Battery not included.pdf

8/10/2019 Battery not included.pdf

1/10

March/April 2013 631527-3342/13/$31.002013IEEE

Digital Object Identifier 10.1109/MMM.2012.2234640

Qi Xu, Zhaolong

Gao, Hao Wang,

Jiping He,

Zhi-Hong Mao,

and Mingui Sun

Qi Xu ([email protected]), Zhaolong Gao ([email protected]), and Jiping He ([email protected]) are with the Key Laboratory of ImageProcessing and Intelligent Control of Education Ministry, Department of Control Science and Engineering, Huazhong University of Science and

Technology, Wuhan 430074, China; Jiping He is also with the Department of Bioengineering, Arizona State University, Tempe 85284, USA.Hao Wang ([email protected]) and Zhi-Hong Mao ([email protected]) are with the Department of Electrical and Computer Engineering,

University of Pittsburgh, Pennsylvania. Mingui Sun ([email protected]) is with the Departments of Neurological Surgery,Electrical and Computer Engineering, and Bioengineering, University of Pittsburgh, Pennsylvania.

Implantable devices have become

increasingly popular in modern medi-

cine. These devices have a wide range

of applications, such as health moni-

toring, disease prevention, delivery of a

therapeutic regimen, and biomimetic prosthesis.

For example, electrical stimulation of nerve tissue

and recording of neural electrical activity are the basis

of emerging prostheses and treatments for spinal cord

injury, stroke, sensory deficits, and neurological disor-

ders [1][5]. Being able to record neural activity from

awake animals with observable behavior has greatly

advanced our understanding of the neural mechanisms

that mediate behavior. Conventional microelectrode

recording techniques typically require a percutane-

ous connector, which is associated with infection risks.

Generally, in order to obtain stable recordings, animals

must be trained to accept some degree of restraint (e.g.,

head fixation). Not only is the mobility of the animal

subject limited, but the results obtained under suchrestricted conditions may not reflect the full repertoire

of brain activity that occurs during natural behaviors

[2]. This issue can be addressed with implantable elec-

tronics to record neural activity and wirelessly transmit

this data through the skin to an external device. A wire-

less technique is then required to transmit both data

and power, connecting the external system and the

implanted devices.

There has been substantial previous work on

miniaturized, implantable electronic circuits that

record neural data and stimulate neuronal networks

during free movement in different animal mod-

els [3][7]. Many designs use radio-frequency (RF)transmission of raw or digitized physiological data

to a remote computer for storage and analysis. How-

ever, the high power consumption of continuous RF

transmission in these battery-powered systems lim-

its the duration of experiment to a few hours [3][4].

Date of publication: 6 March 2013

Batteries

Not Included

FOCUSED

ISSUEFEATURE

ARTVILLE


2/10

64 March/April 2013

Thus, providing power to medical implants has been

one of the most challenging problems in the system

design involving implantable devices. The traditional

approaches to this problem have been based on the

use of implantable batteries or lead wires through

the skin. Such transcutaneous wires are susceptible

to infection and reliability problems. For long-term

implantation, batteries present a problem due to their

size, mass, potentially toxic composition, and finite

lifetime. Even rechargeable batteries may have to be

replaced too often to be practical. Wireless power

transfer (WPT) has distinct advantages over these tra-ditional approaches in enabling implants to operate

for an essentially indefinite period of time without

the risks of battery replacement surgery or infection

from percutaneous wires and allowing the implants

to be drastically miniaturized because of the elimina-

tion of batteries [5][6].

The inductively coupled WPT has been well stud-

ied and utilized to deliver power to implantable

devices ranging typically from several microwatts

to a few tens of milliwatts [7]. This type of WPT sys-

tem requires two coils, a primary coil and a second-

ary coil, to deliver power wirelessly across the skin.

The electromagnetic field produced by the primary

coil penetrates the skin and induces a voltage across

the terminals of an implanted secondary coil, which

powers the implant. For high-power applications, such

as artificial hearts, the current inductive method has

many drawbacks, including limited energy transmis-

sion distance, requirement of internal and external coil

alignment, and low-energy transfer efficiency [7][8].

It has become clear that, without an effective solution

to the wireless transcutaneous power problem, many

promising implantable devices will continue to existonly in research laboratories. Therefore, a more effi-

cient power-transfer mechanism is highly desirable in

order to provide the required power in a reliable man-

ner with a sufficient capacity while satisfying the size

and weight constraints.

Recently, a novel technology called witricity

(wireless electricity) was developed, providing a new

approach to efficient mid-range WPT for implant-

able devices via strongly coupled magnetic resonance

[8][10]. A typical witricity system consists of fourcoils, namely, driver, primary, secondary, and load

coils, as shown in Figure 1. This system uses inductive

coupling between the driver and primary coils as well

as between the secondary and load coils. The primary

and secondary coils (also called resonators as these

coils operate on both their inductive and capacitive

properties) are separated by a distance usually several

times the geometric average of the coils diameters

[8]. The power-transfer mechanism of the witricity

has an attractive property in that two objects with the

same intrinsic resonant frequencies tend to exchange

energy efficiently, while two nonresonant objectsexchange little energy. This property is valuable in

medical implant applications since biological tissues

are generally nonresonant at the operating frequency

of the witricity. The WPT system based on witricity

can deliver a relatively large amount of power with

high efficiency at a mid-range distance. For example,

researchers at the Massachusetts Institute of Technol-

ogy (MIT) illuminated a 60 W light bulb wirelessly

from a power source more than seven feet away [8].

At this distance, WPT was achieved with an efficiency

of about 40%, approximately one million times higher

than that achieved by the traditional inductive cou-

pling method [8]. In addition, WPT using the witric-

ity approach has an advantage over the traditional

inductive coupling in that its bandwidth is fixed and

extremely narrow due to the resonant nature of the

system. This valuable property reduces interference

with the communication channel.

The coupled-mode theory (CMT) has been utilized

to analyze the interaction between resonators in the

witricity system. Detailed theoretical and numerical

analyses have shown that efficient mid-range wireless

energy exchange is feasible between two resonatorswith the same resonant frequency under the condition

of strong coupling [11][12].

In traditional inductively coupled WPT systems, it is

usually required that the primary and secondary coils

are reasonably aligned and their separation distances

are maintained [12][13]. However, in many applica-

tions, these requirements cannot be met. For example,

in medical research, animal models are often utilized

to evaluate effects of new therapeutic or prosthetic

devices. Particularly in the field of neuroengineer-

ing, e.g., neural prostheses and therapies, the rhesus

macaque monkey is a useful animal model as it allowsdecoding of recorded neural data during coordinated

Secondary

Coil

Driver

Coil

Primary

Coil

Load

Coil

MagneticResonance

Figure 1.Typical witricity system configuration consistingof four coils (driver, primary, secondary, and load coils).

Implantable devices have a widerange of applications, such as healthmonitoring, disease prevention,delivery of a therapeutic regimen, andbiomimetic prosthesis.


3/10

March/April 2013 65

limb movements similar to those of humans. In the

study of cortical neural prostheses, wireless devices

are often implanted within the brain of primates to

record a large amount of neural data. These data are

then decoded to control a computer or a prosthetic

device, such as an artificial limb. This study belongs to

a rapidly growing field of research on brain-computer

interface (BCI) with a potential to provide an effective

treatment for amputees or patients suffering from neu-rological injury and disease. Traditionally, transcuta-

neous wires were utilized for power and signal links.

Although important in conducting BCI research, this

method results in tremendous ethical concerns since

a monkey must be constrained within a primate chair

for an extended experimental period (months or years)

suffering from tremendous physical and emotional

stresses [5], [14].

Besides the use of a primate model, a vast major-

ity of the research on neural mechanisms of thera-

pies is currently conducted using the rodent model,

mostly rats. Several fully implantable neural stimula-tors have been developed for freely moving rats. An

implantable, battery-powered stimulator with bidi-

rectional wireless communication has been reported

for investigating neural mechanisms of spinal-cord

stimulation, facilitating motor function improvement

[15]. However, the limited battery capacity for use in

small animals does not support free-behaving exper-

iments for extended periods of time. Other systems

have been built with a transcutaneous wireless induc-

tive power source [16][17]. Although these systems

have replaced wires by fixed primary and secondary

coils, problems exist because attaching a backpack

containing an external battery and an electronic unit

to the animal is required. Such a backpack prevents

the animal from moving freely, and the system still

requires certain restraints of the animal. In order to

solve these problems, a fully implantable stimula-

tion system has been developed for small laboratory

rodents, including rats [18][19]. However, an impor-

tant disadvantage of this system is that the animal

must be placed in a special chamber of limited free-

space surrounded by coils. This setup excludes some

important behavioral tests and training that requirea large open space, e.g., elevated plus-maze tests and

treadmill training.

A significant power supply problem also exists

in implantable systems for use with humans. Lately,

rechargeable stimulators using inductively coupled

WPT techniques have been developed, such as the

Medtronic RestoreULTRA 37712, Boston Scien-

tific Precision Plus, and St. Jude Medical Eon Mini

Implantable Pulse Generator (IPG). The batteries of

these implantable devices can be recharged by exter-

nal wireless chargers. Unfortunately, the chargers are

often inconvenient for patients since losing power bythe implant is often risky [20]. Therefore, a new tech-

nology transmitting both signal and energy, requir-

ing no attachments to the body of humans or animals,

and allowing full freedom of motion within a space

of sufficient size represents a significant advance in

the field of medical implants.

If multiple devices are to be powered or charged

simultaneously by a single system, the transmitting

coil must cover a large area of operation and ensure a

uniform power delivery to devices regardless of their

positions [21]. A planar contactless battery chargingplatform using inductive coupling with transmitting

coil arrays has been demonstrated to generate a mag-

netic field of uniform amplitude over the charging

surface [22]. Moreover, multiple transmitting coils in

parallel have been used to reduce the loading effects

of multiple receivers [23]. In this article, a hexago-

nally packed transmitter (HPT) mat is designed and

utilized in a free-access witricity system for implant-

able devices. As shown in Figure 2, a resonance-

based power mat delivers transcutaneous power to

implanted devices when the subject (which is exem-

plified here as a rat) moves freely on top of the mat.

Note that the same mat can be put within the ceil-

ing (or within both the floor and the ceiling), which

is more suitable for humans in a living quarter. The

mat (or mats) creates a nearly uniformly distributed

magnetic field so that the implant within the body

can receive wireless power effectively regardless of

the location of the subject on the mat. We investigate

this new WPT system design using finite-element

(FE) simulation to visualize the field distribution of

CameraImplanted

Device

Power Mat

DataReceiverRe

Figure 2.A resonance-based mat powering implanteddevices within experimental rats moving freely on the mat.

The power-transfer mechanism ofthe witricity has an attractiveproperty in that two objects with thesame intrinsic resonant frequenciestend to exchange energy efficiently,

while two nonresonant objects

exchange little energy.


4/10

66 March/April 2013

the transmitter coil array. Since the resonant match

of the coils is critical in system performance, we study

the variation of resonant frequency resulting from

the moving implant by simulation and experimental

measurements. We expect our WPT system design

to spur new interests in not only medical implants,

but also nonmedical systems where mobile devices

and appliances can be powered or recharged auto-

matically anywhere within a certain space without

electric cables.

Theoretical Analysis of Mat-BasedWitricity System

The power-mat-based WPT system includes a driver-coil array, an HPT mat, a receiver coil, and a load coil.

Among these components, the HPT mat has a novel

design containing a single or an array of hexagonal

cells (dashed hexagons in Figure 3). Each cell is a

witricity transmitter that emits power either individ-

ually or synchronously with other cells. Decompos-

ing the HPT mat further, each hexagonal cell consists

of seven planar spiral coils (PSCs) constructed using

either wires or flexible printed circuits. The geom-

etry and the number of turns of the PSCs can be

designed flexibly.

The resonant energy exchange system with a single

transmitter and a single receiver has been analyzedusing the CMT [24]. In this article, we extend the same

concept and write CMT into a vector form to allow

the study of multiple transmitters. In CMT, the first

eigenmode is used to analyze a resonant system. The

approximation by the first eigenmode is quite accurate

under the condition that the system operates in strong

coupling [24]. Let the system consist of Ntransmitters

(indexed from 1 to N) and a single receiver (indexed by

N 1+ ). The differential equations describing the sys-

tem are given by

( ) ( ) ( ) ( ) ( ),

, ,

a t j a t j a t f t

i N1,

i i i im

m m i

N

m i0

1

1

f

~ lC= - + +

=

!=

+

o /

( ) ( ) ( ) ( )a t j a t j a t,N N L N N ii

N

i1 0 1 1 1

1

~ lC C= - - ++ + + +=

o / (1)

or in matrix form [as in (2) shown below], where ( ),a ti , ,i N1 f= , and ( )a tN 1+ are, respectively, the first

eigenmodes of the transmitter and receiver resona-

tors corresponding to the natural frequency 0~ ; iC s

are the intrinsic loss rates of resonators due to absorp-

tion and radiation, and LC represents the rate of

energy going into the load; iml s are pairwise coupling

coefficients between resonators; fi s are the inputs to

the transmitter resonators; and j is the imaginary

unit, i.e., j 12 =- . In our case, all fi s are the same, e.g.,

.f f f fN1 2 g= = = = Note that ai s are also known

as positive frequency components in terms of CMT.

Although ai (generally complex valued) does not rep-

resent a voltage or current directly, the energy con-

tained in each resonator can be represented as ai 2 ,

and the power output of the system is a2 L N2

1C + .

Using the CMT concept, the goal of obtaining a uni-

form power output becomes finding a uniform aN 1+

within the WPT space.We introduce the following matrix/vector notation

to express (2) in a more compact form:

.Aa a f= +vo v v (2*)

y

xx

Figure 3.Power mat structure with multiple HPT cells.Each cell consists of seven PSCs. This structure allowsnearly even power delivery to freely moving object(s) oneither (top or bottom) side of the power mat.

( )

( )

( )

( )

( )

( )

( )

( )

( )

( )

( )

( )

( )

( )

( )

a t

a t

a t

a t

j

j

j

j

j

j

j

j

j

j

j

j

j

j

j

j

a t

a t

a t

a t

f t

f t

f t

0, , ,

,

,

,N

N

N

N

N

N

N

N

N

N N

N

N

N N

N L

N

N

N

1

1

1

0 1

21

1

1 1

12

0 2

2

1 2

1

2

0

1

1 1

2 1

1

0 1

1

2

1

1

2

h h h

g

g

j

g

g

h h h h

~

l

l

l

l

~

l

l

l

l

~

l

l

l

l

~

C

C

C

C C

=

-

-

-

- -

+

+ + + +

+

+

+

+ +

o

o

o

o

R

T

SSSSSS

R

T

SSSSSS

R

T

SSSSSS

R

T

SSSSSS

V

X

WWWWWW

V

X

WWWWWW

V

X

WWWWWW

V

X

WWWWWW

(2)

Driver-CoilArray

(a) (b)

TransmitterMat

x

yz

x

0.5 cm 2.2 cm

42 cm

Figure 4.3-D model of the transmitter mat in FEsimulation. (a) A single HPT cell consisting of seven PSCswas driven by the driver-coil array. (b) Dimensions of PSC.


5/10

March/April 2013 67

If the WPT is driven by a sinusoidal input, e.g.,

( ) [ , , , ]f t Fe 1 1 0j t T0 f= ~v , the positive frequency com-

ponent has the form of ( ) aa t ej t0= ~v v in the steady

state. Substituting this form to (2*), we can solve

for ( )a tv

( ) ( )Ba t f t1=- +-vo v , (3)

where

B .

j

jj

j

jj

j

j

j

j

j

j, , ,

,

,

,N

N

N

N

N

N

N

N N

N

N

N N

N L

1

21

1

1 1

12

2

2

1 2

1

2

1

1 1

2 1

1

1

h h

g

g

j

g

g

h h

l

l

l

l

l

l

l

l

l

l

l

l

C

C

C

C C

=

-

-

-

- -+ + +

+

+

+

+

R

T

SSSS

SS

V

X

WWWW

WW

(a)

(b)

H_Field_Zcompab

9.1536e-001

8.5815e-001

8.0095e-001

7.4374e-001

6.8653e-001

6.2932e-001

5.7212e-001

5.1491e-001

4.5770e-001

4.0049e-001

3.4328e-001

2.8608e-001

2.2887e-001

1.7166e-001

1.1445e-001

5.7245e-002

3.6846e-005

H_Field_Zcompab

1.5602e-001

1.4627e-001

1.3652e-001

1.2677e-001

1.1702e-001

1.0727e-001

9.7523e-002

8.7773e-002

7.8024e-0026.8274e-002

5.8524e-002

3.9024e-002

2.9275e-002

1.9525e-002

9.7750e-003

4.8774e-002

2.5266e-005

0 500 1e+103 (mm)

0 500 1e+003 (mm)

Figure 5.Distribution of the z-component of the magnetic field in a plane (a) 16 cm and (b) 42 cm above the HPT mat at theresonant frequency of 29.8 MHz.


6/10

68 March/April 2013

Given iC , iml , and fi , we can compute ( )a ti ana-

lytically by (3). The CMT approach provides a pow-

erful analytical tool for the witricity based WPT

system. For example, it has been utilized to maxi-mize the efficiency of power transfer and investigate

the relay effect by inserting one or more resonators

between the transmitter and receiver [25]. Moreover,

we have studied the dynamics of the system involv-

ing an array of resonators using the CMT approach

[26]. Although the previous studies have shown that

CMT well characterizes the temporal behavior of

the system, it has clear limitations when the system

parameter changes. For example, when the receiving

resonator moves over the HPT mat, the coupling coef-

ficients ( , , )i N1,N i1 fl =+ change, and the variations

of both these coefficients and the system behavior aredifficult to be determined analytically. To study the

motion effect of the receiving resonator and answer

the critical question whether the receiver resonator

can harvest sufficient amount of power at different

locations over the HPT mat, we constructed a FE

model and performed numerical simulations.

Finite Element Simulation ofMat-Based Witricity SystemIn this section, we describe a simulation study on the

HPT mat using commercial FE software HFSS (Ansys

Corp., Pittsburgh, PA). For a clear illustration of the

design principle of the mat-based witricity system,

we simulated only the single HPT cell case consisting

of seven seven-turn PSCs, as limited by the compu-

tational complexity. This simulation does not cause a

loss of generality because the results of multiple HPTs

can be obtained simply by superposition of single cell

results. Figure 4 shows the three-dimensional (3-D)

model of the HPT mat utilized in the simulation, where

each PSC was 42 cm in outer diameter, 0.5 cm in con-

ductive trace width, and 2.2 cm in trace spacing. The

input power was set at 1 W. Particular attention was

paid to the analysis of the magnetic field generated

by the HPT mat at the resonant frequency in order to

evaluate the WPT performance. As stated previously,the goal of the HPT mat design was to obtain a nearly

uniform magnetic field within an extended region to

support WPT to moving targets, rather than optimiz-

ing power transfer eff iciency.

We excited the seven PSCs simultaneously using

a common RF power source. Energy was injected

into the driver coil array to maintain resonance in

the presence of losses and energy drawn from the

magnetic field by the receiver coil. Figure 5 shows

the z-component distribution of the magnetic field

16 cm and 42 cm, respectively, above the HPT mat

(i.e., the XY plane). Color indicates the magnitude ofthe magnetic field in the z-direction. It can be seen

that, at z =16 cm [Figure 5(a)], the magnitude of the

magnetic field was the highest (peak) at the center

of each coil, which formed an equilateral triangle,

and the lowest (valley) at the junction of three coils.

When the distance to the HPT mat was increased to

42 cm, a more uniform magnetic field distribution

was observed [Figure 5(b)]. In order to evaluate the

evenness of distribution quantitatively, the coeffi-

cient of variation (COV), which was defined as the

standard deviation of the field values divided by

the mean, was utilized. Thus, a smaller value of the

COV indicates a more uniform distribution. Figure 6

shows the COVs of the magnetic field in the z-direc-

tion above the HPT mat at distances from 10 cm to

70 cm. It can be observed that the COV achieved a

value less than 8% when the distance was larger than

the size of the transmitter coil.

Although the receiver resonant coil can have an

arbitrary size and shape, for simplicity we utilized a

receiver coil that was identical to the transmitter PSCs

in our simulation. The receiver coil was placed at dif-

ferent locations within a planer region 42 cm above theHPT mat. The input power and resonant frequencies of

the mat were set at 1 W and 29.6 MHz, respectively. As

in the previous case, all seven transmitter PSCs were

excited simultaneously. Figure 7 shows the field dis-

tribution at z =42 cm at two positions off [Figure 7(a)]

and at the center of the HPT mat [Figure 7(b)]. It can

be observed that the receiver PSC distorted the mag-

netic field slightly in both cases. This loading effect

is expected because of the interactions between the

transmitter and receiver resonators [26].

The witricity-based WPT system achieves the best

performance if the intrinsic frequencies of the trans-mitters and receivers are identical and the natural

80

90

100

110

20

30

0

10

60

70

40

50

5 10 15 20 25 30 35 40 45 50 55 60 65

Distance (cm)

COV(%)

Figure 6.Variation in COV of vertical field distribution

as a function of distance above the HPT mat at the resonantfrequency of 29.8 MHz.

The geometry and the number of turnsof the PSCs can be designed flexibly.


7/10

March/April 2013 69

frequency of the coupled system equals the operat-

ing frequency of the excitation signal [24]. When

the operating and natural frequencies deviate from

each other due to certain disturbances, a signifi-

cant reduction in power transfer performance may

occur. To study this potential problem, we conducted

FE simulation to observe the change of the natural

Figure 7.Magnetic field distributions on the plane of the receiver coil (42 cm above the HPT mat) at the resonant frequencyof 29.6 MHz. (a) The receiver coil is off the center of the mat. (b) The receiver coil is at the center of the mat.

(a)

(b)

H_Field_Zcompab

2.3455e+000

2.1127e+000

1.8800e+000

1.6472e+000

1.4145e+000

1.1817e+000

9.4894e-001

7.1618e-001

4.8342e-001

2.5067e-001

1.7908e-002-2.1485e-001

-4.4761e-001

-6.8037e-001

-9.1312e-001

-1.1459e+000

-1.3786e+000

H_Field_Zcompab

2.3863e+000

2.1697e+000

1.9530e+000

1.7364e+000

1.5197e+000

1.3031e+000

1.0865e+000

8.6983e-001

6.5319e-001

4.3655e-001

2.1991e-002

-2.1336e-001

-4.3000e-001

-6.4664e-001

-8.6328e+000

3.2741e-001

-1.0799e+000

Due to its attractive physicalproperties, the witricity enableshigher efficiency and longer operatingdistance for WPT than the traditionalinductive coupling methods


8/10

70 March/April 2013

frequency of the coupled system while the receiver

coil was moved in the XY plane 42 cm above the

HPT mat. The locations of the receiver coil, repre-

sented by its centers projected to the HPT cell, are

shown in Figure 8(a). At each of the 21 locations,the natural frequency of the coupled system was

computed using the HFSS software. Our results

[Figure 8(b)] showed that natural frequencies of

the system with the receiver coil at these locations

differed only slightly. The standard deviation was

0.001 MHz, only 0.003% of the mean 29.581 MHz,

indicating a stable performance in energy transfer

despite the motion of the receiver.

Experiment and ResultsTo validate the simulation results, a prototype of a

single-cell, mat-based witricity system was physically

constructed as shown in Figure 9. The single HPT cell

in this system consisted of seven circular PSCs. Each

PSC was made of a printed circuit board (PCB) in a

shape of equilateral hexagon of 13.2 cm in outer diam-

eter, 2.9 mm in conductive trace width, and 1.6 mm in

trace spacing. The resonant frequencies and Q factor

of all PSCs were measured to be 29.453 ! 0.072 MHz

and approximately 100, respectively. In this witricitysystem, a novel design of the receiver resonator was

Figure 8.The natural frequency of the system is computed

to study frequency detuning as the receiver moves on theXY plane 42 cm above the HPT mat. (a) Each dot denotesa projected location of the receiver coil above the mat. (b)Computed natural frequencies at the 21 locations in (a).

(a)

y

x

y

x

(b)

-300

5

10

15

20

25

30

35

-30-20-10

010

2030

-20-10

010X(cm)

f0(M

Hz)

Y(cm)

2030

-30

-20-10

010

0-20-

010(c (c

m20

Figure 9.Experimental setup of the mat-based witricitysystem.

Transmitter Mat Load Coil Receiver Coilransmitter Mat Load Coil Receiver Coil

Figure 10.Measured induced peak-to-peak voltage V inthe load coil moving in the proximity of the center PSC.

5

-3-3

-5-5-7

-1-1

53

3

11

7

1.5

2

2.5

3

3.5

7

0.5

1.5

1

2

2.5

3

3.5

4

0

-7

Y(cm)X(

cm)

V

oltage

(V)

5

-3-3

-5-7

-1-1

53

11

7

(cm)cm

)

Figure 11.Changes in the mean resonant frequenciesmeasured in parallel to the XY plane as a function ofheight above the transmitter mat.

26.6

26.7

26.8

26.927.0

26.1

26.0

26.4

26.5

26.2

26.3

0 5 10 15 20 25

Distance (cm)

MeanResonantFrequency(MHz)


9/10


10/10

72 March/April 2013

is useful in not only implantable devices for small ani-

mals, but also a variety of other medical applications.

As described previously, it is straightforward to extend

the concept by placing an HPT array within the ceiling

or floor of a room to power implants within primate

animals or humans. By including a small battery within

the implant, the operation of the implant will not stop

as long as the subject returns to the room for a certain

period of time so that the battery can be recharged, andthere is no limit on the activity within the room. In a

broader point of view, the approach presented in this

paper is expected to be applicable in a variety of trans-

portation, consumer, and industrial systems since this

approach supports WPT to a moving target, such as a

vehicle or robot.

AcknowledgmentThe authors would like to thank Yicheng Bai and Jun-

hua Wang for their help in the experimental setup.

This study has been supported by the Natural Sci-

ence Foundation of China (grant numbers 60874035

and 30901716), and in part by the National Institutes of

Health of USA (grant number U01HL091736) and the

Fundamental Research Funds for the Central Universi-

ties of China (grant number HUST:2012QN085).

References[1] J. He, C. Ma, and R. Herman, Engineering neural interfaces for

rehabilitation of lower limb function in spinal cord, in Proc. IEEE,

2008, vol. 96, no. 7, pp.11521166.

[2] B. P. Olson, J. Si, J. Hu, and J. He, Closed-loop cortical control of

direction using support vector machines,IEEE Trans. Neural Syst.

Rehab. Eng., vol. 13, no. 1, pp. 7280, 2005.

[3] J. Mavoori, A. Jackson, C. Diorio, and E. Fetz, An autonomousimplantable computer for neural recording and stimulation in unre-

strained primates, J. Neurosci. Methods, vol. 148, no. 1, pp. 7177,

2005.

[4] C. A. Chestek, V. Gilja, P. Nuyujukian, R. J. Kier, F. Solzbacher, S.

I. Ryu, R. R. Harrison, and K. V. Shenoy, Hermes C: Low-power

wireless neural recording system for freely moving primates,

IEEE Trans. Neural Syst. Rehab. Eng., vol. 17, no. 4, pp. 330338,

2009.

[5] R. R. Harrison, R. J. Kier, C. A. Chestek, V. Gilja, P. Nuyujukian, S.

Ryu, B. Greger, F. Solzbacher, and K. V. Shenoy, Wireless neural

recording with single low-power integrated circuit, IEEE Trans.

Neural Syst. Rehab. Eng., vol. 17, no. 4, pp. 322329, 2009.

[6] S. K. Arfin, M. A. Long, M. S. Fee, and R. Sarpeshkar, Wireless

neural stimulation in freely behaving small animals, J. Neuro-

physiol., vol. 102, no. 1, pp. 598605, 2009.

[7] A. K. RamRakhyani, S. Mirabbasi, and M. Chiao, Design and

optimization of resonance-based efficient wireless power deliv-

ery systems for biomedical implants, IEEE Trans. Biomed. Circuits

Syst., vol. 5, no. 1, pp. 4863, 2011.

[8] A. Kurs, A. Karalis, R. Moffatt, J. D. Joannopoulos, P. Fisher, and M.

Soljacic, Wireless power transfer via strongly coupled magnetic

resonances, Sci. Exp., vol. 317, no. 5834, pp. 8386, 2007.

[9] X. Luo, S. Niu, S. L. Ho, and W. N. Fu, A design method of magnet-

ically resonating wireless power delivery systems for bio-implant-

able devices, IEEE Trans. Magn., vol. 47, no. 10, pp. 38333836, 2011.

[10] B. L. Cannon, J. F. Hoburg, D. D. Stancil, and S. C. Goldstein,

Magnetic resonant coupling as a potential means for wirelesspower transfer to multiple small receivers, IEEE Trans. Power Elec-

tron., vol. 22, no. 4, pp. 18191825, 2009.

[11] J. Wang, S. L. Ho, W. N. Fu, C. T. Kit, and M. Sun, Finite-element

analysis and corresponding experiments of resonant energy trans-

fer for wireless transmission devices, IEEE Trans. Magn., vol. 47,

no. 5, pp. 10741077, 2011.

[12] N. Yin, G. Xu, Q. Yang, J. Zhao, X. Yang, J. Jin, W. Fu, and M. Sun,

Analysis of wireless energy transmission for implantable device

based on coupled magnet ic resonance, IEEE Trans. Magn., vol. 48,

no. 2, pp. 723726, 2012.

[13] T. D. Dissanayake, A. P. Hu, S. Malpas, L. Bennet, A. Taberner, L.

Booth, and D. Budgett, Experimental study of a TET system for

implantable biomedical devices, IEEE Trans. Biomed. Circuits Syst.,

vol. 3, no. 6, pp. 370378, 2009.

[14] A. B. Schwartz, Cortical neural prosthetics, in Proc. Annu. Re-view Neuroscience, 2004, vol. 27, pp. 487507.

[15] H. Zhou, Q. Xu, J. He, H. Ren, H. Zhou, and K. Zheng, A fully

implanted programmable stimulator based on wireless commu-

nication for epidural spinal cord stimulation in rats, J. Neurosci.

Methods, vol. 204, no. 2, pp. 341348, 2012.

[16] B. Smith, Z. Tang, M. W. Johnson, S. Pourmehdi, M. M. Gazdik,

J. R. Buckett, and P. H. Peckham, An external ly powered, multi-

channel, implantable stimulator-telemeter for control of paralyzed

muscle, IEEE Trans. Biomed. Eng., vol. 45, no. 4, pp. 463475, 1998.

[17] R. G. Dennis, D. E. Dow, and J. A. Faulkner, An implantable

device for stimulation of denervated muscles in rats, Med. Eng.

Phys., vol. 25, no. 3, pp. 239253, 2003.

[18] R. E. Millard and R. K. Shepherd, A fully implantable stimulator

for use in small laboratory animals, J. Neurosci. Methods, vol. 166,

no. 2, pp. 168177, 2007.

[19] D. W. J. Perry, D. B. Grayden, R. K. Shepherd, and J. B. Fallon, A

fully implantable rodent neural Stimulator,J. Neural Eng., vol. 9,

no. 1, pp. 18, 2012.

[20] C. Hsu, S. Tseng, Y. Hsieh, and C. Wang, One-time-implantable

spinal cord stimulation system prototype, IEEE Trans. Biomed. Cir-

cuits Syst., vol. 5, no. 5, pp. 490498, 2011.

[21] J. J. Casanova, Z. N. Low, and J. Lin, A loosely coupled planar

wireless power system for multiple receivers, IEEE Trans. Ind.

Electron., vol. 56, no. 8, pp. 30603068, 2009.

[22] W. X. Zhong, X. Liu, and S. Y. R. Hui, A novel single-layer wind-

ing array and receiver coil structure for contactless battery charg-

ing systems with free-positioning and localized charging features,

IEEE Trans. Ind. Electron., vol. 58, no. 9, pp. 41364144, 2011.

[23] J. Achterberg, E. A. Lomonova, and J. Boeij, Coil array structures

compared for contactless battery charging platform,IEEE Trans.

Magn., vol. 44, no. 5, pp. 617622, 2008.

[24] H. A. Haus, Waves and Fields in Optoelectronics. Englewood Cliffs,

NJ: Prentice-Hall, 1984.

[25] F. Zhang, S. A. Hackworth, W. Fu, C. Li, Z. Mao, and M. Sun,

Relay effect of wireless power transfer using strongly coupled

magnetic resonances, IEEE Trans. Magn., vol. 47, no. 5, pp. 1478

1481, 2011.

[26] F. Zhang, J. Liu, Z. Mao, and M. Sun, Mid-range wireless power

transfer and its application to body sensor networks, Open J. Appl.

Sci., vol. 2, no. 1, pp. 3546, 2012.

[27] Q. Xu, M. Sun, H. Wang, Z. Mao, and J. He, A witricity device

for powering biomedical implants in a free-positioning manner,

China Patent 201 210 104 018.7, 2012.

The witricity-based WPT systemachieves the best performance ifthe intrinsic frequencies of thetransmitters and receivers areidentical and the natural frequencyof the coupled system equals the

operating frequency of theexcitation signal.

Battery not included.pdf

Documents

Transcript of Battery not included.pdf