The environment of an electron microscopy lab does not directly impact the electron microscope itself but rather affects the imaging quality and overall performance of the microscope. During the operation of an electron microscope, the fine electron beam needs to travel in a high vacuum environment, covering a distance of 0.7 meters (for Scanning Electron Microscope) to over 2 meters (for Transmission Electron Microscope). Along the path, external factors such as magnetic fields, ground vibrations, noise in the air, and airflows can cause the electron beam to deviate from its intended path, leading to a degradation in imaging quality. Therefore, specific requirements need to be met for the surrounding environment.

Passive low-frequency electromagnetic shielding primarily involves two methods, which differ in the shielding material used: one method uses high-permeability materials (such as steel, silicon steel, and mu-metal alloys), and the other method uses high-conductivity materials (such as copper and aluminum). Although the working principles of these two methods are different, they both achieve effective reduction of environmental magnetic fields.

A. The high-permeability material method, also known as the magnetic circuit diversion method, works by enclosing a finite space (Region A) with high-permeability materials. When the environmental magnetic field strength is Ho, the magnetic reluctance of the high-permeability material is much smaller than that of air (common Q195 steel has a permeability of 4000, silicon steel ranges from 8000 to 12000, mu-metal alloys have a permeability of 24000, while air has an approximate value of 1). Applying Ohm's law, when Rs is much smaller than Ro, the magnetic field strength within the enclosed space (Region A) decreases to Hi, achieving demagnetization (see Figure 1 and Figure 2, where Ri represents the air reluctance within space A, and Rs represents the shielding material reluctance). Inside the shielding material, the magnetic domains undergo vibration and dissipate magnetic energy as heat under the action of the magnetic field.

Since silicon steel and mu-metal alloys exhibit anisotropy in permeability and cannot be hammered, bent, or welded during construction (although theoretically, heat treatment can improve these properties, it is impractical for large fixed products), their effective performance is significantly reduced. However, they can still be used for supplementary or reinforcement purposes in certain special areas without hammering, bending, or welding.

High-permeability materials are expensive, so they are generally not extensively used in electron microscope shielding and are only seen in a few specific areas (such as door gaps, waveguide openings, etc.).

The effectiveness of the magnetic circuit diversion method is roughly linearly related to the thickness of the shielding material, which can theoretically be infinitely thin.

B. The high-conductivity material method, also known as the induced magnetic field method, works by enclosing a finite space with high-conductivity materials. The environmental magnetic field acts on the shielding material through its electric field component, inducing an electromotive force, which in turn generates an induced current and an induced magnetic field. Based on the fundamental principles of electromagnetics, this induced magnetic field is equal in magnitude (slightly smaller due to resistance) and opposite in direction to the original magnetic field (with a slight phase lag). Thus, the magnetic field within the finite space is counteracted and weakened, achieving demagnetization.

Further understanding of the induced magnetic field method can be gained by considering the operation of a three-phase induction motor, which provides insights into the working principles of induced magnetic fields. It is important to note that an asynchronous squirrel cage motor cannot achieve the rotating magnetic field (50Hz × 60s = 3000 RPM) because the squirrel cage bars cannot cut magnetic lines, thus preventing the generation of induced currents, induced magnetic fields, and driving force.

The effectiveness of the induced magnetic field method is independent of the thickness of the shielding material within a certain range.

C. Common characteristics of both methods: Full penetration welding is required, and the height of the weld seam should not be less than the thickness of the shielding material. Attention must be paid to the design of openings at various scales and waveguide ports. Whether the design/production is successful will greatly affect the shielding effectiveness (applying the "Weakest Link" theory to shielding). It is also important to note that the vibration of the electron microscope in the shielding room should not exceed that of the surrounding environment (there have been cases where the magnetic field passed the inspection but the vibration increased compared to the original, causing non-compliance).

From their basic working principles, it is evident that both the magnetic circuit diversion method and the induced magnetic field method are ineffective for DC fields. They are also generally ineffective for near-DC fields (in such cases, an active demagnetizer is necessary to improve near-DC electromagnetic interference).

A．Compare the two methods in a table:

Upon careful analysis, the magnetic circuit diversion method is more advantageous. The passive low-frequency demagnetizer has advantages such as small size, lightweight, low cost, no impact on the environment, and the possibility of post-purchase installation.

However, one important point to note is that magnetic shielding is often an "entrusted" project, meaning that it often includes electrical, water, air conditioning, lighting, and network systems, as well as monitoring, during the construction process. Therefore, if there is a need for remodeling, it offers a higher cost-performance ratio.

Overall, passive magnetic shielding has better effectiveness than demagnetizers, but due to the aforementioned reasons, demagnetizers may still be the only option in some environments.

For Scanning Electron Microscope, the difference between these methods is not significant. However, for Transmission Electron Microscope, it is recommended to use magnetic shielding as much as possible, as the requirements for magnetic fields are generally higher compared to Scanning Electron Microscope.

Capacitive and resistive touchscreens are two common technologies used in touchscreen devices, each with its own principles of operation:

Capacitive Touchscreen:

Capacitive touchscreens work based on the electrical properties of the human body. They are made of layers of glass coated with a conductive material like indium tin oxide (ITO).

When you touch a capacitive touchscreen with your finger (which is conductive), it disrupts the screen's electrostatic field, causing a change in capacitance at the point of contact.

The device detects this change in capacitance and calculates the touch point. This technology allows for multi-touch gestures (e.g., pinch-to-zoom) because it can detect multiple points of contact simultaneously.

Capacitive touchscreens are generally more responsive and durable than resistive touchscreens. They are commonly used in smartphones, tablets, and other modern touchscreen devices.

Resistive Touchscreen:

Resistive touchscreens consist of several layers, typically two flexible sheets separated by a small gap. The inner surface of each layer is coated with a resistive material, and the outer layers are conductive.

When you press on a resistive touchscreen, the two layers come into contact at the point of touch, creating a circuit. This changes the electrical current running through the screen.

The device detects this change in electrical current and calculates the touch point. Resistive touchscreens typically only support single-touch input.

Resistive touchscreens are less expensive to produce compared to capacitive touchscreens, but they are generally less responsive and have poorer visibility because of the additional layers.

They are commonly found in older devices such as some GPS units, industrial control panels, and certain types of kiosks.

In summary, capacitive touchscreens rely on changes in capacitance to detect touch, while resistive touchscreens rely on changes in electrical resistance. Each technology has its own advantages and is suitable for different types of applications.

As technology evolves, Thin Film Transistor Liquid Crystal Display (TFT LCD) modules are becoming the backbone of digital displays, valued for their sharp resolution, fast response times, and vivid color accuracy. TFT LCDs are widely used across industries, including consumer electronics, automotive interfaces, industrial equipment, and medical devices, making them a versatile solution in today’s digital world.

Understanding TFT LCD Technology

A TFT LCD display is a type of LCD that uses thin-film transistor technology to enhance image quality. This technology arranges pixels in a matrix, where each pixel is individually controlled, allowing for higher contrast ratios and better color depth. Unlike traditional LCD displays, TFT technology significantly reduces “ghosting” effects, making it ideal for applications requiring smooth, high-speed graphics.

Key Components of TFT LCD Modules

TFT LCD modules are crafted with multiple layers. These generally include the TFT glass panel, the backlight unit (BLU), and control circuitry. The TFT layer governs each pixel’s behavior, allowing for fine-tuned brightness and color management, while the backlight provides consistent illumination across the display. This layering creates a vibrant visual experience with precise control over color and brightness, making TFT LCDs a top choice for applications demanding clarity and responsiveness.

Advantages of TFT LCD Displays

Enhanced Image Quality: TFT technology allows for high-resolution displays with vibrant colors and deep contrast, ensuring sharp visuals.

Fast Refresh Rates: Ideal for moving images, TFT modules minimize lag, providing a seamless experience for video playback and graphic applications.

Wide Application Range: From mobile devices and cameras to industrial machinery, TFT LCDs adapt well to diverse environments and uses.

Golden Vision Optoelectronic: Leading TFT LCD Manufacturer

As a one-stop LCD and LCM provider, Golden Vision Optoelectronic Co., Ltd is dedicated to developing and manufacturing advanced TFT LCD modules. Our modules meet international standards and are certified for quality (ISO9001, IATF16949) and environmental compliance (ISO14001, RoHS). With a robust infrastructure and a commitment to innovation, we aim to deliver TFT solutions that cater to both emerging and established market needs.

Choosing the Right TFT LCD Module

When selecting a TFT LCD, consider factors like resolution, viewing angle, and environment. Golden Vision Optoelectronic offers a wide variety of TFT LCD options, customizable to your application’s needs, ensuring both functionality and reliability in any setting.

The environment of an electron microscopy lab does not directly impact the electron microscope itself but rather affects the imaging quality and overall performance. During the operation of an electron microscope, the fine electron beam needs to travel in a high vacuum environment, covering a distance of 0.7 meters (for Scanning Electron Microscope) to over 2 meters (for Transmission Electron Microscope). Along the path, external factors such as magnetic fields, ground vibrations, noise in the air, and airflows can cause the electron beam to deviate from its intended path, leading to a degradation in imaging quality. Therefore, specific requirements need to be met for the surrounding environment.

The Active Low-frequency Demagnetization System, mainly composed of a detector, controller, and demagnetization coil, is a specialized device used to mitigate low-frequency electromagnetic fields from 0.001Hz to 300Hz, referred to as a Demagnetizer.

Demagnetizers can be categorized into AC and DC types based on their working ranges, and some models combine both types to meet different working environments. The advantages of low-frequency demagnetizers include their small size, lightweight, space-saving design, and the ability to be installed post-construction. They are particularly suitable for environments where it is difficult to construct magnetic shielding, such as cleanrooms.

Regardless of the brand, the basic working principles of demagnetizers are the same. They use a three-axis detector to detect electromagnetic interference signals, dynamically control and output anti-phase currents through a PID controller, and generate anti-phase magnetic fields with three-dimensional demagnetization coils (typically three sets of six quasi-Helmholtz rectangular coils), effectively neutralizing and canceling the magnetic field in a specific area, reducing it to a lower intensity level.

The theoretical demagnetization accuracy of demagnetizers can reach 0.1m Gauss p-p, or 10 nT, and some models claim even better accuracy, but this is only achievable at the center of the detector and cannot be directly measured by other instruments due to mutual interference at close distances or the "Equipotential Surface" phenomenon at greater distances.

Demagnetizers automatically adjust the demagnetization current based on changes in the environment. At times, the current can be significant. It is important to pay attention to the wiring layout when other sensitive instruments are in close proximity to avoid interference with their normal operation. For example, electron beam exposure devices have been affected by nearby operating magnetic field detectors.

The power consumption of the demagnetizer controller is generally around 250W to 300W.

The detector of the demagnetizer can be a combination type or an AC/DC separate type, and there is no significant difference in performance. It is generally fixed in the middle-upper part of the column or near the electron gun (as the electron beam emitted from the electron gun may have a slow speed, making it more prone to magnetic field interference). During the initial installation, the detector can be tested at multiple positions to determine the most effective location for fixation.

The demagnetization coils usually adopt a "large coil" design, where six coils are fixed on various walls, ceilings, and floors of the room as far apart as possible. Alternatively, rectangular frames with embedded coils can be customized. However, the "frame" design is less common except for cleanrooms or large rooms. This is because the demagnetization effect is slightly inferior, and it can interfere with the operation and usage of Electron Microscopes.

From the basic working principle of the demagnetizer, the following conclusions can be drawn:

1) Due to the inherent hysteresis that is difficult to eliminate, there will always be a phase difference between the anti-phase magnetic field and the ambient interference magnetic field, limiting the demagnetization effectiveness.

2) In the three-dimensional space enclosed by the demagnetization coils, the demagnetized magnetic field is not uniform. It gradually deteriorates from the center of the detector towards the outer surface, as the magnetic field intensity is inversely proportional to the square of the distance from the signal source (i.e., the demagnetization coils). Moreover, the uniformity of the ambient magnetic field is generally superior to that generated by the demagnetizer, resulting in a reduced demagnetization effect as the distance from the center of the detector increases.

3) This phenomenon particularly affects the use of demagnetizers in Scanning Electron Microscope rather than Transmission Electron Microscope.

Three Major Advances in Micro LED Display Technology in 2018

2018 is going to end, the development of Micro LED technology is undoubtedly the most eye-catching block of the LED Display Industry in 2018. Before we meet 2019, let us review the important moments of several Micro LEDs.

01/ KAIST Develops Vertical Flexible Micro LED to Promote Hair Growth

Recently, the Korea Institute of Science and Technology (KAIST) has developed a Micro LED wearable device that uses vertical Micro LEDs to successfully help mice re-grow their hair.

The device was tested on a back of a mouse that shaved hair using a flexible array of 900 vertical Micro LEDs. After 20 consecutive days of treatment, the hair growth of the mice was significantly faster than that of the untreated mice. Moreover, after treatment, the newly grown hair of the mouse is longer and the hair area is wider.

KAIST point out that, Micro LEDs do not heat up to the detriment of the human body and consume only one-thousandth of the energy per unit area compared to conventional phototherapy lasers. The research results can provide a new method for treating human hair loss.

02/ New Substrate Materials for Strengthening Micro LEDs Come Out

France's Soitec has invented a new substrate, InGaNOX, in the production of indium gallium nitride high-brightness blue LEDs, which can crystallize simultaneously on the substrate. Under the same substrate material, the three primary color Micro LEDs can be driven and controlled with the same voltage.

03/ New Innovation and Research Centers are also Bringing out Innovative Micro LED Solutions

The British company Optovate was founded in 2008 and has a long history of developing Micro/Mini LED technology. In March of this year, the company announced that it had made two breakthroughs in Micro LED. First, Optovate developed a esdled Micro LED Display stripping transfer technology that uses an ultraviolet laser and an adjustable pattern mask to lay the Micro LED chip off the substrate and directly onto the receiving substrate. Secondly, Optovate has also developed an optical array that combines the light emitted from the Micro LED chip with the principles of refraction and reflection. This technology can control micron-level chip light output for higher efficiency. When used for LCD and OLED panel backlights, Micro LED panels, etc., it can make the application design thinner.

The Belgian Microelectronics Research Center (IMEC) has also been actively involved in the development of Micro LED panel devices, focusing on the technology of rapidly transferring Micro LED chips to substrates. Through the development of the CSM machine spring structure, the Micro LED screen chip can be transferred to different substrates, and at the same time, the chip spacing can be adjusted to increase the transfer and assembly efficiency. Peter Lemmens, general manager of Imec Taiwan, believes that applications such as headsets or smart glasses will be expected to benefit first from the development of Micro LED Screen technology.

In addition, JBD in Hong Kong has also designed a heterogeneous integration technology that can realize monochrome red, green and blue Micro LED Display array module displays. JBD in On the March of this year, we have noticed that JBD uses wafer bonding (Wafer Bonding) to make Micro LED video wall wafer-level transfer (Wafer Level Transfer) to make a monochrome Micro LED module, especially Its green-light Micro LED array module has a brightness of up to 50K nits.

Micro LEDs have miniaturized chips and huge transfer characteristics, and require different levels of wafer production and processing processes. Therefore, the demand for equipment in the industry is more different than in the past. In order to continue the development of Micro LED commercial display technology, equipment manufacturers will also They have launched their own technology to strengthen the manufacturing of Micro LED.

Two major MOCVD manufacturers(led panel), AIXTRON and Veeco, have demonstrated the advantages of their devices in high-quality epitaxial silicon wafers with high wavelength uniformity and low defect density. Among them, Veeco and ALLOS Semiconductor formed an alliance to demonstrate the reproducibility of ALLOS 200 mm silicon gallium nitride epitaxial silicon wafer technology on Veeco Propel® MOCVD reactors in November.

AIXTRON does not give much to it. Its AIX G5+C and AIX 2800-G4 TM platforms offer MOCVD solutions and can achieve high-volume production targets. The GasFoilRotation® (GFR) Planetary Reactor® technology is a hybrid solution that combines single wafer rotation and batch reactor processing. Its satellite control uses GFR to achieve temperature control and flow regulation for a single wafer. AIXTRON's research and development of Micro LED technology also won the first prize of the Micro LED forward-looking technology competition.

Multifunctional Applications of Biometric Tablets in Modern Technology

In an era where security and efficiency are paramount, the integration of biometrics into portable devices has revolutionized industries. One such innovation is the biometric tablet, a device that combines advanced biometric scanning capabilities with powerful computing capabilities. This blog explores the uses of biometric tablets, focusing specifically on models with IP68 standards, FBI-certified fingerprint scanners, and a powerful set of specs.

Learn about biometric tablets

Biometric fingerprint tablets are specialized devices that utilize biometric authentication methods, such as fingerprint scanning, to enhance security and simplify operations. These tablets are particularly useful in areas where data integrity and user authentication are critical, such as healthcare, finance and law enforcement. The incorporation of biometric technologies not only ensures secure access to sensitive information but also facilitates efficient data management and transaction processing.

Key Features of Biometric Tablets

This biometric tablet is designed to meet the stringent requirements of a variety of professional environments. Compliant with IP68 standard, dustproof and waterproof, suitable for use in harsh conditions. This durability is critical for field work, where exposure to harsh environments can impair the functionality of standard equipment.

The tablet comes with an FBI-certified fingerprint scanner, providing a high level of security. This certification demonstrates that the device meets strict biometric performance standards, ensuring user authentication is reliable and accurate. This feature is particularly beneficial in sectors such as law enforcement, where secure access to sensitive data is critical.

The tablet’s connectivity options are extensive, with 5G network capabilities for fast data transfer and communication. This is critical for professionals who need real-time access to information, such as medical personnel in emergencies or field agents conducting investigations. In addition, the device also includes a rich set of ports such as HDMI, RJ45, RJ232 and Lora, allowing seamless integration with a variety of peripherals and systems.

In terms of performance, the tablet is powered by an octa-core 2.4GHz CPU, ensuring that it can handle demanding applications and multitasking with ease. This processing power is critical for professionals who rely on complex software for data analysis, reporting or real-time monitoring.

Another noteworthy feature is the removable battery with a capacity of up to 10,000mAh. This allows for extended use without the need for frequent charging, making it ideal for professionals who travel frequently or work in remote areas.

 Biometric Tablet Application

The applications for biometric tablets are wide and varied. In healthcare, for example, these devices can be used for patient identification, ensuring medical records are accurately matched to the correct individual. This not only improves patient safety but also streamlines administrative processes.

In the financial sector, biometric tablets can facilitate secure transactions and account access, reducing the risk of fraud. The combination of biometric authentication and high-speed connectivity ensures financial institutions can operate efficiently while maintaining strict security measures.

Law enforcement agencies can utilize biometric tablets for field operations, allowing officers to access databases and verify identities on the spot. This capability can significantly increase the effectiveness of investigations and improve public safety.

In summary, biometric tablets represent a significant advancement in portable technology, offering a combination of security, performance and versatility. With features such as IP68 protection, biometric police tablet, and powerful processing capabilities, these devices are ideal for a variety of professional applications. As the industry continues to evolve and prioritize security and efficiency, biometric tablet adoption is likely to increase, paving the way for a more secure and streamlined future.

By any metric, the New York Marathon is an immense production. The 50,000+ runners who make this the world's largest marathon. Their route will take them through all five of the city's boroughs, from the starting line on Staten Island up through Brooklyn and Queens, across the Queensboro Bridge to Manhattan's Upper East Side, north into the Bronx and then back down along the east side of Central Park to the finish line in the Park itself.

Ensuring that the whole thing goes off without a hitch is a remarkable feat of organization. The race relies on a small army of volunteers, who do everything from staffing the water stations at every mile marker and making sure runners don't get lost to offering medical expertise.

Donni Katzovicz is a ham radio enthusiast who has volunteered at the Marathon since 2018 through Event Hams, a group that has coordinated the Marathon's use of amateur radio for the last decade. He explains that ham radio essentially plays two key roles during the marathon.

The first is as a route for communications that don’t require the use of official channels. “Obviously,” he says, “The marathon has commercial 2 way radio licenses and its own communications infrastructure. You also have all the local emergency services—FDNY, NYPD, EMS. And they all have their own radios and equipment.”

At the most basic level, ham radio is any radio that operates on the radio bands reserved for amateurs. As Katzovicz explains, enthusiasts come up with all manner of uses for their little corner of the electromagnetic spectrum: “The hobby itself is really, really, incredibly broad and encompasses a lot of different parts of science and technology. Some people … have handheld walkie talkies and to talk to other licensed people in their neighborhood; others make their own radios or make their own Rube Goldberg-esque devices to listen and transmit, and others coordinate with local civil bodies and provide backup communications.”

In a scenario where, say, all a city’s power was out, battery-powered walkie talkies would still work just fine, whereas cell phones would be useless.

Ham radio enthusiasts from throughout the region were at the Polk County Fairgrounds on Saturday, drawn by the lure of the semi-annual swap meet.

For some, ham radio is a hobby. Hams tends to use two kinds of gear: HF and VHF/UHF. HF gear is made to talk over long distances, while VHF/UHF radio is for talking around town. But for Kjell Lindgren, it was an out-of-this-world experience.

Ham radios work when other forms of communication don't. "(That's) huge, especially with the first one (Helene) that went through North Carolina. You could listen on the radio. They were able to facilitate getting aid to a lot of people,” said Josh Scott, Yamhill County Amateur Radio Emergency Services Group. “And in those events, there were people getting on their radio that weren't licensed. But they were still able to get on the Frs two way radio and ask for help.”

Oregon isn't home to major hurricanes. But local residents have their own worries. Fires, for example, and a ticking time bomb off the coast.

“If the Cascadia earthquake were to hit, the reality is that we will probably not have cell phones or telephones of any sort. The Internet will be down,”Scott said. "The only way you're going to be able to communicate after Cascadia is with radios.”

“Ham radios used to be more popular. Most of the people in their 70s and 80s were part of ham radio clubs and got their licenses. This was in almost every school,” she said. “Now, there’s a lot less of that going on. It’s a great hobby. But it’s going to be very valuable when the big one hits.”

The environment of an electron microscopy lab does not directly impact the electron microscope itself but rather affects the imaging quality and overall performance of the microscope. During the operation of an electron microscope, the fine electron beam needs to travel in a high vacuum environment, covering a distance of 0.7 meters (for Scanning Electron Microscope) to over 2 meters (for Transmission Electron Microscope). Along the path, external factors such as magnetic fields, ground vibrations, noise in the air, and airflows can cause the electron beam to deviate from its intended path, leading to a degradation in imaging quality. Therefore, specific requirements need to be met for the surrounding environment.

As is well known, electromagnetic waves consist of alternating magnetic and electric fields. However, it is important to consider the frequency when measuring electromagnetic waves using either magnetic or electric fields. In practice, it is necessary to take the frequency into account.

At very low frequencies (as the frequency tends to zero, equivalent to a DC magnetic field), the magnetic component of the electromagnetic wave becomes stronger while the electric component weakens. As the frequency increases, the electric component strengthens and the magnetic component decreases. This is a gradual transition without a distinct turning point. Generally, from zero to a few kilohertz, the magnetic field component can be well characterized, and units such as Gauss or Tesla are used to measure the field strength. Above 100 kHz, the electric field component is better measured, and the unit used for field strength is volts per meter (V/m). When dealing with a low-frequency electromagnetic environment with a strong magnetic field component, reducing the magnetic field directly is an effective approach.

Next, we will focus on the practical application of shielding a low-frequency (0-300 Hz), electromagnetic field with a magnetic field strength ranging from 0.5 to 50 milligauss (peak-to-peak) in a shielded volume of 40-120 cubic meters. Considering cost-effectiveness, the shielding material used is typically low-carbon steel plate Q195 (formerly known as A3).

Since the eddy current loss of a single thick material is greater than that of multiple thin layers (with the same total thickness), thicker single-layer materials are preferred unless there are specific requirements. Let's establish a mathematical model:

1. Derivation of the formula

Since the energy of low-frequency electromagnetic waves is mainly composed of magnetic field energy, we can use high-permeability materials to provide magnetic bypass paths to reduce the magnetic flux density inside the shielding volume. By applying the analysis method of parallel shunt circuits, we can derive the calculation formula for the parallel shunting of magnetic flux paths.

Here are some definitions:

Ho: External magnetic field strength

Hi: Magnetic field strength inside the shielding volume

Hs: Magnetic field strength inside the shielding material

A: Area through which magnetic lines pass through the shield A = L × W

Φo: Permeability of air

Φs: Permeability of the shielding material

Ro: Magnetic resistance of the internal space of the shield

Rs: Magnetic resistance of the shielding material

L: Length of the shielding volume

W: Width of the shielding volume

h: Height of the shielding volume (i.e., length of the magnetic channel)

b: Thickness of the shielding material

From the schematic diagram (Figure 1), we can obtain the following equations:

Ro = h / (A × Φo) = h / (L × W × Φo) (1)

Rs = h / ((2b × W) + (2b × L)) × Φs (2)

From the equivalent circuit diagram (Figure 2), we can obtain the following equation:

Rs = Hi × Ro / (Ho - Hi) (3)

By substituting equations (1) and (2) into equation (3) and rearranging, we get the formula (4) for calculating the thickness b of the shielding material:

b = L × W × Φo × (Ho - Hi) / ((W + L) × 2Φs × Hi) (4)

Note:

In equation (4), the length of the magnetic channel h is eliminated during the simplification process, and physical units such as Φo, Φs, Ho, Hi, and others are also eliminated. It is only necessary to ensure that the length units are consistent.

From equation (4), it can be seen that the shielding effectiveness is related to the permeability and thickness of the shielding material, as well as the size of the shielding volume. A higher permeability and thicker shielding material result in lower magnetic resistance and higher eddy current losses, leading to better shielding effectiveness. When the permeability and thickness are the same, a larger shielding volume will result in poorer shielding performance.

2. Validation of the formula

We can use equation (4) Φo=1, L=5m, W=4m, Φs=4000 to calculate the thickness of the shielding material and compare the calculated results with experimental data (which took several months to collect):

Table 1

Note:

1. The external magnetic field strength is in the range of 5-20 milligauss (peak-to-peak).

2. The measured values are obtained by converting multiple tests under different conditions. Since the test conditions for each measurement are not the same, the presented values represent approximate average measurements.

In reality, due to various factors, it is quite challenging to establish a simple mathematical model for analyzing and calculating low-frequency electromagnetic shielding effectiveness. The significant deviations between the calculated results and experimental data can be attributed to the following reasons.

Firstly, the function relationship in the parallel shunt circuit is linear, while in magnetic circuits, permeability, magnetic flux density, and eddy current losses do not exhibit linear relationships. Many parameters are nonlinear functions of each other (although they may exhibit good linearity in certain ranges). During the derivation of the parallel shunting mechanism in magnetic circuits, some parameters were omitted, approximations were made, and conditions were simplified to avoid complex calculations, linearizing the magnetic circuit. These factors are the main reasons for the differences in precision between calculations and experiments.

Secondly, commercial low-carbon steel plate specifications are usually 1.22m × 2.44m in size. Considering a room size of 5m × 4m × 3m as an example, even with full welding, there would still be over 50 welds, and the thickness of the welds is often smaller than that of the steel plate. Additionally, there may be openings and gaps in the shielding material, resulting in an overall increase in magnetic resistance and a decrease in permeability. Therefore, the calculation formula for magnetic shielding derived from the parallel shunt circuit needs to be modified to approach actual conditions.

3. Modified calculation formula

Based on equation (4), we introduce a correction coefficient μ and consider the permeability of air to be approximately 1. The modified equation for calculating the thickness b of the shielding material is as follows (equation 5):

b = μ × [L × W × (Ho - Hi) / ((W + L) × 2Φs × Hi)] (5)

The value of μ is selected between 3.2 and 4.0. A smaller value is preferred for smaller shielding volumes and higher process levels, while a larger value is better for larger shielding volumes. Using equation (5) with μ = 3.4, the calculated results are compared with experimental data (see Table 2), showing significantly improved agreement.

Table 2

Note: Other conditions remain the same as in Table 1.

It should be noted that multiple test data confirm the high concurrence between the results obtained from equation (5) and various on-site measurements. However, there have been isolated cases with significant deviations. These cases can be attributed to construction issues.

The following are several situations that may occur during construction: 

1. Thin steel plates used in individual areas (such as doors).

2. Non-continuous welding or large gaps in welded joints.

3. Insufficient depth of welds, resulting in decreased permeability at weld locations and multiple "bottlenecks."

4. Larger openings in shielded areas and improper treatment of waveguide openings.

5. Arbitrary shortening of waveguide length or substandard processing.

6. Insufficient wall thickness of waveguide.

7. Multiple grounding points in the shielding material lead to non-uniform current distribution.

8. Connection of the shielding material to the neutral wire of the power supply.

Even a small oversight can lead to a significant deterioration in effectiveness, the capacity of a bucket depends on the shortest piece of wood. For concealed projects like this, quality is often ensured by the craftsmanship. Therefore, it is important to pay careful attention to selecting a reliable construction company, strictly adhering to the design requirements and process, strengthening on-site construction supervision, and implementing phased inspections.

Shielding enclosure aperture design:

When designing a shielding enclosure, one will inevitably encounter the issue of apertures. The theoretical methods commonly used for aperture design are difficult to directly apply to low-frequency magnetic shielding design. Here, we will discuss the example of a room's shielding design.

1. Small apertures: In rooms with small shielded devices, there are usually power supply, energy supply, and cooling water requirements. These auxiliary facilities are mostly located outside the shielding enclosure and are connected through water pipes, air pipes, and cables. These pipes and cables can be appropriately centralized and passed through the shielding enclosure using one or several small holes. These holes, made of the same material as the shielding enclosure, are called "waveguide openings." The length-to-diameter ratio of the waveguide openings is generally considered to be at least 3-4:1 (if the on-site conditions permit, longer is better). For example, if the diameter of a small hole is 80mm, the length should be at least 240-320mm.

2. Medium-sized apertures: Ventilation openings for air conditioning and exhaust openings for fans typically have diameters (or side lengths for squares or rectangles) of around 400-600mm. Calculating the length of a waveguide opening based on these dimensions would result in lengths of 1200-2400mm, which is not feasible in practical construction. In this case, the original aperture can be divided into several smaller openings of the same size using a grid. For example, if a 400×400mm air inlet is divided into nine equal-sized grids, the length would be reduced from 1200-1600mm to 400-530mm (the increase in airflow resistance due to the grids is negligible).

When designing and fabricating, pay attention to the following points:

- The material of the grids should be the same as the shielding enclosure, and the thickness of the material should not be arbitrarily reduced.

- The cross-section of the grids should be as close to square as possible.

- Try to reduce the number of grids as much as possible, within acceptable lengths, to reduce processing difficulties and airflow resistance.

- Ensure continuous welding at all locations of the grids to prevent an increase in magnetic resistance.

- Increase the magnetic permeability by adding silicon steel plates at the junctions of the grids.

3. Large closable apertures: Doors and windows of a room typically have openings measuring 1m×2m or even larger. In this case, the waveguide openings should be designed based on the non-magnetic gaps when the doors and windows are closed (made of the same material as the shielding enclosure). Assuming a non-magnetic gap of 5mm (which is not technically challenging, and additional edge folds can be added in difficult-to-handle areas), the length of the waveguide opening should be 15-20mm. Given that the gap is narrow and long, it is preferable to have a longer length. Note that the waveguide openings are not only formed by the frames of doors and windows; there should be a certain thickness of edge folds at all non-magnetic gap locations to ensure the length of the waveguide opening. To ensure safe evacuation in special circumstances, the door frames of the shielding room should be reinforced, and the shielding doors should open outward.

Here is a practical design example:

The dimensions of the room are length 5m, width 4m, and height 3.3m, with original magnetic field strengths of x=10mGauss, y=8mGauss, and z=12mGauss. The goal is to design a low-frequency electromagnetic shielding that ensures the magnetic field strength in any direction inside the enclosure is less than 2mGauss. See Figure 3.

1. Select commercial low-carbon steel plates with Φs=4000 and specifications of 1.22m×2.44m.

2. Use equation (5) to calculate the thickness of the steel plates from the x, y, and z directions:

Taking μ as 3.8, substitute the given length, width, and height into L×W, corresponding to the original magnetic field strengths in the x, y, and z directions.

bx=3.8〔3.3m×4m×(10mGauss -2mGauss)/(4m+3.3m) 2×4000×2mGauss〕

=3.43mm

by=3.8〔3.3m×5m×(8mGauss -2mGauss)/(5m+3.3m) 2×4000×2mGauss〕

=2.83mm

bz=3.8〔5m×4m×(12mGauss -2mGauss)/(4m+5m) 2×4000×2mGauss〕

=5.28mm   (If lengths and widths are 10m and 6m, respectively, the calculated thickness would be b=2280/56000=8.91mm)

The thickness of all steel plates should be at least 6mm (to allow for environmental magnetic field variations, 8-10mm can be used as well) as a single layer.

All welding seams should be continuous and try to achieve a depth close to the thickness of the base material.

3. Waveguide opening treatment

(Omitted. See the section on shielding enclosure aperture design).

After completion, the shielding enclosure was tested and fully met the design requirements.

Note: Magnetic shielding cannot improve DC interference environments. When there is a need to improve DC electromagnetic interference environments, it should be used in conjunction with demagnetizers that have DC elimination capabilities.