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Low-Power Bed / Seat Occupancy Sensor Based
on EMFi
Francisco Fernandez-Luque 1 , 2 , Juan Zapata 1 ,andRamon Ruiz 1
1 Depto. Electronica, Tecnologıa de Computadoras y Proyectos
ETSIT- Escuela Tecnica Superior de Ingenierıa de Telecomunicacion
Universidad Politecnica de Cartagena
Antiguo Cuartel de Antigones. Plaza del Hospital 1, 30202 Cartagena, Spain
{ juan.zapata,ramon.ruiz } @upct.es
http://www.detcp.upct.es
2 Ambient Intelligence & Interaction SLL. Edif. CEEIM mod. 11, 30100 Espinardo,
Murcia, Spain
ff.luque@ami2.net
Abstract. Ambient Assisted Living (AAL) systems demand is raising.
The use of bed / seat occupancy sensors is imperative for this kind of
ubiquitous monitoring systems. Pressure mats are a first way to solve this
feature, but several environmental dependencies make them weak to be
an ecient and reliable solution for large volume deployments. Solutions
based on force-to-resistor transducer seems to imply a too high power
consumption to be integrated on wireless sensor nodes. A force-capacitive
transducer based sensor has been proposed, implemented and tested in
this paper. This sensor, based on Electro-Mechanical Films (EMFi) is
able to detect force variations in a quasi-passive way. This detection is
used to trigger an active mechanism to measure the weight by means
of the transducer capacity. A low-power wireless sensor node prototype
including this new sensor has been assembled and tested with a wide
range of weights. The occupancy detection was successful and the power
consumption of the node was increased at less that a 15%.
Keywords: seat, chair, bed, occupancy, EMFi, AAL, ubiquitous moni-
toring, WSN.
1
Introduction
Increasing health care costs and an aging population are placing significant
strains upon the health care system. Small pilot studies have shown that meet-
ing seniors' needs for independence and autonomy, coupled with expanded use of
home health technologies, and provide improved assistential outcomes. Diculty
with reimbursement policies, governmental approval processes, and absence of
ecient deployment strategies has hampered adopting non-obtrusive intelligent
monitoring technologies.
In this field, DIA project - Intelligent Warning Device, from Spanish Disposi-
tivo Inteligente de Alerta - aims to develop devices which detect behaviour pat-
terns from their users and use them to take alert actions when significant variations
 
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