This document is a project report submitted by Pranav Ghildiyal to his school, Kendriya Vidyalaya B.E.G, for the 2013-2014 academic year. The project is about the circuit diagram and working of a metal detector. It provides background information on the history and development of metal detectors from their early crude designs to modern portable devices. It describes the different types of metal detectors including Very Low Frequency, Pulse Induction, and Beat Frequency Oscillator detectors. Potential uses of metal detectors are also listed.

1. Project prepared by:
PRANAV GHILDIYAL
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2. ‘XII’ ‘B’
SESSION: 2013-14
ROLL NO::- 12227
KENDRIYA VIDYALAYA B.E.G
CERTIFICATE
ThIs Is To CERTIFy ThAT MAsTER PRANAV GhILDIyAL
sTuDyING IN CLAss XII B oF KENDRIyA VIDyALAyA B.E.G
DuRING ThE ACADEMIC yEAR 2013-14 CoMPLETED ThE AssIGNED
PRojECT AND hAs suBMITTED A sATIsFACToRy ACCouNT oF hIs
PRojECT.
DATE :
sIGNATuRE oF INTERNAL
sIGNATuRE oF
EXTERNAL
EXAMINER
EXAMINER
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3. __________________
__________________
ACKNoWLEDGEMENT
This word acknowledgement is to express my deep sense of gratitude towards those
unseen hands which are my teacher Mrs. H. JADHAV (CHEMISTRY) , our principal
Ms. N. GEETHA RAO and my Parents who gave me the golden opportunity to do
this wonderful project on the fore mentioned topic without their contribution the successful
completion of this project would not have materialized. The project helped me in doing a
lot of Research and I came to know about so many new things I am really thankful to all of
them for assisting me and helping me finish this project in the limited time I had.
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4. SINCERELY
PRANAV GHILDIYAL
AIM OF THE PROJECT:CIRCUIT DIAGRAM:-
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5. BACKGROUND :A metal detector is a portable electronic instrument which detects the presence of metal
nearby. Metal detectors are useful for finding metal inclusions hidden within objects, or
metal objects buried underground. They often consist of a handheld unit with a sensor
probe which can be swept over the ground or other objects. If the sensor comes near a
piece of metal this is indicated by a changing tone in earphones, or a needle moving on
an indicator. Usually the device gives some indication of distance; the closer the metal is,
the higher the tone in the earphone or the higher the needle goes. Another common type
are stationary "walk through" metal detectors used for security screening at access points
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6. in prisons, courthouses, and airports to detect concealed metal weapons on a person's
body.
The simplest form of a metal detector consists of an oscillator producing an alternating
current that passes through a coil producing an alternating magnetic field. If a piece of
electrically conductive metal is close to the coil, eddy currents will be induced in the metal,
and this produces a magnetic field of its own.
History and development
Toward the end of the 19th century, many scientists and engineers used their
growing knowledge of electrical theory in an attempt to devise a machine which
would pinpoint metal. The use of such a device to find ore-bearing rocks would
give a huge advantage to any miner who employed it. Early machines were crude,
used a lot of battery power, and worked only to a very limited degree. Alexander
Graham Bell used such a device to attempt to locate a bullet lodged in the chest of
American President James Garfield in 1881; the metal detector worked correctly
but the attempt was unsuccessful because the metal coil spring bed Garfield was
lying on, confused the detector.
Modern developments
The modern development of the metal detector began in the 1920s. Gerhard
Fisher had developed a system of radio direction-finding, which was to be used for
accurate navigation. The system worked extremely well, but Fisher noticed that
there were anomalies in areas where the terrain contained ore-bearing rocks. He
reasoned that if a radio beam could be distorted by metal, then it should be
possible to design a machine which would detect metal using a search coil
resonating at a radio frequency. In 1925 he applied for, and was granted, the first
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7. patent for a metal detector. Although Gerhard Fisher was the first person granted
a patent for a metal detector, the first to apply was Shirl Herr, a businessman from
Crawfordsville, Indiana. His application for a hand-held Hidden-Metal Detector
was filed in February 1924, but not patented until July 1928. Herr assisted Italian
leader Benito Mussolini in recovering items remaining from the Emperor Caligula's
galleys at the bottom of Lake Nemi, Italy, in August 1929. Herr's invention was
used by Admiral Richard Byrd's Second Antarctic Expedition in 1933, when it was
used to locate objects left behind by earlier explorers. It was effective up to a
depth of eight feet.[2] However, it was one Lieutenant Józef Stanisław Kosacki, a
Polish officer attached to a unit stationed in St Andrews, Fife, Scotland, during the
early years of World War II, who refined the design into a practical Polish mine
detector.[3] They were heavy, ran on vacuum tubes, and needed separate battery
packs.
New coil designs
Coil designers also tried out innovative designs. The original induction balance coil
system consisted of two identical coils placed on top of one another. Compass
Electronics produced a new design: two coils in a D shape, mounted back-to-back
to form a circle. This system was widely used in the 1970s, and both concentric
and D type (or widescan as they became known) had their fans. Another
development was the invention of detectors which could cancel out the effect of
mineralization in the ground. This gave greater depth, but was a non-discriminate
mode. It worked best at lower frequencies than those used before, and
frequencies of 3 to 20 kHz were found to produce the best results. Many detectors
in the 1970s had a switch which enabled the user to switch between the
discriminate mode and the non-discriminate mode. Later developments switched
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8. electronically between both modes. The development of the induction balance
detector would ultimately result in the motion detector, which constantly checked
and balanced the background mineralization.
• Types of Metal detectors:-
Very Low Frequency (VLF)
► Uses two coils:
o
Transmitter coil (search head, antenna)
o
Receiver coil
► There is a delay in the received signal compared to the transmitted signal called phase
shift
► The signal is sent to the control box where it is analyzed by sensors
Pulse Induction (PI)
► Simple when compared to VLF detectors
► Generates “Pulses” of Current Through Search Coil
► Pulse reaches its peak and reverses direction, collapsing very suddenly, thus
creating a sharp
electrical spike.
► Pulses continue to be generated from a mere dozen to about a few thousand
pulses per second.
► Reflected portion of signal becomes delayed which is sampled, amplified, and
sent to
audio circuit to notify user.
=
Beat Frequency Oscillator (BFO)
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9. ► Uses two coils and sends a current through each
► Coils use slightly different frequencies, which produces audible “beats”
► When passed over metal object, induces a current in object
► Current causes a magnetic field, which interferes with field produced
by detector
► Interference changes frequency of current in large coil, and thus an audible change in
“beats”
► BFO Metal Detectors are cheap to make, but aren’t as accurate or dependable as more
expensive types
Uses
 Archaeology
 As a hobby
•
Coin shooting
•
Prospecting
•
General metal detecting
•
Beach combing
 Security screening
DISCLAIMER :I HAVE ALSO MADE THIS PROJECT
TAKING HELP FROM INTERNET
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10. I EXPREE MY REGARDS WHO ARE
ACTUALLY BEHIND THIS PROJECT.
I HAVE UPLOADED THIS ONLY SO
THAT MORE PEOPLE CAN TAKE
HELP FROM THIS UPLOAD
THROUGH MY PROFILE IN
SLIDESHARE… TO REGISTER YOUR
OBJECTION TO THIS UPLOAD PLZ
COMMENT UNDER THE
PRESENTATION IN THE WEBSITE
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11. BIBLIOGRAPHY
www.cbseportal.com
www.cbseportal.com
www.cbseportal.com
•
www.wikipedia.org
•
www.google.com
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12. •
www.ehow.com
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