A NEW REVOLUTIONARY SYSTEM TO DETECT HUMAN BEINGS BURIED UNDER EARTHQUAKE RUBBLE USING PIC MICROCONTROLLER (EMBEDDED SYSTEMS)

ABSTRACT

Embedded systems is the recent emerging technology in the field of electronics. A new revolutionary microwave life detection system, which is used to locate human beings buried (or) trapped under earthquake rubble has been designed. This system operating at certain frequency can remotely detect the breathing and heart beat signals of human beings buried under earthquake rubble. By proper processing of these signals, the status of the person under trap can be easily judged. The entire process takes place within a few seconds as a PIC Microcontroller unit controls the system.














INTRODUCTION

At present as we know the need of the hour is to find an effective method for rescuing people buried under earthquake rubble (or) collapsed building. It has to be done before we experience another quake. Present methods for searching and rescuing victims buried (or) trapped under earthquake rubble are not effective. Taking all these factors in mind, a system, which will be really effective to solve problem, has been designed.

PRINCIPLE OF OPERATION

The basic principle is that when a microwave beam of certain frequency [L (or) S band (or) UHF band] is aimed at a portion of- rubble (or) collapsed building under which a person has been trapped, the microwave beam can penetrate through the rubble to reach the person. When the microwave beam focuses the person, the reflected wave from the person’s body will be modulated (or) changed by his/her movements, which include breathing and heartbeat. Simultaneously, reflected waves are also received from the collapsed structures. So, if these reflected waves from the immovable debris are cancelled and the reflected wave from the person’s body is properly distinguished, the breathing and heart beat signals can be detected. By proper processing of these signals, the status of the person under trap can be easily judged. Thus a person under debris can be identified.

MAJOR COMPONENTS OF THE CIRCUIT
The microwave life detection system has four components. They are
• A microwave circuit, which generates amplifies and distributes microwave signals to different microwave components.
• A micro controller controlled clutter cancelled system, which creates an optimal signal to cancel the clutter cancellation system from the rubble.
• A dual antenna system, which consists of two antennas, energized sequentially. A laptop computer, which controls the micro controller and acts as the monitor for the output signal.
WORKING FREQUENCY

The frequency of the microwave falls under two categories, depending on the type and nature of the collapsed building. They are
1. L (or) S band frequency say 1150 MHz
2. UHF band frequency say 450 MHz

CIRCUIT DESCRIPTION
The circuit description is as follows:

Phase Locked Oscillator
The phase locked oscillator generates a very stable electromagnetic wave say 1150 MHz with output power say 400mW.

Directional Coupler 1 (10 dB)
This wave is then fed through a 10 db directional coupler and a circuital before reaching a radio frequency switch, which energizes the dual antenna system. Also, the ten dB directional coupler 2 (3 dB).

Directional coupler 2 (3 dB)
One output of the 3 dB directional coupler 2 (20mV) drives the clutter cancellation unit. Other output (20mV) serves as a local reference signal for the double balanced mixer.

Microwave life-detecting system using PIC Micro controller.
Antenna system:
The dual antenna system has two antennas, which are energized sequentially by an electronic switch. Each antenna acts separately.

Clutter cancellation unit:
The clutter cancellation unit consists of
• A digital controlled phase shifter 1
• A fixed attenuator
• A RF amplifier
• A digitally controlled attenuator.
Schematic diagram:


















WORKING
Clutter cancellation of the received signal:
 The wave radiated by the antenna 1 penetrates the earthquake rubble to reach the buried person.
 The reflected wave received by the antenna 2 consists of a large reflected wave from the rubble and a small-reflected wave from the person’s body.
 The large clutter from the rubble can be cancelled by a clutter-canceling signal.
 The small reflected wave from the person’s body couldn’t be cancelled by a pure sinusoidal canceling signal because his/her movements modulate it.
 The output of the clutter cancellation circuit is automatically adjusted to be of equal amplitude and opposite phase as that of the clutter from the rubble.
 Thus when the output of the clutter cancellation circuit is combined with the directional coupler 3(3 dB), the large clutter from the rubble is completely cancelled.
 Now, the output of the directional coupler 3(3dB) consists only of the small wave from the person’s body.
 This output of the directional coupler 3(3dB) is passed through a directional coupler 4(6 dB).
 One-fourth of this output is amplified by a RF pre amplifier and then mixed with a local reference signal in a double balanced mixer.
 Three-fourth of the output is directed by a microwave detector to provide a dc output, which serves as the indicator for the degree of clutter cancellation.
 When the settings of the digitally controlled phase shifter and the attenuator are swept by the micro controller control system, the output of the microwave detector varies accordingly.
Demodulation of cluttered signal:
 At the double balanced mixer, the amplifier signal of the reflected wave from the person’s body is mixed with the local reference signal.
 Another digitally controlled phase shifter 2 for an optimal output from the mixer controls the phase of the local reference signal.
 The output of the mixer consists of the breathing and heart beat signals of the human plus some unavoidable noise.
 This output is fed through a low frequency amplifier and a band pass filter (0.1 -4 Hz) before being displayed on the monitor.
 The function of the digitally controlled phase shifter 2 is to control the phase of the local reference signal for the purpose of increasing the system sensitivity.
 The reflected signal from the person’s body after amplification by the pre-amplifier is mixed with the local reference signal in a double balanced mixer.
 The local reference signal is assumed to be A1cos (wt+φ1)
Where A1->amplitude of the local reference signal.
φ1-> phase of the local reference signal.
Let the reflected wave (or) signal from the person’s body=
Ar * cos (wt+ φe +Δ (φ (t)))
Where Ar->amplitude of the reflected wave.
φe-> phase of the reflected wave.
Δ (φ (t))-> phase modulation due to the person’s body movements.
W-> angular frequency
t-> time.
When these two inputs are mixed in the double balanced mixer, the output of the mixer will be A1A2* Δ φ ((t)) cos (φ1- φe –Δ φ(t))
From this expression of the mixer output, it is seen that,
 If φ1-φe=(n+1/2) ∏ where n=0,1,2…
the system has a maximum sensitivity ;
 φ1-φe=( ±n)∏ where n=0,1,2…
The system has a minimum sensitivity;
Because (ð/ ð(Δ φ(t)) cos(φ1- φe –Δ φ(t)))= - sin(φ1- φe –Δ φ(t)) .Δ φ(t) is usually a small phase angle created by the body movement of the person.
φe is the constant phase associated with the reflected signal from the person’s body and it cannot be changed.
φ1 is the phase of the local reference signal and it can be controlled by the digitally controlled phase shifter 2.
The phase shifter will automatically shift φ1 in such a way that φ1 – φe is nearly = (n+1/2) ∏ to attain a maximum sensitivity.




PIC MICROCONTROLLERS
The PIC16F84A belongs to the mid-range family of the PICmicro ® micro controller devices. A block diagram of the device is shown below.
The program memory contains 1K words, which translates to 1024 instructions, since each 14-bit program memory word is the same width as each device instruction. The data memory (RAM) contains 68 bytes. Data EEPROM is 64 bytes. There are also 13 I/O pins that are user-configured on a pin-to-pin basis. Some pins are multiplexed with other device functions. These functions include:
• External interrupt
• Change on PORTB interrupt
• Timer0 clock input


Memory Organization Unit:

There are two memory blocks in the PIC16F84A. These are the program memory and the data memory. Each block has its own bus, so that access to each block can occur during the same oscillator cycle. The data memory can further be broken down into the general purpose RAM and the Special Function Registers (SFRs). The data memory area also contains the data EEPROM memory. This memory is not directly mapped into the data memory, but is indirectly mapped. That is, an indirect address pointer specifies the address of the data EEPROM memory to read/write. The 64 bytes of data EEPROM memory have the address range 0h-3Fh.

Timer0 module:

The Timer0 module timer/counter has the following features:
• 8-bit timer/counter
• Readable and wrightable
• Internal or external clock select
• Edge select for external clock
• 8-bit software programmable prescaler
• Interrupt-on-overflow from FFh to 00h



Timer0 Operation:

Timer0 can operate as a timer or as a counter. Timer mode is selected by clearing bit T0CS (OPTION_REG<5>). In Timer mode, the Timer0 module will increment every instruction cycle (without prescaler). If the TMR0 register is written, the increment is inhibited for the following two instruction cycles. The user can work around this by writing an adjusted value to the TMR0 register. Counter mode is selected by setting bit T0CS (OPTION_REG<5>). In Counter mode, Timer0 will increment, either on every rising or falling edge of pin RA4/T0CKI. The incrementing edge is determined by the Timer0 Source Edge Select bit, T0SE (OPTION_REG<4>). Clearing bit T0SE selects the rising edge. Restrictions on the external clock input are discussed below. When an external clock input is used for Timer0, it must meet certain requirements. The requirements ensure the external clock can be synchronized with the internal phase clock (TOSC). Also, there is a delay in the actual incrementing of Timer0 after synchronization.

MICROCONTROLLER UNIT:
The algorithm and flowcharts for the antenna system and clutter cancellation system are as follows:


Antenna system:

• Initially the switch is kept in position 1(signal is transmitted through antenna 1).
• Wait for some predetermined sending time, Ts.
• Then, the switch is thrown to position 2(signal is received through antenna 2).
• Wait for some predetermined receiving time, Tr.
• Go to step1.
• Repeat the above procedure for some predetermined time, T.





Clutter cancellation system:
• Send the signal to the ruble through antenna 1.
• Receive the signal from the ruble through antenna 2.
• Check the detector output. If it is within the predetermined.Limits go to step5.
• Otherwise send the correction signal to the digitally controlled phase shifter1and the attenuator and go to step1.
• Check the sensitivity of the mixer. If it is optimum go to step 7.
• Otherwise send the correction signal to the digitally control phase shifter 2 to change the phase and go to step1
• Process the signal and send it to laptop.








ADVANTAGES OF L (OR) S BAND FREQUENCY SYSTEM
Microwave of l (or) S band frequency can penetrate the rubble with metallic mesh easier than that of UHF band frequency waves.
ADVANTAGES OF UHF BAND FREQUENCY SYSTEM
Microwaves of UHF band frequency can penetrate deeper in rubble (without metallic mesh) than that of L (or) S band frequency waves.

FREQUENCY RANGE OF BREATHING AND HEART BEAT SIGNALS
The frequency range of heartbeat and breathing of human beings lies between 0.2 and 3Hz.

HIGHLIGHTS

 The location of the person under the rubble can be known by calculating the time lapse between the sending time, Ts and receiving time, Tr.
 Since it will not be possible to continuously watch the system under critical situations, an alarm system has been set, so that whenever the laptop computer system processes the received signal and identifies that there is a human being, the alarm sound starts.
 Also under critical situations, where living beings other than humans are not required to be found out, the system can detect the signals of other living beings based on the frequency of the breathing and heart beat signals.

CONCLUSION

Thus a new sensitive life detection system using microwave radiation for locating human beings buried under earthquake rubble (or) hidden various barriers have been designed. This system operating either at L (or) S band (or) UHF band can detect the breathing and heart beat signals of human beings through earthquake rubble.

REFERENCES

1. “Microwaves” by K.C. Gupta”
2. “Automatic clutter-canceller for microwave life detection system”
3. PIC Micro controller- Microchip’s reference manual.