Signal Transmission by Galvanic Coupling Through the Human Body and inter facing with real world

Transcription

1 Signal Transmission by Galvanic Coupling Through the Human Body and inter facing with real world ABSTRACT: Galvanic coupling is a promising approach for wireless interbody data transmission between sensors. Using the human body as a transmission medium for electrical signals becomes a novel data communication technique in biomedical monitoring systems. Galvanic coupling for intrabody communication denotes the technology of signal transmission through the body for nobody and implanted sensor communication. Thus, the human body becomes the transmission channel of the communication system. A profound understanding of its channel characteristics and the coupling impacts is required for defining the channel constraints and the subsequent system constraints of a transceiver design. Galvanic coupling follows the approach of coupling alternating current into the human body. The signal is applied differentially over two coupler electrodes and received differentially by two detector electrodes KEYWORDS: Galvanic coupling, electrodes, interbody, transmission channel, F.S.K, electrodes, biomedical system, measurement system INTRODUCTION: DATA transmission using the human body as a channel of electric near-field propagation is driven by the vision of a cable-free biomedical monitoring system. Wireless sensors give more freedom to patients and will revolutionize the possibilities in clinical monitoring. Data transfer by capacitive coupling through the human body was first proposed as a personal area network (PAN) It was discovered that certain parts of the near field could be exploited to make the human body act as a medium for data transmission. The electric field, induced by a signal electrode of the PAN transmitter, passes through the body and flows toward the ground reference. Further systems with similar coupling methods have shown the potential of data communication through the human body. All these systems used a fixed carrier frequency. The detector sensibility was increased by electrooptic sensors and 468

2 extended in the signal frequency to above 1 MHz In comparison to capacitive coupling applying static charged electrode, galvanic coupling provides alternating currents over multiple electrodes. Two coupler electrodes induce currents into the human tissue and two detector electrodes sense the potential differences. Ground is not required for reference as in the method of capacitive coupling. Electrical characterizations of the human body with respect to galvanic coupled current flow and identified differences between body parts are shown by Wegmueller et al. The feasibility of the technology has been proven, and its limits regarding tissue sensitivity and body geometry have been assessed. The exposure guidelines of the International Commission on Non-Ionizing Radiation Protection are defined via maximum contact current and current density. State-of the-art intrabody communication transceiver units for usage in close body proximity have been developed for battery powered sensors. However, comparison of different electrode types in the target frequency range has been missing, but the importance of optimal signal coupling became obvious and necessitated further investigation. In particular, there exist open points on the comparison of different electrode coupling materials and the size of the active electrode area. BLOCK DIAGRAM Frequency-shift keying (FSK) is a form of frequency modulation in which the modulating signal shifts the output frequency between predetermined values. 469

3 Usually, the instantaneous frequency is shifted between two discrete values termed the mark frequency and the space frequency. Continuous phase forms of FSK exist in which there is no phase discontinuity in the modulated signal. The example shown at right is of such a form. Other names for FSK are frequency-shift modulation and frequency-shift signaling. The digital data communication and computer peripheral, binary data is transmitted by means of a carrier frequency which is shifted between two preset frequencies. This type of data transmission is called frequency shift keying technique. Frequency keying is a form of frequency modulation in which the carrier switches abruptly from one frequency to another on receipt of a command or keying signal. Most oscillator circuit can be subjected to FSK by simply designing them so that an alternative frequency determining component or parameter is selected on receipt of the key signal. The key signal or input signal may be delivered electro- mechanically via a switch, electronically via transistor gate or via PC etc. The XR 2206 is the waveform generator specifically allocated for FSK use. This IC has two alternative timing resistor pins such as pins 7 and 8. Either pin can be selected by applying a suitable bias signal to pin 9 of the IC. When the pin 9 FSK input terminal is open circuit or externally biased above 2v with respect to negative supply, the pin 7 timing resistor is automatically selected and the circuit operates at a frequency determined by R1 and C1. When pin 9 is shorted to the negative supply or biased below 1V with 470

4 reference to the negative supply, the pin 8 timing resistor is selected and the circuit operates at a frequency determined by R2 and C1. The XR-2206 IC can thus be frequency shift keyed by simply applying a suitable keying or pulse signal between pin 9 and the negative supply. In this circuit the data signal to be modulated is out from PC through serial port. 9 pin D type connector is used to interface the PC and FSK circuit in which 3 pin is transmitting pin. This pin is connected to base of the Q1 transistor. When high pulse is coming Q1 is conducting so collector and emitter is short 0V is given to input of the two serious inverter so -12V is given to 9 th pin of XR When low pulse from PC Q1 transistor is in the cut off region so +12V is given to 9 th pin of XR-2206 vice versa. Depending on the pulse on 9 th pin the timing resistor R1 and R2 is selected from the pin 7 and 8 respectively. Here the capacitor C1 is kept constant. So XR-2206 generating two set of frequency 1200 Hz and 1400 Hz named as F1 and F2 respectively on the 11 th pin. Then the frequency shifted output is given to RF transmitter. Circuit Description: The FSK demodulator is constructed by LM 565 phase locked loop. In the 565 PLL the frequency shift is usually accomplished by driving a VCO with the binary data signal so that the two resulting frequencies correspond to logic 0 and logic 1 state are commonly called the mark and space frequencies. 471

5 The input frequencies are applied to pin 2 and output is taken from pin 7. In addition to the low pass filter, a three-stage RC filter is connected to pin 7 to remove the carrier from the output. The output pin 7 and reference pin 6 are connected to a comparator, which provide the output pulse. The free running frequency is set by VR1. Here we set the free running frequency is 1300Hz. It is also called as centre frequency. The input frequencies are 1200Hz and 1400Hz. When the input frequency is 1400Hz, the output 7 th pin is higher then reference pin 6 th the comparator provides the pulse at the output. When the input frequency is 1200Hz, the output 7 th pin is lower than reference 6 th pin the comparator provides the zero at the output. Now we are getting exact pulse as we transmit from transmitting side PC. The output pulse is given to receiver side PC or to the microcontroller. When output is given to microcontroller, the pulse is converted into 0 to 5v pulse with the help of transistor. CODE: #include<reg52.h> #include "AT_LCD8.h" #include "AT_SERIAL.h" sbit rel1=p1^1; unsigned char A[10],i; void Serial() interrupt 4 { if(ri==1) {A[i]=SBUF; if(a[0]=='@')i++; RI=0; void main() { rel1=1;i=0; Lcd8_Init(); Lcd8_Display(0x80,"GALVANI C COUPLIN"); Lcd8_Display(0xc0,"USING HUMAN BODY"); Delay(65000);Delay(65000); Advantages Serial_Init(110,2); Lcd8_Command(0x0f); while(1) { Lcd8_Decimal(0xcd,i,3,0); if(i>1) { if(a[1]=='o')rel1=0; if(a[1]=='f')rel1=1; i=0;a[0]=0; Lcd8_Command(0xc0); Lcd8_Write(A[0]); Low cost Reliability Durability APPLICATIONS: This project is designed for use in sophisticated real time applications such as 1. Industrial Control 2. Space communication 3. Instrumentation and 472

6 4. Intelligent computer peripherals CONCLUSION Galvanic coupling is a promising approach for intrabody communication. The versatile platform presented here offers sophisticated possibilities for signal application and data transmission using a differential pair of electrodes that are galvanically coupled to the human body. Different electrodes were compared with the proposed measurement system. Pregelled Swaromed electrodes feature lower coupling resistances compared to solid gel electrodes. Nevertheless, solid gel electrodes with lower capacitive values are superior to pregelled electrodes. With application-specific electrodes, the technology is enhanced. The proposed system will be miniaturized with the goal of realizing data transmission based on galvanic coupling in a biomedical system for monitoring vital functions. REFERENCES: 1. K. Hachisuka, Y. Terauchi, Y. Kishi, T. Hirota, K. Sasaki, H. Hosaka and K. Ito "Simplified circuit modeling and fabrication of intrabody communication devices", Proc. 13th Int. Conf. Solid-State Sensors, Actuators Microsyst., vol. 2E4-3, pp M. S. Wegmueller, A. Kuhn, J. Froehlich, M. Oberle, N. Felber, N. Kuster and W. Fichtner "An attempt to model the human body as a communication channel", IEEE Trans. Biomed. Eng., vol. 54, no. 10, pp Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz), M. Wegmueller, A. Lehner, J. Froehlich, R. Reutemann, M. Oberle, N. Felber, N. Kuster, O. Hess and W. Fichtner "Measurement system for the characterization of the human body as a communication channel at low frequency", Proc. IEEE EMBC, pp K. S. Cole and R. H. Cole "Dispersion and absorption in dielectricspart 1: Alternating current characteristics", J. Chem. 473

7 Phys., vol. 9, no. 4, pp EMAG From ANSYS, [online] Available: m 6. C. E. Shannon "A mathematical theory of communication", Bell Syst. Tech. J., vol. 27, pp T. G. Zimmerman Personal Area Network (PAN), 1995 T. Handa, S. Shoji, S. Ike, S. Takeda and T. Sekiguchi "A very low-power consumption wireless ECG monitoring system using body as a signal transmission medium", Proc. Int. Conf. Transducers, Solid-State Sensors Actuators, pp K. Partridge, B. Dahlquist, A. Veiseh, A. Cain, A. Foreman, J. Goldberg and G. Borriello "Empirical measurements of intrabody communication performance under varied physical configurations", Proc. ACM UIST, pp K. Fujii, M. Takahashi, K. Ito, K. Hachisuka, Y. Terauchi, Y. Kishi and K. Sasaki "A study on the transmission mechanism for wearable devices using the human body as a transmission channel", IEICE Trans. Commun., vol. E88-B, no. 6, pp M. Shinagawa, M. Fukomoto, K. Ochiai and H. Kyruagi "A nearfield-sensing transceiver. Ch.Kranthi, studying B.tech at Electronics and communication engineering in KL University. Currently, she is dealing with biomedical waste management. She involves in R&D works of KL university. R.Ravikumar, working in KL university as Assosiate. Professor. Having assortment of experience in communication field and realistic environment. 474