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How Metal Detectors Work

Knowing how metal detectors work will not guarantee success when treasure hunting. However it can be useful information when comparing one detector to another. Successful treasure hunting will never depend entirely upon having the most complex and expensive detector. The best metal detector is still only as good as the person using it. Success comes with persistence and practice.

Not to over simplify the types of detectors but there are broadly three types of metal detectors made for treasure hunters.

  • Gold Detecting
  • Coin and Relic Hunting
  • Underwater and Surf or Wading Detecting

In your quest to understand how metal detectors work remember to keep it simple. The main differences between how metal detectors work can be explained by understanding the following:

  • Technology
  • Type of ground balance
  • The frequency it operates in
  • Type of discrimination capability

No matter what kind of detector you have it consists of three basic parts:

  • The coil
  • Power supply
  • The control box

THE COIL

To understand how metal detectors work you need to understand how search coils work. The coil consists normally of two sets of copper wire windings. As electrical current (supplied by the battery) is passed through one of these copper wire windings and an electromagnetic field is created and sent into the ground. This winding is referred to as the transmit coil. Metal objects buried in the ground conduct electricity and alter the electromagnetic field produced by the transmit coil. This current flows inside of a metal object and produces its own magnetic field. The second coil called the receiver coil picks up this new current and sends it to the control box.

To understand how metal detectors work you will need to understand search coils. Coils come in various shapes and sizes. This can create confusion. What differences are there in coils?

Size:The size of a coil basically influences the depth sensitivity of a detector. The larger the coil the deeper it will detect. However it tends to be less sensitivity to tiny targets. Likewise the smaller the diameter the less depth. With a smaller size you will have a great deal more sensitivity. Smaller coils are lighter in weight and are often chosen for their ability to negotiate difficult terrain or underbrush.

Shape:The most common shape is round. There are also elliptical shaped coils and open web coils. The primary reason for the different shapes has mostly to do with physical requirements of the terrain. It is easier to maneuver an elliptical coil around bushes and rocks than a round coil. Open web coils make it easier to cut through water when wading or underwater detecting. Round coils tend to be more stable and offer a high degree of performance.

The most common types of windings on coils are concentric, double D, and monoloop. The primary difference between each of these is the way the wire is wound within the coil. These concepts are important if you are to understand how metal detectors work.

  • Concentric: with this type of coil there is an inner and an outer circle wire winding. The search pattern for this type are cone shaped and are good for accurately pinpointing the target. However concentric coils are noisier in highly mineralized ground conditions. They also require more ground sweep for through ground coverage.
  • Double D: This type of coil is becoming the preferred coil for most detecting. With this type of winding a blade or chisel shaped signal and covers the ground more uniformly. It is also preferred for its superior ground balancing ability.
  • Monoloop: These coils have only one winding of wire around the circumference of the coil and this is used to both transmit and receive. The signal pattern is cone shaped and requires more overlapping to insure good ground coverage. This type of coil is more difficult to ground balance. However they tend to give a better depth of search than other types.

POWER SUPPLY

Either small nine-volt batteries or AAA size batteries today power most detectors. These types of batteries offer the advantage of less weight and more detecting time in the field. These types of batteries also come in rechargeable varieties. However sometimes when learning about how metal detectors work you will see other types of power supplies but they are the exception.

THE CONTROL BOX

This is where the alteration of the electromagnetic field is interpreted as being caused by a buried metal object, and an audible signal is given to the operator. To understand how metal detectors work you will need to know about the functions of the control box. The control box is also where the operator selects the type of ground balance and types of discrimination.

There are basically there are three types of ground balance:

  • Manual-This type gives the operator the ability to ground balance the various types of soil conditions
  • Automatic-Automatic ground balancing is when the detector tracks the changes in ground mineralisation and automatically adjusts the ground balance.
  • Preset-This is where a detector is preset to a particular type of soil. Because this limits where a detector can be used it is best suited for coin hunting sites.

Discrimination in metal detecting is the ability of the detector to identify the type of metal found. This makes it possible to eliminate the unwanted items and give a signal for only the desired items. Again there are three types of discrimination, variable, notch, and tone.

  • Variable-This type of discrimination is the most basic. Variable discrimination is when the operator sets a level of conductivity and any item below that level is eliminated and all items found above that level are accepted.
  • Notch-If all metals are arranged in their order of conductivity from least to most conductive then it is possible to group these signals in small groups �notches�. Depending on how selective a detector is will determine how selective a detector can be at eliminating junk from good targets.
  • Tone-Some detectors will indicate the identification of a target by the tone. Lower conductivity a lower tone while higher conductivity emits a higher tone.

You will discover when studying how metal detectors work you soon realize microprocessor in modern metal detectors have opened up possibilities, which were unheard of, a few years ago. In the past when a new feature was added it meant more control knobs and switches. The additions of two many knobs become confusing to the operator. With the addition of the microprocessor a liquid crystal display and keypad solved this problem. Now when understanding how metal detectors work remember an unlimited number of features can be added without any additional hardware. It is now possible for a single metal detector to be set up for just about any application of treasure hunting. In addition powerful software can be used to enhance the detectors audio discrimination capabilities and display all kids of information on the Liquid Crystal Display. This will ultimately make the operator�s job of interpreting target responses faster and easier. In the long run it will also make metal detectors less expensive.

TECHNOLOGY

Modern metal detectors use four main types of technology. This technology has to do with the frequency a detector operates in. To understand how metal detectors work it is important to understand what difference frequency makes.

Basically frequency is measured in kilohertz. What you need to know is the lower the frequency used the deeper the ground penetration. In all things there are tradeoffs, it�s a part of life. Low frequency seems the way to go but it is less sensitive to small targets. On the other-hand the higher the frequency, the higher sensitivity too small targets, but will not penetrate as deeply.

When trying to understand how metal detectors work remember most current modern metal detectors use one of the following five technologies:

  • Continuous Sine Wave-This is the traditional type of technology used in most basic detectors. These detectors are commonly known as VLF (very low frequency) detectors. The modern VLF detector has had decades of advances and improvements but more advances will continue to be made. Even though many advances have been made with VLF detectors the basic way the signal is sent out and received back hasn�t changed much. However you can be sure that continuous research will take this technology to the next level.
  • Multiple Band Spectrum-Detectors that uses this technology transmits between 17 and 28 different frequencies simultaneously, rather than a sine wave as in the VLF detectors. Currently multi-frequency detectors are some of the most versatile detectors on the market. With this technology a better and easier ground balance along with better target identification improve one�s treasure hunting experience.
  • Flex Technology- Uses state of the art digital and mixed signal components to improve upon the standard single frequency technology. The advantage to this technology is that it allows the detector to operate in different frequencies depending on the coil being used.
  • Multi-Period Sensing-This is a patented technology Minelab uses in many of its Mine detectors. It is also being introduced in some of the upper end treasure detectors. This unusual technology allows a detector to transmit a stream of alternating short and long pulses of magnetic field into the ground. With this technology it is possible to locate metal objects at a far greater depth. Also small targets can be located in deeper soil.
  • Pulse Induction-You need a general understanding of how Pulse Induction works when studying how metal detectors work. A pulse induction metal detector is very simple when compared to a VLF detector. A single coil of wire is used both for the transmit and receive function. Pulse induction metal detectors switch on a pulse of transmits current, then shut off, then switch on another pulse. The pulse repetition rate (transmit frequency) of a typical pulse detector is about 100 pulses per second. Some models have been produced with much lower frequencies. Higher frequencies are more sensitive to gold and nickel while lower frequencies are more sensitive to silver. This type of detector is best-used underwater or wet sand at the beach. It offers the best chance of finding deep targets.

In your quest to understand how metal detectors work don�t get too hung up on this frequency concept. Frequency is only one of the factors that determine depth and sensitivity. It is certainly not the primary factor in trying to determine which detector to buy; it is only an indicator. When comparing one detector with another there are many factors to consider. How will the detector be used? How large is your budget? What will you primarily search for?

Only you can answer these questions. When studying how metal detectors work it is very important not to put too much weight on price as a factor. There are many excellent detectors with great many features for under $100.00 that will meet the needs of the average treasure hunter. Remember it�s not the detector but the person using it that will ultimately determine treasure-hunting success.