, NY 12180–3590, USA
Q. Shen
Yusuf Hamied Department of Chemistry
University of Cambridge
Cambridge CB2 1EW, UK
C. Guo
School of Electronic Information and Electrical Engineering
Shanghai Jiao Tong University
Shanghai 200240, P. R. China
T. Deng
Shanghai Key Laboratory of Hydrogen Science
School of Materials Science and Engineering
Shanghai Jiao Tong University
Shanghai 200240, P. R. China
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Figure 1. Schematic illustration of the controllable convection generated by human hands. The IR radiation from human hands enables the generation
of the temperature gradient within the liquid, which induces convections in the liquid. The localized convections can be generated both statically and
dynamically and also can be manipulated by hands. With controllable localized convection, the floating “boat” can be touchlessly manipulated by human
hands.
maximum power of 20 W.[35 ]The approach is interesting, but the
need of using high-power energy sources, however, may limit the
application scope of this method. The exploration of alternative
non-contact energy sources that do not need energy supply may
broaden the applications of the convection systems.
Compared with those engineered energy sources, natural en-
ergy sources have the advantages of zero extra energy con-
sumption and sustainability.[36]Currently various natural energy
sources have been broadly used in many engineered systems
such as photovoltaic,[37,38]seawater desalination,[39 ]and interfa-
cial evaporation.[40]Human hands, with relatively stable tem-
perature and the ability of continuously emitting IR light, have
been demonstrated as a new type of intelligent and sustainable
natural energy source.[41–43]An et al. have reported that human
hand can be considered as natural IR light source to interact
with the structured surfaces and the generated signals can be fur-
ther used for sign language recognition[41]and human-machine
interaction.[43]The integration of human hands into engineered
systems brings the advantages of sustainability and intelligent
controllability into these systems. Therefore, the integration of
human hands into the convection systems as the non-contact en-
ergy source can not only reduce the energy consumption but also
improve the intelligence of the convection systems.
In this work, we demonstrate the convection in the fluidic
system could be generated and controlled by sensing the IR
radiation from the human hands. The use of human hands
enables the formation of multiple complex convection patterns
as well as the control of those convections. The control of floating
“boat” through hand enabled convection is also demonstrated.
As shown in Figure 1, the fluidic system sensed the temperature
difference induced by the hand-emitted IR radiation and thus
convection was generated. With the change of the positions of
hands, convections can be sustainably generated at different
locations, which can be further used to control the movement
of the floating “boat” in real-time. In the study, we used the
polystyrene (PS) nanoparticles to trace the flow in the convection
and investigated the influence factors that affect the velocity field
and the lateral size of the convection. The results show that the
velocity and the lateral size increase as the depth of the water
gets larger and the hands get closer to the container. Different
patterns of convections can be generated both statically and
dynamically with the use of human hands. With the established
manipulation of the convection through hands, we further
achieved the control of the motion of a floating “boat” at the
liquid-air interface. The use of human hands as the IR energy
sources offers a powerless and non-contact approach for the
generation and control of the mass transfer in the convection
at will, which may further broaden the potential applications of
convection in low-cost sensing and separation systems.
2. Results
2.1. Generation of Single Convection Using Human Hands
The human hand can be considered as an incoherent IR en-
ergy source with a temperature of ≈310 K and an emissivity of
≈0.98.[44]Based on the Blackbody radiation law, the wavelength
of the IR radiation of the hands mainly concentrates in the range
of 4–16 μm. In this study, we explored the use of the hand as a
natural IR energy source for the generation and manipulation of
convections in liquid. The experimental setup is shown in Figure
S1a (Supporting Information), which includes a high-speed cam-
era and a quartz container half-filled with deionized (DI) water. In
order to be consistent in using the same amount of the IR radia-
tion from the hand, we used the aluminum foil to cover the palm
of the hand with an open emission window of 4 cm ×4cm(≈
0.83 W). The size of the open window is larger than the size of the
sidewall of the container (Figure S1b, Supporting Information).
The PS nanoparticles (Invitrogen Trading Co., Ltd) with average
size of ≈206 nm (Figure S2, Supporting Information) were used
to trace the movement of liquid flows. As shown in Figure S3
(Supporting Information), both the DI water and the quartz can
absorb the IR radiation.[45]During the experiment, the hand was
placed parallel to the left sidewall of the container with a distance
of 5 mm from the container. The IR radiation from the hand can
be absorbed by the left side of the container half-filled with wa-
ter, which leads to the temperature difference within the liquid,
and subsequently induces the convection of the liquid (Figure 2a)
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Figure 2. The generation of the convection by hand. a) The experimental observation of the convection generated by placing one hand on the left side
of the container (top) and the simulated velocity field of the convection (bottom). b) The IR image (top view) of the container shows the temperature
distribution in the water. The plot underneath the IR image shows the temperature along the dotted line across the IR image. c,d) The change of velocity
and lateral size of the convection with the change of c) the depth of the water and (d) the distance between the hand and the container. The error bars
represent the standard deviation (SD) of the mean (n =3) e) The optical images of convection patterns formed in the containers with different lengths
that are induced by the IR radiation from the hand.
and Movie S1, Supporting Information). The response time, the
time from placing hand near the container to the time that the
PS particles start to move, was measured to be ≈5 s. The time
that the PS particles complete one cycle of convection is obvi-
ously longer than the response time and is 6 min, which can be
defined as the cycle time. In Figure 2a and the following experi-
ments (Figures 2–4), we placed the hand close to the container for
one cycle and captured the image of the convection at the same
time, aiming to visualize the complete cycle of the convection for
further characterization.
Numerical calculation was further taken to simulate the for-
mation of the convection. The input power on the left side of
the container is the IR radiation emitted from hands (Section
S1, Supporting Information). With the known input energy, the
velocity field and the temperature field of the fluid can be ob-
tained by using COMSOL Multiphysics (Section S2, Supporting
Information) to solve the Navier-Stokes equations. In this study,
the temperature-induced density change of the liquid is much
less than the density of the liquid, we thus used the Boussinesq
approximation (Section S3, Supporting Information)[46]to sim-
plify the Navier-Stokes equations. The simplified equations can
be given as:
𝜕𝜌0
𝜕t+∇⋅𝜌0u=0
𝜌0
𝜕u
𝜕t+𝜌0u⋅∇(u)=−∇p+∇𝜇∇u+∇uT−2
3𝜇(∇⋅u)I
+F𝜌0Cp
𝜕T
𝜕t+𝜌0Cpu⋅∇T=∇⋅(k∇T)+Q
(1)
where u,Q,p,andFare the velocity vector, the internal heat
source of the fluid, the approximated pressure (Boussinesq ap-
proximation, Section S3, Supporting Information) and the ap-
proximated body force (Boussinesq approximation, Section S3,
Supporting Information), respectively. Iis the identity matrix and
Cpand kare the heat capacity at constant pressure and the ther-
mal conductivity of the liquid, respectively. The approximated
body force by Boussinesq approximation F=− 𝜌0𝛽(T−T0)g,
in which 𝜌0is the initial density of the liquid at the initial tem-
perature T0and 𝛽is the coefficient of thermal expansion of the
fluid at T0. For the original state without hand, the liquid is in
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Figure 3. Static formation of the convections with complex patterns. a–c)
By controlling the distance between hands and the sidewalls of the con-
tainer, convections can be formed both a) symmetrically and b,c) asym-
metrically. d) The generation of two symmetric convection patterns by
placing a finger under the middle bottom of the container. e) Using two
hands and one finger to form three convection patterns (on the right, left,
and backside of the container) at the same time. f) Four convection pat-
terns can be generated symmetrically by placing hands and the finger on
the right, left, and bottom of the container at the same time, with a quartz
plate inserted in the middle of the container.
temperature equilibrium with the environment, which means T
−T0=0, thus Fequals to 0. For the condition of placing hands
close to the container, the IR radiation from hand would lead to
the temperature increase of the liquid. In this case, T−T0≠0,
so F≠0, and there is coupling between density and tempera-
ture. With the temperature-induced buoyancy force, the convec-
tion could be generated. Figure 2a shows that the simulating re-
sults are in good agreement with the experimental results. We
also ran a control experiment to prove that the convection was
induced by the temperature change (Figure S4, Supporting Infor-
mation). Without putting hand on the left side of the container,
the liquid and the container can only receive the IR radiation
from ambient. Since the ambient has the same temperature with
the liquid, the IR radiation from the ambient would not cause the
change of temperature in the liquid and thus the convection was
not formed in the fluid.
An IR camera (FLIR T640) was used to visualize the temper-
ature distribution of the water when hand was placed close to
the left side of the container. Both Figure 2b and Figure S5 (Sup-
porting Information) show that the temperature of the left side
of the container is higher than that of the right side. We also ex-
plored the effect of environmental temperature and movements
of extra IR light sources on the convection. As shown in Figure
S6 (Supporting Information), the velocity and the lateral size of
the convection, which is the length of convection along the lat-
eral direction, decreased with the increase of the environmen-
tal temperature due to the smaller temperature difference within
the fluid. Under different environmental temperatures, the con-
vection keeps stable, with the standard deviation (SD) of the lat-
eral size and the velocity in all experiments about 0.06 cm and
0.004 mms−1, respectively. To explore the effect of the movement
of an extra IR light source, we placed one hand on the left side
of the container to generate a stable convection. We then con-
trolled another hand moving behind the container with a speed of
1.2 cm s−1and the distance to the container of 5 cm. As shown
in Figure S6b (Supporting Information), the lateral size and the
velocity of the convection did not change with the movement of
the extra IR light source (another hand). The convection pattern
was stable, with little interference from the moving hand.
We further analyzed the factors that influence the generation
of the convection, including the depth of the liquid, the distance
between the hand and the container, and the length of the
container. We first investigated the effect of the depth of the
DI water on the velocity and the lateral size of the convection.
Despite the penetration depth of IR radiation in liquid water
is less than 100 μm (Section S4, Supporting Information), the
lateral size of the convection flow is in the centimeter scale since
the temperature difference would exist in a much longer distance
in the medium due to the thermal conduction. As shown in
Figure 2c, the velocity of the convection (Experimental Section)
increased with the increase of the water depth from 10 to 30 mm
in the container with 9 cm length. The lateral size of convection
also became larger with the increase of the depth of the water.
When the depth of water was over 20 mm, the convection circle
was confined by the container and thus the lateral size of the
convection was all ≈9 cm. Therefore, in order to ensure the for-
mation of the convection circle completely, the depth of the water
was set as 15 mm in most of the experiments in this study. The
other factor that affects the convection is the distance between
the hand and the container. As shown in Figure 2d, the velocity
and the lateral size of the convection decreased with the increase
of the distance between the hand and the container. In the study
we set the distance between the hand and the container as 5 mm
to obtain clear convection patterns. We further used COMSOL
to numerically calculate the change of the convection properties
with the change of water depth and distance between the hand
and the container. As shown in Figure 2c,d, the calculated results
of the convection are in good agreement with the experimental
results.
We explored the effect of the thermal absorption characteristics
of the container and the liquid medium on the effective working
distance range by COMSOL simulation. As shown in Figure S7
(Supporting Information), the hand would not induce any con-
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Figure 4. Dynamic control of the convection. a) The convection can be controlled dynamically by switching the hand position to different sides of the
container. Numerical simulation shows the change of the velocity field during this process. b) With the moving of the finger position below the bottom
surface of the container, the convections move with the moving of finger. Numerical simulation shows the change of velocity field during this process.
vection if both the container and the liquid are non-absorbing and
thus there is no effective working distance in this scenario. For
the fully IR-absorbing container and non-absorbing liquid, the
convection still exists when the hand is 110 mm away from the
container, and the effective working distance range is thus from 0
to 110 mm. Compared to fully IR-absorbing container and non-
absorbing liquid, the system with non-absorbing container and
fully-absorbing liquid always forms convections with larger lat-
eral sizes and the effective working distance range is also larger,
which is 0–125 mm, since the IR radiation could be directly ab-
sorbed by the liquid, with less heat loss by the wall of the con-
tainer.
From Figure 2c, we found that the lateral size of the convection
was limited by the available length of the container, which is the
distance between two sidewalls. We further studied the effect of
the length of the container on the lateral size of the convection
(Figure 2e). In this experiment, the liquid depth was kept at
15 mm and the distance between hand and container was 5 mm.
When the hand was placed at the left side of the containers,
clockwise convections were stably formed in all three containers
with different lengths (3 cm, 6 cm, and 9 cm). When the length
of the container was small, the lateral size of the convection was
limited by the length of the container. When the length of the
containers was larger, the lateral size of the convections was not
limited by the length of the container and all showed similar
size of ≈5 cm. These results are consistent with the theoretical
study by Ganzarolli and Milanez.[47]The accuracy and sensitivity
of the fluid velocity changes with energy are the crucial physical
parameters of the convection systems (Section S5 and Figure S8,
Supporting Information). In the unconstrained system (9 cm
container), the accuracy was calculated to be 0.03 mm s−1and
the sensitivity was 0.441 mm s−1W−1. Under different input
energy, the generated convection also shows high stability with
the SD of ≈0.003 mm s−1. In the constrained system (3 cm con-
tainer), the stability, accuracy, and sensitivity were calculated to
be 0.002, 0.025, and 0.344 mm s−1W−1, respectively. Compared
to unconstrained system, the constrained system has the similar
accuracy and stability but the lower sensitivity of velocity change
with energy, which might be due to the smaller temperature
difference in shorter container. In the following experimental
study, we chose the containers with lengths of 9 cm or larger to
avoid the limitation of the length of the container.
2.2. Static Generation of Complex Convection Patterns Via Hands
With the demonstration of the generation of convection inside
the fluid by the IR radiation from the hand, we further explore
the use of hand to generate convections with different complex
patterns. We first tried using two hands on both left and right
sides of the container to generate convections (Figure 3a–c). With
the symmetric placement of hands on both left and right sides
of the container, the input energy from both sides was the same,
so two convection patterns with symmetric shapes were formed
(Figure 3a). By controlling the distance between the hands
and the sidewalls of the container, the two convections with
asymmetric shapes can also be formed. As shown in Figure 3b,c,
when we place two hands on both sides of the container with
different distances, the input thermal energy is different between
the left side wall and the right side wall of the container. The
velocity and the lateral size of the convection decreased with the
increasing distance between the hands and the container. Thus,
if the distance between the hand and the sidewall on the left was
larger than that on the right, the convection generated on the
left side of the container would be smaller than that on the right
side. Similar experimental results were also obtained when the
distance between the right hand and the container was larger
than that of the left hand. In ideal situation, the convection
pattern in Figure 3b,c should mirror each other. In real exper-
iments, however, the two convection patterns and also other
convection pattern pairs did not mirror each other due to the pos-
sible variations in experiments including the slight variation of
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the dropped tracing solution (solution of PS nanoparticles), the
slight variation of the relative position and angle of the hand, and
the slight variation of the environmental and hand temperature.
All of these factors may contribute to the variation of the convec-
tion patterns generated. We also used COMSOL to simulate the
formation of the convections and the results are consistent with
the experimental results (Figure S9, Supporting Information).
The IR light emitted from the hand should be generated not
only by the palm of the hand but also by individual finger. We
further explored the formation of the convections with different
patterns inside the container by placing the index finger at differ-
ent positions underneath the bottom surface of the containers
(Figure 3d and Figure S10, Supporting Information). The dis-
tance between the index finger and the bottom surface of the
container was still set as 5 mm. We first placed the index finger at
the center of bottom surface of the container (Figure 3d). In such
condition, the patterns of the convections were formed symmet-
rically in the container since the temperature difference was the
same for both sides. The simulating result of the velocity field of
the convection is consistent with the experimental result (Figure
S11, Supporting Information). When we placed the index finger
underneath the left bottom surface of the container, the convec-
tion was formed asymmetrically. The velocity and the lateral size
of the convection on the left side of the containers was smaller
than those on the right side (Figure S10i, Supporting Informa-
tion). Such phenomenon can be attributed to two key factors. The
first one is the temperature difference. According to Equation S5
(Supporting Information), the received radiation from fingers at
different positions of the bottom surface of container is related
to the distance between the finger and the position. When the
finger is placed at the left side underneath of the container, the
left far end of the bottom surface of the container receives more
radiation than that on the right far end. Thus, the temperature
difference within the right side of the container is greater than
that at the left side. The velocity and the lateral size of the convec-
tion on the right side thus is larger than that of the left side. The
other factor is the distance between the finger (warm side) and
the sidewall (cold side). The convection on the left was confined
by the distance between the finger and the left sidewall and same
as the convection on the right of the container. The simulating
results of the velocity field of the fluid inside the container are
consistent with the above analysis (Figure S12, Supporting Infor-
mation). Similarly, when we placed the index finger under the
right side of the bottom of the container (Figure S10ii, Support-
ing Information), the convection was also formed asymmetrically
and the only difference was that the velocity and the lateral size
of the left convection in the container was larger than those of the
right convection. The simulating results are also consistent with
experimental results (Figure S12, Supporting Information).
We also explored the generation of complex convection pat-
terns by placing multiple hands or fingers at different positions
close to the container sidewalls. As shown in Figure 3e,whenwe
placed the hands and the finger on the left, right, and backside
of a 9 cm container, the convection was formed not only along
the lateral direction but also the longitudinal direction. With the
same distance of 5 mm between the energy source and the con-
tainer, the energy input from the hand and the finger are appar-
ently different, due to the larger surface area of the hand than that
of the finger. The velocity of the convection formed on the back-
side was smaller than that of the convections on the left side and
right side, which is attributed to the less energy input from the
finger. Moreover, more complex pattern of four circulated convec-
tions was also generated by hands (and fingers) in a 12 cm con-
tainer with a quartz plate inserted in the middle (Figure 3f). The
convection pattern formed symmetrically due to the symmetrical
energy input. By using just one finger as the energy source un-
der the center of the bottom surface of the container, the energy
input on the inserted quartz plate at the center of the container is
smaller than the energy input on the left and right sidewalls of the
container from the palm of the hands. The lateral sizes of both
convections formed in the middle were thus smaller than those
of the convections on the left and right. We also used the COM-
SOL to numerically calculate the velocity field and the results are
in good agreement with the experimental results (Figure 3e,f).
2.3. Dynamic Manipulation of Complex Convection Patterns Via
Hands
Besides the static generation of convections by hands, we also
designed the following experiments to achieve dynamic control
of the convections by hands and fingers. As shown in Figure 4a,
we first placed the hand on the right side of the container with
the distance of 5 mm. After the convection stabilized, we then
switched the hand to the left side of the container. At the begin-
ning the IR radiation was absorbed by the right side of the con-
tainer and the convection was stably formed on the right. After
switching the hand to the left, the IR radiation was absorbed by
the left side of the container. The previous temperature gradient
on the right gradually decreased and the new temperature gra-
dient established on the left. Consequently, the new convection
began to generate on the left while the lateral size and the veloc-
ity of the convection on the right side gradually decreased. The
right convection still existed for a few minutes, which was due to
the residual heat from the right sidewall. The response time in
the dynamic control of the convection, which is the time from the
positioning of the light source at the new position to the starting
of the formation of the new convection pattern, is ≈5s,whichis
similar to the response time of the static generation of the convec-
tion. The stable convection was formed on the left after placing
the hand on the left position for ≈6 min.
Similarly, dynamically control of the convections was also
achieved by using just one finger, as shown in Figure 4b.Wefirst
placed the index finger under the right side of the bottom surface
of the container with a distance of 2 cm. After the convection
stabilized, we then moved the index finger to the left side of
the bottom surface of the container (Figure 4b). The convection
patterns also showed dynamic change that corresponded to
the change of the finger position. When the finger was on the
right side, two asymmetric convection patterns formed in the
container. After moving the finger to the left side, the convection
pattern changed. As shown in the middle picture in Figure 4b,
before the system reached the steady state, there were three
convections coexisted in the container, including two convec-
tions newly generated on the left and one on the right due to
the residual heat. The convections became stable after placing
the index fingers on the left bottom for 6 min. We also used
COMSOL Multiphysics to simulate the change of the convection
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with the dynamic change of the hand/finger position. For such
dynamic changes of the convection, transient simulation was
used to investigate the intermediate state of the processes. As
shown in Figure 4a,b, both simulation results were in good
agreement with the results of the experiment.
The gradient temperature field induced by hands is the key
for both the static and the dynamic manipulation of convection
patterns. We thus compared the experimental thermal field and
the simulated thermal field for the above different forms of con-
vection manipulation. For the static generation of convections,
we compared the thermal field between the experiment and sim-
ulation by placing one hand at one side (Figure S13a, Support-
ing Information), placing two hands at the left and right sides
symmetrically and asymmetrically (Figure S13b, Supporting In-
formation), placing the index finger underneath the container
(Figure S13c, Supporting Information), and placing two hands
and the index finger at three different positions of the container
(Figure S13d,e, Supporting Information). For the dynamic con-
trol of convections, we compared the thermal field between the
experiment and transient simulation by placing the hand (Figure
S14a) and the index finger (Figure S14b, Supporting Informa-
tion) on the right side of the container and then switching to the
other side of the container. In both Figures S13 and S14 (Sup-
porting Information), the experimental and simulated thermal
fields show similar temperature distributions. The slight differ-
ences between the thermal fields observed in the experiment and
shown in the simulation might be due to the conditions we used
in the simulation. In the simulation, we simplified the model of
hand as a slab with the size of 4 cm ×4 cm and the thickness of
1 cm and the model of the index finger as a stick with the size of
1cm×1 cm and the length of 4 cm. We also simplified the en-
vironment condition with uniform temperature and without air
convection.
2.4. Demonstration of the Potential Applications of the Touchless
Hand-IR Driven Convection System
With the demonstration of static and dynamic control of the con-
vections by hands, we further explored the control of the motion
of a floating “boat” at the liquid surface inside a container. Al-
though the stable and clear convective patterns require placing
hand for 6 min, the respond of the convection is rapid. For the
demonstrations of driving “boat”, which are transient processes,
the hands can move at will and do not need to wait the stable
convection formed. We first demonstrated the static control of
the “boat” by placing one hand on the left side of the contain-
ers (Figure 5a,i). With such placement of the hand, single clock-
wise convection was formed on the left side of the container. With
the convection induced mass transport of fluid, the “boat” moved
from the left to the right inside the container (Movie S2, Support-
ing Information). When we placed the hand on the right of the
container the convection formed at the right side of the container
with counter clockwise motion and the “boat” moved back to the
left side (Figure 5a,ii).
We further explored the use of IR radiation from the finger to
control the motion of the floating “boat” on the DI water surface
at any direction through the control of convection (Figure 5b).
A container with size of 30 cm ×30 cm ×3 cm was used in
this demonstration. Such container is much larger than the con-
tainers used in the previous experiments, so the influence from
the sidewalls of the container can be avoided. For a proof-of-
concept demonstration, with the control of convection by finger,
the floating “boat” first moved forward from the starting point,
then turned left, and eventually arrived at the destination. As
shown in Figure 5c and Movie S3 (Supporting Information), the
movement of the floating “boat” followed the local fluid motion
of the convection generated by finger. We further used COMSOL
to simulate the temperature distribution of the liquid when a fin-
ger is placed 1 mm above the water surface (Figure S15a,Sup-
porting Information). The simulating result of the temperature
field proved that the absorption of IR radiation from the finger
by water played a major role to generate the convection that pro-
vides the driving force of the floating “boat”. Since the convection
was generated close to the finger, with the movement of the fin-
ger, the movement of floating “boat” can follow the change of the
finger position (Figure S15b, Supporting Information).
Besides the control of the movement of a floating “boat”,
we further demonstrated the potential applications of the hand-
controlled convection in sensing and separation systems. For
bio/chemical sensing systems, the convection has the potential
to shorten the sensing time. As a proof-of-concept demonstra-
tion, we ran an experiment for the rapid detection of chloroau-
ric acid aided by the hand-induced convection. We first prefilled
40 mL of DI water in the 9 cm-long container and then dropped
15 μL of chloroauric acid solution (6.8 mg mL−1) on the left side
of the container and 15 μL of ascorbic acid (3.5 mg mL−1)on
the right side of the container. The hands were placed on both
sides of the container and the distance between the hands and
the container was 5 mm. We also ran a control experiment, in
which the hands were not placed near the container. As shown
in Figure 5d, hand-induced convection could promote the trans-
portation of both the chloroauric acid and the ascorbic acid to
the middle of the container for the formation of the reddish gold
nanoparticles in 6 min. In comparison, the gold nanoparticles
cannot be observed in 6 min in the experiment without hands.
For the separation system, the convection could transport the
mixtures to the target for separation by the liquid flow. We ran the
following experiments to demonstrate the separation of the mag-
netic PS nanoparticles and the non-magnetic PS nanoparticles
that was also assisted by the hand-induced convection. First both
the initial non-magnetic PS solution of 8.0% w/v and magnetic
PS solution of 2.5% w/v were diluted with DI water to a concen-
tration of 1.0% w/v. We then dropped 15 μL of non-magnetic PS
solution and 15 μL of the magnetic PS solution simultaneously
on the left side of the 6 cm-long container that was prefilled with
27 mL DI water. The non-magnetic PS nanoparticles showed
the white color in the fluid and the magnetic PS nanoparticles
showed the reddish color in the fluid. The hand was placed on
the left side of the container and the magnet was placed on the
right side of the container. After the convection was generated (≈
6 min), the top layer of convection transported the mixed non-
magnetic and magnetic PS nanoparticles to the right side of the
container and the magnet could attract the magnetic PS nanopar-
ticles (Figure 5d). The bottom layer of the convection, which
flowed back to the right side of the container, thus only contained
the non-magnetic PS nanoparticles after the separation of the
magnetic PS nanoparticles. In such control experiment without
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Figure 5. Demonstrations of the potential applications of the touchless hand-IR driven convection system. a) The hand generated convection can induce
the movement of “boat” inside the container. The “boat” sails from one side to another side when the hand is placed close to the side wall of the container.
b) The localized convection can be generated near the “boat” using hand. c) The movement of the floating “boat” can be controlled with the movement
of finger dynamically to sail on the liquid surface to the desired destination. d) With the hand-generated convection, the chloroauric acid could react
with ascorbic acid in 6 min and form the gold nanoparticles. e) With the hand placed on the left side of the container, the mixed PS nanoparticles could
be transported to the right side of the container and be separated by the magnet. Without the hand-generated convection, the mixed PS nanoparticles
were randomly distributed in the fluid.
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the hand, the mixed non-magnetic and magnetic PS nanopar-
ticles could not be transported to the right end of the container
for the separation within the same time period (6 min).
The above demonstrations show that objects with different size
levels could be transported by the hand-IR controlled convection
system. Despite that the response time is a few seconds, the sys-
tem could still be leveraged in some possible applications. For
example, in the field of polymerase chain reaction (PCR), the tem-
perature difference-induced convection could reduce the ampli-
fication time of the PCR to <30 min, which was only 1/3 to 1/2
of the normal PCR amplification time.[48,49]
3. Discussion
In summary, we demonstratedthe use of hand, which is a nature
light source without the need of electricity, for the generation and
manipulation of the convection with comparable performance
to those reported in literature that were powered by engineering
light sources (Table S1, Supporting Information). The absorption
of the IR radiation emitted from hand results in the generation
of the temperature difference inside the fluid for the formation
of the convection. The experimental results and numerical cal-
culations demonstrated that both the velocity and the lateral size
of the convection increase with the increase of the depth of the
water and the decrease of the distance between the hands and
the container. Complex convections, with both symmetric and
asymmetric patterns, could be formed along various directions
by controlling the positions of the hands. Besides generating
the convection statically, the convection can also be dynamically
formed and controlled by changing of the positions of the hand
or finger. By taking the advantage of the dynamic control of
the localized convections, the sustainable flexible control of the
floating “boat” at the liquid-air surface was further demonstrated
in this study. The findings in this work show the feasibility of
controlling the fluidic convections at will by integrating hands
as sustainable and flexible IR energy sources into the system,
which may further expand the possible application scope of the
convection in low-cost sensing and separation systems.
4. Experimental Section
Generation and Observation of the Convection:The containers were
made of quartz with the same cross-section area of 3 cm ×3cmbut
with different lateral lengths (3 cm, 6 cm, and 9 cm). The PS nanospheres
with sulfate functional groups were purchased commercially from Invit-
rogen Trading (Shanghai) Co., Ltd. The average diameter of PS particles
is about 206 nm. The initial PS solution of 8.0% w/v was diluted with DI
water to a concentration of 1.0% w/v. Before the experiments, the 3 cm,
6 cm, and 9 cm containers were prefilled with 13 mL, 27 mL, and 40 mL
DI water, respectively. A planar LED light source (Juhua Vision Technology
Co., Ltd) with an illumination area of 13.8 cm ×7.3 cm was used as the
background light for the capture of convection images. The hands and the
fingers are placed on different sides of the containers to control the con-
vections. About 8 μL of the above diluted PS solution was slowly dropped
into the DI water for tracing the flow of the fluid. In order to isolate the IR
radiation from the other part of the hand, the hand was wrapped by alu-
minum foil with an emitting window of 4 cm ×4 cm, which could cover the
sidewall of the container. The temperature distribution of the DI water and
the containers was measured by an IR camera (FLIR T640, Teledyne FLIR
LLC). The high-speed camera (S-VIT LS, AOS Technologies AG) was used
to record the formation and final state of the convection with a recording
speed of 8 frames per second.
The Measurement of the Velocity and the Lateral Size of the Convection:
We first placed the hand next to the container. The stable convection was
formed after 6 min. Then one drop (≈8μL) of diluted PS solution was
slowly dropped into the liquid to trace the flow. A digital camera (Canon
EOS 7D) was used to record the formation of the convection with a record-
ing speed of 30 frames per second. In all experiments, we picked PS par-
ticles at one specific position (≈0.12 cm to the liquid/air surface and ≈
2 cm to the left side of the container) and measured the moving distance of
these PS particles in 20 s. The average velocity of the convection can thus
be calculated. The lateral size of the convection was obtained by measur-
ing the length of the convection patterns along the lateral direction.
Convection Controlled Movement of Floating “Boat” by IR Radiation Emit-
ted from Hand:In this demonstration, we used the hands and the fingers
as the IR energy sources to drive a “boat” floating at the surface of water.
The “boat” (15 mm ×8mm×5 mm) was made of polylactic acid (PLA)
by 3D printing. The static control of the boat was demonstrated by placing
one hand close to the side wall of the quartz container (9 cm ×3cm×
3 cm) that was prefilled with 80 mL DI water. The high-speed camera was
placed in front of the container to record the movement of the floating
“boat”. A polymethyl methacrylate (PMMA) container with size of 30 cm
×30 cm ×3 cm was used in the dynamic control experiment, and the float-
ing “boat” was initially placed in the center of the container. The finger was
placed close to the liquid-air interface without touching the water and the
floating “boat”. The moving of the “boat” was recorded by the digital cam-
era and the high-speed camera, which was placed on the side and the top
of the container, respectively. By manipulating the pointing direction and
the motion of the finger, the movement of the floating “boat” could be
controlled.
Supporting Information
Supporting Information is available from the Wiley Online Library or from
the author.
Acknowledgements
The authors want to thank Feiyu Zheng, Nicolas TIA TIONG FAT and Bon-
ing Shi for their help with the experiments. The authors acknowledge the
Center of Hydrogen Science of Shanghai Jiao Tong University, the Instru-
mental Analysis Center, the Shanghai Jiao Tong Grant and the Zhi-yuan
Innovative Research Center of Shanghai Jiao Tong University for their sup-
port. This work was supported by the following fundings: The National
Key R & D Project from Minister of Science and Technology of China
(SQ2022YFA1200152), Innovation Program of Shanghai Municipal Edu-
cation Commission (grant 2019-01-07-00-02-E00069), The National Nat-
ural Science Foundation of China (51973109 and 51873105), The China
Postdoctoral Science Foundation (2022M722045), The Zhi-Yuan Endowed
fund from Shanghai Jiao Tong University, Shanghai Jiao Tong University
Overseas Study Grants.
Conflict of Interest
The authors declare no conflict of interest.
Author contributions
H.Z. and Z.L. contributed equally to this work. T.D, W.S., S.A., H.Z., and
Z.L. designed research. H.Z., L.Z., Q.S., R.Y., W.C., Y.Z., M.J., and C.G. per-
formed fabrication, testing, and characterizations. All authors discussed
and analyzed the results and contributed to the writing of the paper.
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Data Availability Statement
The data that support the findings of this study are available from the cor-
responding author upon reasonable request.
Keywords
convection controlling system, human hand, infrared radiation
Received: September 23, 2023
Revised: November 7, 2023
Published online: January 18, 2024
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