Innovative Movement Monitoring System for Elderly using Passive Infrared and Linear Phased Antenna Arrays

Transcription

1 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 Suceava, Romania 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 ISBN:

2 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:

3 low cost margins we choose to use a common glassreinforced 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 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 b) c) Fig. 3. Bowtie antenna reflection coefficients, Directivity for phi = 0 b), Directivity for phi = 90 c) and 3D radiation pattern From Fig. 3. 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 b) c) Fig. 5. Patch antenna reflection coefficients, Directivity for phi = 0 b), Directivity for phi = 90 c) and 3D radiation pattern 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., 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. is a bell shape type. As seen on Fig. 5. 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). φ = k N i) d sin( ) (1) i 0 ( θ 0 ISBN:

4 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. 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 dB. 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. Fig elements bowtie antenna array, Directivity for θ0 = 0 b), Directivity for θ0 = 22 c) and Directivity for θ0 =45 Fig. 6. 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 Fig elements bowtie antenna array, Directivity for θ0 = 0 b), Directivity for θ0 = 22 c) and Directivity for θ0 =45 The design of a printed linear antenna arrays with 5 bowties elements is shown in Fig. 7.. 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:

5 maximum amplitude of dB. 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 db and 2 grating lobes are present. Scanning further to 45 as in Fig. 7. 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. 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 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 db. Further changing the array scanning angle to 45 as in Fig. 8. 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. Fig elements bowtie antenna array, Directivity for θ0 = 0 b), Directivity for θ0 = 22 c) and Directivity for θ0 =45 Fig. 8. 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 degree is plotted for spacing between elements of 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 db. At 0.75 λ the two main lobes have an opening of 7 degree. 22 secondary lobes are visible, having maximum amplitude of db. Scanning the array to 22 Fig elements bowtie antenna array, Directivity for θ0 = 0. b), Directivity for θ0 = 22 c) and Directivity for θ0 =45 In Fig. 9. is shown the design of 11 elements bowties printed antenna array. In Fig. 9.b) the normalized directivity of the array scanned to 0 degree is plotted for spacing between elements of 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:

6 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 dB. 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. e) f) g) Fig elements patch antenna array, 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, 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. 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, 15 b), 30 c) and 45. ISBN:

7 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 e) Fig elements reflector bowtie antenna array, Bowtie antenna reflection coefficients b), Directivity of reflector bowtie and patch antenna for θ0 = 0 c), for θ0 = 22 and for θ0 = 45 e) e) Fig D radiation pattern of 9 elements reflector bowtie antenna array at θ0 = 0, θ0 = 15 b), θ0 = 30 c) and θ0 = 45 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 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 , and by contract no. POSDRU/107/1.5/S/ References: [1] S. Hekimi, L. Guarente, "Genetics and the specificity of the aging process" Science, Vol. 299, n. 5611, pp , [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 [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 , [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 , [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 ISBN: