Design and development of signal sensing equipment for measuring light transmission efficiency of POF fabrics
L Ashok Kumara, C Vigneswaranb & T Ramachandranc
a Department of Electrical and Electronic Engineering,
b Department of Fashion Technology,
c Department of Textile Technology,
PSG College of Technology, Coimbatore 641 004, Tamilnadu, India Received 5 November 2009; revised received and accepted 11 March 2010
An attempt has been made to design the light signal sensing equipment with microcontroller AT89C52 based circuit using 02n5777 optical receiver for measuring the light transmission efficiency of poly(methyl methacrylate) based plastic optical fibre (POF) and then to develop POF integrated woven fabrics using three different methods, namely sequential work, handloom and powerloom using 0.25 mm, 0.5 mm and 1.0 mm POF. The signal transferring efficiency of the handloom, powerloom and sequential integrated woven POF fabrics is analysed using the microprocessor designed with optical receiver for bullet wound detection. The signal loss percentage of these fabrics has been studied and reported using the red LED, white light LED (SPL) and laser light LED with input voltage of +5 V. These POF integrated woven fabrics are having good scope for the development of signal transferring garment for defence personnel, telecommunication and data transferring purpose.
Keywords: Bullet wound detection, Light transmission efficiency, Optical fibre, Plastic optical fibre, Poly(methyl methacrylate), Signal transferring efficiency
1 Introduction
An optical fibre is a cylindrical dielectric waveguide that transmits light along its axis by the process of total internal reflection. The fibre consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding material1,2. The boundary between the core and cladding may either be abrupt in step-index fibre, or gradual in graded-index fibre. Plastic optical fibre (POF) has been called the ‘consumer’ optical fibre, because the fibre and associated optical links, connectors, and installation are all inexpensive. The traditional poly(methyl methacrylate) (PMMA) fibres are commonly used as core on POF for low-speed, short-distance (up to 100 m) applications in digital home appliances, home networks, industrial networks (PROFIBUS, PROFINET), and car networks (MOST). The fluorinated polymer fibres are commonly used as cladding material for much higher speed applications such as data center wiring and building LAN wiring. Due to the future request of
high-speed home networking, there has been an increasing interest in POF as a possible option for next generation Gigabit/s links inside the house3. Regarding optical fibre in telecommunication, one or more layers of cladding material of lower refractive index are used in intimate contact with a core material of higher refractive index. Fibre optics is the overlap of applied science and engineering concerned with the design and application of optical fibres. Optical fibres are widely used in fibre-optic communication, which permits transmission over longer distances and at higher data rates than other forms of communications.
Fibres are used instead of metal wires because signals travel along them with less loss, and they are immune to electromagnetic interference. Optical fibres are also used to form sensors, and in a variety of other applications4. Wireless communications are impacting all areas of the military, from logistics and training to collaboration and medical support. In military offices, wireless communications keep people mobile with continual access to information anywhere and any time. Laptop computer users attending meetings and conferences now maintain instant access to data files and internet searching and hence can obtain immediate answers to questions raised. Outside the
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aTo whom all the correspondence should be addressed.
E-mail: lak@eee.psgtech.ac.in
office, mobility increases productivity by allowing users to work in previously unproductive situations, such as while traveling or waiting for appointments5, 6. Wireless technologies are transforming health-care services also. Wearable computers and sensors, embedded in clothing or strapped directly to the body, allow continuous monitoring of patients and instant feedback to medical personnel from war fighters in battle7, 8. Wireless in the medical field can also improve telemedicine and remote consultation.
Already, telecommunication is enabling medical specialists to consult on cases around the world using video teleconferencing software. Wireless communication extends these capabilities to the soldier in a foxhole, allowing medical experts to be many ‘places’ at once, advising medics and monitoring patients through a variety of sensors9,10.
An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fibre. An OTDR injects a series of optical pulses into the optical fibre and extracts the light that is scattered and reflected back from the points in the fibre. This helps in measuring the index of refraction changes. This is equivalent to the way by which an electronic time-domain reflectometer measures reflections caused by changes in the impedance of the cable under test. The strength of the return pulses is measured, integrated as a function of time and plotted as a function of fibre length. An OTDR may be used for estimating the fibre length and overall attenuation, including splice and mated-connector losses. It may also be used to locate faults such as breaks, and to measure optical return loss. In addition to required specialized optics and electronics11, OTDRs have significant computing ability and a graphical display.
They also provide significant test automation.
However, proper instrument operation and interpretation of an OTDR trace still require special technical training and experience, and are found to be expensive. OTDRs are commonly used to characterize the signal loss of plastic optical fibres. This depends on length of fibres as they go from initial manufacturing to cabling, warehousing while wound on a drum, installation and then splicing. The last application of installation is more challenging, as extremely long distances, multiple splices spaced at short distances, and fibres with different optical characteristics joined together are involved. OTDR test results are often carefully stored in case of later fibre failure or warranty claims. Fibre failures can be
very expensive, both in terms of the direct cost of repair, and consequential loss of service12. Limited study has been reported on the development of illuminated clothing using optical fibres and light signal transferring for telecommunication using PMMA optical fibres including the selection and possibility of optical fibre for integration with fabrics for signal transferring clothing development for military and medical applications13-15.
In this study, an attempt has been made to design the light sensing equipment with microcontroller based 02n5777 optical receiver, and the signal transferring efficiency of various diameters of optical fibres and their performance are studied. The POF integrated woven fabrics have been developed and their bullet wound detection and counting test are studied.
2 Materials and Methods
Four different diameters of plastic optical fibres (POF) (PMMA) such as 0.25 mm, 0.5 mm, 0.75 mm and 1.0 mm were used. The fibres were procured from Mitshubishi Rayon Co. Ltd, Japan. These optical fibres were used to prepare fabrics using three different methods, namely (i) sequential method with POF integrated in the fabric, (ii) weaving of the POF using handloom and (iii) weaving of the POF using powerloom.
2.1 Design and Development of Signal Transferring Fabrics
The sequential method is a process of integrating the plastic optical fibre into the textile fabric, i.e.
embedding on the surface by embroidery technique (Fig. 1). The POF is placed over the fabric in the required matrix format and stitches are made on it to hold the POF on the fabric. Secondly, the plastic optical fibres are inserted in warp and weft direction to produce desired matrix for detecting the bullet penetration using handloom and powerloom. The
Fig. 1 — Sequential method for integrating POF on various fabrics
woven fabric has been designed with plastic optical fibre to produce specific matrix format. Figures 2 (a) and (b) represent the signal transferring fabric developed by handloom and powerloom respectively.
The matrix should have the maximum pixel of 5 mm diameter. The maximum bullet size used in military is 7.62 mm. The reason for choosing matrix format is to detect the location of bullet where it wounded and to count the number of bullets penetrated in the body.
2.1.1 Weaving Machine Specification
Plastic optical fibres were woven on handloom and powerloom machines using the following specifications:
Handloom (Sample No.1)
Weave design : 1/1 plain weave
Loom width : 42 inch
Jacquard used : Single lift single cylinder Hooks capacity : 120
Repeat size : 3 inch
Warp material : 2/6s Ne cotton
Weft material : Plastic optic fibre (PMMA)
Total ends : 370
Fabric width : 20 inch
Powerloom (Sample No. 2)
Type of weave : 1/1 plain weave Warp material : 2/20s Ne cotton
Weft material : Plastic optic fibre (PMMA) Ends per inch : 24
Picks per inch : 32 (POF) Fabric width : 54 inch
2.1.2 Design of Signal Transferring Test Kit
A low-power LED was used at one end of the plastic optical fibre (POF) to send light signal that lit up the structure, indicating that personnel computer PC/LCD unit is armed and ready to detect any interruptions in the light flow that might be caused by a bullet penetrating the garment. At the other end of the POF, a photodiode connected to a power-measuring device measures the power output from the POF. The penetration of PC/LCD
unit resulting in the breakage of POF was simulated by cutting the POF with a pair of scissors; when the power output at the other end on the measuring device falls to zero, the location of the actual penetration in the POF can be determined by developed test reflectometer to pinpoint breaks in fibre optic cables.
2.2 Bullet Wound Detection Circuit
The bullet wound and location detection technique is one of the essential precaution measures in the defence environment. In this epoch of technological world, it is a mandatory requirement to design a protective garment, which will protect and intimate about the soldiers health and bullet wound status to the remote location. In that sense some of the bullet wound detection circuits has been built and tested to send the soldiers status to the remote location. Also, an application using Visual Basic 6.0 has been created to monitor the soldier’s status in the combat situations. It requires flexible integrated circuit to reduce the load of the electronic components, but the basic research needs for understanding the potential of developing the signal transferring garments using POF. The block diagram for signal transmission circuit and bullet wound detection with transmitter unit is shown in Fig. 3.
2.2.1 Circuits Developed using 8×8 Matrix Format
To detect the bullet wound and location it is decided to weave the plastic optical fibre (POF) in matrix format. The actual matrix format size for the finished garment varies depending upon the size of the garment.
So, it is decided to develop a prototype with 8×8 matrix format to detect the number of bullet wounds and bullet wound location. This prototype will serve as a basic platform from which required modification could be made. Using this circuit, information about the number of bullets and bullet wound location can be derived.
The signal collected from the soldier who wears the garment is being transmitted to the remote end server, where the details about the soldiers are kept in a database. The bullet wound detection circuitry mainly consists of three units, such as (a) transmitter, (b) receiver, and (c) server station. For designing 8×8 matrix detection in the fabric, it requires 80 LED and 80 detectors separately in warp and weft directions.
Fig. 2 — POF integrated fabric using (a) handloom and (b) powerloom
Fig. 3 — Block diagram for signal transmission circuit
2.2.2 Circuit Description
The optical transmitter contains light source for transmitting light to receiver. Here, the high bright white LED’s are chosen as they consume low power and are of optimized size. Power supply for transmitter circuit is +5v and it is given to the LED through limiting resistor. The transmitter unit plays a major role in detecting the number bullets and bullet wound location. This circuit is attached in a fabric, which is integrated with POF. A light source is used to transmit the signals as photons and a photo detector is used to get the information from the POF. The fabric is continuously monitored for the signal transmission. If the POF is broken by a bullet penetration, the signal to the photo detector is being interrupted. Here, a microcontroller is used to get the information about the number of bullets and bullet wound location. Also, the information about the bullet detection is displayed on a liquid crystal display (LCD) device and the same is being transmitted to the remote end receiver.
2.2.3 Optical Testing with 02n5777 Optical Receiver
Optical receiver consists of photodiodes for receiving signals from the POF. The high sensitive photodiodes of 3mm size are chosen. Plastic optical fibres are spaced 0.5 mm distance apart. Light source is used at the one end of the optical fibre and a photodiode is used at another end of the optical fibre.
The microcontroller circuits with display unit and matrix format connected with POF fabrics are shown in Figs 4 (a) and (b). Light source and photodiode assembly consists of a high bright LED. A photodiode 02n5777 is used to detect the signals in the receivers end. As the number of lines increases, the input to the
microcontroller is given by multiplexing the output from the photodiode. Various experiments were conducted to select the light source, photo detector and plastic optical fibre. The block diagram of signal transferring equipment with microcontroller AT89C52 is shown in Fig.5.
Fig. 5 — Block diagram of signal sensing equipment with microcontroller AT89C52
Fig. 4 — (a) Fabric testing with optical transmitter and receiver, and (b) connection to matrix format
3 Results and Discussion
In this research work, the signal transferring test results obtained using the signal transferring unit which is designed for optical fibres to measure the light transferring efficiency at various light sources (LED) using various integrated POF fabrics made out of sequential, handloom and powerloom have been reported.
3.1 Signal Transferring Test of Optical Fibre at Various Light sources
The signal transferring test results of POF (0.5mm and 1.0mm diameter) measured in 2 and 10 feet lengths at input voltage of 4.5v and 6v respectively are shown in Fig. 6. The hardware set-up was designed to transfer the light at one end and receive the light at other end of POF. The lumens level of the light is varied by using adjustable input voltage. The input source of infrared LED, high bright white LED, high bright red LED and laser light were used. The received light signal from the phototransistor and the variation in the phototransistor signal amplified. The amplified signals are converted into the digital signal using the analog-to-digital converter. The digital signal is given to the microcontroller, which is being programmed to display the result in terms of voltage.
For 0.25 mm diameter POF, it is easy to weave the fabric but the light transfer capacity is very low and the fixing of sensors/transducers in this case is very tedious process. POF of 1 mm diameter is not suitable for weaving due to its very large thickness. This does not make the fabric flexible, in the electrical means the signal transmission rate and the feedback are very positive as compared to that in case of the POF diameters 0.25mm and 0.5mm. POF of 0.5 mm diameter is appropriate for the weaving compared to 1 mm diameter POF, and the signal transmission and light transfer capacity are more suitable when compared to 0.25mm POF. Light transmission property of the 0.5 mm plastic optical fibre is found to be satisfactory. Also, 0.5 mm POF is having better flexibility and minimum signal loss at bending condition.
3.2 Signal Transferring Efficiency of Integrated POF Fabrics
The signal transferring behaviour of sequential work fabric (SW), handloom fabric (HL) and powerloom fabric (PL) integrated with POF at various light sources is shown in Fig.7. The signal transferring efficiency of the handloom, powerloom and sequential integrated woven POF fabrics are analysed using the microprocessor designed with
02n5777 optical receiver for bullet wound detection (Fig.8). The signal is received in terms of output voltage for the various fabrics with various optical fibre length, such as 15cm, 20cm and 30cm using the red LED, white light LED (SPL) and laser light LED with input voltage of +5 V. The signal values were measured in various places of fabrics at 15cm, 20 cm, 30cm optical length which are made into cumulative average and their signal output voltages are found 3.13 V, 3.88 V and 3.01 V for powerloom, handloom and sequential integrated POF fabrics. From this signal transferring analysis, the signal loss percentages for powerloom, handloom and sequential integrated POF fabrics are 37.44%, 22.40% and 39.84% respectively. It is observed that the signal transferring loss percentage is found to be less for handloom fabrics as compared to those for other fabrics.
Fig. 6 — Signal transferring test results of POF at various light sources
Fig. 7 — Signal transferring behavior of sequential work (SW), handloom (HL) and powerloom (PL) fabrics integrated with POF at various light sources
To count the number of bullet wounds in the soldier’s body, voltage level at the receiver end of the POF is continuously monitored. If any POF is interrupted between the transmitter and the receiver end, logic high signal is given to the microcontroller.
A variable with a count increment will be made in the microcontroller if any port gives a logic high signal.
This count is taken as number of bullets penetration into the garment. When there are no breakages, the microcontroller ports will be low in logic. It is proposed that arranging the POF in matrix format could perform the bullet detection mechanism. The matrix format of the POF integrated fabric with microcontroller LCD display unit which is connected with photodiode is shown in Fig. 9 (a) and digital converter unit is shown in Fig. 9 (b). The signal transmission unit and electronic LCD display unit detect the number of bullet counts in respective matrix rows which is shown in Figs 9 (c) and (d) respectively. Whenever there is a bullet penetration in the garment, the particular co-ordinates will be affected. This information is used to justify the location of the bullet penetration.
4 Conclusions
The developed POF integrated garment gives the bullet wound information and location of a soldier at the remote end server from the soldier status monitoring system. The signal from the garment is transmitted to the remote end with RF and GSM communication techniques. An application based on visual basic gives the physiological details about the soldier along with the bullet count and location information.
The handloom POF integrated woven fabrics show 77.6% signal transmission efficiency which is higher
as compared to the sequential (60.16%) and powerloom fabrics (62.56%) due to lower stress and mechanical fatigue during fabrication processes. The developed light signal transferring unit test results are comparable with an optical time domain reflectometer which is used in the characterization of optical fibres.
A test kit with microcontroller based circuit
Fig. 8 — Signal loss of POF (0.5mm) measured at various light sources for 2 feet and 10 feet lengths
Fig. 9 — (a) Transmitter circuit assemblies with POF fabric, (b) light source connected to POF integrated fabric, (c) signal transmission circuit, and (d) electronic display for detection of bullet count
installation is also developed and testing charges are found to be lower than that of the tests carried out using optical time domain reflectometer.
Further research is required for finding the various applications of signal transferring fabrics made out of plastic optical fibres (POF). POF can be used for the development of tele-garment and protective garment for defence purposes to protect the soldiers during combat situation, monitoring them using GSM and gathering their health status and bullet wound information. The tele-intimation garment will be the ideal solution in the future. The light source and photodiode integration methodologies could be improved for higher rigidity of the circuits. The bullet detection technique could be altered instead of POF with the copper conductors woven into the fabric. To power the circuits used in this garment, the renewable energy sources such as solar power could be explored.
The software application developed at the remote end could be enhanced by designing a specimen structure of human body positions. The graphical user interface developed in such a way will directly give the bullet wound locations of the soldier.
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