Handheld measurement Equipment for Extremely Low frequency Electromagnetic Fields. Phase-1

Transcription

1 Handheld measurement Equipment for Extremely Low frequency Electromagnetic Fields Phase-1 Introduction to the problem: It is very controversial to say that electromagnetic fields are harming us. Public concerns about power-frequency fields first emerged in the late 1960s as power companies turned increasingly to extra high voltage (EHV) transmission lines to handle large increases in electricity use. A look at the news headlines of recent years allows some insight into the various areas of public concern. Over the course of the past decade, numerous electromagnetic field sources have become the focus of health concerns, including power lines, microwave ovens, computer and TV screens, security devices, radars and most recently mobile phones and their base stations [1]. Natural sources of electromagnetic fields Electromagnetic fields are present everywhere in our environment but are invisible to the human eye. Electric fields are produced by the local build-up of electric charges in the atmosphere associated with thunderstorms. The earth's magnetic field causes a compass needle to orient in a North-South direction and is used by birds and fish for navigation [1]. Human-made sources of electromagnetic fields Besides natural sources the electromagnetic spectrum also includes fields generated by human-made sources: X-rays are employed to diagnose a broken limb after a sport accident. The electricity that comes out of every power socket has associated low frequency electromagnetic fields. And various kinds of higher frequency radio waves are used to transmit information whether via TV antennas, radio stations or mobile phone base stations [1]. Also when it was concluded that these radiations do not harm us is long back around 30 years ago. But today the electricity demands is raising enormously, Per capita population is increasing day by day, more and more electrical & electronics gadgets are around us etc. are though making our life very comfortable but in other way round it is disturbing circulation of electromagnetic fields around our body. It behaves like a Silent Killer which is killing us gradually day by day in form or irritation, giddiness, frequent headaches, and we are unaware of it. A very simple statement to realize this situation is in microwave ovens the uncooked food gets cooked, so just realize we are surrounded everywhere by electromagnetic sources. It is gradually and gradually cooking our body and mind giving us a slow death. What are the main sources of low, intermediate and high frequency fields? The time-varying electromagnetic fields produced by electrical appliances are an example of extremely low frequency (ELF) fields. ELF fields generally have frequencies up to 300 Hz. Other technologies produce intermediate frequency (IF) fields with frequencies from 300 Hz to 10 MHz and radiofrequency (RF) fields with frequencies of 10 MHz to 300 GHz. The effects of electromagnetic fields on the human body depend not only on their field level but on their frequency and energy. Our electricity power supply and all appliances using electricity are the main sources of ELF fields; computer screens, anti-theft devices and security systems are the main sources of IF fields; and radio, television,

2 radar and cellular telephone antennas, and microwave ovens are the main sources of RF fields. These fields induce currents within the human body, which if sufficient can produce a range of effects such as heating and electrical shock, depending on their amplitude and frequency range. (However, to produce such effects, the fields outside the body would have to be very strong, far stronger than present in normal environments.) So our main motive is to look for 50 Hz electromagnetic sources around us. Shielding 50 Hz sources is a bit tough, so we are proposing a solution in order to design such gadgets which make people aware of the exposure levels using 10 LED indicative circuit. Design Approach: Electric fields Plugging a wire into an outlet creates electric fields in the air surrounding the appliance. The higher the voltage the stronger the field produced. Since the voltage can exist even when no current is flowing, the appliance does not have to be turned on for an electric field to exist in the room surrounding it. Magnetic fields Magnetic fields are created only when the electric current flows. Magnetic fields and electric fields then exist together in the room environment. The greater the current the stronger the magnetic field. High voltages are used for the transmission and distribution of electricity whereas relatively low voltages are used in the home. The voltages used by power transmission equipment vary little from day to day, currents through a transmission line vary with power consumption. Electric fields around the wire to an appliance only cease to exist when the appliance is unplugged or switched off at the wall. They will still exist around the cable behind the wall. So according to above analysis we need to prepare two separate gadgets one for detecting Electric field & one for detecting magnetic field. So for electric field we chose Helical Antenna and for Magnetic field we chose Loop Antenna. We first tried measuring with various sizes of helical and loop antenna in order to have better reception of 50 Hz electromagnetic field because 50 Hz is a very small frequency and antenna size would be much larger, so we opted for designing such antenna which has better reception of electric and magnetic field at 50 Hz of frequency. Electric Field Measuring Equipment Design: The design which we are proposing consists of various parts which are as follows Antenna Amplifier Filter Rectifier Peak Voltage Detector Indicator Circuit Various parts Description:

3 Antenna: We started testing with antennas which antenna is good for reception of electric field being released from power supplies and everyday appliances. So we started testing with the helical antenna as they are more directional and also they have better reception of electric field. So as to start we implemented and created two different antennas with different pitch and diameter in order to grab more & more 50 Hz electric field being transmitter from Power supplies. We first tested the antennas by making single turns and multiple turns over the DSO (Digital Signal Oscilloscope). Here I am attaching few images and results using the antennas The left side figure shows the good peak to peak voltage of 0.654V from the SMPS (Switch Mode power Supply) of DSO. The right figure indicates the result taken from the 50 Hz power supply.the result is very small because the parameter taken to achieve this is also small for example it is very difficult to design perfect antenna for receiving 50 Hz as wavelength is too high so we need extremely large antenna which won t make our design Portable.

4 So we prefer to use the antenna which is more portable and which have the maximum reception of 50 Hz. Now this is what we have already tested and came to final proper design. The parameters of final antenna to be used are No. of Turns: 126 Length: 16cm Pitch: 1mm Diameter: 6mm Now this is what we have done so far I am proposing the further design in order to create and test the further circuit Amplifier and Filter: What is the need of using filter and amplifier? Since the antenna is not perfect for the 50 Hz frequency we need to extract the 50 Hz frequency from all the frequency thus absorbed by the antenna. Also we need the amplifier as the voltage received by antenna is too small as it is not perfectly made for this frequency only. So we are planning to build and test two stage amplifier inbuilt with the filter specifications probably the low pass filter using Operational amplifier. This help we have taken from the datasheet of LM324 Quad- OpAmp IC and the circuit we are going to use with some modifications is shown below as impedance with antenna needs to be matched with the rest of circuitry. The final parameters of two stage amplifier circuit we will elaborate more in the next report soon.

5 Rectifier and Peak Detector: Rectifier is to be used in order to forward the half wave voltage as the signal received by the antenna is a pure sinusoidal signal.so using this rectifier we are converting the output into half wave signal so that constant DC voltage can be extracted from it. Peak Detector Circuit: We are going to use this circuit in order to create DC voltage from the half rectified wave from the rectifier. It is similar to charging and discharging phenomenon of Capacitor. It generates perfect DC voltage or detects peak of the rectified wave. Indicator Circuit: We are going to prepare this circuit using LM3914 IC which is a Linear dot/ bar display driver IC which indicates the strength of the signal we will be actually receiving from the antenna in terms of glowing LEDs.Maximum number of LEDs it can support is 10 and the led levels shows the exposure to the Electromagnetic field near gadgets and power supplies in our home or nearby. This is what we had done and planned so far. More on this we will update soon. References: [1].World Health Organisation--