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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.