Impact of an Aortic Valve Implant on Body Surface 

UWB Propagation: A Preliminary Study

Wen-Bin Yang, Kamran Sayrafian-Pour, John 

Hagedorn, Judith Terrill 

Information Technology Laboratory 

National Institute of Standards and Technology 

Gaithersburg, Maryland, USA 

{wyang, ksayrafian, hagedorn, Judith.terrill}@nist.gov 

Kamya Yekeh Yazdandoost, Attaphongse 

Taparugssanagorn, Matti Hämäläinen, Jari Iinatti 

Center for Wireless Communications 

University of Oulu, Finland 

yazdandoost@ieee.org, attaphongset@gmail.com, 

{matti.hamalainen, jari.iinatti}@ee.oulu.fi

Abstract — Efficient transceiver design in body area networks 

requires in-depth understanding of the propagation channel 

which in this case involves the human body. Several studies have 

been done to characterize RF propagation on the body surface 

and determine the parameters of an appropriate model. 

However, the possible effect of an already existing medical 

implant on body surface propagation has not been considered 

until during a recent measurement experiment. There it was 

discovered that an aortic implant may have an impact on Ultra 

Wide-Band (UWB) propagation between wearable nodes that are 

in the vicinity of the implant location. In this paper, we use a 3D 

immersive visualization environment to study and observe the 

impact of an aortic implant on body surface propagation. 

Specifically, we focus on the UWB impulse response of the 

channel between nodes located around the upper body. The 

difference in the obtained impulse responses (for scenarios with 

and without the implant) both in measurement and simulation 

points to the possible impact that such medical implants could 

have on body surface RF propagation. 

Keywords – Body Area Networks; Ultra-WideBand (UWB); 

Immersive visualization system; Aortic Valve Implant 

I. INTRODUCTION

Recent advances in microelectronics indicate that the 

technology to achieve ultra-small and ultra low power 

wearable and implantable devices is mostly available. 

Communication protocol between such radio-enabled devices 

constitutes a Body Area Network (BAN). Although, there are 

still numerous challenges in vast commercialization of such 

products, BAN is poised to be a promising interdisciplinary 

technology with novel uses in pervasive health information 

technology. For example, RF-enabled wearable sensor nodes 

offer an attractive set of applications, among which we can 

point to electrocardiogram (ECG) and various other medical 

monitoring applications such as temperature, respiration, heart 

rate, blood pressure and pH [4]. 

Due to the medical nature of these applications, successful 

adoption of this technology heavily depends on the existence 

of a global standard for its radio communication. Although 

factors such as interference and co-existence with other 

wireless technologies are extremely important in the choice 

for BAN operating frequency, worldwide availability (i.e. 

partially) and also the opportunity to have small-sized 

antennas make UWB a favorable candidate for wearable BAN 

applications. Understanding the propagation channel which in 

this case involves the human body is a major requirement in 

order to design efficient BAN transceivers. For the case of 

wearable sensors, physical channel measurements have been 

the focus of several research studies in recent years. The 

results of these studies specify the parameters of an 

appropriate statistical channel model [8, 9] for wearable 

nodes. However, none of these studies consider the possible 

effect of an existing medical implant (such as a metallic heart 

valve) on body surface propagation. 

During a recent measurement experiment at the Center for 

Wireless Communications at the University of Oulu, Finland, 

it was discovered that an aortic implant may have an impact 

on Ultra Wide-Band (UWB) propagation between wearable 

nodes that are in the vicinity of the implant location [5, 6]. The 

difference between impulse responses of two UWB nodes 

located around the upper body for the case of subjects with 

and without an aortic valve was significantly observable. This 

result prompted us to further study the possible impact of such 

medical implants on body surface propagation. To the best of 

our knowledge, this is the first study of its kind to consider 

this issue. 

The complexity of the media and other practical issues in 

performing physical measurements (e.g. finding volunteers 

with implants and various safety issues) only allow for a very 

limited number of experiments. Therefore, we are using a 

sophisticated 3D immersive visualization platform to emulate 

the physical experiment and obtain further data that would 

have been normally very difficult or impossible. This 

innovative platform easily allows us to vary all relevant 

parameters (e.g. implant location, shape, size, material) and 

investigate the impact of each one of them on the channel 

response. 

In the following sections, we briefly describe the results of 

the experiment and simulation and how they both point to the 

possible effect of the aortic implant on the observed channel 

impulse response. Here, we are only reporting preliminary 

results of this study. The authors plan to continue this work to 
extensively investigate the impact of medical implants on 

body surface propagation. The rest of this paper is as follows. 

Section 2 will describe the measurement setup and its results. 

The immersive 3D platform that has been used for our 

simulations is discussed in Section 3. Then, description of the 

simulated scenarios and results are provided in Section 4. 

Finally concluding remarks and future plans are expressed in 

Section 5. 

II. MEASUREMENT SETUP & RESULTS 

The channel measurement system consisted of an HP 

Agilent 1 8720ES Vector Network Analyzer (VNA), P200 

BroadSpecTM antennas [10], 5-m long SUCOFLEX® RF cables 

with 7.96 dB loss and a control computer with Lab-VIEWTM 7 

software. The VNA is operated in a transfer function 

measurement mode, where port 1 and port 2 are the 

transmitting and the receiving port, respectively, as seen in 

Figure 1. This corresponds to a S21 parameter measurement 

set-up, where the device under test is the radio channel. The 

BroadSpecTM antennas are azimuthally omni-directional with 

the antenna radiation patterns as shown in [12]. The sweep 

time of the network analyzer depends on the number of 

frequency points within the sweep band, being automatically 

adjusted by the VNA. The frequency band used in the 

measurements is from 3.1 GHz to 10 GHz covering almost the 

whole frequency band of the UWB mask allotted by the FCC 

(i.e. 3.1-10.6 GHz) [6]. Therefore, the bandwidth (B) of the 

probe signal is 6.9 GHz. The maximum number of frequency 

points per sweep M is 1601. This leads to a maximum 

detectable channel delay (τmax) of 231 ns. The measurements 

were carried out in the frequency domain but transferred to the 

time domain at the VNA, which gives the impulse responses of 

the channel as outputs for further analysis. 

Figure 1. Measurement setup using the Vector Network Analyzer 

The UWB channel measurement experiments were 

conducted in an anechoic chamber to minimize the effect of the 

environment when measuring the channel around the body. 

The measurements were taken at the chest level (around the 

body) as illustrated in Figure 2. The Rx antenna (the rectangle 

 1 Identification of the Agilent VNA does not imply recommendation or 

endorsement by the National Institute of Standards and Technology.

in the figure) is fixed at the middle front of the torso and the Tx 

antenna (the circles in the figure) is placed at various positions 

at separations of about 10 cm. Further details about the 

experiments can be found in [5, 6]. 

10 cm

The transmitter on front -side body

The receiver

The transmitter on back -side body

1

2

8

7

6 3

5 4

positions

10 cm

The transmitter on front -side body

The receiver

The transmitter on back -side body

1

2

8

7

6 3

5 4

positions

Figure 2. Antenna positions around the chest 

The results were obtained for 3 men; one of them has a 

titanium alloy aortic valve implant made by Medtronic 2

 as 

shown in Figure 3. 

Figure 3. Medtronic Hall Aortic Heart Valve 

0 5 10 15 20 -110

-105

-100

-95

-90

-85

-80

Delay [ns]

Channel Impulse Response [dB]

with implant

no implant

Figure 4. Average channel impulse response for position 2 

 2 Medtronic Hall Aortic Heart Valve is a product of Medtronic Inc. 

Identification of this product does not imply recommendation or endorsement 

by the National Institute of Standards and Technology.
One hundred realizations of the measured channel impulse 

responses were averaged for each position. Figure 4 shows that 

the average channel impulse response (for position 2) of the 

subject with an aortic implant in comparison with the subjects 

with no implants. As observed, there is a clear difference 

between the magnitudes of the channel responses in these two 

scenarios. In this paper, results for the other positions have 

been omitted for brevity. Although, the valve implant is located 

inside the heart, the metallic material used in its construction 

(i.e. titanium) seems to be making an impact on RF 

propagation along the chest surface. To better understand this 

impact, we have decided to emulate this experiment in a 3D 

virtual reality platform and see if similar results are observed. 

This simulation platform is briefly descried in the next section. 

III. A 3D IMMERSSIVE SYSTEM FOR WEARABLE &

IMPLANTABLE MEDICAL SENSORS 

Figure 5 shows the block diagram of our simulation 

environment. As observed, the main components of this system 

include: a three-dimensional human body model, the 

propagation engine which is a three-dimensional full-wave 

electromagnetic field simulator (i.e. HFSS 3 ) and the 3D 

immersive & visualization platform. The 3D human body 

model includes frequency dependent dielectric properties of 

300+ parts in a male human body. These properties are also 

user-definable if custom changes or modifications are desired. 

The human body model has a resolution of 2 mm. The HFSS 

propagation engine enables us to compute a variety of different 

electromagnetic quantities such as the magnitude of electric 

and magnetic fields Poynting vectors, and Specific Absorption 

Rate (SAR). 

The 3D immersive platform as shown in Figure 6 includes 

several components: three orthogonal screens that provide the 

visual display, the motion tracked stereoscopic glasses, and the 

hand-held motion tracked input device. The screens are large 

projection video displays that are placed edge-to-edge in a 

corner configuration. These three screens are used to display a 

single three-dimensional stereo scene. The scene is updated 

based on the position of the user as determined by the motion 

tracker. This allows the system to present to the user a 3D 

virtual world within which the user can move and interact with 

the virtual objects. The main interaction device is a hand-held 

three button motion-tracked wand with a joystick. A user in 

this virtual environment can look at data 

representations at any scale and position, move through data, 

change orientation, and control the elements of the virtual 

world using a variety of interaction techniques including 

measurement and analysis [1]. All of these 

capabilities are extremely useful when studying RF 

propagation for wearable or implantable medical sensors [7, 

11]. 

Input parameters to the 3D simulation system include: a 

wearable/implantable antenna and all its relevant attributes (i.e. 

 3 HFSS is registered trademark of ANSYS Inc. The HFSS has been used in 

this research to foster understanding. Such identification does not imply 

recommendation or endorsement by the National Institute of Standards and 

Technology, nor does it imply that this product is necessarily the best 

available for the purpose.

its characteristics, exact position on the body and its 

orientation), operating frequency, transmit power, resolution, 

range and the choice of the desired output parameter. 

Resolution of 4 mm has been selected to run the simulations in 

this study. 

Human Body

Model

Propagation Engine 3D Immersive

Platform

Input

Parameters

Human Body

Model

Propagation Engine 3D Immersive

Platform

Input

Parameters

Figure 5. System block diagram 

Figure 6. A User in the NIST Immersive Visualization Environment 

For UWB simulations, we have used the loop antenna 

shown in Fig. 7. This antenna has an operating frequency 

range of 3.1-5.1 GHz and its size is 29.25×38.5×1 mm. It is 

printed on a side of FR4 substrate with dielectric constant of 

εr= 4.4 and loss tangent of tanθ = 0.02. To avoid performance 

degradations such as pattern distortion, power absorption and 

central frequency shift, the influence of human body has been 

carefully accounted for in the design of this antenna. Figure 8 

displays the VSWR (Voltage Standing Wave Ratio) of the 

antenna in proximity to human body. Detailed study of the 

characteristics of this antenna in free space and also in close 

proximity to human body has been provided in [2, 3]. 

Figure 7. The UWB Loop Antenna 

We have also simulated the aortic valve implant based on 

the size (and approximate shape) information provided in the 

Medtronic product specification data sheet [12]. Figure 9 
displays the simulated aortic implant in the 3D immersive 

platform. Attention was also given to the proper location of the 

valve with respect to the body surface. 

Figure 8. The UWB antenna VSWR in proximity to the body surface 

Figure 9. Simulation of the aortic heart valve in the NIST Immersive 

Visualization Environment 

IV. SIMULATION SCENARIOS & RESULTS 

Figure 10 displays the relative positions of the receivers and 

transmitters in our simulation. The circle indicates the crosssection of the chest around the upper body. The receiver 

positions are marked with red circles while the transmitter 

position is marked with a green box. The receiver locations 

have been chosen to mimic their corresponding positions in 

the experiment described in section 2 (i.e. positions 1 through 

8). In all cases, the antenna was located about 12 mm away 

from the body surface to have the best performance. Also, 

although, the exact location of the aortic valve is 

approximately identifiable in our 3D system, in order to gain 

more insight, 2 different depths were chosen for the initial 

placement of the implant. Those were 32 mm and 80 mm 

below the body surface. This will lead to 3 different scenarios 

for our simulations: 1) no aortic valve, 2) with aortic valve at 

32 mm below body surface and 3) with aortic valve at 80 mm 

below body surface. 

For each receiver location, the frequency response of the 

channel was calculated across the UWB frequency range of 3.1 

to 5.1 GHz with a step size of 40 MHz. Figure 11 displays the 

frequency responses (i.e. S21) corresponding to position ‘a’ for 

the 3 scenarios just mentioned. As observed, all channel 

responses are highly frequency dependent and not quite 

identical. 

x b

a

c

e d

f

g

h

x b

a

c

e d

f

g

h

Figure 10. Transmitter and various receivers locations around the chest 

3200 3400 3600 3800 4000 4200 4400 4600 4800 5000 -60

-55

-50

-45

-40

-35

-30

-25

Freq (MHz)

S21 (dB)

no implant

implant (32mm)

implant (80mm)

Figure 11. Frequency domain channel response for position ‘a’ 

Using IFFT (Inverse Fast Fourier Transform) with 

appropriate Kaiser filtering, we can obtain the temporal 

response of the channel. For example, Fig. 12 represents the 

time-domain impulse response of the channel for position ‘a’. 

Due to the close proximity of position ‘a’ to the transmitter, the 

3 curves are very similar; however, more variation is observed 

when the implant is located closer to the body surface (i.e. the 

blue curve). 

Figures 13, 14 show the corresponding frequency and time 

domain impulse responses for position ‘b’, respectively. The 

difference between the implant and no-implant cases is more 

pronounced compared to position ‘a’. This is especially visible 

for the case where the implant is 32 mm below the body 

surface. However, this difference is not as significant as the 

result obtained by the measurements (Figure 4). There are a 

few main factors that mostly contribute to this discrepancy; for 

example type of the antenna used, the covered UWB 

bandwidth, and exact whereabouts (i.e. location & orientation) 

of the transmitter and receivers as well as the aortic implant. 

The transmitter antenna and its gain pattern could greatly 

impact the results of both simulation and experiment. Keep in 

mind that the antenna used for the experiment was an off-theshelf antenna, while the antenna used in the simulation has 

been optimized for BAN application. Also, in the experiment, 

the entire UWB band (i.e. 3.1-10 GHz) has been used; where 

only the lower portion (3.1-5.1 GHz) was used in the 
simulation. Finally, the locations of the node on the chest have 

only been approximately matched. 

0 5 10 15 20 0

0.5

1

1.5

2

2.5x 10-3

Delay time (nsec)

Amplitude (linear)

no implant

implant (32mm)

implant (80mm)

Figure 12. Channel impulse response for position ‘a’ 

3200 3400 3600 3800 4000 4200 4400 4600 4800 5000 -70

-65

-60

-55

-50

-45

-40

-35

-30

Freq (MHz)

S21 (dB)

no implant

implant (32mm)

implant (80mm)

Figure 13. Frequency domain channel response for position ‘b’ 

0 5 10 15 20 0

0.2

0.4

0.6

0.8

1

1.2x 10-3

Delay time (nsec)

Amplitude (linear)

no implant

implant (32mm)

implant (80mm)

Figure 14. Channel impulse response for position ‘b’ 

While the results of the simulation and experiment do not 

exactly match, the fact that they both exhibit an effect on UWB 

body surface propagation due to the presence of an aortic 

implant is clear. And, therefore, more in-depth study is 

required to investigate this issue. Results for positions ‘c’ 

through ‘h’ also indicated some difference in the channel 

impulse response either in magnitude or delay. Those results, 

however, have been omitted for brevity. 

V. CONCLUSION

Using a 3D virtual reality environment, we have studied the 

possible impact of an aortic valve implant on the body-surface 

propagation for wearable sensors. In particular, we looked at 

the impulse response when the transmitter/receivers were 

located around the upper body and in the vicinity of the 

implant. The results of both experiment and simulation point to 

the fact that the existence of the implant with titanium alloy 

material does indeed impact the magnitude of the channel 

impulse response. Since extensive physical experiment is very 

difficult to perform, the 3D immersive system proves to be a 

valuable scientific tool to investigate this issue in detail. The 

authors plan to continue this study by coordinating both 

experiments and simulations using the same set of parameters 

and scenarios. 

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