test facility in Germany. A second, incompatible high-speed prototype was unveiled in January 2021. Developed at Southwest Jiaotong University in Chengdu, the design uses high-temperature superconducting magnets, is designed for and was demonstrated on a test track. Technology In the public imagination, "maglev" often evokes the concept of an elevated monorail track with a linear motor. Maglev systems may be monorail or dual rail—the SCMaglev MLX01 for instance uses a trench-like track—and not all monorail trains are maglevs. Some railway transport systems incorporate linear motors but use electromagnetism only for propulsion, without levitating the vehicle. Such trains have wheels and are not maglevs. Maglev tracks, monorail or not, can also be constructed at grade or underground in tunnels. Conversely, non-maglev tracks, monorail or not, can be elevated or underground too. Some maglev trains do incorporate wheels and function like linear motor-propelled wheeled vehicles at slower speeds but levitate at higher speeds. This is typically the case with electrodynamic suspension maglev trains. Aerodynamic factors may also play a role in the levitation of such trains. The two main types of maglev technology are: Electromagnetic suspension (EMS), electronically controlled electromagnets in the train attract it to a magnetically conductive (usually steel) track. Electrodynamic suspension (EDS) uses superconducting electromagnets or strong permanent magnets that create a magnetic field, which induces currents in nearby metallic conductors when there is relative movement, which pushes and pulls the train towards the designed levitation position on the guide way. Electromagnetic suspension (EMS) In electromagnetic suspension (EMS) systems, the train levitates above a steel rail while electromagnets, attached to the train, are oriented toward the rail from below. The system is typically arranged on a series of C-shaped arms, with the upper portion of the arm attached to the vehicle, and the lower inside edge containing the magnets. The rail is situated inside the C, between the upper and lower edges. Magnetic attraction varies inversely with the square of distance, so minor changes in distance between the magnets and the rail produce greatly varying forces. These changes in force are dynamically unstable—a slight divergence from the optimum position tends to grow, requiring sophisticated feedback systems to maintain a constant distance from the track, (approximately ). The major advantage to suspended maglev systems is that they work at all speeds, unlike electrodynamic systems, which only work at a minimum speed of about . This eliminates the need for a