ULTRASONIC SENSORS FOR THE ELDERLY AND CAREGIVERS
IN A NURSING HOME
Toshio Hori
Digital Human Research Center, National Institute of Advanced Industrial Science and Technology & CREST, JST.
2-41-6, Aomi, Koto-ku, Tokyo 135-0064, JAPAN
Email: t.hori@aist.go.jp

Yoshifumi Nishida
Digital Human Research Center, National Institute of Advanced Industrial Science and Technology & CREST, JST.
2-41-6, Aomi, Koto-ku, Tokyo 135-0064, JAPAN
Email: y.nishida@aist.go.jp
Keywords:

Intelligent nursing home, ultrasonic 3D tag system, location awareness.

Abstract:

Workloads on caregivers in nursing home are increasing as the imbalance between the number of elderly
people and that of caregivers becomes larger. Excessive workloads on caregivers must be reduced not only
because they become burdens for caregivers but also because they deteriorate the quality of nursing care. Oneof such workloads is routine patrol for monitoring the status of the elderly and for detecting accidents on theelderly as soon as possible. If the number of unnecessary patrols is minimized, caregivers will be able to spend
their time on high touch care and humane communication. The authors have been developing an ultrasonic 3D
tag system which locate ultrasonic tags in real time, and employed the system in a nursing home to monitor
positions of the elderly people. If the system locates the elderly people continuously and robustly, and if it
can notify caregivers about the occurrence of accident-prone activities promptly, caregivers will be releaved
from their unnecessary workloads. This paper describes the research background, system overview, system
implementations, and experimental results.

1

INTRODUCTION

The world has been rapidly aging during the last few
decades and it is projected that this trend will continue for several more decades. Aging of population
has become one of the most serious and urgent problems that almost all the countries are facing and must
tackle. Problems incurred by aging are not only the
problem of decreasing working populations but also
the problem related to the shortage of caregivers for
elderly people. The number of the elderly of whom
each caregiver takes care in nursing homes is certainly
increasing and the imbalance between the number ofthe elderly and that of caregivers will deteriorate thequality of nursing care.
In nursing home, caregivers patrol the entire homeregularly to prevent the elderly from meeting with serious accidents and, even if they have accidents, to detect occurrence of accidents promptly. Besides such
patrolling, caregivers must often visit nursing rooms
where nurse calls sounded from to take care of inhabitants. The number of caregivers is usually much lessthan that of the elderly so they are very busy taking
care of the elderly. There is an overwhelming needfor alleviating such workloads on caregivers.

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On the other hand, the authors are involved in research on “human behavior modeling”(Hori, 2001;
Nishida et al., 2004) and have been developing an environment in which a system observes inhabitants andrecognizes their behaviors(Kitamura et al., 2004). By
installing such observation system into elderly carehomes, we believe that the system can recognize thebehaviors of elderly people and provide some usefulsupport for caregivers. To be concrete, if the system
can detect accident-prone activities of the elderly beforehand and notify caregivers of the occurrence, theirexcessive patrols for detecting accidents or accidentprone activities will be minimized and, consequently,
caregivers will be able to spare their time for hightough care for and humane communication with theelderly.
This paper introduces an ultrasonic sensor system
for a nursing home. The system uses ultrasonic sensors to observe activities of the elderly people in anursing room. The system is composed of two subsystems, a wheelchair locator subsystem and an ultrasonic radar subsystem; the former works for tracking
position of a wheelchair which an elderly person uses
and the latter monitors human head’s position on andaround bed. When these two subsystems work coop-

ULTRASONIC SENSORS FOR THE ELDERLY AND CAREGIVERS IN A NURSING HOME

eratively, activities of the elderly in a nursing room aremonitored continuously and remotely without invading his/her privacy, so their accidents will be avoided
or minimized if the system can recognize and notify
the accident-prone activities to caregivers beforehand.
This paper is organized as follows: Section 2
presents several works related to location systems andsupport technologies. Secondly, Section 3 describes
background of the system and outline of the system,
briefly. Then Section 4 presents the system implementations and several experimental results and, finally, Section 5 concludes this paper.

Touch Sensor

Floor Mat
Sensor(a) Touch sensor on a (b) Floor mat sensor at
handrail of a bed
bedsideFigure 1: Sensors used in a nursing home

3
2

RELATED WORKS

Concerning location systems and their technologies,
Hightower and Borriello presented a good survey andtaxonomy in IEEE Computer(Hightower and Borriello, 2001).
The Active Bat system(Harter et al., 1999) developed at AT&T Cambridge is the system which is almost same to ours. The system uses ultrasonic emitters, Active Bats, and a grid of ceiling-mounted ultrasonic receivers. Bats are attached to objects or personnel and their positions are computed with the accuracy of approximately 3cm.
The Cricket Location Support System(Priyantha
et al., 2000) takes the opposite approach. In thissystem, ultrasonic emitters are installed in the environment and receivers are embedded in the objects.
So triangulation computation is performed on the objects’ side and, therefore, privacy of humans who have
objects is not invaded.
As for support technologies, many interesting articles are posted in IEEE Pervasive Computing.
Stanford introduced an elder care home, the Oatfield Estates(Stanford, 2002). The home had employed IR and RF wireless communication technologies not only for surveillance but also for monitoring
health condition of the elderly.
The CareMedia project is an on-going research
project at CMU(Hauptmann et al., 2004). They installed four cameras and microphones in a nursing
home in Pittsburgh and recorded video images over a
week in their preliminary study. Analyzing the video,
they tried to track the elderly’s movement and to extract their activities in the nursing home.
SIMBAD (Smart Inactivity Monitor using ArrayBased Detectors) is a sensor system developed by Sixsmith(Sixsmith and Johnson, 2004). They utilize IR
sensor arrays as thermal imaging detectors to observe(in)activities of inhabitants.
Similar systems are too numerous to mention. We
believe that this is because these support technologies
are getting a lot of attention all over the world.

ULTRASONIC SENSORSYSTEM FOR ELDERLY CARE
HOMESThis section firstly presents the background of thisproject. Then the Ultra Badge System developed by
the authors is introduced briefly and, lastly, we outline
our proposed system for elderly care homes.

3.1 Background of the Project
The authors started the “Sensorized Elderly CareHome” project in the mid-summer of 2003 and havebeen implementing a system which reduces workloads on caregivers using a sensor network. This isa cooperative project with a nursing home in Tokyo.
To begin with, we interviewed caregivers of thenursing home and categorized accidents of the elderly
into the following two cases:
1. Falls—Users of wheelchair or walker tend to fall
down when they transfer from their wheelchair/
walker to their bed or a toilet seat and vice versa.
2. Wanders—Elderly people who suffer from senile
dementia, such as Alzheimer’s disease, tend to
wander around day and night.
To detect these accidents, several kinds of contacttype sensors are already used in the nursing home. For
example, touch sensors (Figure 1(a)) were attached tohandrails of beds and floor mat type pressure sensors(Figure 1(b)) were put at bed side. Both sensors had
been used for detecting the elderly falling down from
his/her bed or trying to sneak out of the bed. However,those sensors had little effect on preventing accidents
from occurring because: (1) the elderly, though suffering from senile dementia, often learn how to escapebeing detected by the sensors, (2) the sensors often
emit false alarms when, for example, a person turns
over and touches the sensor by chance while sleeping,and (3) the sensors detect the occurrence of accidents
but cannot prevent accidents from occurring even if
they work correctly.

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Ultrasonic
Emitters(a) Tiny type (1×1×2cm; (b) Long life battery typecomparison with an US (Active for 2mon. withcent coin)
Li-Ion battery)

UltrasonicUltrasonic Receivers
Signal for Network
LocatorUltrasonic
Signal for
Radar

Nurse
Call

Figure 2: Variety of Ultra Badges

According to the caregivers, more than 85% of theresidents are suffering from senile dementia so theycannot expect the residents to put on any devices.
Therefore, we have to monitor the elderly without
putting any devices on their bodies. And, moreover,cameras are unacceptable because they may invade
the privacy of the elderly.

Detection
Areas

Figure 3: Schematic diagram of the Ultrasonic Sensor Network System for a nursing home

• The system monitors beds, bedsides and the side of
toilet seats because the locations where falls occur
are relatively limited to those places,

3.2 The Ultra Badge System• The system monitors the elderly remotely and does
not expect them to put any devices on their bodies,

The authors have been developing an ultrasonic 3D
tag system(Nishida et al., 2004; Hori et al., 2003)
which tracks positions of multiple ultrasonic tags continuously for monitoring human behaviors. We call it
Ultra Badge System.
The Ultra Badge System consists of ultrasonic receivers embedded in the environment and wirelesssmall ultrasonic emitters. We named the emitter Ultra Badge. Figure 2 shows two types of Ultra Badges
developed by the authors. The left picture is a tiny
type whose size is 1cm×1cm×2cm, and the right one
is a long life battery type which uses a Li-Ion batteryof mobile phone and is active for two months using
sleep mode.
By embedding many receivers whose 3D positions
are known beforehand in an environment, the system
can obtain a badge’s position from distance data using
multi-lateration technique. Experiments conducted in
our laboratory exhibited that the accuracy of position
estimation was about 20 to 80mm and the resolution
was about 15mm in horizontal directions and about
5mm in vertical direction by using a robust estimator,
RANSAC(Fischler and Bolles, 1981).

• The system expects the elderly to use wheelchairs
or walkers,

3.3 Outline of the Ultrasonic Sensor
System for Detecting Falls in a
Nursing Home
From the interview with caregivers, we summarized
the targets of our sensor system as follows:• The system prevents falls from occurring in thenursing home,

112• The system uses an existing nurse call system tosend alarms to caregivers when it detects accidentprone activities, and• The system must respect and must not invade theprivacy of the elderly.
We designed an Ultrasonic Sensor Network System
for the Nursing Home based on the above considerations. Figure 3 is a schematic diagram of the system. The system consists of (1) embedded ultrasonicreceivers, (2) embedded/wireless ultrasonic emitters(Ultra Badges) and (3) a sensor network which connects receivers and emitters. In addition to these main
components, the system uses a synchronous signal
generator to synchronize the emitters/receivers internal timers, an RF transmitter to activate wireless emitters, and a PC for data processing.
The system is composed of two subsystems: wheelchair locator and ultrasonic radar. The wheelchair locator subsystem uses Ultra Badges attached
to wheelchairs to monitor their position remotely andthe ultrasonic radar subsystem uses ultrasonic emitters embedded in the ceiling to monitor activities ofthe elderly on their beds. The subsystems are connected to a nurse call system and they call caregivers
whenever they detect predefined events leading to accidents. Details of these subsystems are described in
Section 4.
In this system, information transmitted throughthe air is wireless emitters’ IDs only, and ultrasonicpulses sent from any emitters do not carry any information on the individuals being monitored. The sys-

ULTRASONIC SENSORS FOR THE ELDERLY AND CAREGIVERS IN A NURSING HOME

Ultrasonic
Receivers

Figure 4: Ultrasonic receivers on the ceiling

Ultrasonic
ReceiverUltrasonic
3D TagFigure 5: Enlarged view of areceivertem does not collect unnecessarily rich information,such as the images taken by cameras. We can therefore conclude that the level of privacy invasion is minimized in this ultrasonic sensor network system.

Figure 6: A wheelchair and an Ultra Badge attached

WashstandToilet4

IMPLEMENTATIONS OF THE
SYSTEM AND EXPERIMENTAL
RESULTSThis section presents a wheelchair locator subsystem
and an ultrasonic radar subsystem in detail. The aimof the former subsystem is to detect the wheelchairapproaching one of areas where falls are likely to occur and the aim of the latter is to detect the elderly
getting up and going out of their beds.

4.1 Wheelchair Locator Subsystem
The authors installed the Ultra Badge System formonitoring positions of a wheelchair in one room of
the nursing home. We embedded 99 ultrasonic receivers on the ceiling of the room. Appearance of theceiling and an enlarged view of a receiver are shownin Figure 4 and 5, respectively. All the other apparatus are hidden behind the ceiling so the room looks
the same as the other rooms except for the ceiling.
An Ultra Badge was attached to the wheelchair thatthe subject of this experiment uses. Figure 6 shows
the wheelchair and an Ultra Badge attached to theback of the seat. The system activates the badge at
5 Hz and tracks its position continuously.
In the room, we defined detection areas in front of
the bed that the subject uses and at the entrance ofa toilet. The subsystem is connected to a nurse callsystem and, when it detects the wheelchair entering
one of the areas, it notifies caregivers that the subject
is approaching the place where accident is likely tooccur. Though we have not measured the time fromthe nurse call alarm to caregivers’ arrival, it seems that

Bed

Bed

Bed

Bed

Figure 7: Trajectory of the wheelchair

both the position of detection areas and the timing ofalarm work for caregivers to support the subject.

4.2 Experimental Results of the
Wheelchair Locator Subsystem
This subsystem has been running since January, 2004,
and taking logs of wheelchair’s position. Figure 7 is
its trajectory obtained during the operation. The line
segments are the trajectory and purple dots are the receivers’ positions on the ceiling. Yellow and blue rectangles indicate bed positions and detection areas, respectively. The subject uses the lower-left bed so we
preset the detection areas in front of the bed and at theentrance of the toilet.
This experimental data was obtained from 8:00AM
to 10:00AM on Aug. 15th, 2004 and, according to thelog, the system correctly sent alarms when the wheelchair got into either detection area. So we may saythat the system was almost working fine.

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head location
measured location
receivertransmitter
1800

50

900
250 200

100

1200

250

250

345

z (cm)

250

220

75

150
-20
0

200
20

Ultrasonic Radar150

y (cm)

40

100
60

50
80

Figure 8: Ultrasonic emitters/receivers on the ceilingx (cm)

0

Figure 9: Evaluation of localization accuracy of humanhead

In one night, the system sent alarms several
times so a caregiver went to the nursing room tofind that the subject was going to the toilet withher wheelchair.
The contact-type sensors used for the subject could
not have detected such events at all so no caregivers
had thought the subject went out of bed in the night.
But, with the assistance of this system, they found thatthe subject had symptoms of frequent urination.
Such sneaking out could not be detected with awearable-type device if the subject (deliberately) forgot to put the device on. Cameras could have detected
the events if their installation was permitted in thenursing room, but they need someone to keep watching all monitors to detect such events. So we are confident that this is a good example which exhibits theeffectiveness and the superiority of our system.

4.3 Ultrasonic Radar Subsystem
The wheelchair locator subsystem is a system to locate wheelchair so, theoretically, it cannot detect theactivity of the elderly on their beds. But, of course,
falls from bed must also be avoided and we need tomonitor the activity on beds to detect such accidents.
So we developed this ultrasonic radar subsystem.
The subsystem comprises several ultrasonic emitters and receivers embedded on a ceiling. The subsystem activates emitters one by one and measures
time-of-flight of ultrasonic pulses, just the same as thewheelchair locator subsystem. When the system obtains the distance data, the reflection point is locatedon a spheroid whose foci are the emitter and the receiver. So the position of the reflection point is calculated by solving simultaneous equations of at least
three spheroids.

114

170

170

160

160

z [cm]

z[cm]location of a human head

During the operation, the system detected the otherevents that even caregivers did not know at all. Oneof such events that the system disclosed was the following:

150

150

140

140

130
80

130
80

y[cm]

40 0

0

50

100 150 200

x[cm]

40 0

y [cm]

050

100 150 200

x [cm]

Figure 10: Tracking a head of moving human

Figure 8 depicts our experimental setup. In thissetup, we set 18 ultrasonic emitters and 32 receivers
on a panel, and placed it as a ceiling at 230 cm heightfrom the floor level. In this experimental system, thesampling frequency is 1 Hz, i.e. every emitter is activated every one second in turn.
This subsystem is still under development and is
not installed in the nursing home. So the experimental
results presented in the next subsection were obtainedby this experimental setup.

4.4 Experimental Results of the
Ultrasonic Radar Subsystem
The accuracy of localization was measured to evaluate the ability to detect the human head location.
Figure 9 shows the results, where the blue dots andthe red crosses indicate true positions of the head andpositions measured by the subsystem, respectively.
All the distance errors between corresponding points
were within 5 cm so we think that the system has sufficient accuracy to locate human head.
As the subsystem calculates the reflection point periodically, it can obtain a trajectory of a human head,though the resolution is not so precise because of thesampling rate. Figure 10 illustrates the tracking results. The upper parts show the trajectories when thesubject moved as shown in the lower parts.

ULTRASONIC SENSORS FOR THE ELDERLY AND CAREGIVERS IN A NURSING HOMEACKNOWLEDGMENT
The authors wish to express our great gratitude to Mr.
Yuichi Motomura at the nursing home Aizenen for his
great help on conducting this project. We express ourappreciation to Mr. Hiroshi Aizawa and Mr. Shin’ichi
Murakami for their fruitful research results.

REFERENCES
Figure 11: Coordination of the wheelchair locator subsystem and the ultrasonic radar subsystem

4.5 Integration of Two Subsystems
When these two subsystems work cooperatively, they
can monitor the activities of the elderly on beds andin the room. We integrated them into an experimental system shown in Figure 11. The figure illustrates
an example of cooperation of two subsystems. In the
figure, a person is sitting on a bed and transferring toa wheelchair. The red rectangle indicates the positionof his head and the white cross indicates the positionof the Ultra Badge attached to the wheelchair.
One of the advantage of this integration is thatboth subsystems use the same ultrasonic technology;
that is, installing a large-scale ultrasonic sensor network system suffices both subsystems’ requirements.
The total system is expected to work for detecting
accident-prone activities and for preventing accidents
from occurring in a nursing home.

5

CONCLUSIONSThis paper presented an ultrasonic sensor network
system for nursing homes. We developed two subsystems. The wheelchair locator subsystem was installed
in a nursing home and has been running successfully.
The ultrasonic radar subsystem is still under development but will be installed in the nursing home soon as
its experimental results satisfied our requirements.
The authors think that accidents on the elderly will
be avoided or minimized when both subsystems work
cooperatively; i.e., the total system monitors the elderly, recognizes accident-prone activities and notifies their occurrence to caregivers beforehand. If thissensor network system works in place of caregivers,
their workloads are alleviated and they will be able tospare their time for high touch care for the elderly.
The authors believe that nursing homes will befully sensorized in the near future.

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