Embedded Systems

Topics: Frequency, Microwave, Electromagnetic radiation Pages: 7 (1955 words) Published: September 2, 2012
Embedded systems
(Life detecting circuit using PIC microwave controller)


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 the system is controlled by a PIC Microcontroller unit.

1. Introduction

At present as we know the need of an hour is to find an effective method for rescuing people buried under the 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.
2. 2. Principle of operation

The basic principle is that when a microwave beam of certain frequency [L or S band of 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 person is focused by the microwave beam, the reflected wave from the person’s body will be modulated or changed by his/her movements, which include breathing and heart beat. 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.

3. 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 microcontroller controlled clutter cancelled system, which creates an optimal signal to clutter cancellation system from the rubble. •A dual antenna system, which consists of two antennas, energized sequentially. •A laptop computer which controls the microcontroller and acts as the monitor for the output signal.

4. Working frequency

The frequency of the microwave falls fewer than two categories, depending on the type and nature odd the collapsed building. They are L (or) S band frequency say 1150 MHz
Uhf band frequency say 450 MHz

5. Circuit description
The Circuit description is as follows:

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

5.2 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).

5.3 Directional coupler 2 (3 dB):
One output of the 3 dB directional coupler 2 (20 mV) drives the clutter cancellation unit. Other output (20mV) serves as a local reference signal for the double balanced mixer.
5.4 Antenna system:
The dual antenna system has two antennas, which are energized sequentially by an electronic switch. Each antenna acts separately.

5.5 Clutter cancellation unit:

The clutter cancellation unit consists of
1.A digital controlled phase shifter 1
2.A fixed attenuator
3.A RF amplifier.
4. A digitally controlled attenuator.

6. Working
6.1 Clutter cancellation of the received signal:

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