Why RF Fabrics Are Ineffective for AM Systems and More on the Physics of Shielding
In an era of technological development, when Acousto-Magnetic (AM) and Radio Frequency (RF) systems have become an integral part of theft protection strategies, questions of effective shielding against these systems have gained particular importance. The significance of these questions is determined not only by the desire to provide reliable protection for objects but also by the need to understand the physical principles underlying the operation of these systems.
In this article, we will analyze these principles, focusing on the differences between AM and RF technologies, and why materials such as foil can effectively shield signals of both types of systems. We will explore how simple laws of physics and electromagnetism determine the capabilities and limitations of various shielding materials, investigate alternative approaches to shielding that may offer more practical and economically justified solutions. The goal of our article is not only to provide readers with a deep understanding of the mechanisms of AM and RF systems but also to share scientifically based methods of their shielding, which will help dispel common misconceptions and contribute to your development and new understanding of the methods that I describe in many of my materials.
So, let's clarify one thing before talking about how one can 'trick' anti-theft gates in stores, as most of us might think that using something like foil or special devices would make the tag 'invisible' to the gates, but in reality, it's not that simple!
And the reality tells us that even if we apply various tricks, the gates are still able to 'sense' the presence of a tag nearby, and anti-theft systems are initially designed in such a way as to minimize the number of false alarms. This is achieved through complex algorithms for analysis and decision-making, which require multiple confirmations of the presence of a tag between the gates (and not somewhere nearby inside the store, for example) before activating an alarm. Such confirmations include not only reaching a minimum power level of the return signal from the tag but also analyzing changes in these signals over a certain number of time intervals, in standard AM systems with typical settings this is a minimum of 8 confirmations in one very large measurement period.
Let us remind you of the hype video in which a Chinese woman was shaking a SuperTag, it immediately presents multiple reasons why AM gates do not see it:
– constant change of the axis position in space = change in the power of the response to the frame that receives the signal-response;
– constant displacement of AM "strips" inside the sensor = constant change in response characteristics;
– constant movement in space due to motion, but this is a minimal factor.
!BUT this only applies to sticker tags… Of course, you can also rotate a coil tag at a speed of a hundred times per second, but it is unlikely that a person can do this.
And here is the video with our post-processing:
In addition to traditional shielding methods, such as the use of foil, which acts due to its reflective properties, there are also more modern and innovative approaches. One such approach is the application of specialized fabrics capable of effectively shielding RF signals.
Moreover, there are other technological solutions, such as AM or RF jammers, as well as universal 2-in-1 jammers, which provide another level of protection. These devices, by blocking the signals of anti-theft systems, allow objects to move through protected areas undetected. Their use underscores the importance of innovation in the field of shielding and protection, and also offers users flexible and effective ways to bypass security systems.
So, first, we need to recall some year of the invention of foil and in which years Queen FOLga ruled with it… 🤣 OOPS.. Wrong, correcting myself:
– foil is effective as a shielding material for both RF and AM systems for several reasons. Its effectiveness is based on its excellent conductive properties and the ability to create a "Faraday cage" effect, which blocks electromagnetic fields and waves, preventing them from penetrating through the shield.
Why foil works:
1. For RF systems:
foil reflects RF waves thanks to its conductive properties. When an RF wave encounters the surface of the foil, it is reflected back, thus it cannot detect objects protected by a foil-wrapped package.
The effectiveness of shielding fabrics in application to RF systems operating at a frequency of 8.2 MHz is determined by several key physical principles. Firstly, the main mechanism is the principle of reflection and absorption of electromagnetic waves by metallic components embedded in the fabric structure. Metals, due to their conductive properties, create a "Faraday cage" effect, preventing the penetration and spread of RF waves into the protected space.
Secondly, effectiveness also depends on the parameters of the skin effect, which limits the penetration of electromagnetic waves into the conductor to a certain depth, depending on the frequency of the wave and the electrical properties of the material. At the frequency of 8.2 MHz, metallic components in the fabric effectively block RF waves, preventing them from penetrating through the screen.
Moreover, the principle of interference plays an important role, where waves reflected from the fabric surface can interact with incoming waves, resulting in their amplitudes either enhancing or weakening each other, which contributes to further reduction of the RF signal intensity.
2. For AM systems:
AM systems use low-frequency magnetic fields, which can also be effectively blocked by foil. Since foil is a good conductor, it redistributes magnetic fields around the protected object, thus creating a barrier that prevents the magnetic field from penetrating inside.
Acousto-Magnetic anti-theft systems, operating at a frequency of 58 kHz, present a unique challenge for shielding with fabrics for several reasons. Unlike radio frequency systems, AM systems use low-frequency magnetic fields, which can easily penetrate through most non-metallic materials, including fabrics. This is because magnetic fields interact with materials differently, unlike electromagnetic waves, which can be reflected or absorbed by metallic fibers in the fabric.
A key factor here is the penetrating ability of magnetic fields. Magnetic fields generated by AM systems can penetrate through most non-conductive materials, rendering non-metallic shielding fabrics practically useless for blocking them. For effective shielding of magnetic fields, materials with high magnetic permeability are required, capable of redirecting magnetic field lines around the protected object, which is not a characteristic of most fabrics.
The effect of through holes or cracks:
For AM systems:
Even the slightest through hole or crack in a foil-wrapped package can completely negate its effectiveness as a screen against AM systems. This is because magnetic fields can "leak" through these openings, allowing AM systems to detect protected objects. Unlike RF waves, a magnetic field can penetrate through very small gaps, making the protection incomplete.
For RF systems:
In the case of RF systems, small holes or cracks in the foil are not always critical, as the effectiveness of the shielding depends on the size of the hole compared to the wavelength of the RF signal. If the hole is smaller than the wavelength, then the foil can still be effective in blocking RF waves. However, the larger the hole, the less effective the shielding becomes.
This difference in sensitivity to holes and cracks between RF and AM systems is due to the fundamental differences in how these systems operate and the ways in which electromagnetic and magnetic fields interact with materials. The foil, with its ability to conduct electricity and redistribute magnetic fields, acts as a universal shielding medium, but its effectiveness critically depends on the integrity of the coverage.
Imagine that RF waves from an anti-theft system are like light from a flashlight, and the shielding fabric is like an umbrella. If you turn on the flashlight and point it at the umbrella, the light cannot pass through the fabric of the umbrella and illuminate something underneath it. This is how shielding fabrics work with RF waves: they prevent the "light" from the anti-theft system from passing through them, thus protecting the goods from being "illuminated".
In this analogy, the metal fibers in the fabric are like little mirrors or sparkles on the umbrella, which reflect light. Therefore, when RF "light" tries to pass through our "umbrella", it simply reflects back, and the goods remain in the "shade", i.e., protected from the anti-theft system.
Let's recall our example with the flashlight and umbrella, but this time imagine that instead of flashlight light, we have a magnet. If you bring the magnet close to the umbrella, you'll notice that the magnetic field passes through the fabric of the umbrella without any obstacles. This happens because the fabric of the umbrella cannot block or reflect the magnetic field in the same way it could block light.
In the case of AM anti-theft systems, the "magnet" is the magnetic field they create, and the "umbrella" is the shielding fabric. Since the fabric cannot stop the magnetic field as it could stop light (or RF waves), the magnetic field easily passes through it. This means that using fabrics to block or shield from AM systems is ineffective, as magnetic fields "pass through them" as if the fabrics weren't there at all.
Let's imagine we have a magic cloak that we want to use to hide from two different types of guards in a labyrinth. The first type of guards uses flashlights (like RF systems) to search for us, and the second type uses magic wands that can sense our presence even through walls (like AM systems).
Why foil works:
Flashlights (RF systems):
Our magic cloak is made of a special material that reflects the light of flashlights. It's as if we were wearing a mirror coat, and when the guards shine their flashlights on us, the light reflects back, and they cannot see us.
Magic wands (AM systems):
Our cloak can also absorb the spells of magic wands, thanks to which the guards with wands also cannot find us. It's as if the cloak were made of a material that "absorbs" magic and doesn't allow it to reach us.
The impact of through holes or cracks:
Magic wands (AM systems):
If even a tiny hole or cut appears in our cloak, the magic of the wands can seep through it and detect us. It's as if there was a hole in our magic coat, and through it, one could see our real clothes.
Flashlights (RF systems):
With holes and cuts, the situation is a bit better. If the hole is small, the light from the flashlights still may not penetrate the cloak, and we remain invisible. But if the hole becomes larger, then light will start passing through it, and the guards will notice us. It's as if there was a small hole in the mirror coat: a small hole won't allow someone to see our entire body, but if the hole is large, then our game of hide and seek is over.
Thus, our magical cloak helps us remain invisible to both types of guards as long as it is intact. However, should it acquire holes, its magical properties might be compromised, and the guards with magic wands will surely catch us at the most unpredictable moment, as we can never see cracks the size of millimeters with our mere human eyes!
But I haven’t finished yet... 🤣
In the modern world, where security technologies in stores are becoming increasingly advanced, finding effective means to circumvent anti-theft systems becomes a crucial task. In this context, besides specialized fabrics that have already proven their effectiveness, it is worth considering the use of AM or RF jammers, as well as a universal “2-in-1” jammer for both AM and RF systems.
Jammers are devices capable of disrupting the decision-making logic of AM or RF systems, thereby allowing the movement of goods between gates without detection.
The use of such devices can significantly expand the possibilities for action within stores:
- they allow placing the merchandise practically anywhere: be it a pocket, sleeve, plastic bag, or even holding the item directly in hands. This opens up wide avenues for creativity and inventiveness, making the process of moving goods unnoticed much more flexible.
- when using a jammer in disguise, for example, as a PowerBank or another everyday device, it does not arouse suspicion even in the event of a search. This provides an additional level of security and stealth for the user.
- the convenience of carrying a jammer disguised as an ordinary item makes its constant presence unobtrusive and potentially useful in various situations.
Initially, problems associated with using foil to create so-called "shields" become apparent with regular use. Foil requires regular inspection as micro-cracks that may appear reduce its effectiveness. Additionally, foil lacks the necessary flexibility for convenient use with bulky items and requires constant replacement, leading to additional time and financial costs.
Unlike foil, black RF fabric offers a number of significant advantages:
- metal detectors do not react to this fabric, as it contains no metallic elements, making it an ideal choice for inconspicuous use.
- the fabric is highly durable, maintaining its shielding properties over several years of active use.
- the possibility of manufacturing bags of various sizes from black RF fabric allows for customization to specific needs, providing flexibility and versatility in application.
- the fabric can be used to create pockets and linings in bags, making it unnoticed by others and avoiding unnecessary suspicion.
It should be noted that black RF fabric works exclusively with RF systems, ensuring its effectiveness in corresponding conditions. While foil may offer versatility in working with AM and RF systems, a number of critical drawbacks make its use less preferable in the long term.
Thus, the combination of using black RF fabric and AM/RF or universal 2-in-1 jammers can offer a comprehensive approach to overcoming anti-theft systems, combining flexibility, stealth, and high efficiency.
Phew... Well, that’s all, Carlson has flown away, but he promised to return)))
Respect to those who read through!
