What Is A Metal Detector?

What is a metal detector?

National Museum of Health and Medicine, Armed Forces Institute of Pathology

What is a metal detector? In 1881, Alexander Graham Bell invented a electromagnetic device in which he called induction balance. The device was invented for a sole purpose, a noble although unsuccessful purpose, to locate a lodged bullet inside a dying president.

President James Garfield was laying on his bed dying from an assassins bullet and this induction balance device was hoped to be his savior. The detector was at first thought to have failed as the metal bed frame in which Garfield was lying hindered its operation. However, later, Bell’s metal detector proved to be quite capable as a modified version was used in WWI to uncover land mines.

An interesting side note is that there were three modern commercial inventions that came about because of Garfield’s assassination: the metal detector, the air conditioner and a reinvention of the water bed.

Now that we know a little history behind the metal detector lets move on to the question at hand, what is a metal detector? A metal detector is a device used to find metal objects just under the ground. We are talking just a short distance here, not more than about 10-15″, and this depth depends on many factors.

That may seem like a rather short distance but you will truly be amazed by how many interesting objects can be found with in those depths. In the UK, farms are very popular because of the constant turning of the soil. The beach is very popular for more than the obvious reason of lost items, but because of the constant renewal of the sands through tidal surges.

Besides, inches of ground coverage on an undisturbed relic can still take a very long time for nature to achieve. The vast amount of discoveries both monetary and historic made possible by the use of a metal detector make this hobby not only exciting and fun but educational and rewarding, heck, it may even put a few bucks in your back pocket on occasion.

The metal detector consists of a stabilizer, a control box, a shaft and a search head. For a complete overview of a metal detector see this page. The search head also called the coil is the business end of the detector. The search head creates an invisible magnetic field that penetrates the ground. When this field comes into contact with a metal object, receptors in the search head sense this and alert the user.

The alert is in the form of  a display on the control panel and tones that can be discerned as a potential target in the ground worth digging up. One of the skills developed over time is the deciphering of tones given off by your metal detector especially around the fringe areas (outer limits) of the search detection field. This is why most detector users plug in a good pair of head phones into their detector instead of relying on the detector’s speaker.

The metal detector is operated by holding the detector with one hand by its grip and waving the search head back and forth in front of you. The angle of the metal detector to the ground should be comfortable and the search head should be as parallel as possible to the ground underneath. Most metal detectors will have adjustments to lengthen/shorten the shaft and adjust the search head angle.

The pace a metal detector operator takes is usually steady and dependent on both the difficulty of the terrain and the aspect of the terrain. Sometimes, the aspects of the terrain may deserve closer inspection like around well trodden paths. Likewise, once a interesting tone is heard, the pace can not be so fast as to make it difficult to relocate the location of the sound.

Metal detectors have a few ways of relaying information about target objects detected back to the operator.

First, as mentioned previously, is by tones announced about its find. The metal detector will have different tones for different types of objects (thankfully just a few to learn).

Second, on the control box’s display panel, there is often a visual way to discriminate between detected objects. This is called target identification and the better a detector (the more expensive) ,  the more precise and detailed are the target identification adjustments and displays.  Target identification is really a fancy way of filtering the input of the detector’s sensory given that different types of metals have signatures that the circuitry can discriminate between.

Another thing that is interesting about target identification, is that the reverse of identification can be specified. That is, you can actually turn off or adjust out targets or ranges of targets. For instance, if you are uninterested in finding iron or tin, you can simply turn off these targets.

Target identification is sometimes presented in conjunction or independently on the control panel with two other adjustments known as discrimination and notch filtering. One thing to note is that there is a trade off  between filtering out targets or not because by filtering out targets you may miss targets that are of interest.

Other features that are often found on the metal detector’s control panel are a ground balance adjustment, sensitivity adjustment, mode control and sometimes a pinpointer button.

On many metal detectors a  ground balance adjustment will not be found as it will be automatic. Ground balance adjustments tune the detector to different types of soil make ups and is important for maximizing depth.

The sensitivity adjustment is a way to raise and lower the sensitivity of the metal detector. A good sensitivity level is imperative in just about any environment as it allows you to tune out excessive chatter and false positives for a more smooth signal response that focuses on good targets.

A lot of metal detectors now a days have modes that can be engaged for identifying only certain types of objects. Modes are simply a preset range of target identification. For instance, a detector with a “coins only” mode should only alert you to coins sensed by the detector.

A pinpointer is a handy feature to have for isolating a target to a smaller given location. A metal detector is essentially a motion detector. For the detection of an object to occur, movement is required by the search head. This is because of how electromagnetic induction works and to see why you will need to read my article here.

So, while the pinpointer on a metal detector is not all that necessary, especially since you will probably want a hand held one as well, it allows you to not have to move the metal detector for detection to occur. In this way, you can hold you metal detector steady directly over your target.

There are many more features in todays metal detectors – more than have ever been dreamed of until just a few years ago. GPS systems, state of the art micro processors and more sophisticated digital sensors and controls have been slowly making there way into metal detector control centers.

Soon cell technology, the internet and video streaming may be possible. Metal detection is one of those hobbies that really has no limits as far as technology in concerned. There is always another feature that can improve some aspect of the treasure hunt. And, with this I shall leave you. There is much to discover in your journey to becoming a capable metal detectorist and it is my hope that this article pointed you in the right direction. I wish you well in all your endeavors.

Good Digging!

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