innovative movement monitoring system for elderly · pdf fileinnovative movement monitoring...

Innovative Movement Monitoring System for Elderly using Passive

Infrared and Linear Phased Antenna Arrays

S. SFICHI, A. GRAUR, V. POPA, I. FINIS, A. LAVRIC

Department of Computers, Electronics and Automation, “Stefan cel Mare” University of Suceava,

Str. Universitatii nr.13, RO-720229 Suceava, Romania

[email protected]

Abstract: - This paper presents the development of a complex innovative system for detecting and monitoring

the movement of elderly people inside a living area. In order to achieve a desired low power consumption the

purposed system comprise of Passive Infrared (PIR) sensors for coarse movement detection and

Radiofrequency ZigBee network nodes equipped with phased antenna arrays for precise location estimation.

Each person wears a compact ZigBee personal identification node. The PIR sensors detect the movement of

persons inside the living area and activate the corresponding scanning nodes operating on 2.4 GHz band. The

scanning nodes perform a sweep across the living area and use scanning angle and RSSi information in order to

determine the location estimation of each ZigBee node worn by monitored persons. By placing the antenna

array node at one corner of room to be monitored the sweep must be of 90 degree. Various printed arrays

designs having patch and bowtie antenna as array elements were analysed with the help of Ansoft High

Frequency Structure Simulator suite in order to select a best match configuration for our purpose. In the end an

antenna array setup consisting of 9 bowtie shielded elements, placed at a distance of half wavelength was

chosen for implementation of the system.

Key-Words: - Linear antenna arrays, Microstrip antenna arrays, Motion detection, Phased arrays.

1 Introduction As a result of increased living standards and with

the help of new medical achievements that reduce

premature mortality, the aging of the population is

an important factor in today society. People

nowadays have more freedom to choose whether

and when they want to raise children and many

young people prefer to devote themselves to gain

professional recognition and leave in the second

plan the raising of children. This leads to a

pronounced decrease in the birth rate and many

fears that life will be much more difficult in an older

society in which we live and there will be inevitable

tensions or even open conflicts between generations.

The aging process brings a number of changes in

the body that influence its physical functioning. The

levels of these changes are accentuated by the

presence of certain chronic diseases or genetic

predisposition [1]. Various modifications may be

identified at the sensory functions, at the level of

organs and anatomical systems, psychomotor

functioning, as well as the personality. These

changes may be a result of the normal aging process

called senescence or they are the consequence of the

pathological process which accelerates and

exaggerates the normal aging process, defined by

the concept of senility.

Age may create a situation of temporary or

permanent dependency or loss of personal autonomy

depending on the evolutionary potential of each

disease diagnosed.

Thus there are depended people with health

problems or any other kind that have to be

supervised inside a living area such as a healthcare

facility or even inside their house. Many don’t need

to be under specific supervision. They don’t need

another person to be around all the time and hiring

someone to act as a personal assistant or as a

superintendent in this case is very expensive and

unreasonably.

An automated and thus less costly system that

will keep track of the movement of these persons

inside a living area is a more feasible solution [2].

The system will also monitor vital signs status and it

will send an alarm to an Emergency Dispatch

Service when necessary. Such a system must be

integrated in healthcare facility or in the house of

depended people; it must have low power

consumption and its operation and functioning must

be completely transparent to an elderly person.

This article is focused on the development of an

innovative movement monitoring system for elderly

peoples, based on passive infrared and linear phased

antenna arrays operating on 2.4 GHZ ISM band.

The general system architecture and the study of

various antenna arrays configurations consisting of

printed antenna elements are presented. In order to

achieve precise location estimation the antenna

Advances in Automatic Control, Modelling & Simulation

ISBN: 978-1-61804-189-0 219

array must have a sweep of 90 degree, a narrow

main beam, low intensity and preferably few side

lobes [3]. Due to cost and size restrictions, the

number of antenna elements is also an important

factor in the design of the array. Simulations of

designed phased antenna arrays were performed on

Ansoft – High Frequency Structure Simulator.

2 System architecture The system presented in Fig. 1 and described in this

article is designed to accomplish the monitoring

process of elderly or depended persons at healthcare

facilities or at their own house. Thus, it is conceived

to be integrated in living areas without disturbing

the residents when used and to be highly

autonomous. The system consists of roughly four

major components: low power coarse movement

detection, accurate location estimation, vital signs

monitoring and a server which keeps track of

people’s activities, issues an alert when necessary

and act as a gateway to Emergency Dispatch

Services. The low power movement detection subsystem

comprises of Passive Infrared (PIR) sensors places

in every room. The PIR intrusion detection sensors

are used on massive scale on house alarm systems

and in industry, thus making them a mature, low

power and very inexpensive technology. Passive

infrared sensors are more energy efficient because

they detect electromagnetic radiated energy from

external sources, particularly that emitted by people,

while active infrared sensors generate a multiple

beam pattern of modulated infrared energy and react

to a change in the modulation of the frequency. This

emission of IR radiation makes the active infrared

system power hungry. The PIR sensors are

connected to the server via low power ZigBee

wireless network nodes (Yc). When a person moves

inside the area monitored by the PIR sensor, the

movement is detected and the sensor send a message

to server via ZigBee network.

The accurate location estimation subsystem is

built around a phased antenna array (AA) in order to

avoid limitations of path loss and indoor reflections,

operating on 2.4GHz [4]. The array makes a sweep

of the room to precisely locate the Vital Sign

Monitor (VSM) which acts as a beacon and it is

worn by the monitoring person. To preserve power

and to limit the use of electromagnetic spectrum, the

array scanning process is activated by the server

after the PIR sensor located in the same room

detects movement. The sweep is also initiated at

regular intervals to locate the persons which do not

move after periods of time.

Fig. 1 Movement Monitoring System implementation

inside a living area. PIR Sensor, Phased antenna array

and the ZigBee vital sign monitor are shown.

The phased antenna array subsystem uses beam

forming to create and steer a main beam from -45

degree to 45 degree measured to the array normal,

thus fully covering the 90 degree of sweep angle

inside a living area. The antenna array controller

initiate the scanning process by forming and

orienting the main beam to an angle of -45 degree,

and then ask the corresponding Vital Sign Monitor

to report the value of Received Signal Strength

indicator (RSSi). Next, the controller steers the main

beam to the next incremented scanning angle and

the process is repeated. When a full sweep is

completed, the antenna array controller computes

the location estimation based on received RSSi and

the corresponding steering angles. This information

is then transmitted to the server, and the antenna

array enters a low power state.

The server component of the system comprise of

a server connected to the entire ZigBee network. It

receives information from the PIR sensors when

they detect movement and activates the

corresponding antenna array in order to determine

the location estimation of persons inside the room

and records each person’s vital signs. The server

also keeps track of previous location for each person

and creates a map of movement in order to predict

the behaviour of peoples. In case a person does not

move for a longer period of time, or if the received

vital signs fall below a previously establish

threshold, an alarm is composed and transmitted to

an Emergency Dispatch Service, either as a voice

message, or as a SMS or data message.

3 Antenna arrays radiating elements As part of the development of the antenna array

creating the array radiating elements is an important

step. Since the antenna array must have relatively

low size in order to be installed indoors, we choose

to implement the radiating elements on printed

circuits board [5]. In order to maintain the array to


ISBN: 978-1-61804-189-0 220

low cost margins we choose to use a common glass-

reinforced epoxy FR4 printed circuit board. The

technical documentation specifies for the chosen

material a dielectric thickness of 1.5mm, a relative

permittivity of 4.4, and a loss tangent of 0.015.

These information where used to design two types

of printed antenna, bowtie and rectangular patch

antenna with a resonant frequency of 2.4GHz.

Numerical simulations where conducted with the

help of Ansoft High Frequency Structure Simulator

suite. Ansoft HFSS is a well proven tool for 3D full

wave electromagnetic field simulation, offering

multiple solver technologies based on either the

finite element method, or the integral equation

method.

The shape and dimensions of the printed bowtie

antenna are shown in Fig. 2. The arm length is

12.9mm, outer radius is 9.34mm, outer width is16.9

mm, the port gap and the inner width is 0.71mm.

Fig. 2 Bowtie antenna radiating element shape and

dimensions

a) b)

c) d)

Fig. 3. Bowtie antenna reflection coefficients a),

Directivity for phi = 0° b), Directivity for phi = 90° c)

and 3D radiation pattern d)

From Fig. 3.a) the proposed bowtie printed

antenna has a large bandwidth and resonates at

2.4GHz. Normalized antenna directivity is plotted

for H and E plane on Fig. 3.b) and c). A 3D plot of

radiation pattern is shown in Fig. 3.c).

Fig. 4. Patch antenna radiating element shape and

dimensions

a) b)

c) d)

Fig. 5. Patch antenna reflection coefficients a),

Directivity for phi = 0° b), Directivity for phi = 90 ° c)

and 3D radiation pattern d)

The shape and dimension of patch antenna are

presented on Fig. 4. The patch dimension along x

Axis is 38.04mm and 29.48mm along y Axis. Inset

distance is 9.78mm, inset gap is 1.43mm, and the

feed width is 2.86mm. The FR4 substrate is of

rectangular shape measuring 6.6cm along the x axis

and 9.1cm along y axis. The bandwidth of the patch

antenna, as shown on Fig. 5.a), is narrower than that

of bowtie antenna. Another difference between

bowtie and patch antenna is the antenna directivity

and radiation pattern. The bowtie antenna directivity

presents a quasi-omnidirectional characteristic on H

plane as seen on Fig. 3.b) and the radiation pattern is

of toroid shape. The patch antenna directivity on H

plane shown on Fig. 5.a) is a bell shape type. As

seen on Fig. 5.d) the radiation pattern of patch

antenna in form of an apple extends only to the front

side of the antenna.

4 Phased antenna arrays The envisioned location estimation subsystem uses

linear phased antenna array to create and to steer the

main lobe. The width of the main beam, the number

and the intensity of side lobes or grating lobes

depends on the number of elements in the array, the

spacing between them and the scanning angle. To

steer the main beam to a desired direction θ0, one

need to feed the array elements by applying

progressive phase shifts ϕi according to (1).

)sin()( 00 θφ diNki −−= (1)


ISBN: 978-1-61804-189-0 221

where k0 is the free-space wavenumber (2π/λ0)

and d represents the distance between antenna array

elements. N is the total number of array elements.

Having designed two types of printed antenna

array, the next step was to develop the antenna

array. We simulated various configurations of linear

antenna array with elements number ranging from 3

to 11, and spacing between antenna elements

between 0.25 and 0.75 wavelengths (λ). To

accomplish the requirements of our application the

antenna array should have a narrow main beam,

preferably no grating lobes in visible space, a low

number and low power of side lobes and the ability

to steer the main lobe from -45 degree to 45 degree

to the array normal.

a)

b) c)

d)

Fig. 6. 3 elements bowtie antenna array a), Directivity for

θ0 = 0° b), Directivity for θ0 = 22° c) and Directivity for

θ0 =45° d)

Fig. 6.a) shows the design of a printed linear

antenna arrays with 3 bowties elements. In Fig. 6.b)

the normalized directivity of array scanned to 0

degree is plotted for spacing between elements of

0.25λ, corresponding to an antenna length of 12 cm,

0.5λ for a length of 20 cm and 0.75 wavelength in

which case the array length is 28 cm. At 0.25λ

spacing the array pattern has 2 very broad main

lobes with beam width of 90 degree and no

additional side lobes. Increasing the spacing to 0.5λ

we observe two 42 degree main lobes and two side

lobes with -5.98dB. At 0.75λ the main lobes have an

opening of 23 degree. Six secondary lobes are

presented with maximum amplitude of -9.2dB.

Scanning the array to 22° as shown in Fig. 6.c)

radiation pattern has one main lobe of 204° at 0.25λ.

By increasing the spacing to 0.5λ we observe 2 main

lobes of 40° and 3 side lobes with maximum

intensity of -8.4dB. At 0.75λ the main lobes have 22

degree of wide, 3 side lobes with a maximum of -

9.75dB. Scanning further to 45° one large beam of

154° and one side lobe of -11dB is visible for 0.25λ

spacing. At 0.5λ, one large 124° main lobe and 3

side lobes with -2.2dB of maximum intensity are

visible. For 0.75λ spacing 2 main lobes of 37° and 2

side lobes of -9.4dB are present. There are also

visible 2 grating lobes.

a)

b) c)

d)

Fig. 7. 5 elements bowtie antenna array a), Directivity

for θ0 = 0° b), Directivity for θ0 = 22° c) and Directivity

for θ0 =45° d)

The design of a printed linear antenna arrays

with 5 bowties elements is shown in Fig. 7.a). The

normalized directivity of array scanned to 0 degree

is plotted in Fig. 7.b) for spacing between elements

of 0.25λ, corresponding to an antenna length of

18cm, 0.5λ for a length of 32cm and 0.75λ when the

array length is 48cm. At 0.25λ spacing the array

pattern has 2 main lobes with beam width of 58

degree and 2 side lobes with an intensity of -8.5dB.

Increasing the spacing to 0.5λ we obtain 2 main

lobes 19° wide and 6 side lobes with a maximum

intensity of -10.5dB. Further, increasing the spacing

to 0.75λ, the two main lobes have an opening of 15

degree and we observe 10 secondary lobes with


ISBN: 978-1-61804-189-0 222

maximum amplitude of -10.26dB. When we

increase the scanning angle of the array to 22° we

observe for 0.25λ spacing 2 main lobes with 46

degree of beam wide. At 0.5λ of spacing 2 main

lobes of 20° are visible and 6 side lobes with

maximum intensity of -7.2 dB. At 0.75λ the 2 main

lobes have a wide of 10°. Nine side lobes with

maximum intensity of -13.5 dB and 2 grating lobes

are present. Scanning further to 45° as in Fig. 7.d) a

large beam of 122° and 3 side lobes with -13.9dB

maxim intensity are visible for 0.25λ spacing. At

0.5λ two 30° main lobe and 7 side lobes with -7.9dB

of maximum intensity are visible. For 0.75λ spacing

2 main lobes of 21° and 8 side lobes of -11 dB are

present. There are also visible 2 grating lobes.

a)

b) c)

d)

Fig. 8. 9 elements bowtie antenna array a), Directivity for

θ0 = 0° b), Directivity for θ0 = 22° c) and Directivity for

θ0 =45° d)

Fig. 8.a) presents the design of a printed linear

antenna arrays with 9 bowties elements. In Fig. 8.b)

the normalized directivity of array scanned to 0


0.25λ, corresponding to an antenna length of 30 cm,

0.5λ for a length of 56cm and 0.75 wavelength in

which case the array length is 88cm. At 0.25λ

spacing between the elements the array pattern has 2

main lobes with main beam of 20° width and 6

additional side lobes with a maximum intensity of -

12dB. By increasing the spacing to 0.5 λ we observe

two 11 degree main lobes and 14 side lobes with a

maximum peak of -13.35 dB. At 0.75 λ the two

main lobes have an opening of 7 degree. 22

secondary lobes are visible, having maximum

amplitude of -11.9 dB. Scanning the array to 22°

scanning angle, the radiation pattern has 2 main

lobes of 30° at 0.25 λ and 6 side lobes with a

maximum intensity of -7°. Increasing the spacing to

0.5 λ we observe 2 main lobes of 12° and 15 side

lobes with maximum intensity of -12.3 dB. At a

spacing of 0.75 λ the 2 main lobes have a width of

7°. There are also present 20 side lobes with a max

of -14.29 dB. Further changing the array scanning

angle to 45° as in Fig. 8.d) it can be observed two

large beams of 106° and 6 side lobes of -15dB

visible for 0.25λ spacing. At 0.5λ, 2 main lobes of

19° and 14 side lobes with -8.5 dB of maximum

intensity are visible. For 0.75λ spacing 2 main lobes

of 9° and 19 side lobes of -9.4 dB are present. There

are also visible 2 grating lobes.

a)

b) c)

d)

Fig. 9. 11 elements bowtie antenna array a),

Directivity for θ0 = 0°. b), Directivity for θ0 = 22° c) and

Directivity for θ0 =45° d) In Fig. 9.a) is shown the design of 11 elements

bowties printed antenna array. In Fig. 9.b) the

normalized directivity of the array scanned to 0


0.25λ, corresponding to an antenna length of 36cm,

0.5λ for a length of 68cm and 0.75 wavelength in

which case the array length is 108cm.

At spacing between array elements of 0.25λ the

array pattern has 2 main lobes with beam width of

17 degree and 8 additional side lobes with a

maximum intensity of -13.2dB. Increasing the

distance between elements to 0.5λ the radiation

pattern presents two 10 degree main lobes and 18

side lobes with a maximum intensity of -12.3dB. At

0.75λ the main lobes have an opening of 6 degree.

30 secondary lobes are presented with maximum


ISBN: 978-1-61804-189-0 223

amplitude of -13.2dB. Changing the array scanning

angle to 22°, radiation pattern has two main lobes of

22° at 0.25λ. The eight side lobes have a maximum

intensity of -8.6dB. Increasing the spacing to 0.5λ

we observe that the 2 main lobes have a wide of 11°

and the 18 side lobes have a maximum intensity of -

12.3dB. At 0.75λ spacing between bowtie elements

the 2 main beams have a wide of 6°. The 27 side

lobes have a maximum value of -14.7dB. Scanning

further to 45° the two large main beams of 26° and 7

side lobe of maximum -15dB is visible for 0.25λ

spacing. At 0.5λ, two main lobes of 15° wide and 19

side lobes with a maximum intensity of -8.6dB are

visible. For spacing of 0.75λ two main lobes of 9°

and 26 side lobes of -11.6dB maximum intensity

plus 2 grating lobes are present.

a)

b) c)

d) e)

f) g)

Fig. 10. 9 elements patch antenna array a), Directivity for

θ0 = 0° with spacing between 0.35λ and 0.5λ b),

Directivity for θ0 = 0° with spacing between 0.5λ and

0.75λ c) Directivity for θ0 = 22° with spacing between

0.35λ and 0.5λ d), Directivity for θ0 = 22° with spacing

between 0.5λ and 0.75λ e) Directivity for θ0 = 45° with

spacing between 0.35λ and 0.5λ f), Directivity for θ0 =

45° with spacing between 0.5λ and 0.75λ g)

Analysing the results of bowtie array simulations

we concluded that the best compromise between

array size, array elements, the beam width of the

main lobe, the number and intensity of side lobes, is

to use an array with 9 elements spaced at 0.5λ in the

case of bowtie antenna elements. One important

characteristic of bowtie antenna array is the

presence of two main beams, one on each side of the

array. This may seem to be an inconvenience since

it is introducing an uncertainty factor if the signal

from the back of antenna penetrates the wall of an

adjacent room. However a setup consisting of a

bowtie antenna array can be used for simultaneous

scanning in two neighbouring room and

differentiation of targets can be done via PIR sensor

information, Wrist Vital Signs Monitoring id or by

the patterns of movement computed and stored by

the server.

In cases where the wall attenuation is too great to

use such a setup with good results it is necessary to

have an antenna array with only one main beam.

Therefore based on results already obtained we

designed a rectangular patch antenna array with 9

elements. We conducted various simulations with

spacing of antenna elements varying from 0.35λ to

0.75λ at several scanning angles and the directivity

of array in H plane was plotted in Fig. 10. Again, we

considerate that the best configuration for our use is

the antenna array with half wavelength spacing

between array elements.

Another antenna design developed during this

research was made by placing a reflector plate at the

back of a bowtie antenna array as shown in Fig.

11.a) in order to obtain only one main beam directed

to the front of the antenna. The reflector plate

connected to the ground was placed at 4 cm behind

the array. This modification altered the reflection

coefficient of the antenna elements, changing the

resonant frequency. We changed the dimensions of

the printed bowtie in order to make antenna resonant

again at 2.4 GHz, by increasing the outer width to

17mm and the outer radius to 11.3mm. The

reflection coefficient S11 values for original and

modified bowtie antenna element are plotted in Fig.

11.b). The directivity of 9 elements reflector bowtie

antenna in H plane is plotted on Fig. 11. c) to Fig.

11.e) along the directivity of 9 elements patch

antenna array for scanning angles of 0°, 22° and

45°.

Fig. 12 plots the 3D radiation pattern of 9

elements reflector bowtie with interspacing of 0.5 λ

between array elements at scanning angles of 0° a),

15° b), 30° c) and 45° d).


ISBN: 978-1-61804-189-0 224

a)

b) c)

d) e)

Fig. 11. 9 elements reflector bowtie antenna array a),

Bowtie antenna reflection coefficients b), Directivity of

reflector bowtie and patch antenna for θ0 = 0° c), for θ0 =

22° d) and for θ0 = 45° e)

b) c)

d) e)

Fig. 12. 3D radiation pattern of 9 elements reflector

bowtie antenna array at θ0 = 0° a), θ0 = 15° b), θ0 = 30°

c) and θ0 = 45° d)

5 Conclusions The aging process of human body may affect the

locomotors functions or personality. Depending on

their pathology some persons need assistance or

monitoring. This paper describes the architecture of

an automated Movement Monitoring System for

elderly or dependent people. The major advantage

of our approach is the use of low cost and low

power technology such as Passive InfraRed and

ZigBee network nodes. The PIR sensors detect

movement of persons inside living area and then the

antenna array subsystem makes a full sweep in order

to determine the precise location of persons. We

developed the antenna array for use in location

estimation applications considering various factors.

We simulated diverse printed antenna array

configurations such as patch and bowtie with the

help of Ansoft High Frequency Structure Simulator

suite. In the end we opted for two configurations of

printed bowtie antenna array with 9 elements placed

at half wavelength. The bowtie antenna has a large

bandwidth and the proposed configurations offer the

best compromise regarding size, cost, and beam

width.

6 Acknowledgement

This work was supported by the project "Knowledge

provocation and development through doctoral

research PRO-DOCT - Contract no.

POSDRU/88/1.5/S/52946", project co-funded from

European Social Fund through Sectoral Operational

Program Human Resources 2007-2013, and by

contract no. POSDRU/107/1.5/S/78534.

References:

[1] S. Hekimi, L. Guarente, "Genetics and the

specificity of the aging process" Science, Vol.

299, n. 5611, pp 1351-1354, 2003.

[2] S. Sfichi, A. Graur, V. Popa, I. Finis, A.-I.

Petrariu, "An Original Movement Monitoring

System for the Elderly using a WSN protocol",

11th International Conference on Development

And Application Systems, Suceava, Romania,

2012, pp. 91-94

[3] O. Manu, M. Dimian, A. Graur, "Radiation

Pattern Analysis and Advanced Phase Shifter

Development for designing Phased Smart

Antenna Arrays", Electronics and Electrical

Engineering, No. 1 (117), pp. 105-110, 2012.

[4] G. Buta, E. Coca and A. Graur, "Path Loss

Exponent Influence on Distance Estimation

between Wireless Sensor Nodes", Advances in

Electrical and Computer Engineering, vol. 10,

no. 1 pp. 110-115, 2010.

[5] D. Busuioc and S.-N. Safieddin, "Low-cost

antenna array and phased array architectures -

Design concepts and prototypes", in

International Symposium on Phased Array

Systems and Technology (ARRAY), 2010

IEEE, Waterloo, Canada, 2010, pp. 965-968.


ISBN: 978-1-61804-189-0 225

innovative movement monitoring system for elderly · pdf fileinnovative movement monitoring...

Documents