ArticlePDF Available

# Footwear and Wrist Communication Links using 2.4 GHz and UWB Antennas

Authors:

## Abstract and Figures

It is reported that wearable electronic devices are to be used extensively in the next generation of sensors for sports and health monitoring. The information obtained from sensors on the human body depends on the biological parameters, the measurement rate and the number of sensors. The choice of the wireless protocol depends on the required data rates and on system configurations. The communication link quality is achieved with narrowband technologies such as Bluetooth or Zigbee, provided that the number of sensors is small and data rates are low. However, real-time measurements using wideband channels may also be necessary. This paper reports narrowband link performance at 2.45 GHz for comparison with two UWB channels centered at 3.95 GHz and 7.25 GHz. A monopole antenna covering 2.45 GHz and UWB is optimized for an on-body communication link between the footwear and the wrist. The cumulative distribution function of several path loss measurements is reported and compared for a subject standing and walking. Results show that the larger bandwidth in the UWB channel reduces fading and stabilizes the channel predictability.
Content may be subject to copyright.
Electronics 2014
Article
Footwear and Wrist Communication Links using 2.4 GHz and
UWB Antennas
Domenico Gaetano 1,*, Patrick McEvoy 1, Max J. Ammann 1, 2, Colm Brannigan 3,
Louise Keating 3 and Frances Horgan 3
1 AHFR, Dublin Institute of Technology, Kevin Street, Dublin 8, Ireland;
E-Mails: Patrick.Mcevoy@dit.ie (P.M.); max.ammann@dit.ie (M.J.A.)
2 CTVR, Dublin Institute of Technology, Kevin Street, Dublin 8, Ireland
3 School of Physiotherapy, Royal College of Surgeon of Ireland, 123, St. Stephen’s Green, Dublin 2,
Ireland; E-Mails: colmbrannigan@rcsi.ie (C.B.); lkeating@rcsi.ie (L.K.); fhorgan@rcsi.ie (F.H.)
* Author to whom correspondence should be addressed; E-Mail: domenico.gaetano@mydit.ie;
Tel.: +353-1-402-4905.
Received: 19 February 2014; in revised form: 21 May 2014 / Accepted: 26 May 2014 /
Published:
Abstract: It is reported that wearable electronic devices are to be used extensively in the
next generation of sensors for sports and health monitoring. The information obtained from
sensors on the human body depends on the biological parameters, the measurement rate
and the number of sensors. The choice of the wireless protocol depends on the required
data rates and on system configurations. The communication link quality is achieved with
narrowband technologies such as Bluetooth or Zigbee, provided that the number of sensors
is small and data rates are low. However, real-time measurements using wideband channels
may also be necessary. This paper reports narrowband link performance at
2.45 GHz for comparison with two UWB channels centered at 3.95 GHz and 7.25 GHz.
A monopole antenna covering 2.45 GHz and UWB is optimized for an on-body
communication link between the footwear and the wrist. The cumulative distribution
function of several path loss measurements is reported and compared for a subject standing
and walking. Results show that the larger bandwidth in the UWB channel reduces fading
and stabilizes the channel predictability.
Keywords: 2.4 GHz; UWB; Rician channel; on-body antenna
1. Introduction
Wearable technologies are electronic devices located in everyday clothing and accessories.
Nowadays, there is an increasing demand to monitor performance of various activities in sports [1],
Electronics 2014, 3 2
daily routines [2] and health care scenarios [3]. The goals include measurement of biological and
physical parameters with subsequent processing for different applications. These wearable devices are
required to be small to avoid user discomfort. They may be integrated in a belt [4], necklace [5], shirt
[6] or shoes [7]. Normally the sensor position depends on the biological and physical parameters to be
measured. Sensors are placed in footwear to measure various biological parameters, including plantar
pressure [8], speed [9], walking and running gait [10]. These data are useful to monitor everyday
activity, to detect gait abnormality [9] and to detect the onset of various medical conditions [11].
These sensors need to be simple and consume low power. Combining information from different
on-body deployed sensors requires a smarter and more complex node. This hub is responsible for
collecting all the information to be processed, simplifying it and ultimately displaying it to the final
user. The position and the technology used in the communication link between the different nodes and
the main hub is important for overall system reliability. The main hub is typically located at the waist
area of the body [12, 13] which is equidistant to other on-body nodes thereby reducing the maximum
communication distance over the whole body. It has been demonstrated that using directional antennas
on footwear achieves equal or better performances than a waist-centric paradigm with omnidirectional
antennas [14]. However, the expansion of advanced handheld devices such as smartphones and
smartwatch is shifting the hub-centric scenario from waist to the hand area. This on-body area is
critical because of the rapid changes of the body posture responsible for shadowing and multipath
fading behavior. The communication link must be reliable during everyday activities, including walking.
Different technologies are already used in the communication layer in the 2.45 GHz frequency band
such as Bluetooth [15] and WiFi [16]. These technologies are well known and widely used in many
systems. However, new emerging technologies have greater data rates and are more secure. Within this
framework, UWB technologies are characterized by wider bandwidths, lower power consumption and
smaller range in comparison to the narrowband systems. Because of these advantages, UWB is a
promising technology for the development of Body Area Networks [17]. The antenna design must take
the operational environment into consideration [18]. On-body scenarios are characterized by close
proximity to high water-content and low water-content materials which can influence the antenna
performance. Besides it is important to include body movement because of fading and shadowing.
In this paper a communication link between the footwear and the wrist is studied for three different
frequency ranges for a subject while walking. The footwear can be a hub location or can relay
footwear sensor information to a handheld device.
Performances for footwear located antennas should consider the rapid and repetitive movement of
the foot for a walking/running subject and the close proximity to the ground. The performance of a
monopole antenna on the toe cap is not impaired by the ground proximity because the foot behaves as
a screen, decreasing the back lobe radiation.
An antenna is designed to cover the 2.4 GHz and UWB bands and can be integrated with
multimode transceivers to mitigate on-body multipath effects and to adjust the data rate to the
particular request.
In the first section of the paper the antenna performances are shown in the free space and in close
proximity to the body. In the second section the three frequency ranges are compared for a subject
walking using S21 measurements.
Electronics 2014, 3 3
2. Antenna Geometry and Free Space Performance
A single-sided printed monopole antenna is easier to integrate on the surface of the upper part of the
footwear or above the textile strips of a garment, without the requirement of another layer. An antenna
optimized for this purpose is prototyped on a 0.2 mm single-sided FR4 layer and shown in Figure 1a.
For simplicity the antenna is fed by coplanar waveguide (CPW) which is connected to a SMA
connector and optimized for on-body performance from 2.4 GHz to 10 GHz. The antenna size is
40 × 50 mm2. A transition in the CPW is required for matching due to the connector flange. The width
of the feed line and slot line under the connector is 1 mm and 1.2 mm respectively. Beyond the
connector, these become 3.3 mm and 0.2 mm respectively. The antenna is then shaped with splined
lines, resulting from the on-body optimization. The ground plane shape is also optimized to increase
the bandwidth of the antenna with the dimension GP1 = 13 mm, D1 = 1 mm and D2 = 0.8 mm. The
parameters of the splines are given in Table 1.
Figure 1. (a) Antenna geometry; (b) comparison of simulated and measured S11 for the
antenna in free space; (c) photo of the prototyped antenna.
(a)
(b)
(c)
The antenna free-space S11 is shown in Figure 1b. The simulated bandwidth of the antenna is
10 dB matched across 2.110 GHz. In the measurement there is a shift of the lower 10 dB frequency
of 177 MHz. The measured −10 dB bandwidth for the free space antenna is within the range of 2 GHz
to 8 GHz. The small disagreement between simulation and measurement is due to an imperfectly flat
dielectric layer and non-uniform distance between the printed copper feed line on the dielectric of the
CPW and the flange of the connector. A photograph of the prototyped antenna is shown in Figure 1c.
P2
P2
P4
P4
P1
P3
D2
GP1
S2
S4
S1
S3
W
H
D1
0 2 4 6 8 10
-50
-40
-30
-20
-10
0
f [GHz]
S11
Measurement
Simulation
Electronics 2014, 3 4
Table 1. Parameters value of the spline.
Antenna [red points]
Parameter
Dimension [mm]
Parameter
Dimension [mm]
P1
12
S1
5
P2
11
S2
5
P3
8
S3
4
P4
6
S4
3
3. On-Body Antenna Performances
In this section the antenna on-body performances are investigated for two different body locations:
the footwear toe-cap and the wrist. The body model consists of voxel files representing the wrist and
the foot. In the wrist model case the distance between the antenna and the body is equal to 5 mm. For
the footwear case the antenna is located next to the skin voxels. The voxel model of the foot is
non-planar, so the distance between the antenna and the foot varies from 1 mm to 8.5 mm. The foot
and wrist models include different body tissues, such as skin, fat, muscle and bone. The electrical
properties of these materials are frequency dependent [19].
The antenna located on the simulated voxel model and the electrical properties of the tissues are
shown in Figure 2.
Figure 2. (a) On-body model; (b) Electrical properties of the human body materials
(continuous line ε1, dotted line ε2).
(a)
(b)
The voxel file resembles the shape of the human body parts and it reproduces the internal geometry.
The voxel foot model is mostly composed of bones, characterized by small values of permittivity and
losses. The voxel wrist model is mostly composed of high water-content material such as muscle,
although there is a thin layer of skin and a thicker layer of fat closer to the antenna. A comparison
between simulation and measurement of the antenna located on the footwear and on the wrist are
shown in Figure 3. The shoe materials are not considered in the simulation model. The thin toe cap
layer is negligible compared to the close proximity to the high dielectric constant and lossy body tissues.
The measured and simulated S11 of the wrist and toe-cap mounted antennas is less than 8.5 dB
across the band of interest.
Z
X
Y
θ
φ
Z
X
Y
θ
φ
2 4 6 8 10
0
10
20
30
40
50
60
f [GHz]
Permittivity
real and imaginary part of
Bone
Fat
Muscle
Skin
Electronics 2014, 3 5
Figure 3. Comparison of measured and simulated S11 for wrist (a) and footwear (b).
(a)
(b)
Small disagreements between simulation and measurement are due to differences between the voxel
model shape and the actual human case. The antenna was perfectly centered on the wrist with human
body tissue equally distributed below the antenna. The loading of the toes in the footwear case is not
symmetrical due to the presence of air-spaces and the non-constant antenna-foot separation. The
simulated radiation patterns are shown in Figures 4 and 5. The realized gain as a function of frequency
is summarized in Table 2.
Figure 4. Realized gain patterns for monopole antenna on footwear for φ = 0° and φ = 90°.
θ
θ
Figure 5. Realized gain patterns for monopole antenna on wrist for φ = 0° and φ = 90°.
θ
θ
0 2 4 6 8 10
-50
-40
-30
-20
-10
0
f [GHz]
S11
Wrist Meas
Wrist Sim
0 2 4 6 8 10
-50
-40
-30
-20
-10
0
f [GHz]
S11
Footwear Meas
Footwear Sim
-40
-30
-20
-10
0
10
-150
-120
-90
-60
-30
0
30
60
90
120
150
180
-40
-30
-20
-10
0
10
2.45 GHz
3.95 GHz
7.25 GHz
-40
-30
-20
-10
0
10
-150
-120
-90
-60
-30
0
30
60
90
120
150
180
-40
-30
-20
-10
0
10
2.45 GHz
3.95 GHz
7.25 GHz
-40
-30
-20
-10
0
10
-150
-120
-90
-60
-30
0
30
60
90
120
150
180
-40
-30
-20
-10
0
10
2.45 GHz
3.95 GHz
7.25 GHz
-40
-30
-20
-10
0
10
-150
-120
-90
-60
-30
0
30
60
90
120
150
180
-40
-30
-20
-10
0
10
2.45 GHz
3.95 GHz
7.25 GHz
Electronics 2014, 3 6
Table 2. Directivity parameters for the on-body antennas.
Frequency
[GHz]
Maximum realized
gain magnitude [dBi]
3-dB beamwidth
for φ = 0° [deg]
3-dB beamwidth
for φ = 90° [deg]
efficiency
Wrist
Footwear
Wrist
Footwear
Wrist
Footwear
Wrist
Footwear
2.45
2.09
0.16
131.3
131.9
86.6
84.3
21%
30%
3.95
5.37
4.07
86.6
83.4
61.4
80.5
54%
55%
7.25
4.41
4.46
57.1
42.7
44.3
46.1
65%
64%
The antenna radiation efficiency increases with frequency because the electrical distance between
the antenna and the body increases. The difference in the shapes of the radiation pattern for the
footwear and the wrist locations is due to dissimilar body geometries and to the different positions of
the antenna respect to the body. The antenna is characterized by the maximum realized gain for the
3.95 GHz frequency for the wrist case. Considering a walking subject, the 3 dB beamwidth for φ = 90°
for the toe-cap mounted antenna is wide enough to cover the arm swing of the walking subject.
4. Measurements
The S21 was measured using a Rohde & Schwarz ZVA 25 for a subject standing and walking. The
measurements are made in a room 8.1 × 7.9 m2 with furniture and reinforced concrete walls and floors.
The person is walking along one side of the room as shown in Figure 6a. The first antenna is located
on the right-side shoe toe-cap and the second antenna is located above the right wrist, as shown in
Figure 7. Three different frequency bands are analyzed as shown in Figure 6b:
50 MHz centered at 2.45 GHz
500 MHz centered at 3.95 GHz
500 MHz centered at 7.25 GHz
Figure 6. (a) Layout of the room; (b) investigated frequencies with bandwidth.
(a)
(b)
The three frequencies represent the centre frequencies for the narrowband and UWB physical layer
for wireless BAN networks in IEEE 802.15.6.
0 2 4 6 8 10
0
0.2
0.4
0.6
0.8
1
f [GHz]
Investigated Frequencies
2.45 GHz
3.95 GHz
7.25 GHz
Electronics 2014, 3 7
Figure 7. Walking subject with antennas on wrist and toe-cap footwear.
To avoid obstruction of the cables by the subject walking, the VNA was placed at the side of the
room and the cables located behind the subject. In this way the cables trail the walking subject, without
impacting on the gait. Photos of the measurement setup are shown in Figure 8.
Figure 8. Photos of the on-body antennas
In total there are five measurements with 330 frequency sweep samples for a subject walking and
standing. The first 10 s are related to a stationary subject at one side of the room. Then the subject
walks to the other side of the room. Finally the subject stands still at the other side of the room. There
is a measurement every ~100 ms. The total time for each measurement is ~33 s. The measurements
were made on a subject of mass 70 kg and 1.75 m tall. Path loss results are displayed in terms of
Cumulative Distribution Function (CDF) and compared with the Rician distribution using the
Maximum Likelihood Estimation (MLE) criteria.
Electronics 2014, 3 8
4.1. Narrowband Channel2.45 GHz
In this paragraph the results for the 2.45 GHz narrowband channel is investigated. The link channel
measured in the five campaigns of measurements as a function of time is shown in Figure 9a. For the
first 10 s, the variation in the channel is small (between 59 dB and 50 dB). When the subject starts
walking the S21 oscillation increases, but remaining between 67.8 dB and 48 dB. Finally the subject
is standing in front of a wall, and the S21 is almost constant for each set of measurements. The CDF of
the five measurements is shown in Figure 9b. The minimum and the maximum values of the five
measurements are summarized in Table 3. Considering all the measurements, the maximum range is
equal to 19 dB. The CDF is compared with the MLE for the corresponding Rician Distribution,
assuming that there is a main ray between the foot and the wrist.
Figure 9. (a) measured S21 for a subject walking; (b) CDF of the path loss for the five cases.
(a)
(b)
Table 3. K-factor estimation for the different measurements for the 2.45 GHz channel.
Minimum path loss [dB]
Maximum path loss [dB]
K-factor [dB]
Meas 1
53
67
9.16
Meas 2
52
65
9.97
Meas 3
50
66
10.5
Meas 4
48
68
7.5
Meas 5
48
63
9.7
The K-factor of the Rician distribution is summarized in Table 3. All the measurements are
characterized by a K-factor always greater than 7.5 dB, evidencing the presence of a main component
of the received signal greater than the scattered components. The range of K-factors spans from 7.5 dB
to 10.5 dB. The path loss is always smaller than 67 dB.
4.2. Lower UWB Channel 3.95 GHz
In this section the results of the lower UWB channel are shown. The investigated centre frequency
is 3.95 GHz with 500 MHz bandwidth. The S21 measurements of a walking subject as a function of the
010 20 30 40
-65
-60
-55
-50
t [s]
S21
Meas 1
Meas 2
Meas 3
Meas 4
Meas 5
45 50 55 60 65 70
0
0.2
0.4
0.6
0.8
1
Path Loss
CDF
Empirical CDF
Meas 1
Meas 2
Meas 3
Meas 4
Meas 5
Electronics 2014, 3 9
time, is shown in Figure 10a. The S21 is almost constant for the stationary subject at the starting point
and in front of the wall. When the subject is walking the S21 oscillates with a greater range of values,
with peaks of maximum S21 equal to 51.89 dB and minima of 57.23 dB. The CDF of the
five measurements is shown in Figure 10b.
Figure 10. (a) Measured S21 for a walking subject; (b) CDF of the path loss for the five cases.
(a)
(b)
The CDF distributions for the measurements are very similar. Table 4 summarizes the minimum
and maximum values and the K-factor for the corresponding Rician distribution. The K-factor for the
3.95 GHz frequency range is always greater than 16.2, corresponding to a more directive link between
the footwear and the wrist compared to the 2.45 GHz case. This is also due to a greater antenna
realized gain compared to the 2.45 GHz case. The increased bandwidth decreases the fading, reducing
the maximum path loss variation to 4 dB. The greater K-factor compared to the narrowband channel
can also be explained by the smaller antenna beamwidth, reducing reflected signals from the
surrounding environment.
Table 4. K-factor estimation for the different measurements for the 3.95 GHz channel.
Minimum path loss [dB]
Maximum path loss [dB]
K-factor [dB]
Meas 1
52
52
20.5
Meas 2
53
57
18.0
Meas 3
53
57
16.2
Meas 4
55
56
17.2
Meas 5
52
57
17.3
4.3. Upper UWB Channel 7.25 GHz
The performance for the upper UWB band is also investigated. The centre frequency is 7.25 GHz
with a 500 MHz bandwidth. In Figure 11a the measured S21 for the walking subject as a function of
time are shown. As observed for previous cases, the S21 is almost constant for the first 10 s, with a S21
value equal to ~53.5 dB. When the subject is walking, the S21 range remains between 54.22 dB and
51.56 dB. Finally when the subject is stationary at the end of the room the S21 is almost constant and
010 20 30 40
-65
-60
-55
-50
t [s]
S21
Meas 1
Meas 2
Meas 3
Meas 4
Meas 5
45 50 55 60 65 70
0
0.2
0.4
0.6
0.8
1
Path Loss
CDF
Empirical CDF
Meas 1
Meas 2
Meas 3
Meas 4
Meas 5
Electronics 2014, 3 10
equal to 53.75 dB. The CDFs of the five measurements are shown in Figure 11b. In this case the
measurements are much closer to each other. The measured path loss values and K-factors are
summarized in Table 5. The K-factor is greater than the previous case and always greater than 20.9 dB.
The difference between the maximum and the minimum K-factor is equal to 5.1 dB.
Figure 11. (a) Measured S21 for a walking subject; (b) CDF of the path loss for the five cases.
(a)
(b)
Table 5. K-factor estimation for the different measurements for the 7.25 GHz channel.
Minimum path loss [dB]
Maximum path loss [dB]
K-factor [dB]
Meas 1
52
54
20.9
Meas 2
52
54
23.7
Meas 3
52
54
26.0
Meas 4
52
54
24.9
Meas 5
52
54
23.3
As expected, the K-factor is greater than the previous cases. Although the maximum realized gain is
less than the 3.95 GHz case, the beamwidth of the antenna is smaller, resulting in a decreased signal
scattering in the surrounding environment. The minimum path loss values are similar to the 3.95 GHz
because of the greater realized gain for the footwear antenna.
5. Conclusions
The S21 link between the wrist and footwear toe-cap is reported for a subject standing and walking.
A monopole antenna is optimized for different on-body locations at 2.45 GHz, 3.95 GHz and
7.25 GHz. The results are summarized in terms of Cumulative Distribution Functions and the
Maximum Likelihood Estimation criteria are used for K-factor parameter fit to a Rician distribution.
In the subject standing pose, the S21 remains persistent for each of the three frequencies. When the
subject is walking, the S21 varies rapidly with lower S21 values for lower frequencies. This is attributed
to channel fading and shadowing by the hand during the arm swing motion associated with walking. At
the lower frequency, the fading is more noticeable because the selected channel is narrowband.
010 20 30 40
-65
-60
-55
-50
t [s]
S21
Meas 1
Meas 2
Meas 3
Meas 4
Meas 5
45 50 55 60 65 70
0
0.2
0.4
0.6
0.8
1
Path Loss
CDF
Empirical CDF
Meas 1
Meas 2
Meas 3
Meas 4
Meas 5
Electronics 2014, 3 11
The UWB channels are an easier fit to a Rician distribution, with small changes of the K-factor. In
the 2.45 GHz case, the Rician K-factor is ~10 dB lower than that for the UWB channels. This is due to
the larger beamwidth at 2.45 GHz which increases the signal scattering from surrounding environment.
The minimum path loss for each of the UWB channels is the same due to higher antenna efficiency.
The 7.25 GHz channel is characterized by the largest K-factor due to its smaller beamwidth. The
communication link complies with the standard for each of the measured cases for a subject standing
and walking.
Further work will consider the receiving node in different body locations; hence it will establish the
optimum frequency band for different body locations. The antenna will be tested in an outdoor
environment and with different transceivers to mitigate cable effects.
Acknowledgments
This work was supported by the Science Foundation Ireland under Grant 09/IN.1/I2652.
Conflicts of Interest
The authors declare no conflict of interest.
References
1. Ermes, M.; Pärkka, J.; Mantyjarvi, J.; Korhonen, I. Detection of daily activities and sports with
wearable sensors in controlled and uncontrolled conditions. IEEE Trans. Inf. Technol. Biomed.
2008, 12, 2026.
2. Hu, Y.; Stoelting, A.; Wang, Y.; Zou, Y.; Sarrafzadeh, M. Providing a cushion for wireless
healthcare application development. IEEE Potentials 2010, 29, 1923.
3. Crumley, G.C.; Evans, N.E.; Scanlon, W.G.; Burns, J.B.; Trouton, T.G. The design and
performance of a 2.5-GHz telecommand link for wireless biomedical monitoring. IEEE Trans.
Inf. Technol. Biomed. 2000, 4, 285291.
4. Zuckerwar, A.J.; Pretlow, R.A.; Stoughton, J.W.; Baker, D.A. Development of a piezopolymer
pressure sensor for a portable fetal heart rate monitor. IEEE Trans. Biomed. Eng. 1993, 40,
963969.
5. Vidojkovic, M.; Huang, X.; Harpe, P.; Rampu, S.; Zhou, C.; Huang, L.; van de Molengraft, J.;
Imamura, K.; Busze, B.; Bouwens, F.; et al. A 2.4 GHz ULP OOK Single-Chip Transceiver for
Healthcare Applications. IEEE Trans. Biomed. Circuits Syst. 2011, 5, 523534.
6. Nemati, E.; Deen, M.J.; Mondal, T. A Wireless Wearable ECG Sensor for Long-Term
Applications. IEEE Commun. Mag. 2012, 50, 3643.
7. Sazonov, E.S.; Fulk, G.; Hill, J.; Schutz, Y.; Browning, R. Monitoring of posture allocations and
activities by a shoe-based wearable sensor. IEEE Trans. Biomed. Eng. 2011, 58, 983990.
8. Available online: http://www.tekscan.com/medical/system-fscan1.html (accessed on 27 May
2014).
Electronics 2014, 3 12
9. Bamberg, S.J.M.; Benbasat, A.Y.; Scarborough, D.M.; Krebs, D.E.; Paradiso, J.A. Gait analysis
using a shoe-integrated wireless sensor system. IEEE Trans. Inf. Technol. Biomed. 2008, 12,
413423.
10. Morris, S.J.; Paradiso, J.A.; Development, A.H. Shoe-Integrated Sensor System For Wireless Gait
Analysis And Real-Time Feedback. In Proceedings of the Second Joint EMBS/BMES
Conference, Houston, TX, USA, 2326 October 2002; pp. 24682469.
11. Mariani, B.; Jim, C. On-Shoe Wearable Sensors for Gait and Turning Assessment of Patients
With Parkinson s Disease. IEEE Trans. Biomed. Eng. 2013, 60, 155158.
12. Cotton, S.L.; Conway, G.A.; Scanlon, W.G. A Time-Domain Approach to the Analysis and
Modeling of On-Body Propagation Characteristics Using Synchronized Measurements at 2.45 GHz.
Trans. Antennas Propag. 2009, 57, 943955.
13. Nechayev, Y.I.; Hall, P.S.; Hu, Z.H. Characterisation of narrowband communication channels on
the human body at 2.45 GHz. IET Microwa. Antennas Propag. 2010, 4, 722732.
14. Gaetano, D.; Sipal, V.; McEvoy, P.; Ammann, M.J.; Brannigan, C.; Keating, L.; Horgan, F.
Footwear-centric body area network with directional UWB antenna. IEEE Electron. Lett. 2013,
49, 860861.
15. 802.15.1-2002IEEE Standard for Telecommunications and Information Exchange Between
SystemsLAN/MANSpecific RequirementsPart 15: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Wireless Personal Area Networks (WPANs); The
Institute of Electrical and Electronics Engineers, Inc.: New York, NY, USA, 2002.
16. 802.11a-1999IEEE Standard for Information TechnologyTelecommunications and
Information Exchange Between SystemsLocal and Metropolitan Area NetworksSpecific
RequirementsPart 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications; The Institute of Electrical and Electronics Engineers, Inc.: New York, NY, USA,
1999.
17. Alomainy, A.; Sani, A.; Rahman, A.; Santas, J.G.; Hao, Y. Transient characteristics of wearable
antennas and radio propagation channels for ultrawideband body-centric wireless communications.
Trans. Antennas Propag. 2009, 57, 875884.
18. Gaetano, D.; McEvoy, P.; Ammann, M.J.; Browne, J.E.; Keating, L.; Horgan, F. Footwear
Antennas for Body Area Telemetry. Trans. Antennas Propag. 2013, 61, 49084916.
19. Gabriel, S.; Lau, R.W.; Gabriel, C. The dielectric properties of biological tissues: III. Parametric
models for the dielectric spectrum of tissues. Phys. Med. Biol. 1996, 41, 22712293.
... Interesting examples of wearable antennas intended for integration into the shoes and thus potential use for sports applications are presented in [66,67]. In [66], two different UWB wearable antenna prototypes, (a monopole and a Vivaldi type) are proposed in order to provide a link between the footwear sensors and the rest of the body centric network, while in [67], mainly the channel aspects and the influence of the rapid and repetitive movement of the foot on the overall communication are considered. ...
... Interesting examples of wearable antennas intended for integration into the shoes and thus potential use for sports applications are presented in [66,67]. In [66], two different UWB wearable antenna prototypes, (a monopole and a Vivaldi type) are proposed in order to provide a link between the footwear sensors and the rest of the body centric network, while in [67], mainly the channel aspects and the influence of the rapid and repetitive movement of the foot on the overall communication are considered. • Dipole antennas. ...
Thesis
Wearable electronics are occupying an increasing portion of our daily activities. The span of wearable applications extends from purely medical, over different security services to various sports and fashion devices. Antennas play one of the most important roles in wearable networks as they have a key contribution to the overall efficiency of a wearable wireless link. This work focuses on the design and practical realization of robust wearable antennas intended for voice communication inside the Ultra High Frequency (UHF) band. The proposed antennas are mainly envisioned for security services such as military, police or rescue services. To this aim, several questions have been addressed while analyzing and designing the proposed antennas. The on-body environment significantly affects the characteristics of an antenna. The coupling between the antenna and the host body influences both the antenna and the body characteristics. On one hand, the complex lossy nature of the hosting body tends to deteriorate the radiation performances of the wearable antenna, while on the other hand, the radiation from the antenna can cause an increase of the temperature of the wearer’s body (localy and/or of the entire body). The wearability aspect also requires that the size and the profile of the antenna are appropriate so that it can be easily integrated into the wearer’s garment. The size of the wearable antennas becomes more critical at lower frequencies (for instance UHF), where the wavelengths become comparable with the size of the body, thus adding an additional limitation while selecting the type of the antenna. A Planar Inverted F Antenna (PIFA) was selected as an appropriate antenna candidate addressing the introduced specifications. In parallel with the antenna prototype, a suitable technology, combining flexible conductors and stretchable substrates, has been proposed. The suggested technology also enables an adjustment of the electric properties of the designated substrate materials. Several antenna prototypes were successfully designed, fabricated and characterized. Finally, a set of tests in realistic everyday conditions were performed, thus validating the performance of the proposed antenna concepts along with the proposed technology and assessing their potential of being used for commercial purposes. We believe that the obtained results provide useful guidelines for future design of robust flexible wearable antennas. Key words: Wearable antennas, security services, Ultra High Frequency (UHF), Planar Inverted F Antenna (PIFA), polydimethylsiloxane (PDMS), copper meshes, robustness, flexibility, waterproof, Specific Absorption Rate (SAR).
... II. DESIGN OF THE UHF/UWB ANTENNA READER Due to their simple construction, ease of manufacturing, good wideband properties, and omnidirectional radiation patterns, circular disc monopole antennas are promising solutions for UHF/UWB RFID applications [23][24][25][26]. ...
Article
Full-text available
This paper presents a new circular monopole antenna with triple-band characteristics that can operate in both ultra-high frequency (UHF) and ultra-wideband (UWB) and can be integrated into a radio-frequency identification (RFID) system reader board. The antenna was built with a patch and a coplanar waveguide (CPW) feed microstrip line to meet the UHF/UWB bandwidth requirements for RFID applications. The designed antenna has a size of 70 mm × 60 mm × 0.8 mm. CST Microwave Studio simulations were used to validate the proposed antenna, which had a maximum gain of 4.8 dBi. Furthermore, the designed antenna had a radiation pattern that spanned the full working band. To interact with RFID tags, the antenna was built and installed into the RFID reader board. The simulation and measurement findings showed good agreement. Experiments indicated that the UHF-RFID performance of the monopole antenna was comparable to that of existing commercial solutions.
... En termes de bande passante, l'antenne monopole fait partie des antennes ultra large bande (ULB). La plupart des antennes monopôles utilisée dans la littérature sont imprimées ou planaires pour être facilement intégrables dans les vêtements [61]. ...
Thesis
Grâce aux progrès de marché des objets connectés ces dernières années, la conception de réseaux intelligents, tels que les réseaux centrés sur les personnes (Body Area Network en anglais ou WBAN) a connu une croissance très élevée, qui explique le grand engouement des industriels autour de cette nouvelle technologie. De nouveaux concepts d'applications émergentes capables de détecter des phénomènes physiologiques, environnementaux et plus particulièrement des applications centrées sur l'homme en utilisant des capteurs et des antennes susceptibles de communiquer et de collecter des informations en temps réel afin d'assurer une interaction intelligente du corps humain et son environnement grâce à la mise au point d'une interface physique capable de détecter, de réagir et de s'adapter, comme les vêtements intelligents. Dans ce cadre, nous nous sommes attachés dans ce travail de recherche à la conception et la réalisation d’antennes textiles susceptibles d’être intégrées dans des vêtements pour les applications de l’internet des objets (IoT), ces antennes sont conçues pour fonctionner dans la bande Wi-Fi (2.45 GHz, 5.8GHz) et la bande 5G inférieure à 6 GHz (3.5 GHz). Nous avons également utilisé des structures métamatériaux de type bande interdite électromagnétique (BIE) afin d’augmenter leurs performances en rayonnement et diminuer le couplage avec le corps humain. Puis récemment la bande millimétrique a été mise en avant pour le développement des réseaux de communication sans fil. L’intérêt de cette bande pour les applications 5G et IoT s'explique par les avantages qu'elle bénéficie par rapport aux bandes de fréquence plus basses (possibilité de débits de données supérieurs à 10 Gbit/s, réduction des interférences avec les réseaux voisins, compacité des dispositifs, etc.). Dans la deuxième étude, la première antenne textile destinée à la bande de fréquence 5G-26 GHz a été présentée. Une amélioration du gain et une limitation des interactions avec le corps ont été obtenues grâce à une nouvelle technique d'amélioration en utilisant des surfaces BIE. Les résultats de mesure effectués ont bien validé les conceptions développées et ont démontré qu'il existe de nombreuses possibilités d'exploitation de ces prototypes pour les futures applications IoT.
... The size of the probe should be moderate (around 15 cm to 20 cm) and to be handy for being used in the proposed NFIT setup. Among the many types of E-field antennas [12][13][14][15][16][17][18][19] L-probe fed circular patch antenna (for brevity onward as L-probe antenna) was chosen because of its relatively simpler geometry, small size, and wideband characteristics [20,21]. The L-probe antenna used in this study is an enhanced version of monopolar wire patch antenna [14,15,20,22] which broadens its bandwidth. ...
Article
Full-text available
This study presents a near-field immunity test (NFIT) method for the fast debugging of radiated susceptibility of industrial devices. The proposed approach is based on the development of an NFIT setup which comprises of developed near-field electric and magnetic field probes and device under test (DUT). The developed small-size and handy near-field testing probes inject the high electric (up to 1000 V/m) and magnetic (up to 2.4 A/m) fields on the DUT in the radar pulse ranges (1.2 to 1.4 GHz and 2.7 to 3.1 GHz) with the lower fed input power (up to 15 W) from the power amplifier in the developed NFIT setup. The proof of concept is validated with the successful near-field immunity debugging of an electric power steering (EPS) device used in the automotive industry with the developed NFIT setup. The radiated susceptibility debugging test results of developed NFIT method and conventional method of ISO 11452-2 test setup turned out to be close to each other for the tested DUT in immunity performance. The proposed procedure has advantages of industry usefulness with fast, handy, and cost-effective radiated immunity debugging of the DUT without the requirement of large antenna, high-power amplifiers, optical DUT connecting harness, and an anechoic chamber as needed in ISO 11452-2 standard setup for the debugging analysis.
... In addition, a 2.4-11.0 GHz spline-shaped monopole antenna printed on 0.2 mm flexible FR4 assessed toe-cap to wrist nodes links [16]. While ground proximities influences were excluded, the path-loss measurements for indoor walking scenarios fitted a Rician channel distribution. ...
Article
Full-text available
A 433 MHz antenna is proposed for integration with the insole of footwear for a body area network. The folded dipole design with an asymmetric groundplane radiates from its edges and considers the close proximity of the human foot and ground surfaces. It functions for different ground conductivity conditions and an on-body communication link with an Inverted-F Antenna in the upper body area was evaluated on a static and dynamic human subject. The antenna solution was compliant with Specific Absorption Rate requirements, remains matched and links with upper-body nodes regardless of the body posture and node location.
Article
Full-text available
Antennas designed to link footwear sensors within body centric networks are introduced with two small UWB antennas, one directional and another quasi-omnidirectional. The radiating characteristics are evaluated for three positions on a sample sports shoe using a detailed simulation model and measurements with a homogenous foot phantom. Antenna performance is assessed for resilience to close proximity loading by the footwear materials and the phantom foot.
Article
Full-text available
A footwear-centric body area network employing a directional antenna is compared with waist-centric systems using omnidirectional and directional antennas. The effect of body movements on path gain is analysed for two bands at 3.99 and 7.99 GHz. The path gain and data rate results demonstrate that footwear-centric configurations are equivalent to or better than waist-centric body area networks.
Article
Full-text available
Monitoring of posture allocations and activities en-ables accurate estimation of energy expenditure and may aid in obesity prevention and treatment. At present, accurate devices rely on multiple sensors distributed on the body and thus may be too obtrusive for everyday use. This paper presents a novel wearable sensor, which is capable of very accurate recognition of common postures and activities. The patterns of heel acceleration and plan-tar pressure uniquely characterize postures and typical activities while requiring minimal preprocessing and no feature extraction. The shoe sensor was tested in nine adults performing sitting and standing postures and while walking, running, stair ascent/descent and cycling. Support vector machines (SVMs) were used for clas-sification. A fourfold validation of a six-class subject-independent group model showed 95.2% average accuracy of posture/activity classification on full sensor set and over 98% on optimized sensor set. Using a combination of acceleration/pressure also enabled a pronounced reduction of the sampling frequency (25 to 1 Hz) with-out significant loss of accuracy (98% versus 93%). Subjects had shoe sizes (US) M9.5-11 and W7-9 and body mass index from 18.1 to 39.4 kg/m2 and thus suggesting that the device can be used by individuals with varying anthropometric characteristics.
Conference Paper
Full-text available
We are developing a sensor system for use in clinical gait analysis. This research involves the development of an on-shoe device that can be used for continuous and real-time monitoring of gait. This paper presents the design of an instrumented insole and a removable instrumented shoe attachment. Transmission of the data is in real-time and wireless, providing information about the three-dimensional motion, position, and pressure distribution of the foot. Using pattern recognition and numerical analysis of the calibrated sensor outputs, algorithms will be developed to analyze the data in real-time. Results will be validated by comparison to results from a commercial optical gait analysis system at the Massachusetts General Hospital (MGH) Biomoti on Lab.
Article
Assessment of locomotion through simple tests such as timed up and go (TUG) or walking trials can provide valuable information for the evaluation of treatment and the early diagnosis of people with Parkinson's disease (PD). Common methods used in clinics are either based on complex motion laboratory settings or simple timing outcomes using stop watches. The goal of this paper is to present an innovative technology based on wearable sensors on-shoe and processing algorithm, which provides outcome measures characterizing PD motor symptoms during TUG and gait tests. Our results on ten PD patients and ten age-matched elderly subjects indicate an accuracy ± precision of 2.8 ± 2.4 cm/s and 1.3 ± 3.0 cm for stride velocity and stride length estimation compared to optical motion capture, with the advantage of being practical to use in home or clinics without any discomfort for the subject. In addition, the use of novel spatio-temporal parameters, including turning, swing width, path length, and their intercycle variability, was also validated and showed interesting tendencies for discriminating patients in ON and OFF states and control subjects.
Article
Modeling of on-body propagation channels is of paramount importance to those wishing to evaluate radio channel performance for wearable devices in body area networks (BANs). Difficulties in modeling arise due to the highly variable channel conditions related to changes in the user's state and local environment. This study characterizes these influences by using time-series analysis to examine and model signal characteristics for on-body radio channels in user stationary and mobile scenarios in four different locations: anechoic chamber, open office area, hallway, and outdoor environment. Autocorrelation and cross-correlation functions are reported and shown to be dependent on body state and surroundings. Autoregressive (AR) transfer functions are used to perform time-series analysis and develop models for fading in various on-body links. Due to the non-Gaussian nature of the logarithmically transformed observed signal envelope in the majority of mobile user states, a simple method for reproducing the fading based on lognormal and Nakagami statistics is proposed. The validity of the AR models is evaluated using hypothesis testing, which is based on the Ljung-Box statistic, and the estimated distributional parameters of the simulator output compared with those from experimental results.
Article
This paper presents transient characterization of ultrawideband (UWB) body-worn antennas and on-body radio propagation channels for body-centric wireless communications. A novel miniaturized CPW-fed tapered slot antenna is proposed and used for transient measurements of UWB radio channels for body area network (BAN) and personal area network (PAN) scenarios. Unlike conventional UWB CPW-fed antennas, the proposed antenna employs two diverging tapered slots to provide smooth and stable impedance matching. Fidelity analysis is applied to evaluate the time-domain behavior of body-worn antennas and it is found that average fidelity obtained is 88% and 86% for the conventional coplanar waveguide fed antenna and the tapered slot antenna, respectively. However, the tapered slot antenna shows a significant size reduction and hence is suited for body-centric wireless communications.
Article
A number of propagation measurements of belt-to-head and belt-to-wrist channels have been performed with inverted F-antennas, planar inverted F-antennas (PIFAs), monopole, loop and dipole antennas, and propagation models were derived. It is found that the channel can be separated into short-term and long-term fading components. The short-term fading can generally be modelled with a Rician distribution, whereas in many cases, long-term fading is lognormal, the best distribution is dependent on the channel, antenna type and orientation. Variation of channel parameters with time is studied and an alternative approach to modelling long-term fading deterministically is suggested. Power spectral densities, autocorrelation functions, fade probabilities, level crossing rates and average fade durations are also investigated.
Article
Recent advances in the electronics industry and wireless communication have enabled the evolution of innovative application domains. Smaller embedded processors and systems have allowed a new level of mobile communication and interaction in everyday life. In particular, the expansion of broadband wireless services and the advancement of handheld technology have allowed for real-time patient monitoring in locations where not previously possible. Low-cost sensors and wireless systems can now create a constantly vigilant and pervasive monitoring capability at home, work, and in conventional point-of-care environments (e.g., primary care physician offices, outpatient clinics, and rehabilitation centers). A large research community (e.g., the UCLA Wireless Health Institute) and a nascent industry is beginning to connect medical care with technology developers, vendors of wireless and sensing hardware systems, network service providers, and enterprise data management communities. Wearable devices focusing on personal health, rehabilitation, and early disease detection are now being prototyped. All of this has led to the new notion of "wireless healthcare." In this paper, we have presented an infrastructure for a typical wireless healthcare application-a smart cushion for back pain prevention. Many other interesting applications can be developed based on similar frameworks. For instance, the Nike+iPod sport kit can be simply implemented by integrating the on-cushion circuitries into the insole of the shoes. Due to the configurability of the system, design issues such as power and reliability can be optimized through modifications of the data sampling rate, communication frequency, and the analysis algorithms running on the handset.
Article
This paper describes an ultra-low power (ULP) single chip transceiver for wireless body area network (WBAN) applications. It supports on-off keying (OOK) modulation, and it operates in the 2.36–2.4 GHz medical BAN and 2.4–2.485 GHz ISM bands. It is implemented in 90 nm CMOS technology. The direct modulated transmitter transmits OOK signal with 0 dBm peak power, and it consumes 2.59 mW with 50% OOK. The transmitter front-end supports up to 10 Mbps. The transmitter digital baseband enables digital pulse-shaping to improve spectrum efficiency. The super-regenerative receiver front-end supports up to 5 Mbps with $-75~{\rm dBm}$ sensitivity. Including the digital part, the receiver consumes 715 $\mu {\rm W}$ at 1 Mbps data rate, oversampled at 3 MHz. At the system level the transceiver achieves ${\rm PER}=10 ^{-2}$ at 25 meters line of site with 62.5 kbps data rate and 288 bits packet size. The transceiver is integrated in an electrocardiogram (ECG) necklace to monitor the heart's electrical property.