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CHAPTER 9
DESIGN AND DEVELOPMENT OF SUPPORTING
DEVICES FOR IMMOBILE PATIENTS
9.1 INTRODUCTION
In this part of this research, a wireless communication device
integrated with woven antenna, which could be incorporated into the bed
sheets or the medical jacket of the patients, who are confined to wheel chair
or bed, is developed and scrutinized for its performance.
To analyze the performance of the mattress developed, the devices
used for measuring interface pressure and temperature were also discussed in
this chapter.
9.2 DESIGN AND DEVELOPMENT OF WIRELESS
COMMUNICATION DEVICE INTEGRATED IN APPAREL
AND BED LINEN
9.2.1 Materials and Methods
In this work, the first phase focused on the development of Radio
Frequency communication device with a patch antenna made of conductive
fabric. The antenna was then tuned to a particular range, avoiding traffic
congestion with other radio signals. In the second phase, the device is
miniaturized and simplified so as to be incorporated in a hospital jacket or bed
linen. Effective connections between components were designed in such a
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way, so as to reduce power consumption. Then the device is embedded in the
garment so that it is totally inconspicuous and does not hinder the wearability
in any manner. The controls are set near the fingers, so that its operation
becomes evenmore user friendly.
9.2.1.1 RF Transceiver
A Transceiver is a two-way radio transceiver that is a combination
of transmitter/receiver in a single package. Sound waves in the form of
amplified electrical waveform, having a transmission frequency of 20.950
MHz. are transmitted through the antenna.
9.2.1.2 RF receiver
A radio frequency receiver (RF receiver) is a radio receiver that is
usually composed of several tuned radio frequency amplifiers followed by
circuits to detect and amplify the audio signal. The antenna picks up the radio
waves. This produces a very weak electrical signal, by electromagnetic
induction. This very weak signal is detected and demodulated into very weak
audio frequency. This is amplified by the pre-amplifier to a usable size. The
power amplifier is used to produce a large enough waveform to drive the
speaker. The speaker converts the electrical signal to sound energy that we
can hear.
9.2.1.3 Structure of Antenna
It is a component designed to send and receive the signals from one
place to other. For this work, the antenna was developed using woven
conductive fabric. The objective is unobtrusive incorporated into a garment
and suitable for mobile communication use. This antenna was characterized
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by first and second layer of electrically conductive woven fabric and a layer
of electrically insulating material between the first and second layer.
9.2.2 Results and Discussion
9.2.2.1 Development of RF Transceiver
Whenever the high output pulse is given to base of the transistor,
BF 494, the tank circuit is oscillated. The tank circuit consists of L2 and C4
generating 20.950 MHz carrier signal. Then the modulated signal is given to
LC filter section. After the filtration, the RF modulated signal is transmitted
through antenna. The circuit is shown in Figure 9.1 and the electrical
characteristics of the transceiver are given in Table 9.1.
Table 9.1 Electrical Characteristics of RF Transmitter
Parameter Sym. Min. Typ. Max. Unit
Operating Frequency(200 KHz) Vcc 20.950 MHz
Data Rate ASK 8K Kbps
Peak Input Current, 12 Vdc
SupplyITP 45 mA
Peak Output Power PO 10 mW
Turn On/Turn Off TimeT ON/
T OFF1 US
Power Supply Voltage Range Vcc 3 12 VDC
Operating Ambient Temperature TA -20 +85 Centigrade
Tx Antenna Out(3V) +2.4dB Vcc mA
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Figure 9.1 RF Transceiver
9.2.2.2 Development of RF receiver
The RF receiver is used to receive the encoded data which is
transmitted by the RF transmitter. Then the received data is given to transistor
which acts as an amplifier. Then the amplified signal is given to carrier
demodulator section in which transistor Q1 conducts depending on the signal.
Due to this, the capacitor C5 is charged and discharged, so that carrier signal
is removed and saw tooth signal appears across the capacitor. Then this saw
tooth signal is given to comparator. The comparator circuit is constructed by
LM558. The comparator is used to convert the saw tooth signal to exact
square pulse. Then the encoded signal is given to decoder in order to get the
decoded original signal. The circuit was designed as in Figure 9.2 and the
electrical characteristics of the receiver given in Table 9. 2.
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Table 9.2 Electrical Characteristics of RF Receiver
Parameter Sym. Min. Typ. Max. Unit
Operating Radio Frequency FC 20.950 MHz
Sensitivity Pref. -108 dBm
Channel Width -500 +500 KHz
Noise Equivalent BW NEB 5 4 KHz
Baseboard Data Rate 3 KB/S
Receiver Turn on Time 3 ms
Figure 9.2 RF Receiver
9.2.2.3 Woven Antenna
The special feature of the present invention is a woven antenna
capable of unobtrusive incorporation into a garment and suitable for mobile
telecommunications.
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The antenna is characterized by the following features,
First and second spaced layers of electrically conducting
woven antenna.
A layer of electrically insulating fabric between the first and
second layers.
Electrical contact between the first and second layers.
A connection of the first and second layers to
telecommunication equipment.
The antenna is incorporated into a chest portion of a garment or on
the bed. It is highly preferable that the layer of electrically conducting fabric
adjacent to a wearer of the garment is of substantially greater area than the
other layer of electrically conducting fabric and is connected as a ground
plane so that the user is isolated from the strongest electrical fields emitted by
the antennas.
In a preferred arrangement the antenna comprises a single piece of
electrically conducting fabric folded around the insulting fabric, whereby the
fold in the conducting fabric constitutes the first connection means.
The remainder of the handset can be made smaller and lighter than
the previous one, through separation of the component parts, particularly as
the overall size of many mobile telephone handsets is constrained by the size
of the antenna assembly used. Such an antenna is flexible and lightweight and
does not impede the movements of the user. The mobile telecommunications
equipment may be a mobile telephone or a pager or a wireless Local Area
Network.
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l
Figure 9.3 Principle of Woven antenna
A chest pad patch antenna comprises a lower layer of conducting
fabric in a ‘D’ shape as in the figure 9.3, a number of layers of insulating
fabric of the same size and shape as the lower layer and an upper layer of
conducting fabric which is approximately rectangular in shape and
substantially smaller than the lower layer. The upper and lower layers are
connected by a neck of conducting fabric.
A co-axial cable feeds the antenna, the core being connected to the
upper layer and the outer conductor being connected to the lower layer where
the insulating layers are cut away. The cable is connected to an item of mobile
telecommunications equipment.
The lower layer is to be positioned in a garment so as to be adjacent
to the wearer. The lower layer is connected as the ground plane of the antenna
and the relative shapes of the upper and lower layers are such that the ground
plane extends substantially beyond radiating edge of the upper layer and this
isolates the wearer from the strongest electrical fields. In addition, the overall
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bandwidth of the patch antenna is increased, and the amount of signal
absorbed by the wearer is reduced.
The antenna can be flexed in use to fit the chest of the wearer or on
the bed and therefore to be comfortable in use, but the antenna will still
remain fully operative. The conducting fabric is cut to have a “D” shaped part
and a smaller rectangular part joined by a short neck. The insulating layers are
also cut to have a “D” shaped part only, with a cut-out to allow electrical
connection. The rectangular part of the conducting layer is folded over the
insulating layers to form the upper conducting layer and good electrical
connection between upper and lower layer is therefore ensured. Other suitable
conducting fabrics are woven nylon plated with a layer of copper or silver or
nickel. For the insulating layers, typical garment and/or chest pad materials
are suitable, such as acrylic, horse hair, cotton, polyester, wool and tailor’s
foam. The fabric antenna is shown in figure 9.4.
Figure 9.4 Woven Antenna
The radiating region of the antenna, i.e. the open end of the patch,
will be on the user’s back so as to be farther from the user’s head than the
curved end of the patch at connection. As an alternative to using a folded
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layer of conducting material, the upper and lower layers may be shaped
superlatively and electrical connection established by sewing them with
electrically conductive thread, or by conductive gluing, or by sewing the
conductive layers together using a seam which places them in pressurized
contact. Considering the co-axial cable and its connection to the conducting
layers, it will be understood that the location of the connection along the edge
of the upper conducting layer is determined by the impedance of the feed line;
as is well known, for lower impedance feed lines, the connection should be
nearer the connection between the upper and lower layers, while for higher
impedance feed lines, the connection should be farther away from this
connection.
Figure 9.5 Antenna Impedance Graph
An alternative to a co-axial cable as a feed connection is a micro
strip or strip line or twin line or tri-plate, all of which compromise layers of
parallel conductors separated by a dielectric. It is therefore possible to use
conducting and insulating fabric layers, similar to the fabric of the antenna, to
make the feed connection. Such a connection would be joined to the
conducting layers by conductive adhesives.
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Whichever type of feed connection is used, connection to the
antenna upper and lower layers can be made by a low temperature solder or,
for improved flexibility, by use of conductive stitching, conductive glues
and/or pressure bonding.
9.2.2.4 Testing of Antenna
The antenna was constructed in the prescribed way and its gain,
bandwidth, frequency were tuned accordingly. The antenna was then
connected with the circuit and was tested for its signal range. The properties
were then tuned so that it will not create any interference with other radio
signals. The antenna’s gain was found to be as it is in the following
Figure 9. 5.
9.2.2.5 Integration of components in Apparel
The components can be integrated within the clothing in such a way
that it does not disturb the wearability of the user. The transmitter circuit can
be patched up behind the chest portion of the clothing or on the bedlinen. The
controls could be taken to the sleeve portion of the apparel. The fabric patch
antenna can be patched up on the back yoke part of the apparel or on the
bedlinen. This placement of the antenna results in maximum gain of the
signals.
9.3 MEASUREMENT OF INTERFACE PRESSURE
BETWEEN BODY AND THE MATTRESS
A new pressure measurement system with self-inflatable balloon,
Kikuhime, (TT Medi Trade, Soleddet 15, DK 4180 Soro) was used to
measure the interface pressure between body and the mattress. The instrument
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composed of two self inflatable air filled balloons, a connecting tube and a
measuring unit as shown in the Figure 9.6
Figure 9.6 Pressure measuring device with inflatable balloons
The small, flexible, air-filled pressure bladder has a dimension of
30 X 38 mm and is about 3 mm thick when calibrated to zero and the other
one is of 120 x 100 mm. The outer membrane of the balloons are made of
polyurethane membrane of thickness about 200 micro meters for normal size
and 100 micro meters for smaller size and inside the balloon also a
polyurethane foam sheet is built in with a thickness of 3 mm. Normal size
balloon is suitable for measuring a pressure at sacrum area, and so on. Smaller
one is good at pressure measurement at limited area like a bone prominent
area as heal. The instrument is capable of measuring pressure up to
200 mmHg.
9.4 MEASUREMENT OF BODY TEMPERATURE USING LM35
The LM35 series are precision integrated circuit temperature true
sensor whose output voltage is linearly proportional to the Celsius
temperature. The LM35 thus has an advantage over linear temperature sensor
calibrated in Kelvin as the user is not required to subtract a large constant
voltage from its output to obtain convenient centigrade scaling. The LM35
does not require any external calibration or trimming.
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.
Figure 9.7 Temperature measuring device
The LM35 low output impedance; linear output and precise
inherent calibration make interfacing to readout or control circuitry especially
easy. It can be used with single power supply. The temperature sensor and its
circuit diagram are shown in the Figure 9.7 and in annexure 2.
9.5 CONCLUSION
Wireless communication device covers a wide range of applications
as it could be used by patients confined to wheel chair, bed ridden patients,
and workers of all sectors e.g. constructional personnel, defense personnel
and police personnel. The patients who can't move because they are
paralyzed, recuperating from surgery for a prolonged time, being treated in
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intensive care for a long time, or are incapacitated by severe arthritis, stroke
or a neurological problem, can use this device to easily communicate to care
takers whenever they need. This device can also be incorporated in the wheel
chair cover or in the mattress with the switch alone extending to the fingers of
the patient.
This device serves as the quickest means of communication at low
cost. In mass production, this device could be produced at a low cost of
Rs. 700 to Rs. 800. The main advantage of this project is the work simplicity.
Tremendous gain is obtained from the woven antenna and could be used for a
range of 5 miles, if the antenna is tuned perfectly. The device can be used in
extreme temperature ranges from -5oC to +130
oC. The weight of the device is
just 72grams, whereas a normal handheld radio device weighs around 400 to
500grams. The thickness of the device is about 14mm, which does not disturb
the wearability. The heat sink was not used in the device which helps to
conceal the circuit completely and as a result the board can be made
waterproof. The Gain of the woven antenna is 275milliHenry. The resistance
of the antenna is 150 . This gain and the resistance of the woven antenna are
very much equal to that of helical antenna which helps to cover a wide area of
signal range.
The measuring devices used for assessing pressure and temperature
can be successfully used to measure the interface pressure and temperature
developed in the patients body.