1. Diagnose – Use EMF Meters to identify problems.
2. Distance – Use extension cords to increase distance.
3. Deactivate – Disable sources by turning them off with switches and timers.
4. Defend – Apply EMF shielding to reduce radiation exposure.
1- Diagnose with a meter
This step is the key to successful mitigation. Even if you know you are bothered by a specific device (your wifi router for example), there will surely be other sources of EMF in your environment that are contributing to your exposure burden, and so raising your overall sensitivity.
EMF Meters are easy to use and are affordable, and they are the only way to identify hidden sources of trouble. And they can help you check if your efforts have indeed resulted in reducing the overall exposure.
Depending on the source of the high fields, there are several strategies for reducing them:
2- Increase your distance
Like heat from a candle, EMF strength decreases with distance from the source. Here are some common examples of how to increase your distance:
- Hold your cell phone away from your head/body (use speakerphone or a headset)
- Move the bed to a place in the room away from a hot spot
- Move the alarm clock across the room from the bed
- Put a window air conditioner in the window furthest from the people
- Use a hose on your hairdryer
- Locate the wifi router away from the people
- Get shielded extension cables and move computer peripherals away from the user
- Use a remote keyboard on a laptop (and don’t ever put the laptop on your lap!)
- Stand back from the microwave oven when in use
3- Turn off the source
Turning off the source of the field results in an immediate and complete reduction of the problem. Turning off could look like this:
Turn it off permanently
- Turn off wifi and run wires for internet connection
- Take your microwave oven to the curb or sell it on Craig’s List
Install a switch or timer
Replace it with a low EMF device
- Use a manual toothbrush instead of an electric one
- Use a towel instead of a hair dryer
- Replace compact fluorescent bulbs with incandescent or LED
- Swap your induction stove for a gas one
Shielding involves placing a proper barrier between the source of the EMF and the people. There are many types of shielding material, and it is critical to choose the right one, in the right quantity, and install it in the right way. The shielding material can often be placed directly on the source of the EMF, or perhaps on or near the body of the person. We are always willing to assist you in choosing the proper material for your situation.
Here are some common examples:
- Faraday Canopy over a bed to reduce RF exposure while sleeping
- Shielding window film to reduce RF coming in through windows
- Shielding paint to reduce RF coming in through walls
- Magnetic shielding on a circuit breaker box
- Use a shielded box on the wifi router
- Add shielding to your laptop or desktop computer
- Cover your cell phone with a shield
- Wear shielded clothing
- Choose shielded bedding
- Install a shield on your “smart” meter
- Install Stetzer filters on circuits with high levels of dirty electricity
The concept of radiofrequency (RF) shielding is simple: simply put a barrier between the source of the radiation and the area you want to protect. But keep in mind that in many ways, RF behaves like light and can reflect off of some surfaces… working its way around any shield which is less than a complete enclosure.
Image that you are outdoors on a sunny day. You set a large mirror on a stand above your head. The attenuation for the mirror is very high, perhaps 120 dB or more, so basically no light comes through the mirror. If leakage was not an issue, you would be in total darkness. We all know this is not the case. Leakage from the sides easily illuminates the shaded area. Granted, the amount of illumination is less than standing in full sunlight, but the attenuation is nowhere near 120 dB. Maybe more like 20 dB. Furthermore, using a shield with even better attenuation will not yield any more benefits.
To achieve a high level of shielding, you must control leakage VERY carefully. Gaps under doors, joints between shield sections, and even pinholes from sewing shielding material can permit these high-frequency signals to penetrate. You need to create a “complete” enclosure. Any part that is not shielded is a leakage point.
In addition, it is critical that you remove RF sources that are inside the room. Check with an RF meter for cordless phones, wifi routers, laptops, baby monitors, etc. An RF meter will also guide and evaluate the effectiveness of your shielding installation.
Start by shielding the windows
Windows will most certainly permit RF to enter the room. Think about the type of windows you have and whether or not you plan to open the windows. There are 3 basic approaches to shielding windows:1] apply a shielding film to the glass itself. ScotchTint (currently unavailable) and RadioClear are two good choices. 2] create an indoor screen that fits into the window opening. Use Copper Wire Mesh or VeilShield 3] create a shielded curtain or curtain liner. Naturell, ArgenMesh®, and Soft&Safe are good choices. If you need transparency, choose High Performance Silver Mesh, Daylite, or VeilShield.
Actual photos of various windows shielding materials:
Shield the walls and ceiling
Painted surfaces are easily shielded with CuPro-Cote® or Y-Shield paint. This includes trim and doors. Be sure to caulk any gaps or cracks prior to painting so that you have a continuous, unbroken painted surface. You can paint over the shielding paint with any color of latex paint to achieve any appearance you like. You could also use a shielding fabric such as Nickel Copper RipStop or AL60 behind the wall. Attach these materials directly to the studs before installing the drywall. Pay attention to whether or not a vapor barrier is desired in your location.
How about the floor?
Floors are best shielded during construction. The subfloor can be painted, or a shielding fabric layer can be applied before the final floor surface is installed. If the floor is already installed, you can lay shielding fabric, and cover it with a large area rug or sheet linoleum. Remember to control leakage, such as the gap around the door, switch plates, mounted light fixtures, vents, and so on. Contact us if you need advice.
How can I shield my Smart meter?
A Smart meter is a radiofrequency (RF) emitting device that the utility company has installed on your gas or electric meter. The RF signal emitted transmits information back to the utility company about your gas or electric usage. The signal is intermittent but operates 24/7. Usually, the utility company will not permit you to completely block this transmission. However, you can shield your body and your living space to minimize the amount of RF exposure you receive.
There are two main categories of shielding materials that can be used:
RF reflectors and RF absorbers
An RF Reflector will cause the majority of the signal to bounce off, somewhat like a mirror reflects light. It can have very high shielding performance, and in general, should be grounded for peak efficiency. It will usually offer better shielding (less RF transmission) than an absorbing material. An RF Absorber will absorb much of the signal, and minimize reflection. The energy absorbed is released as a tiny, almost unmeasurable amount of heat. Grounding is usually not needed. In both cases, SOME amount of RF does get through the shield, as no shield is 100% effective. You can use double or triple layers of shielding to improve performance.
So where should I put the shield? And how much area do I need to cover?
First, the shield must be positioned BETWEEN you and the source of the radiation. Generally, this means that the shield will be placed on the interior surface of the wall adjacent to the Smart meter. Think about the Smart meter emissions as coming from a light bulb located at the meter, and the shield casting a shadow. Cover enough walls so that the people would be in the protective “shadow” cast by the shield. Notice the small shield in the floor plan at the right. In this example, the majority of the bedroom area is protected, but that is not true for the rest of the living space.
So which one is right for your situation? In a hypothetical world where your Smart meter is the only source of RF radiation, either absorbers or reflectors would work well. However, in the real world, there will be multiple sources of RF radiation. Some of them might be right inside your own home. Some might be coming from other directions. In such a situation, if you use a reflecting material, it will reflect on BOTH sides, and you could end up increasing the amount of RF in your living space.
On the other hand, if you use an absorber, it will absorb on BOTH on both sides, so you cannot increase your exposure. If, you use both materials, a reflector on the side closest to the RF source, and an absorber on the side closest to the living space, you get the best of both materials… and the absolute lowest RF transmission. Any small amount of Smart meter signal penetrating the reflector will be absorbed by the absorber. Any signal coming from the opposite direction will have to pass through the absorber, then reflect off the reflector, and finally pass through the absorber again before it re-enters the living space. This would be a very small amount indeed.
Which shielding materials do you recommend?
You can cover over your shielding materials with almost any decorative medium that you like. The shielding should be protected from abrasion, excessive flexing, and moisture… and it should be grounded.
|Which meter do you recommend?|
We recommend the
High Frequency Meter
Magnetic fields are common in automobiles. Even cars with gasoline engines can have high levels, depending on the wiring configurations and the locations of the tires and other moving engine parts relative to the passengers. Electric or hybrid vehicles can have very high levels due to the high current demand and re-charging mechanisms. Every vehicle will have multiple sources of a magnetic field, some of which may be in areas that are difficult to access for shielding. With persistence, a satisfactory reduction of field levels is usually achievable. But don’t expect the levels to drop to zero.
Begin by diagnosing the fields in your vehicle. Use a 3-axis gaussmeter with a range of at least 200 mG, and a flat frequency response.
- – A 3-axis meter “looks” in all directions simultaneously, so you won’t risk missing important data because you were holding the meter at the wrong angle.
- – If the range of the meter is too small (10 mG for example), you may only see “over range” on the meter everywhere. This will not help you determine the “hot spots” and therefore the location of the offending sources of the field.
- – If you use a meter that is frequency weighted (instead of flat frequency response), you will get artificially high readings due to the mixture of frequencies present, which can be very misleading.
The Trifield TF2 is a good choice for this work.
Select a location away from powerlines and other sources of background magnetic fields. Notice the background level with the car not running. You will subtract this number from all further meter readings. Park the car, but leave the engine running. Slowly move the gaussmeter in the passenger areas. Check all areas that will be occupied by passenger bodies, including the seat, head, and floor areas. If you have an electric or hybrid vehicle, you should have an assistant drive the vehicle while you take meter readings. Check during the various modes of power: electric only, gas only, accelerating, cruising, braking, etc. Identify areas that have high levels (above 3mG).
Next, for each “hot spot”, sweep around that immediate area looking for the source of the high field. Naturally, the true source may be hidden under the floor, behind a panel, or on the other side of the firewall. But identify the accessible area closest to the source. This will be the surface with the highest readings. Remember to check under the dash as well!
Starting with the area with the highest field, place the meter in a location that you can find again after shielding is installed. You may need to measure its position relative to landmarks in the car, such as bolts, wires, etc. It is important that the meter position be repeated in exactly the same position (before and after shielding), as changing the meter position will change the readings.
Now lay a piece of shielding in the area of the hot spot. Magnetic Shielding Foil was used in this example. Giron is also a good choice. (Caution! The edges are sharp!) Use the largest piece of shielding that will fit. You can always trim edges or corners to work around odd shapes. If your largest piece of shielding is not wide enough, you can place pieces next to each other, with 1-2 inches of overlap where they meet.
Later, you will lock these pieces in position and cover them with protective carpeting. It is imperative that they do not come loose and create a driving hazard!
Complicated shapes and multiple barriers in a vehicle may not permit the placement of shielding in all locations that need it. You have to accept some level of compromise because of these limitations.
Now, place the meter back in the same position and take a reading. The level should be lower. Sweep around the shielded area to identify the remaining “hot spots”. You may need to add more shielding to the edge of the shield. Or try another layer of shielding. Or you may need to shield an area opposite the shield (In this example, we shielded the driver’s foot area, and needed to add shielding to the underside of the dash.)
Keep adding shielding until either you are satisfied with the results, or you find that adding more shielding does not yield any further decrease in readings.
Refine the shapes of the shielding pieces by trimming and bending. You can number them with a marker or tape to help you remember where they go. Take up carpeting if possible and lay the shielding in its final position. Fasten it securely. Use screws, pop rivets, tape, glue or any other mechanism you can think of to keep the shielding material in place. In this case, we were able to achieve an 84% reduction (1.47-0.25 / 7.61-0.25 = 16% field remaining).Tape any seams with sturdy, water-resistant tape. You can also roll tape over sharp edges to keep the carpet and passengers safe.
Please the carpeting back over the shielded area (or add new carpeting as needed).
At this point, that area is done. You can move on to the next worst area and repeat the process.
- 1- Make written notes as you go. Trust me, after a few meter readings, you won’t remember what the second reading was, or the exact position of the meter
- 2- Use caution when handling the shielding. It has sharp edges!
- 3- Use tin snips to cut the shielding material
- 4- Tape cut edges with a sturdy and waterproof tape to protect people and prevent corrosion to the shield
- 5- Lock the shielding material in place so it cannot become a hazard to people and pets, nor create a driving hazard. One option is to cover floor shielding with custom-fitted floor mats
Surface resistivity is measured in Ohms per square (Ohm/square). Ohms are units of resistance, but what about the square?
Engineers know that you can measure surface resistivity from one point on the surface to another using an ordinary ohm-meter. Then the units would be Ohms per distance between points or Ohm/m. But this method yields very inconsistent results, especially with surfaces that are not perfectly homogeneous.
More consistent results are obtained by measuring the surface resistivity between two bars. For simplicity, two parallel bars of equal length are placed exactly 1 length apart on the surface to be measured. They form two opposite sides of a square. It doesn’t matter how long the bars are since longer bars will be placed proportionally further apart. The resistance measured between the two bars in Ohms is the resistivity of the surface in Ohms per square!
First, let’s understand that the magnetic fields from a single conductor wire emanate from that wire in a pattern that could be described as concentric cylinders. The image at the right represents a cross-section view of a current-carrying wire. Notice the concentric circles of magnetic field lines around the wire. Notice also, that the magnetic field lines are more concentrated near the wire, and less concentrated as the distance to the wire increases.
Now, understanding that magnetic shielding “works” because it is a better “conductor” of magnetic field lines than air or just about any other material, let’s see what happens with 2 different shield designs. First, let’s make a shielding cylinder around the wire. In the cross-section image at the right, we see that the magnetic field lines that would have occurred at the radius of the shield will exist INSIDE the shield. However, magnetic field lines at all other radii will not be affected. Net effect: no shielding.
But what happens if we use a flat shield? As you can see from the image below, the magnetic field lines which intersect the flat shield will be compressed into the shield, leaving the less magnetic field on either side of the flat shield.
But also, note the following:
- There is an area near the shield which enjoys LOWER field strength
- The areas near the edge of the shield show HIGHER field strength
- The magnetic fields of large radius are unaffected
- The wider the shield, the larger the shielded area, both in width and depth
If the edges of the shield are bent slightly TOWARDS the source, the high field area at the edge of the shield will move further away from the “shielded area”.
In conclusion, for net current, flat (or nearly flat) shielding is more effective for fields from wiring in the area adjacent to the shield. The wider the shield, the larger the shielded area. Contact us if you have specific questions about your shield design.
For situations where you have balanced current (that is equal current in the hot and neutral wires), a cylindrical shield can be effective. Take a look at this 13 minute video from Michael Neuert which demonstrates this phenomenon:
The sad short answer is: there is no such thing as a safe distance.
Here are the reasons:
- The magnetic field from a powerline decreases with distance, for sure. But the magnetic field from a powerline varies from moment to moment depending on how much current is flowing in the wire at the time. It will be higher during peak electricity usage times. So the only way to know how strong the field is at a given distance, AT ANY PARTICULAR MOMENT, is to measure it with a gaussmeter. We always recommend taking multiple measurements at various times during the day.
- There could easily be additional sources in the field. They might come from underground wires, ground-mounted transformers, or even common sources within the home. They will add to the strength of the field emitted by the powerlines. Either field alone could be within tolerable limits, but could possibly exceed tolerable limits when combined.
- The safety or danger of a magnetic field from a powerline depends on more than just the strength of the field. Some research has shown that harmonics (higher frequency fields), radio-frequency signals in the line, and power spikes may have more to do with health effects than just the normal 60 Hz magnetic field.
- The time of day that you are exposed to may be very important. Some research shows that exposure during sleep may be more harmful than exposure during waking hours as it affects the melatonin balance which is a hormone that, among other things, fights cancer cells.
- Whether you are located upwind or downwind of the powerline may also be important. Recent research has shown that the corona field around high tension lines can ionize the air around the lines. This ionized air has been thought to attract and concentrate radioactive particles and automotive pollutants that can be harmful.
- There are probably other factors that determine how much EMF your body can tolerate, such as genetic predisposition, how much exposure you receive at work or school, your age, your exposure to harmful chemicals (pesticides, preservatives, etc.) which may be activated by the EMF, your overall health, and so on.
- Most important of all, scientists simply do not yet know how much exposure is safe or harmful.
While there are official standards for exposure to electric and magnetic fields, they are based on the amount of field needed to cause immediate harm. There is plenty of evidence to show that biological effects occur at levels well below the standard limits. In the end, we are each left to decide how much exposure we are willing to accept. One rule of thumb that is used by some experts is that you should limit your exposure to 60 Hz magnetic fields which are in excess of 2.5 mG. There is not a lot of scientific evidence to support this recommendation, but it is based on the Swedish recommendation for exposure to ELF fields from computer monitors.
You should get a gaussmeter and make some measurements. At least find out if the fields from the powerline exceed the 2.5 mG guideline.
In general, there are 5 ways to reduce your exposure to magnetic fields:
- Reduce power to the source (if there is no current, there will be no field)
- Apply shielding to the source
- Apply shielding to yourself
- Increase the distance between yourself and the source
- Cancel the incoming field with an equal and opposite field
When it comes to powerlines, the options are limited as you do not have control over the powerlines themselves. The first step should always be to record readings of the magnetic field strength over a period of a few days using a reliable AC Gaussmeter to find out if you truly have a problem. Remember that the field will vary according to how much current (not the voltage) is being carried by the powerline. Also, remember that the only relevant readings are those taken where people actually spend time. High readings up close to the powerline are meaningless if the field inside your house is low.
Armed with this documentation, your next step should be to contact the utility company that owns the powerlines. Explain your concern and ask for their help in reducing your exposure. If the utility company wants to, they can do several things to lower your exposure:
- Relocate the lines (further from your home or even underground)
- Reconfigure the lines to achieve better field cancellation between lines
- Re-route the power to another line so that less current flows through the line near your home.
Should you fail to get assistance from the power company (likely), you may be tempted to consider shielding. Naturally, the most effective shielding approach would be to shield the wires. Unfortunately, this is also impossible as the power company would never permit it. Shielding your home is possible, but not very practical. To achieve a reasonable degree of shielding, you would have to create a metal vault around your house, using thick metal plates with no windows. It would also be very expensive. Placing magnetic shielding material around your body is possible, but again not very practical.
Moving your house further back from the powerlines may be an option, but certainly not a very easy one. Make sure you carefully survey every proposed location for your house to make sure the fields are actually sufficiently lower at the new location that you are considering. Selling your home and moving to another location also comes under this heading. Make sure to use your gaussmeter to survey all homes you are considering, to avoid jumping from the frying pan into the fire.
Our experience in measuring monitors of all kinds is that one cannot make generalizations about which type or which brand has higher or lower emissions.
A few years ago, we took our meters to a large electronics store to try to settle this question. We measured dozens of different types of TVs and monitors, including CRT, LCD, and plasma. Some were high, some were low. Some were high on E but not M, some were high on M but not E. Size had no correlation either. We found one unit which was the lowest on both. It was a Motorola product. The display model had a black bezel (plastic frame), but we wanted the gray one so we took a boxed unit OF THE SAME MODEL, but with a gray bezel. When we got it back to the office, we set it up and tested it again. It was worse than the worst unit in the store!!
Furthermore, a few months later, we went back and found that almost all the units available were different models.
From this, we have learned:
1- this month’s recommendation will be obsolete in a very short time, as new models appear in the stores very regularly
2- the best advice we can offer is to take your meters to the store and select the best FLOOR MODEL. Then expose yourself to that unit for a short while to determine if YOU have any symptoms of it. Take THAT FLOOR MODEL UNIT home if it passes both of these tests.
Compared to magnetic field shielding, shielding a home from cell tower radiation is reasonably straightforward. In theory, you want to create a continuous, highly conductive enclosure around the home. Any areas that are not conductive, even cracks under a door, will allow radiation to leak in. Perfect total shielding requires a perfect total enclosure. However, in a home environment, total radiation elimination may not be required. For example, perhaps a 90% reduction is adequate.
There are several materials you can use to create the conductive enclosure, depending on your needs and your budget. Some materials are more appropriate for walls and ceilings, while others are better for windows. The higher the conductivity of the material, the better the shielding it will provide. Keep in mind additional factors such as durability, corrosion resistance, toxicity, ease of installation, appearance, and size.
For doors, walls, floors, and ceilings, CuPro-Cote® or Y-shield conductive paints offer very good shielding and are very convenient. Apply like ordinary paint on interior surfaces. You can paint over the conductive paint with standard latex paint to achieve the desired color and to protect the conductive surface.
You can also cover the walls with a conductive fabric such as Pure Copper Polyester Taffeta or ArgenMesh. Apply the fabric as you would wallpaper, remembering to overlap slightly at the seams to avoid leakage. You can cover over the fabric with a standard wallpaper, paneling, or drywall.
Cover windows with a conductive plastic film such as RadioClear or ScotchTint and/or shielded drapes (or drape linings) with conductive fabric such as High-Performance Silver Mesh.
Remember to treat openings such as switch plates, outlet covers, dryer vents, etc. But because shielding materials are conductive, be very careful to avoid allowing them to come into contact with electric wires to avoid a shock hazard. Also, remember to provide proper grounding to each component that is not in contact with the others.
There is only one important 1 key to successful RF shielding: control leakage.
Remember that the attenuation spec for a shielding material is how much radiation penetrates through the shield. Let’s look at an analogy:
In many ways, RF behaves much like visible light, and RF shielding materials behave much like two-sided mirrors. An image that you are outdoors on a sunny day. You set a large mirror on a stand above your head. The attenuation specification for the mirror is very high, perhaps 120 dB or more, so basically no light comes through the mirror. If leakage was not an issue, you would be in total darkness. We all know this is not the case. Leakage from the sides easily illuminates the shaded area. Granted, the amount of illumination is less than standing in full sunlight, but the attenuation is nowhere near 120 dB. Maybe more like 20 dB. Furthermore, using a shield with even better attenuation will not yield any more benefits.
Now imagine you are in a small room with only one window. Bright sunlight comes in the window and illuminates the room. When you place your mirror shield over the window, you get a dramatic attenuation of the light. But the extent to which leakage of light occurs around the perimeter determines how far from total darkness you will achieve in the room. We have all experienced this when trying to draw a curtain over a bedroom window. You must control the leakage to get it really dark. There is nothing wrong with the shield, light is leaking around the shield.
Because RF shields are reflective on both sides, radiation that does leak in will be reflected by the inner surface of the shield, effectively amplifying the amount of radiation in the room. Even the tiniest leakage at a seam can reduce attenuation by many dB. The obvious solution is to pay serious attention to leakage points. A great how-to book is available which describes materials and methods for controlling leakage in detail.
There are several ways to interpret this question.
First, let’s look at it from the perspective of the cellphone owner:
For the cellphone to work, it must radiate. The microwave radiation emitted by the phone must reach the cell tower. Furthermore, the emissions from the tower must reach the phone. The trick is to allow this communication to take place, but minimize the amount of radiation that is “wasted” by being absorbed by the user’s body. There are several ways to accomplish this.
Increase the distance between the phone and the body. By increasing the distance, the intensity of the radiation is decreased… just like the flame from a candle is hotter close up to the flame and cooler as distance increases. Using a built-in speakerphone is one way to accomplish this. Using a hands-free headset is another. Of course, if you hold the phone in your hand, or in a pocket or purse near your body, you have not reduced your exposure, only transferred it from your head to another part. Naturally, the further the phone is from the body, the less radiation is absorbed by the body. Use an extension cord on the headset if you can, and put the phone down.
Place a shield between the phone and your body. There are several styles of cellphone shields that block the emitted radiation on one side of the phone. Naturally, you will want that shield on the side of the phone that is between the phone and your body. You can use the shield style that goes right onto the phone, or you can line a pocket or purse with a shielding fabric. The shield should be at least as big as the phone since the entire phone radiates… not just the antenna.
Notice that these techniques reduce the user’s exposure. Because the room is still filled with the microwaves emitted by the phone, exposure is not eliminated, and of course, there is no benefit to others in the room.
Now, what’s so hard about blocking a cell phone signal completely?
Let’s say you don’t own a cellphone and want to shield your house completely from external signals. Or maybe you have a secure area (such as a hospital, data center, prison, or movie theater) and you want to prevent incoming or outgoing calls. There are many shielding materials you can put on walls and windows. But there is a big problem: cellphones can operate very nicely with only a very small fraction (less than 1 millionth) of a normal signal.
1- Therefore your shielding materials must provide very high attenuation levels. Typically, 100 dB or more shielding materials are required. Think about this way analogy: when you put sunglasses on the amount of light entering your eyes might be reduced by 90%, but you can still easily see where you are going. To block your vision completely, you would need a much higher level of reduction.
2- You must control leakage points VERY carefully. Gaps under doors, joints between shield sections, and even pinholes from sewing shielding material can permit these high-frequency signals to penetrate. You need to create a “complete” enclosure. Any part that is not shielded is a leakage point.
A small pouch is not that difficult to make with the proper material. Shielding a whole house, or even a whole room is a more difficult challenge… if you want to completely kill the signal.
Conventional speakers incorporate both a permanent magnet and an AC magnetic field to produce sound. The field from the permanent magnet is present whether the speaker is active or not. The AC magnetic field is only present when the speaker is activated and varies in frequency and strength with the pitch and volume of the sound produced. The magnetic field from the two sources can deflect the electron beam in a cathode ray tube monitor (TV) causing distortion of the image, sometimes called jitter (and possible damage to the equipment).
You will have to use magnetic shielding alloys to shield these magnetic fields and you have a choice of several methods. Keep in mind that with magnetic fields, you can either shield the source of the offending field or shield the thing(s) that you wish to protect.
Note: Unlike the bucking magnet method, these shielding methods do not alter the sound quality of the speaker.
1] Method for maximum aesthetics
To achieve maximum aesthetics you will need to be able to open the speaker cabinet and get access to the back of each speaker. There, you will find a donut-shaped magnet, proportional in size to the size of the speaker, over which you will place a cup-shaped shield.
Because you will be placing the shielding material in close proximity to this strong magnetic field, you will have to take saturation into account. This means using at least 2 layers of shielding.
For the layers closest to the magnet, choose a high saturation material such as MagnetShield. This material has the ability to “absorb” the initial blast of the field without saturating and becoming useless, but it will only give a limited attenuation. It is very low cost, so 2 or 3 layers are practical.
The outermost layer should be a high permeability material such as Joint-Shield. This outer layer will “absorb” much of the field which has evaded the first layer and yield a very high degree of attenuation. Note that attenuation will be the greatest close to the speaker magnet, where the field is strongest (most interfering) anyway.
MagnetShield and Joint-Shield are both offered in a convenient 4-inch wide strip. The material is thick enough to provide good shielding, but still can be cut with scissors and shaped by hand. For especially strong magnets, you may need more than one layer of each material.
Here is how you do it:
Wrap the MagnetShield around the speaker magnet (notice that it is attracted to the magnet) in a cylinder shape. Cut it so that you have about 1″ of overlap at the seam. Use duct tape to tape the seam securely. Cut the material which extends backward at several locations so you can bend these “tabs” inward to form the “bottom of the cup” shape. Leave this layer in place.
Joint-Shield is provided with a peel-and-stick adhesive on one side. Before removing the adhesive backing, cut and shape the material just like the first layer, but on top of the first layer. Remove the adhesive backing and press the second layer onto the first layer. You are done!
Just be careful not to disturb or allow the shield to touch the electrical contacts on the speaker.
2] The Quick and Easy Way (and Maximum Field Reduction!)
If you need maximum field reduction, cannot open the speaker cabinet, or simply want to take the easy route, you can simply place a flat magnetic shielding alloy between the speaker and the TV.
The magnetic fields at the side of the speaker magnet have different characteristics compared to those at the back of the magnet, and different shielding materials are required. Take this into account when considering where your speakers will be positioned relative to the TV.
Shielding the side of the speaker:
Most times you can get away with one or two layers of Magnetic Shielding Foil. On each speaker, place the foil flat against the side of the speaker cabinet which faces the TV, or place it against the side of the TV. A good, inexpensive way to check for shield performance and the best position for the shield is to use a Pocket Magnetometer. You can get additional attenuation by using multiple layers of foil, especially if you use a spacer (such as cardboard) in between the layers. This may offer some aesthetic challenges, but you don’t need much technical expertise.
Shielding the back of the speaker:
A high saturation material of significant dimensions such as 36″x15″ MagnetShield Plate is required here. If your speaker cabinets are small, you can cut the 36″x15″ sheet in half to get two 18″x15″ pieces. Note: There will be a position somewhere between the back of the speaker magnet and the front of the TV which will yield “near perfect” shielding. Move either towards the speaker or towards the TV from this point and you will lose shielding effectiveness. Therefore be sure to check the position with a Pocket Magnetometer or digital DC Gaussmeter. Naturally, some situations may require shielding of both the back and the sides of the speaker cabinet.
3] The Third Alternative
You can always place the entire TV or monitor inside a shielded enclosure. This will protect the monitor from external fields produced by the speakers and any other sources.
3] The Fourth Alternative
Place a pre-fab Speaker Magnet Shield on the back of the speaker if the speaker magnet is less than 3.125 inches in diameter.
The most direct way to reduce your exposure to a laptop is to increase your distance from the device. Use a wired remote keyboard and mouse (not the wireless type!!) and place the laptop as far away as you can while still being able to view the screen. You can increase the text size on the screen if needed.
Laptops usually produce three types of electromagnetic fields: Radiofrequency (wifi), AC electric fields, and AC magnetic fields. You can either shield the laptop (source) or shield yourself.
To shield the electric fields and wifi from the laptop screen, use a Computer Monitor Shield to cover the screen. Be sure to connect the ground cord. Covering the keyboard area of the laptop with a shielding fabric such as High-Performance Silver Mesh will reduce electric fields from these areas while still allowing you to see the keyboard.
To shield the magnetic fields, you have two choices: HARApad under the laptop, or for more complete shielding use the WrapTop® on the keyboard part of the laptop.
A SafeGuard Apron worn on the body will help block the electric fields. Shielded Gloves can be used to protect the hands.
In the strictest sense, magnetic shielding is not truly shielding at all. Unlike the way a lead shield stops X-rays, magnetic shielding materials create an area of lower magnetic field in their vicinity by attracting the magnetic field lines to themselves. The physical property which allows them to do this is called “permeability“.
Unlike X-rays, sound, light, or bullets, magnetic field lines must travel from the North pole of the source and return to the South pole. Under usual circumstances, they will travel through the air, which by definition has a permeability of “1”. But if a material with a higher permeability is nearby, the magnetic field lines, efficient creatures that they are, will travel the path of least resistance (through the higher permeability material), leaving the less magnetic field in the surrounding air.
Air ……….. 1
Copper …… 1
Aluminum … 1
Tin …………. 1
Lead ………. 1
Nickel ……………… 100
Commercial Iron … 200
Stainless Steel ……. 200
MagnetShield …….. 4000
* such as Magnetic Shielding Foil, Mag-Stop Plates, and Joint-Shield
Now it is easier to see why a magnetic shield in the shape of an enclosure (sphere, box, tube, etc.) offers much better shielding than a flat shape or partial enclosure. A source within the shield will produce field lines which will travel through the air immediately surrounding the North pole until they reach the shield. Then traveling through the shield, they will emerge into the air surrounding the South pole and back to the source. Traveling through the low permeability air outside the shield does not offer any efficiency advantage! (Notice that the diagram to the right is a cut-away view of a tube-shaped shield.)
Similarly, if the source of the field is outside of the enclosure, the magnetic field lines will travel through the material of the enclosure on their way back to the source, never finding it more efficient to permeate the air space inside the enclosure. For these reasons, enclosing either the source of the field, or the thing(s) that you wish to protect from the field, offers the most effective use of the shielding material, and is usually the most cost-efficient as well!
An important consideration when shielding magnets is that the magnets will be attracted to the shielding material. There are no magnetic shielding materials that will not be attracted to a magnet.
Shielding repulsion between 2 magnets is easy:
Use a high saturation alloy like Giron or MagnetShield. Simply stack enough layers between the 2 magnets until the attraction to the shield balances the repulsion between the magnets. The proper number of layers will depend on the strength of the magnets, the distance between them, and the size and shape of the shield. A little experimentation quickly gets the correct result.
Shielding attraction between 2 magnets requires that each magnet have its own shield. The shield does not need to be in contact with its respective magnet, but it must be held fixed in position relative to its magnet. Again, the proper number of layers will depend on the strength of the magnets, the distance between them, and the size and shape of the shield. Simply add one layer at a time until the two magnets drop away from each other.
Finally, a word about shielding just one pole of a magnet:
While this is not technically possible, it is possible to distort the magnetic field lines around one pole of a magnet. Remember to think about the magnetic field lines as traveling through the shield more easily than through air. Therefore, the shield acts as a “conduit” for some of the magnetic field lines. They still must travel from the magnet’s N pole to its S pole… but the path they take is what can be manipulated. This means that if you “shield” one pole of a magnet, you are basically relocating the place where those magnetic field lines emerge into the air. The effect is the same as if you bend the magnet itself into a different shape.
Radiofrequency radiation (what we might also call radiowaves, microwaves, or wireless radiation) is a common part of modern life. Sources both inside and outside our homes (such as cell phones, wifi, microwave ovens and cell towers) bathe our environments in radiofrequency radiation.
In many ways, radiofrequency radiation behaves like light. It travels in straight lines, it can be blocked by some materials, and it can reflect off of surfaces. Because we cannot see it directly, its behavior can be puzzling to the person casually using an RF meter.
The animation shows the principle:
- First the ball is illuminated by a single source.
- When we shield this single source, the shielding is effective and casts a shadow on the ball.
- Now, we see multiple sources and reflections hitting the ball.
- Shielding just the primary source has a small effect on how much radiation hits the ball… the same shield appears as if it is not effective!