The Design Corner / Hobby Corner - Electronic Field Disturbance Monitor
designed by David A. Johnson, P.E.
Updated on:  Thursday, December 17, 2015 01:44 PM

  Electronic Field Disturbance Monitor:  Introduction - Monitor Design - Monitor Operation

Circuit Description:    Front-end Circuit Section - Alarm Threshold Detector 
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Battery Voltage Monitor - Monitor Assembly
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Introduction

My friend wondered if some useful device could be developed that used the concepts described in the book. Although Feynman's lecture did not suggest any specific applications, my intuition told me that some useful products could be built based on the phenomenon. Both my friend's questions and the illustrations in Feynman's book piqued my curiosity. Since I had never heard of the phenomenon, I decided to conduct some of my own research. I wanted to see if the electric field fluctuations described by Feynman could be detected by some simple electronic circuits.

Although my first experiments were crude, but they did prove that the disturbances could be easily monitored. I continued to experiment and my later circuits made some refinements to the original ones. I built several prototype devices. Although some attempts were made, no commercial device was ever marketed. But, the prototypes constructed did generate a lot of interesting data. The data clearly suggested that the signals produced by moving objects could be used as the basis for a variety of products. For this construction project, I have modernized some of the circuits to take advantage of some ICs that didn't exist 20 plus years ago.
This project shows you how to build a unique monitoring device that you can use to measure the voltage fluctuations or disturbances of the earth's natural electric field, caused by conductive objects moving near the device. The magnitude and frequency of the fluctuations can be used to determine the actual nature of the object. As an example, large moving objects, such as trucks, produce large voltage swings with low frequency components while small fast moving objects, such as birds, produce smaller field changes with higher frequencies. Moving humans, on the other hand, produce a variety of frequencies associated with arm and leg motion.
Unlike other projects in certain hobby type magazines that have very specific purposes in mind, this construction project provides the experimenter with an electric field change monitor that can be used as an instrument to conduct a wide variety of object motion experiments including simple motion alarm applications. For example, with sufficient signal processing and analysis it may even be possible for the experimenter not only to detect the motion of a human but to determine which human was moving. The objective of this construction project is to provide the experimenter with the equipment necessary to conduct research in the nature of the field changes. I'm hoping that the device will excite a new generation of experimenters into exploring this little known phenomenon.

Illustration

The earth's electric field gradient

Before we get into the details of the circuit, let's cover some of the basics first -- the phenomenon of the earth's electric field gradient. In his Lectures on Physics, Richard Feynman stated that as you go up from the surface of the earth, the electrical potential increases by about 100 volts per meter. Thus a vertical electric field gradient of 100 volts/meter exists in the air.
As a means of explanation, imagine the existence of a very sensitive voltmeter that could measure the voltages present in the open air. If you pushed the negative terminal of the instrument's probe into the earth's surface and you positioned the positive lead one meter above the surface, about 100 volts would be detected. If you then moved the probe vertically by another meter above the surface, the voltmeter would measure 200 volts. This voltage difference would continue to increase as you moved the positive probe upward until it reached the top of the atmosphere, some 150,000 feet (46,000 meters) up. At that point, the instrument would finally measure an average potential difference of about 4 million volts.
This naturally occurring 100 volts per meter electric field gradient exists everywhere in the earth's atmosphere and can even penetrate inside most buildings. You might ask: "If such voltages exist in open air, then why isn't the average 2 meter tall human shocked by the 200 volts that should be present between his feet and the top of his head?" The reason you don't feel anything is that the air is too poor a conductor of electricity to allow enough current to be delivered by the voltage. Also, since the human body is filled with salt water, which is a good conductor, the body actually distorts the voltages as it moves through the field, reducing the actual potential difference across the body. To illustrate this effect, suppose an air potential voltmeter was positioned to measure the atmospheric voltage between ground level and a position two meters above the ground surface. Without any conducting objects nearby, the meter would measure a potential of 200 volts. But, when a conducting human walked next to the probe the voltage is shunted to a near ground level potential and the instrument's reading would drop toward zero volts. As the human walked away from the meter, the field would again gradually be restored to the 200-volt reading. In addition to the average voltage changes as a person walks near the detector, the shifting contact of the human's foot on the ground, as well as arm motion, causes small higher frequency fluctuations in the measured voltage. Such signal changes are used as the basis for detecting human motion near the detection circuit.

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