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The Doppler Effect describes the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave. One of the most significant applications of the Doppler Effect is in Doppler radar technology. Doppler radar detects motion by measuring the frequency shift of returning radar signals, which is crucial for accurate speed measurement and weather forecasting. This technology has been instrumental in advancing meteorology, enabling precise tracking of storm systems and providing early warnings for severe weather events.

First Experiments with Doppler Effect

The development of radar technology dates back to the early 20th century. Initial radar systems could only detect the presence and distance of objects. However, integrating the Doppler Effect allowed for the detection of object velocity, vastly improving radar capabilities.

Christian Doppler first presented his principle in 1842 in his paper titled “On the Colored Light of the Double Stars and Certain Other Stars of the Heavens.” His work initially focused on the frequency changes in sound waves, but the principles he described were later found to apply to all types of waves, including light and radio waves.

The Doppler Effect was experimentally confirmed in 1845 by the Dutch scientist Christophorus Buys Ballot. Using a group of musicians playing trumpets on a moving train, Buys Ballot demonstrated the change in pitch predicted by Doppler. This experiment was one of the earliest confirmations of Doppler’s theory.

In the early 20th century, the application of the Doppler Effect expanded significantly. French physicist Henri Becquerel used the Doppler Effect to study gamma rays, and the development of radio technology paved the way for Doppler radar. By World War II, radar technology had become sophisticated enough to incorporate Doppler shifts, allowing for more accurate detection and tracking of moving objects.

Speed Measurement with Doppler Radar

One of the remarkable capabilities enabled by the Doppler Effect in radar technology is precise speed measurement of moving objects. Doppler radar calculates the velocity of an object by analyzing the frequency shift between the emitted and received radar signals. If a radar system emits a signal at 100 MHz and receives a reflected signal at 101 MHz, it indicates that the target is moving towards the radar at a speed that causes this frequency shift.

Applications in Law Enforcement and Traffic Control

Doppler radar is widely used in law enforcement for speed enforcement. Police radar guns measure the speed of vehicles by detecting the Doppler shift in radar waves bounced off moving vehicles. This technology allows police officers to accurately determine if a vehicle is exceeding the speed limit.

Aerospace Applications

In aviation, Doppler radar is used to measure the ground speed of aircraft. By analyzing the frequency shift of radar signals bounced off the ground, aircraft speed relative to the ground can be accurately determined, aiding in navigation and flight control.

Radar and the Doppler Effect

As the radar source moves towards a target, the radar waves become compressed, resulting in an increase in frequency. Conversely, when the radar source moves away from the target, the radar waves are stretched, leading to a decrease in frequency. This change in frequency due to motion is the essence of the Doppler Effect and is crucial in detecting and measuring the speed of objects using radar technology.

Future Directions and Innovations

The Doppler Effect continues to inspire innovations in radar technology. Ongoing research aims to enhance radar systems’ sensitivity and accuracy, particularly in adverse weather conditions and complex terrain. Advances in signal processing and radar engineering promise to further refine Doppler radar applications across various industries, from automotive safety systems to aerospace navigation.

The Doppler Effect’s impact on radar technology underscores its significance in modern science and industry. From meteorology to military applications, this fundamental principle continues to shape our understanding of waves and their interaction with moving objects, driving technological advancements.

The Birth of the Magnetron

In the early 20th century, the limitations of existing radar technology became apparent. The need for more precise and higher frequency signals was crucial for effective operations. Radar systems of the time were bulky and limited in range and accuracy, relying on longer wavelengths that couldn’t provide detailed information about distant objects.

The breakthrough came in 1940 when British physicists John Randall and Harry Boot developed the cavity magnetron, a device capable of generating microwaves at high power levels. The magnetron operates by using a stream of electrons interacting with a magnetic field to generate microwaves. These microwaves are then emitted through resonant cavities within the magnetron, producing powerful and precise high-frequency signals. This innovation was a game-changer, providing the ability to produce small wavelength signals essential for high-resolution radar systems.

The Magnetron and Radar Technology

The development of the cavity magnetron significantly enhanced radar capabilities. Radar systems equipped with magnetrons could detect aircraft and ships with much greater precision. Before the magnetron, radar systems used lower frequency signals that were less effective at detecting smaller objects and were easily scattered by atmospheric conditions. The high-frequency signals generated by magnetrons allowed for smaller and more sophisticated radar systems, capable of discerning finer details and operating more effectively in various environments.

The success of radar technology accelerated advancements in both military and civilian applications. The ability to detect and track objects with high precision had far-reaching implications, leading to innovations in air traffic control, weather forecasting, and navigation systems. The principles of radar technology, powered by the magnetron, became foundational for many modern technological systems.

Magnetron in Everyday Life: The Microwave Oven

The magnetron also found a revolutionary application in the kitchen. In 1945, Percy Spencer, an engineer at Raytheon, discovered that microwaves generated by a magnetron could cook food quickly and efficiently. This serendipitous discovery led to the development of the first commercial microwave oven, radically changing cooking methods worldwide.

The early microwave ovens were large and expensive, but as the technology improved and manufacturing costs decreased, they became more accessible to the general public. Today, almost every household contains a microwave oven, showcasing the magnetron’s versatility and lasting impact.

The Evolution of Radar Technology

The evolution of radar technology did not stop with the initial developments. Advances in digital technology and signal processing have further refined radar capabilities. Modern radar systems utilize sophisticated algorithms and digital signal processing to enhance performance, offering improved accuracy, resolution, and reliability.

These advancements have expanded radar’s applications beyond traditional uses. In civilian aviation, radar ensures the safe and efficient management of air traffic. In meteorology, radar systems track weather patterns, helping predict storms and other severe weather events. In automotive technology, radar systems assist in adaptive cruise control and collision avoidance, contributing to vehicle safety.

Conclusion

The invention of the magnetron was a revolutionary milestone that transformed radar technology and had a profound impact on both military and civilian life. Its role showcased its potential for high-precision detection and tracking, while its adaptation into microwave ovens demonstrated its versatility. As radar technology continues to evolve, the legacy of the magnetron endures, highlighting the ongoing importance of this groundbreaking invention. The magnetron’s journey from pioneering technology to everyday convenience underscores its significance and enduring relevance in the modern world.

The Inspiration Behind Radar

Christian Hülsmeyer, a German inventor, was inspired by a tragic boating accident on the Rhine, where two ships collided in foggy conditions, resulting in several fatalities. This incident spurred Hülsmeyer to develop a solution for preventing such tragedies caused by poor visibility. His quest led to the creation of the “Telemobiloscope,” the first patented device to use radio waves for detecting the presence of distant objects, such as ships.

How the Telemobiloscope Worked

The Telemobiloscope was an ingenious apparatus composed of a large wooden box, a spark-gap transmitter, two simple parabolic antennas, and a crude detector. The transmitter generated radio-frequency electromagnetic waves, and the antennas, positioned on a movable platform, could rotate 360 degrees. When the transmitted signals hit an object and reflected back to the receiver, an electric bell inside the device would ring, indicating the object’s presence. Hülsmeyer also devised a toothed-wheel mechanism called Kompass, allowing the user to determine the direction of the detected object.

The Historic Demonstration

On May 17, 1904, Hülsmeyer publicly demonstrated the Telemobiloscope in the courtyard of the Dom Hotel in Cologne. Using a metal gate as the target, Hülsmeyer proved his device could detect objects even when not directly visible. This demonstration was widely reported, showcasing the practical applications of his invention and earning him significant acclaim.

Breakthrough at the Maritime Conference

Following the success in Cologne, Hülsmeyer presented the Telemobiloscope at a maritime safety conference in Scheveningen, Netherlands. During a tour aboard the ship-tender Columbus in the Rotterdam harbor, his device successfully detected passing vessels, impressing shipping industry leaders and highlighting radar’s potential for preventing maritime collisions.

Challenges and Legacy

Despite the initial excitement, Hülsmeyer faced financial difficulties in further developing and commercializing the Telemobiloscope. He eventually sold the rights to his invention to the Trading Company Z.H. Gumpel in Hannover. Subsequent demonstrations faced technical challenges, and competition from Marconi’s Wireless Telegraph Company hindered widespread adoption of his radar technology.

However, Hülsmeyer’s pioneering work laid the foundation for future developments. In 1953, at a radar conference in Frankfurt, Hülsmeyer and Robert Watson-Watt, a key figure in British radar development, were both honored. Watson-Watt acknowledged Hülsmeyer’s contribution by saying, “I am the father of radar, whereas you are its grandfather.” Today, Christian Hülsmeyer is celebrated for his groundbreaking invention, which has had a lasting impact on navigation and safety technologies.

To answer this question, a new funded research project was set up.
In the project “MaRSCH – On-line material classification by radar in slags”, the TU Bergakademie Freiberg and the startup mecorad are using state-of-the-art radar to detect the composition of different slags and to determine their specifics. In this way, a process is to be developed over the next two years to determine the properties of molten-liquid phases of slags and their individual levels in real time.

TU Bergakademie Freibergs Institute for Iron and Steel Technology and Institute for Non-Ferrous Metallurgy and High-Purity Materials are contributing their expertise to the project. The mecorad GmbH puts in its know-how in radar development and the highly complex field of signal evaluation.

“Surveys on the properties and recycling of metallurgical slags are a current research focus. Using radar sensors for this and their testing directly at our test facilities is an exciting new issue for us.” says Dr Thilo Kreschel from the Institute of Iron and Steel Technology at TU Bergakademie Freiberg. 

Professor Alexandros Charitos from the Institute of Nonferrous Metallurgy and High Purity Materials adds: “Modern sensors are the basis for digitalisation in the metallurgical industry and will contribute to the efficiency of processes. Our partner mecorad will develop this radar technology for sophisticated applications in metallurgy as part of the project. We are happy to be involved and look forward to working together over the next two years.”   

As happy is mecorad, Dr. Marc Banaszak admits: “The expertise of the colleagues here at the TU Bergakademie Freiberg and the opportunity to test the research results with them in the laboratories are a real stroke of luck for us. We hope the joint project will lead the way for automation of the separation of slag phases prior to disposal.”

The project is being funded as part of the “KMU innovativ” programme on behalf and with funds from the German Federal Ministry of Education and Research. PT Jülich Research Center joins the project as the executing organization.

Find more information on the KMU innovative programme on the programme site.

Among other things, our Managing Director Dr Marc Banaszak talks about the motivation behind mecorad’s products, presents our continuous casting solution and describes a learning from the pandemic.

You can find the full article also here (German version only).

Our new development can provide geometrical information of slab casting processes directly from below the mould exit in the cooling zone.
While existing systems only check the dimensional accuracy at the end of the straightening zone, mecorad succeeds in measuring the width of the cast strand at a distance of around four metres below the mould level, while the surface of the red-hot strand is just solidifying.  Accuracy of measured width is well below one millimetre.

Furthermore, the determined data is processed real-time by mecorad´s intelligent software application and can be connected via interfaces into the customers applications. This direct feedback means that the casting process can be far better matched to the tolerances to be maintained. Time-consuming reworking, as well as material- and thus cost-intensive overcasting, are significantly reduced. The measured values generated also allow casting models to be further improved and compared across plants.

The new development was presented for the first time together with Aperam Châtelet Belgium at the European Steel Technology and Application Days 2021 in Stockholm.

As part of the project, mecorad is testing the measurement of complicated geometries in hot forming processes with radar technology.

Our radar sensors are predestined for work under extreme conditions, such as those found in hot forming. So now, we are curious to take radar based measurement to the next level. 

More information on Fraunhofer IWU 

We at mecorad looked at our customers’ specific situation in the up- and downstream processing of hot steel and metal, which is – as you might imagine – extremely challenging.

The following considerations led the way to our choice and might help you with your decision:  

• What level of accuracy has to be realised?
• What about prevailing environmental conditions? Is there dust, steam, heat? A vacuum? 
• Are there any specific characteristics of the object’s material? 

To answer the above issues, one has to take at least a short look at the pros and cons of the measuring principles.

In this article, we limit our comparison to the contactless methods of laser, ultrasound and radar. These three are often chosen and – compared to isotopic solutions, such as X-ray – do not imply hazardous radioactive exposure of the worker and workplace.  

Ultrasound

Ultrasound sensors measure distances by using the time-of-flight principle.

Ultrasound waves are pulses of sound at a frequency between 20 kHz and 1 GHz, higher than humans can hear. Bursts of these waves are emitted in a certain time cycle from a sensor and move in the air at the speed of sound. Hitting an – in our case metallic- object, they are reflected by the object’s surface. These reflected echoes return to the sensor. By measuring the time shift of the reflected echo, the distance covered is determined and displayed to the user.

Ultrasound is very suitable for complex objects, even transparent or highly shining ones within homogeneous material, where there is only low sound absorption.  That is why it is often used for quality control to mark defective structures of the material, inclusions, or impurities within a certain material.

However, moving in a heterogeneous environment, the speed of the waves can be interfered by several conditions, such as instable temperatures or a change in the air composition surrounding the object. 

Metal processing usually is not a clean room. So imagine your rather dusty workspace. Or think about the steam of the cooling water. The ultrasound waves are distracted at the micro water drops in the air, leading to an interruption of the transmission and reflection of the signal. The measurement results are no longer precise. Hot objects, like glowing steel slabs, also cause heat convection in the surrounding air by themselves. These convections again interrupt the ultrasound signal. 

Laser

The word laser is the acronym for light amplification by stimulated emission of radiation. Laser beams consist of electromagnetic waves that move at the speed of light (approx. 300000 km/s).

Today, there is a range of laser use cases with a variety of measurement tasks. Lasers can be used for detection, counting of objects, etc. A well-known example for electro-optical measurement of distances and the derived calculation of speeds is even used by the police for speed control. 

In our industrial context, measurements are based on one of the following principles: triangulation, phase shift or time-of-flight, the last as explained before.

Laser sensors are highly precise under determined conditions and therefore often used for measurement tasks in industrial environments. But they lack, if dust or deposits block the view, so the beam can not be emitted properly. And nobody wants to check or clean the laser sensor every once in a while, right? 

Also, at open flames or glowing objects, measurement with standard red-light-laser supplies incorrect signals. The reason for this is the similar frequency of infrared radiation of the laser and the color spectrum of the glowing surface. The dimensions of the object are not recognized correctly, the laser might measure into the surface. In these cases, blue-light laser with a huge spectral distance might be a solution, but they are rather expensive and not the first choice for other measuring tasks. 

Wet, dusty or smeared surfaces have strongly changing reflective properties, declining measurement accuracy, as well. The distance between a laser sensor and the measuring object is restricted to very little variations to deliver robust signals.  And huge water drops, as one can find in the steel industry´s cinder wash, refract the laser signal. 

Radar

Radar measurement is based on electromagnetic waves. The sensor emittes the high-frequency signal, which also propagates at the speed of light, and calculates the distance to an object by measuring the reflection of the signal from that object.  

Radar measurement captures a spot that can be focussed by lenses or antennas. Comparable to focussing a flashlight on a wall, this spot can be more or less focussed. Because of this, even when obstructions occur in the direct line of sight, the sensor still captures the rolling stock.

Radar waves are insensitive to adverse environmental conditions such as high temperatures or polluted air.  Fog, for example, is much more permeable to radar radiation than to visible laser light. Even under zero-view conditions or while measuring through vapour, water drops, dust, cinder and open flames, the beams are still being controllable at high accuracy. 

Though radar – compared under laboratory conditions – may not be as precise as laser, it is from our point of view, the most suitable solution for measurement of width, thickness and length of hot metal. 

That is why we use it in our innovative IIoT measurement solutions.