The term metal detector means different things to different people. For some, when they hear the word, they imagine a treasure hunt on the beach. For others, it means the devices used for airport and event security. All these are correct definitions of this term. The principle behind these devices, however, is the same in all instances. Metal detectors rely on the unique relationship that exists between electricity and magnetism. This unique relationship is what powers up most home. For instance, electric companies use giant rolls of copper wire cutting through magnetic fields to generate power. The power is then used in a reverse role in homes to power up tiny magnetic generators. This is what keeps refrigerators, vacuum cleaners and other appliances running.
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The most basic component of any detector is the transmitter. The front end of a metal, usually in the shape of a loop, has a coil inside it. This coil transmits an electric current, which generate a magnetic field. This current changes direction many times a second. The exact number of times the current reverses is called the frequency of the electromagnetic field. Due to this fast-changing current, the magnetic field also regularly changes direction. As a result, any object in the ground receives a magnetic field that is constantly changing polarity. In most cases, the field generated in the metal object will be of a different polarity to that of the transmitter.
This is a basic component of any metal detector. This coil is located close to the transmitter coil. As the transmitter coil generates a magnetic field, it leads to a current being generated in this coil. However, this current is very weak and it needs to be magnified a few times. The signal developed in the receiver coil is usually delayed compared to the one in the transmitter coil. This detectable delay is known as phase shift. A bigger phase shift occurs when the detector meets objects such a gold or copper. Other material that may cause a current to be generated are objects such as iron and bottle caps.
Years of study have revealed that different elements produce a distinctive phase shift. With the development of digital technology, this has further been refined. For instance, the phase shift varies greatly between silver and aluminum. This process of differentiating the different type of materials is known as discrimination’. This is an important property of metal detectors that helps reduce the amount of time for treasure hunters for instance. However, one needs to be careful when using the discrimination feature. It will mean one misses some artefact during a treasure hunt. For instance, one may miss silver or iron coins depending on the setting.
The other option is to use a visual discrimination. With this type of detector, all objects are displayed. However, only valuable metals have to be dug out since they are clearly indicated on the display. The display can be in either analogue format or a digital display. In some instances, a digital processor is used. The advancements in technology mean that a detector with a processor is likely to be highly refined. As a result, one is able to make a better judgement on where to scoop out the soil.
In the ordinary soil or sand, there are usually trace element of iron or other minerals. This can make the process of searching for precious objects quite tiresome. However, innovators have had time to look into this problem and come up with a good solution. The principal behind this solution is that mineral composition in an area is likely to be constant. Most advanced detectors can perform this task automatically. However, older detectors require that the operator performs this task manually. This is made possible using a rotatable knob on the metal detector. Ground balance is important because the operator raises and lowers the detector at various instances. As a result, the detector is made in a way that it accounts for this when it is working.
This is a relatively new technique compared to VLF. With this type of detector, there is usually only one coil. As the current in the coil shuts on and off. It creates an electromotive force, which can be detected by the same coil. This type of detector works on the principle of reflection. The e.m.f. generated is supposed to remain unchanged as it bounces back and forth. However, if there is interference, there will be a noticeable change in the signal. This type of detector, however, has a very low discrimination. It is thus best suited for bomb-detecting or at security checkpoints. Although it can be programmed to detect several types of minerals, there is still a lot of development that needs to take place before this can happen.
Use of Processors
Processors used in metal detectors have simplified the task many times over. It is advisable for one to look for a detector with a good processor. In most cases, things that could have required a huge manual can be achieved with just a few buttons. The microprocessor has also increased the usability of metal detectors. In the formative years, the level of signal processing was too basic. This was because it required huge detectors in order to fit all the components on the detector. This would simply not have been practical. The processor allows users to have capabilities that would have been impossible two decades ago.
Different people view metal detecting differently. While some use it as a hobby, others save lives using this technology. This simplified explanation of metal detecting should make it easier to use the device. Users of these devices need to understand the limitations and capabilities of these devices in order to get the best results. The problems faced by most people who use metal detectors is that they do not even understand the concept behind it. As a result, one may search an area for weeks only for another more informed hunter to come by and find something valuable in hours.