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Supplementary Information: Conformal phased surfaces
for wireless powering of bioelectronic microdevices
Devansh R. Agrawal1, Yuji Tanabe2, Desen Weng1, Andrew Ma2, Stephanie
Hsu2, Song-Yan Liao3, Zhe Zhen3, Zi-Yi Zhu3, Chuanbowen Sun5, Zhenya
Dong5, Fengyuan Yang5, Hung Fat Tse3,4, Ada S. Y. Poon2, and John S. Ho1,5
1Singapore Institute for Neurotechnology,
National University of Singapore, Singapore
2Department of Electrical Engineering,
Stanford University, CA 94305, USA
3Cardiology Division, Department of Medicine,
University of Hong Kong, Hong Kong, China
4Hong Kong-Guangdong Joint Laboratory
on Stem Cell and Regenerative Medicine,
the University of Hong Kong, Hong Kong, China and
5Department of Electrical and Computer Engineering,
National University of Singapore, Singapore
1
Supplementary Information: Conformal phased surfaces
for wireless powering of bioelectronic microdevices
Devansh R. Agrawal1, Yuji Tanabe2, Desen Weng1, Andrew Ma2, Stephanie
Hsu2, Song-Yan Liao3, Zhe Zhen3, Zi-Yi Zhu3, Chuanbowen Sun5, Zhenya
Dong5, Fengyuan Yang5, Hung Fat Tse3,4, Ada S. Y. Poon2, and John S. Ho1,5
1Singapore Institute for Neurotechnology,
National University of Singapore, Singapore
2Department of Electrical Engineering,
Stanford University, CA 94305, USA
3Cardiology Division, Department of Medicine,
University of Hong Kong, Hong Kong, China
4Hong Kong-Guangdong Joint Laboratory
on Stem Cell and Regenerative Medicine,
the University of Hong Kong, Hong Kong, China and
5Department of Electrical and Computer Engineering,
National University of Singapore, Singapore
1
Supplementary Information: Conformal phased surfaces
for wireless powering of bioelectronic microdevices
Devansh R. Agrawal1, Yuji Tanabe2, Desen Weng1, Andrew Ma2, Stephanie
Hsu2, Song-Yan Liao3, Zhe Zhen3, Zi-Yi Zhu3, Chuanbowen Sun5, Zhenya
Dong5, Fengyuan Yang5, Hung Fat Tse3,4, Ada S. Y. Poon2, and John S. Ho1,5
1Singapore Institute for Neurotechnology,
National University of Singapore, Singapore
2Department of Electrical Engineering,
Stanford University, CA 94305, USA
3Cardiology Division, Department of Medicine,
University of Hong Kong, Hong Kong, China
4Hong Kong-Guangdong Joint Laboratory
on Stem Cell and Regenerative Medicine,
the University of Hong Kong, Hong Kong, China and
5Department of Electrical and Computer Engineering,
National University of Singapore, Singapore
1
Supplementary Information: Conformal phased surfaces
for wireless powering of bioelectronic microdevices
Devansh R. Agrawal1, Yuji Tanabe2, Desen Weng1, Andrew Ma2, Stephanie
Hsu2, Song-Yan Liao3, Zhe Zhen3, Zi-Yi Zhu3, Chuanbowen Sun5, Zhenya
Dong5, Fengyuan Yang5, Hung Fat Tse3,4, Ada S. Y. Poon2, and John S. Ho1,5
1Singapore Institute for Neurotechnology,
National University of Singapore, Singapore
2Department of Electrical Engineering,
Stanford University, CA 94305, USA
3Cardiology Division, Department of Medicine,
University of Hong Kong, Hong Kong, China
4Hong Kong-Guangdong Joint Laboratory
on Stem Cell and Regenerative Medicine,
the University of Hong Kong, Hong Kong, China and
5Department of Electrical and Computer Engineering,
National University of Singapore, Singapore
1
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
SUPPLEMENTARY INFORMATIONVOLUME: 1 | ARTICLE NUMBER: 0043
NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 1
CONTENTS
List of Figures 3
Additional Methods 4
Phased Surface Design 4
Theory 4
Passive Loading 5
Microdevice Construction 7
Power Measurement Apparatus 7
Construction 7
Calibration 8
Usage 8
Field Mapping 9
Numerical Methods 9
Thermal Monitoring Calculation 10
Imaging 10
2
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SUPPLEMENTARY INFORMATION
LIST OF FIGURES
S1 Structure of the phased surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
S2 Surface current distribution on the phased surface . . . . . . . . . . . . . . . . 12
S3 Circuit and layout schematic of the microdevice . . . . . . . . . . . . . . . . . 13
S4 Wireless powering measurement setup . . . . . . . . . . . . . . . . . . . . . . . . . . 14
S5 Field shaping in air and homogenous tissue . . . . . . . . . . . . . . . . . . . . . 15
S6 Effect of curvature on the field shape . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
S7 Performance during physiological motion . . . . . . . . . . . . . . . . . . . . . . . 17
S8 Printed Ag ink trace under mechanical deformation . . . . . . . . . . . . . . 18
S9 Effect of substrate thickness on performance . . . . . . . . . . . . . . . . . . . . 19
S10 Dependence of transferred power on orientation . . . . . . . . . . . . . . . . . . 20
S11 Specific absorption rates (SAR) distribution on neck and arm. . . . . . 21
S12 Surface thermal effects during wireless powering operation . . . . . . . . 22
S13 Wireless powering performance with bone structures . . . . . . . . . . . . . 23
S14 Spectral characteristics of the phased surface . . . . . . . . . . . . . . . . . . . . 24
S15 Wireless pacing in the right atrium at different power levels . . . . . . . 25
S16 Portable integration of the phased surface on rigid substrates . . . . . . 26
3
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SUPPLEMENTARY INFORMATION
ADDITIONAL METHODS
Phased Surface Design
Theory
The system is described by the scattering matrix formalism
b = Sa (1)
where a are the forward wave amplitudes and b the backward amplitudes. We
seek to maximize the fraction of power transferred to the last port labelled by
subscript L. The S matrix is symmetric as a consequence of reciprocity and can
be partitioned as bS
bL
=
ΣS κ
κT σL
aS
aL
. (2)
where κ is the coupling vector, σL the scalar reflection coefficient of the last port,
and ΣS the remaining submatrix in the partition. The load on the last port is
selected so that all power is absorbed aL = 0. We then have
bL = κTaS (3)
and
bS = ΣSaS. (4)
The power transferred to the last port is given by
PR = |bL|2 = |κTaS|2 (5)
The total power dissipated within the system is then
PT = |aS|2 − |bS|2 − |bL|2 = aHS (I − Σ†SΣS − κκH)aS (6)
The efficiency is given by
η =PR
PT
=|κTaS|2
aHS (I − ΣHS ΣS − κκH)aS
(7)
4
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NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 4
SUPPLEMENTARY INFORMATION
Maximizing η with respect to aS is a matched filtering problem. The solution is
given by
aS,opt = (I − ΣHS ΣS − κκH)−1κ∗. (8)
The corresponding currents in the ports are given by
i =a−b√
Z0
=(I − S)a√
Z0
(9)
where Z0 is the characteristic impedance of the port.
Passive Loading
The components that realize the optimal currents are determined by first solv-
ing for the corresponding unconstrained impedances, which may include active
ports, then using coordinate descent to optimize over the space of passive (strictly
reactive) elements.
The unconstrained impedances are solved by considering the impedance matrix
for the N -port structure. For simplicity, the receiver is neglected as it is weakly
coupled to the structure. The impedance matrix is given by
v = Zi. (10)
The source port is isolated by partitioning the impedance matrix asv0
vP
=
z0 ζT
ζ ZP
i0
iP
. (11)
Each remaining port, labeled 1 through N − 1, is terminated by a passive compo-
nent with impedance zL,n. This yields an additional set of equations vP = −ZLiP
where ZL is the diagonal matrix with entries zL,n. Incorporating this into Eq. (12),
we obtain the set of balance equationsv0
0
=
z0 ζT
ζ ZP + ZL
i0
iP
. (12)
5
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SUPPLEMENTARY INFORMATION
The lower row yields the expression
i0ζ + (ZP + ZL)iP = 0 (13)
from which the load impedances can be solved
zL,n = − i0iP,n
ζn +∑m
ZP,nm
iP,miP,n
. (14)
These impedances are unconstrained such that the real parts may be positive
(passive) or negative (active). Note that the input impedance of the structure can
be computed by taking the Schur complement of Eq. (12)
zin =v0i0
= z0 − ζT (ZP + ZL)−1ζ. (15)
Coordinate descent is used to select a locally optimal set of strictly reactive
(imaginary) impedances. We form the diagonal matrix
ZL =
ix1
. . .
ixN−1
(16)
consisting of only the imaginary part of the unconstrained solution Eq. (14). The
efficiency η corresponding to this choice of reactances can be found by solving for
the currents flowing through each source port
iP/i0 = −(ZP + ZL)−1ζ (17)
and substituting into Eq. (7) and (9). We define the following cost function
C(x1, . . . , xN−1) = η(x1, . . . , xN−1) + λL|z0 − zin(x1, . . . , xN−1)|2 (18)
where λL is a Lagrangian multiplier. The cost function is then minimized by
sequential coordinate descent using the reactances of the unconstrained solution
as the initial vector. The reactances were found to be all capacitive and are realized
using the closest available commercial components (Table S1).
6
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SUPPLEMENTARY INFORMATION
Microdevice Construction
The microdevice circuit consists of a two-stage voltage doubler with the helical
coil across the input terminals and a LED across the output terminals (Supplemen-
tary Fig. 3). The input capacitance of the circuit was designed to resonate with
the inductance of the coil (Advanced Design Systems, Keysight). The circuit was
implemented using commercial Schottky diodes and capacitors on a commercially-
produced printed circuit board (PCB; Interhorizon Corporation).
Construction of the implants requires the following components: (1) the PCB,
(2) 10 nF capacitor (Murata Electronics, GRM033R61A103KA01D), (3) 10 pF ca-
pacitor (Johanson Technology, 250R05L100GV4T), (4) Schottky diode (Skyworks
Solutions, SMS7630-061), (5) 36-gauge enameled wire (Belden, 8058), (6) solder
paste (Chip Quik, SMD291SNL10). Furthermore, it requires the following tools:
(1) microscope, (2) soldering iron and cartridge (JBC, C105-101), (3) tweezers, (4)
wire cutters. Ample solder is applied on the solder pads using the soldering iron
with a soldering tip. Surface mount components are then placed onto the PCB.
The solder is heated to 270 C to attach the components.
The device is encapsulated by pouring polydimethylsiloxane (PDMS) over a 3D-
printed mould (ABS filament). PDMS is prepared by mixing an elastomer base
(Sylgard, 3097366-1004) with a silicone elastomer curing agent (Sylgard, 3097358-
1004) at a 10:1 ratio for 15 minutes. The mixture is degassed in a vacuum chamber,
and then cured in an oven at 70 C overnight.
Power Measurement Apparatus
Construction
Construction of the measurement probe requires the following components:
(1) optical fiber (Thorlabs, M74L01), (2) photodetector/transimpedance ampli-
7
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SUPPLEMENTARY INFORMATION
fier (Thor Labs, PDA36A-EC), (3) 30-gauge Kynar wire (Pro-Power, 100-30-far;
100-30BK-far), (4) LED (Vishay, VLMB1500-GS08), and (5) the microdevice prior
to encapsulation (see Microdevice Construction).
The optical fiber is cut so that one end is bare fiber and the other is a FC/PC
connector. The bare end is passed partially into a clear thin plastic tube. The LED,
terminals attached to two 30-gauge wires, is inserted into the tube and secured
with a drop of transparent glue. The stability of the optical link between the LED
and the photodetector was tested for each probe by shaking the fiber as the LED
was powered by a DC power supply. The wires are cut to a minimal (< 2 mm)
length and soldered to the output terminal of the microdevice. Heat shrink tubing
is further applied around the LED to secure the junction. The FC/PC end of the
optical fiber is attached to a photodetector (Thorlabs, PDA36A-EC). The gain of
the transimpedance amplifier is set to 70 dB and is connected to an oscilloscope
(Tektronix, MDO3012) using a coaxial cable with BNC connectors.
Calibration
Prior to attachment of the helical coil, the input terminals of the microdevice
rectifier are connected to a network analyzer (Keysight, N9915A Field Fox). The
forward power of the analyzer is varied from −10 dBm to 5 dBm as the return
loss (calibrated for cable losses) and the voltage output of the photodetector is
recorded. The optical output, measured by the photodetector, as a function of the
power injected into the rectifier is then computed. This process is repeated for
each probe and at each operating frequency.
Usage
Following calibration, the input terminals of the microdevice rectifier are at-
tached to the helical coil. The entire device is encapsulated in silicone elastomer.
8
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SUPPLEMENTARY INFORMATION
The probe is inserted into a tissue volume and wirelessly powered in pulsed (50 ms
width, 50% duty cycle) by the phased surface in the configuration shown in Sup-
plementary Fig. 5. The amplitude of the optical pulse is recorded by the photode-
tector, enabling the received power to be inferred from the calibration curve.
Field Mapping
Field mapping experiments used a RF magnetic field probe (Detectus AB, RF-
R 0,3-3) mounted on a 3D positioning system (Detectus AB, RSE644). The signal
from the probe is monitored by a network analyzer (Rohde & Schwarz, ZVL Net-
work Analyzer) at each position by a computerized system. Step sizes of 2-mm
were used. Fields were generated in a tissue-mimicking cylindrical volume (vary-
ing diameters, constructed from 0.15-mm thick PVC sheets) filled with water by
a phased surface conformally attached to the cylinder wall at a 8-cm height above
the floor.
Numerical Methods
Field simulations used the finite-difference time-domain method (CST Mi-
crowave Studio). A computational human body model was used for SAR cal-
culations (adult male, ‘Gustav’, CST Microwave Studio). SAR is defined using
10-g averaging mass (IEEE/IEC 62704-1 method), consistent with the most re-
cent safety standards (IEEE C95.1-2005). Dielectric permittivity of tissues were
with modeled using ColeCole dispersion with values for different tissue types as
in Ref. [31]. A table of the relative permittivities used in this paper at 1.5 GHz is
given below.
9
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SUPPLEMENTARY INFORMATION
TABLE I. Dielectric properties of biological tissues at 1.5 GHz
Tissue type Relative permittivity Loss tangent Conductivity (S/m)
Air 1.0 0.0 0.0
Muscle 53.9 0.26 1.19
Heart 57.2 0.33 1.57
Skin 44.4 0.29 1.09
Bone (Cancellous) 19.76 0.30 0.5
Bone (Cortical) 11.98 0.23 0.23
Thermal Monitoring Calculation
For thermal experiments, the rise in temperature attributed to RF heating is
calculated as ∆T = (TPS,P−TSS,P )−(TPS,0−TSS,0), where TPS,P is the temperature
under the phased surface with output power of P watts and TSS,P is the average
surface temperature of a reference skin area not in contact with the phased surface.
TPS,0 and TSS,0 are the corresponding average temperatures when the output power
is set to P = 0, controlling for temperature change due to skin contact with room
temperature silicone.
Imaging
Computed tomography (256 Flash CT scanner, Siemens) was performed on pig
carcass (male, 70 kg) in the National Large Animals Research Facility (NLARF).
The scan parameters for the lower abdomen, upper abdomen, and neck configu-
rations were: (i) 120 kVp , 133 mAs, helical; (ii) 120 kVp, 174 mAs, helical; and
(iii) 120 kVp, 120 mAs, helical. The slice thickness was 0.5 mm in all scans.
10
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SUPPLEMENTARY INFORMATION
C4 C3 C2 C1 C4C3C2C1
MMCX
FIG. S1. Structure of the phased surface. All dimensions are to scale. Components
are listed in Table II. Scale bar, 1 cm.
TABLE II. Phased surface components
Component Description Company Part No
MMCX Connector Amphenol RF 908-22/01T
SMA-MMCX Cable Amphenol RF 245106-02-03.00
C1 Capacitor, 0.7 pF Venkel C0402HQN500-0R7BNP
C2 Capacitor, 0.2 pF Venkel C0402HQN500-0R2BNP
C3 Capacitor, 1.0 pF Venkel C0402HQN500-1R0BNP
C4 Capacitor, 0.7pF Venkel C0402HQN500-0R7BNP
11
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SUPPLEMENTARY INFORMATION
0 11
Surface Current (A/m)
a
b
FIG. S2. Surface current distribution on the phased surface. (a) Schematic of
phased surface over a non-planar tissue volume with radius-of-curvature R = 10 cm. (b)
Top-down projection of the instantaneous surface current vector distribution at 0.5 W
input. Scale bar, 1 cm.
12
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SUPPLEMENTARY INFORMATION
Top
Bo
tto
m
X1 X2
C2 C3
C1 C4
D1
D2
D3
D4
LED
X1
X2
C2
C3
C1
C4
D1
D2
LED
D3
D4a
b
c
3mm
1.5
mm
FIG. S3. Circuit and layout schematic of the microdevice. (a) Circuit diagram
of the microdevice consisting of a two-stage voltage doubler. (b) Top and (c) bottom
view of the component layout on the printed circuit board (PCB). X1 and X2 indicate
terminals of helical coil. The dimensions of the PCB are 3.0 mm × 1.5 mm. Components
are listed in Table III.
TABLE III. Microdevice components
Component Description Company Part No
C1, 2, 3 Capacitor, 10 pF Johanson Technology 250R05L100GV4T
C4 Capacitor, 10 nF Murata Electronics GRM033R61A103KA01D
D1, 2, 3, 4 Schottky Diode Skyworks Solutions SMS7630-060
LED Blue LED, 475 nm Vishay VLMB1500-GS08
X1-X2 Magnet Wire Belden 8058
13
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SUPPLEMENTARY INFORMATION
Signal
generatorPower
amplifier
Receiver
coil
Phased
surface
Rectifier
Photodetector/
transimpedance
amplifier
Optical fiber Oscilloscope
Coaxial
cable
LED
Microdevice
Cable
Coaxial
cable
Optical pow
er
density (
mW
/mm
2)
0
0.5
1
1.5
2
2.5
Received power (mW)
0 1 2 3
a b
FIG. S4. Wireless powering measurement setup. (a) A pulsed 1.6 GHz signal is
produced by a RF signal generator and a power amplifier. The signal is injected into
the phased surface at a 50 Ω port. The field in the body is shaped by the phased surface
and transfers energy to an implanted receiver coil. Radio-frequency power is converted
to an optical signal by the rectifier circuit, which is guided outside of the body by an
optical fiber. The optical signal is monitored by the photodetector on an oscilloscope.
(b) Optical output intensity as a function of the RF power received by the microdevice.
The power transferred to the microdevice can be inferred from the pulse amplitude.
14
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SUPPLEMENTARY INFORMATION
75
-25
-40 -400-30 0
60
0
Measurement Simulation
0
75
-25
-40 -400-30 060
0
0
Body
a
b
Free-space
yx
z
x (mm)
x (mm)
z (
mm
)z (
mm
)
Air Air
Saline Tissue
Lo
g m
ag
ne
tic f
ield
inte
nsity (
a.
u.)
z (
mm
)z (
mm
)
Min
Max
FIG. S5. Field shaping in air and homogenous tissue. (a) Measured and simulated
magnetic field intensity in air. (b) Measured and simulated magnetic field intensity
in saline and in homogenous muscle tissue, respectively. The radius of curvature is
R = 10 cm.
15
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SUPPLEMENTARY INFORMATION
SimulationMeasurement
0
1
-30 300-30
30
0
x (mm)
y (
mm
)
Flat R=10 cm R=8 cm R=5.75 cm
Sim
ula
tio
n
-50 500
x (mm)
1 1.5
Frequency (GHz)
c
d
|S
|1
1 (
dB
)M
ag
ne
tic f
ield
inte
nsity (
a.
u.)
0
1
0.5
Ma
gn
etic f
ield
am
plit
ud
e (
a.
u.)
2
-30
0
-10
-20
e
Me
asu
rem
en
t
Phased surfaceRigid
Conformal
Radius of
curvature R
d=4 cm
a
Curvature
Focal plane
Radius of curvature R (cm)
68101214161820
Pre
c/P
max
0
0.2
0.4
0.6
0.8
1
b
Rigid
Conformal
FIG. S6. Effect of curvature on the field shape. (a) Illustration of a conformal and
rigid phased surface on an interface with radius-of-curvature R. (b) Normalized received
power as a function of R. (c) Simulated and measured magnetic field amplitudes at the
z = 4 cm focal plane at varying curvatures. Measurements were performed in saline in
cylindrical polyethylene containers (150 µm thickness). (d) Intensity profile along the
along dashed line in (c). (e) Simulated and measured reflection coefficient (S11) at the
curved interfaces.
16
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SUPPLEMENTARY INFORMATION
On leg
On chest
Ch
an
ge
in
po
we
r (%
)
Sit Stand Sit Stand Sitd
0
0.01
0.02
-0.02
-0.01
Ch
an
ge
in
po
we
r (%
)
0
-20
-40
-10
-30
|S11| (d
B)
c
Stand Walk Stand Walk Stand
Stand Walk Stand Walk Stand
Stationary Motion Stationary Motion Stationary
a
Tegaderm
RF cable
0
0.01
0.02
-0.02
-0.01
Sit Stand
Stand Walk Stand
Sit
Subject 1
Subject 2
Subject 3
b
-8
-6
-4
-2
0
On body
Above body
> 4 cmCh
an
ge
in
po
we
r (%
)
e
Control
FIG. S7. Performance during physiological motion. (a) Photograph of phased
surface attached to body surface. (b) Physiological motions. (c) Reflection coefficient
S11 during stand-walk motion for three subjects. The phased surface is attached to the
leg while the control consists of the phased surface in air. (d) Change in power coupled
into the body during physiological motions for phased surface attached to the chest and
to the leg. (e) Change in power when the phased surface is removed from the body by
distance greater than 4 cm. Scale bars, 10 seconds.
17
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SUPPLEMENTARY INFORMATION
Crease
D
Trace
D (mm)
0102030405060708090100
Resis
tance (Ω
)
0
0.5
1
1.5
2
2.5
3
3.5
4
Flat Crease
FIG. S8. Printed Ag ink trace under mechanical deformation. Resistance of the
trace shown by the white line as the curvature is increased by reducing distance D. At
D = 0, the resistance is measured after sufficient force is applied to crease the substrate.
18
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SUPPLEMENTARY INFORMATION
0 2 4 6 8 10
Substrate thickness t (mm)
0
0.2
0.4
0.6
0.8
1
Pre
c/P
ma
x
Phased surface
Microdevice
t
Design
FIG. S9. Effect of substrate thickness on performance. Normalized received power
as a function of substrate thickness for the phased surface design. The thickness modu-
lates the proximity of the metal layer from tissue and can alter the coupling between the
rings. The phased surface was optimized for a thickness of 3 mm, such that the coupling
is inductive and the passive elements used to resonate the rings are all capacitive.
19
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NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 19
SUPPLEMENTARY INFORMATION
Azimuth angle
Altitude angle
0
π/2
π
3π/2
θ
0
π/2
π
3π/2
φ
1
0.5
0N
orm
aliz
ed r
eceiv
ed p
ow
er
0.5
1
a
b
θ
x
y
k^
E^
Local Incident field
φ
x
z
E^
k^
Local Incident field
1
0.5
0
0.5
1
Sim
Fit
Sim
Fit
Norm
aliz
ed r
eceiv
ed p
ow
er
FIG. S10. Dependence of transferred power on orientation. Received power as
the helical coil receiver is rotated in (a) azimuthal (xy) and (b) altitudinal (xz) plane in
the focal spot on the z = 50 mm plane (homogenous muscle tissue), normalized to peak
received power of fit function. Fit function: r(θ) = a sin2(θ + c) + b cos2(θ + c).
20
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 20
SUPPLEMENTARY INFORMATION
SA
R 1
0-g
(W
/kg)
10
0
Neck Arma
b
d
eTransmitter
Transmitter
10
00 70
5
SA
R 1
0-g
(W
/kg)
Position (mm)
10 20 30 40 50 60-100
5
10
Max. 10-g
SA
R (
W/k
g)
Arm Neck
c f
Safety Threshold
1
2
3
4
6
7
8
9
Arm
Neck
Abdomen
Abdomen
FIG. S11. Specific absorption rates (SAR) distribution on neck and arm.
(a, b) Neck and (d, e) arm SAR distribution in a computational human body model.
The phase surface is slightly removed from skin (<1 cm) to prevent intersection with
the computational domain. (c) SAR profile along white dashed line in (b) and (e).
Scale bars, 2 cm. Position of 0 mm is defined as skin surface. (f) Maximum SAR for
arm, neck, and abdomen (Fig. 3a) positions. The simulated output power is 0.8 W.
SAR is defined using 10-g averaging mass (IEEE/IEC 62704-1 method).
21
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 21
SUPPLEMENTARY INFORMATION
0 m
ins
1 m
in2
min
s3
min
s4
min
s
Arm
30 40
Temperature (oC)
2W
Neck
1.25W 0.8W
32 42
Temperature (oC)
2W 1.25W 0.8W No PowerNo Power
0
3
2W
1.25W
0.8W
0 4
ΔT
(oC
)
Time (mins)
a d
b c e f
0
3
0 4
2W
1.25W
0.8W
ΔT
(oC
)
Time (mins)
FIG. S12. Surface thermal effects during wireless powering operation. Infrared
images of skin surface at varying times and power levels on (a) neck and (d) forearm. (b,
e) Photograph of placement position. (c, f) Change in surface temperature from t = 0.
Error bars indicate standard deviation in temperature in the target circular region (black
circle) in (a) and (d). The diameter of the black circle is 4 cm. Scale bars, 1 cm.
22
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NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 22
SUPPLEMENTARY INFORMATION
1
1.1
0.9
No
rma
lize
d r
ece
ive
d p
ow
er
40-40 0
Δx (mm)
Phased surface width
-20 20
1
1.2
0.87010 4020 30 6050
Devic
e
Tis
sue S
urf
ace
-20
80
0
40
500-50
z (
mm
)
x (mm)
Late
ral
Bone
Device
Magnetic fie
ld a
mpltid
ue (
dB
A/m
)
15
-22
a
b
c
1
1.5
0.971 42 3 65 8 9 100
Vert
ical
Layere
d
Phased surface
Phased surface
Phased surface
Bone
Bone
Device
Device
d e f
Δz (mm) T (mm)
No occlusion
Δz
Δx
T
Lateral Vertical Layered
-20
80
0
40z (
mm
)
-20
80
0
40z (
mm
)
FIG. S13. Wireless powering performance with bone structures. (a, b) Magnetic
field amplitude as the position of a bone structure is varied along (a) the lateral direction
(x direction, at z = 25 mm depth) and (b) the vertical direction (z-axis at x = 0 mm).
The bone structure is an elliptical cylinder (10-mm major axis, 6-mm minor axis) in
otherwise homogenous muscle. (c) Magnetic field amplitude with curved layered bone
of varying thickness. (d–f) Received power as a function of bone position and thickness.
Supplementary Videos 1 and 2 show (a) and (b) animated. Since the dielectric contrast
between bone and muscle is one of the largest in the human body, other potential
obstructions (such as scar tissue) are expected to have less effect on wireless powering.
23
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NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 23
SUPPLEMENTARY INFORMATION
a
-40
-10
0
-30
-20
Frequency (GHz)
1.5 1.6 1.7
In air
On body
|S11| (d
B)
Bandwidth
60 MHz
50 μs 100 μs30 μs 200 μsb
FIG. S14. Spectral characteristics of the phased surface. (a) S11 of the phased
surface in air and on the surface of the body. The 10-dB bandwidth of the phased surface
over the body is 60 MHz. (b) Optical output of the microdevice during pulsed operation
of the wireless powering system with pulse widths 30 µs, 50 µs, 100 µs, and 200 µs. No
pulse distortion is observed above 200 µs. The bandwidth is limited by the microdevice
rather than the phased surface.
24
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 24
SUPPLEMENTARY INFORMATION
Heart
Rate
(bpm
)
60
80
100
120
140
Heart
Rate
(bpm
)
60
80
100
120
140
RA, 142 mW
RA, 108 mW
100 bps
120 bps
a
b
10 s 10 s
10 s 10 s
FIG. S15. Wireless pacing in the right atrium at different power levels. (a,b)
ECG recording and heart rate during 10-s stimulation and rest intervals with (a) pulse
width 10 ms and period 500 ms; and (b) pulse width 10 ms, period 600 ms, and peak
input power 1.5 times higher than (a).
25
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 25
SUPPLEMENTARY INFORMATION
y (
mm
)
-20
-10
0
10
20
0 10 20-10-20
x (mm)
Magnetic fie
ld inte
nsity (
a. u.)
0
1
0 10 20-10-20
x (mm)
30-30
0.2
0.4
0.6
0.8
Backa b
c d
Battery
Signal source
Magnetic field (A/m)
10
In contact with skin
FIG. S16. Portable integration of the phased surface on rigid substrates. (a)
Image of the front of the phased surface which should be in contact with the skin.
(b) Image of the back of the phased surface showing the battery and signal source
(Crystek). (c) Magnetic field amplitude at the z = 50 mm focal plane in saline. The
air-liquid interface is flat. (d) Magnetic field intensity profile (normalized to peak) along
the dotted line in (c). Full width at half maximum is 2.2 cm. The substrate material
is FR4. The maximum output power is 1 W and the operating frequency range is
1.623–1.678 GHz.
26
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NATURE BIOMEDICAL ENGINEERING | DOI: 10.1038/s41551-017-0043 | www.nature.com/natbiomedeng 26
SUPPLEMENTARY INFORMATION