A Guide to Metal Detectors
Back in the eighties, “metal detector” more than likely brought to mind the image of a lone man holding a broom-like gizmo, swinging it back and forth along the beach in search of buried coins, metal artifacts or other treasures. After September 11, airport security might have been the first thought.
We have prepared a 3 part discussion of this fascinating technology:
1. Metal Detector Types
2. How Metal Detectors Work
3. Metal Detectors & Airport Security After 911
Metal Detector Types
Just like most early inventions, metal detectors were initially crude instruments which were, of course, not anywhere as advanced as today’s models. However, both older and modern-day versions of metal detectors use the same operating principles - that is to say that they use electromagnetic signals to detect metal objects or traces of metal inside solid objects. Having stated this, it should be mentioned that there are exceptions to this rule. This is because some manufacturers have come up with a new kind of metal detector. Unlike other detectors, these fire a high voltage of electricity into the ground in order to detect even the slightest traces of metal. This process is known as pulse induction. The detector also has an electronic box that measures the amount of voltage received from any detected object. If metal is present in the ground, then the user would know this by the longer time it takes for the voltage meter to fall to zero. On the other hand, if there is no metal, the voltage meter would show a flat-lined frequency signal.
The original detectors typically consisted of an electronic box, battery, telescoping shaft, insulated wires, and the coil. The coil was comprised of a network of sensitive wires which were called “receivers”. Together with the battery, the coil was able to generate powerful electromagnetic signals which were used to detect specific magnetic signatures in the ground. In the case of metal being present, the receivers will read the charge and send the signals back to the electronic unit which contains the microprocessor. The microprocessor will in turn send the signal to a speaker which amplifies it into an audible beeping sound. It is worth mentioning that these metal detectors played significant roles in the finding of many important archeological artifacts.
After these pioneering detectors there came an improved version, which was called the discriminator. This detector incorporated what is called the “induction balance system”. The system involved using a pair of coils that were set to read an equilibrium electrical frequency of zero. Once the coil comes across any metal in the ground, the frequency in the two coils will immediately become unbalanced. This in turn leads to a change in the sound of the detectors speaker. At the time when these detectors were manufactured, inventors had discovered that each metal has its own distinct response to electrical stimulation.
As such, manufacturers were now able to create a detector which could differentiate between metals. This feature is particularly important when one considers that some precious metals are in the same vicinity as lower value ones. In any case, the discriminator did have a flaw. This was due to the fact that making it less sensitive to metals like tin and copper and more sensitive to metals like gold implied that it was less likely to find deeply embedded objects. This is because setting the discriminator to find more precious metals meant that the coil lost much of its sensitivity.
Today the most sophisticated detectors are fully computerized and hence more efficient than previous versions. This means that they are also more practical in terms of size and portability. They use advanced microprocessors and microchip technology, which allows users to have access to an array of enhancing functions and features. At their fingertips, users can now set sensitivity levels, discrimination degrees, and track speed and threshold volume. It does appear that advancements in the production of detectors is set to continue well into the future. Whatever form the detector of the future takes, it is certain that they will be even more widely used.
How Metal Detectors Work
Metal detectors are certainly one of the most innovative inventions that have ever been made. Their history goes all the way back to 1882 when they were first used in the field of medicine. At this time, they were mostly used as a diagnostic tool, which could detect foreign metal objects in the body. These objects could have entered the body either through injury or ingestion. Metal detectors are effective and efficient in the way they work. This has enabled them to become an indispensable tool not only in medicine, but also in modern society as a whole. It is also worth mentioning that metal detectors are safe in terms of radioactive emissions, and they are also very user friendly. The way in which metal detectors actually function is very straightforward. They use an electromagnetic signal that is powerful enough to penetrate most solid surfaces such as rock and concrete. The typical metal detector that can be purchased from a store will consist of three components. These include a battery, the coil, and the electronic unit. In the standard metal detectors, an insulated wire runs down the telescoping shaft into the plastic coil.
All that is required is for a user to sweep the coil over the area in question. If the detector makes a beeping sound, then it means that it has detected the presence of a metal object or traces of metal. At this junction, it should be said that the coil is perhaps the most important part of a metal detector. This is because it uses the battery to generate the powerful electromagnetic signal that is required for a metal detector to work. So, in a sense, the coil acts as a sort of transmitter. The coil also consists of a network of very sensitive wires. These wires are called receivers, because they are responsible for reacting to any magnetic field they sweep over. The receiver is sensitive enough to detect and differentiate between the signatures of different metals. It is this quality of receivers that enables some metal detectors to identify the specific metals it detects. This feature of metal detectors is also made possible by microprocessors in the electronic box. These microprocessors are able to quantify the time between when the coil passes over a magnetic field to when the receivers obtain the magnetic charge. This is called measuring the phase shift and it can be used to identify different metals.
As soon as the receiver detects a metal object, it will immediately send the electromagnetic signal back to the electronic box. The electronic box in turn transfers the signal to a speaker, which causes the detector to make a beeping sound. The most sophisticated and advanced metal detectors allow the user to adjust the sensitivity of the coil. This allows for more accurate and specific metal detections. Nowadays, metal detectors come in different models and sizes. They are also not as expensive or inaccessible as they used to be. This means that just about anyone can own a metal detector. The majority of private individuals who own detectors use them for their favorite leisure activities and hobbies. When not used in hospitals and for recreational purposes, metal detectors are used to safeguard public areas from potentially dangerous metal objects and weapons.
The fact is that metal detectors not only work in a straightforward way, they are practical and also very easy to use. This is certainly one of the reasons why they have a lot of appeal. With more metal detector manufacturers engaging in further research and development, there is no doubt that in the future, metal detectors will work in even more sophisticated fashions.
Metal Detectors & Airport Security After 911 and the TSA
Airport security has never been as important as it has in the last five years. Since congress enacted the Airport Security Federalization Act in 2001 a slew of new legislation and procedures have been adopted with the single view of a making flight safe from potential terrorism. One of the provisions of that act was to provide all airport security screening staff federal employees with the training necessary to do their jobs. It also created a Federal Transportation Security Administration (TSA) under the department of Transport with overall authority for the security of commercial passengers on land, sea and air. Under this new law all airport security screening personnel must be American citizens. What this means for travelers is that from at least 31 December 2002 all checked baggage must be screened for explosives as well as X-Rayed, and boarded passengers matched to checked luggage. What’s more the Computer Assisted Passenger Pre-screening system was implemented to cross reference travelers with known suspects and felons.
Air marshals made a welcome reintroduction to flights, cockpit doors were reinforced, video cameras monitored the cabin from the cockpit, and 911 capable phones had to be available to passengers. In addition the Act provided for the future use of voice stress technology to identify potential threats on the terminals side, before that person boards the plane. All sensible measures in the security mix and indeed somewhat surprising many of them weren’t already in place. However, if history is any guide, safety features are usually developed after events have proven them necessary. As a result airports and airlines have been scrambling since 2001 to catch up with new technologies and legislation that are also effective and won’t create bottlenecks.
Inevitably anti-terrorism procedures often have an ad-hoc, reactive aspect to them that is inescapable. Consider the steps taken after the recent British thwarted terror plots of summer 2006. Hand luggage was banned from the air cabin, no liquids allowed on flight (to the chagrin of nursing mothers!) and all shoes inspected at the gate security check. Panicky and counter-productive was the unavoidable accusation, only time will tell how effective they will be and the strict prohibition on hand luggage has since been somewhat relaxed. Certainly it has inspired our local Transport Administration to follow suit and ban the presence of liquids in carry-on baggage; with, thankfully the exception of baby formula, milk and prescription medicine. In purely security terms there is something to be said for improvised initiatives such as these, for one thing they make planning an attack that little bit harder, and the downside is the disruption, which inexorably translates into dollar and cents.
The dilemma is this: you cannot future-proof your security measures, if there is a protocol it can be circumvented, if there is a new technology there will be eventually a counter-measure. Look at it this way; in many ways 9/11 was a one-off opportunity the bad guys ruthlessly exploited, and to plan to prevent another 9/11 is to risk missing the security flaws in the measure you implement doing so. What can be done? Well, think of it as an arms race where rolling out new detection technology is essential before someone finds a way of working round it. Consider metal detectors. Current models are fully computerized and can set sensitivity, discrimination, track speed, threshold volume, notch filters and other parameters. These deeper seeking metal detectors can also hold data in memory and potentially match patterns for better discrimination. Where previously height detection was a novelty it is now industry standard and with a raft of new engineering coming down the line, like beat balance and coil coupled operation metal detectors will keep their pre-eminent place in the security of our airports and other public buildings.