The coil box was tightly screwed between the core and the webs of the magnet coil, making loosening impossible. The further development of the track brake now appeared to have been completed for the time being. The coefficient of friction between the rail shoe and the rail is dependent on the speed, i.e. with increasing speed, the coefficient of friction decreases. As the project "speed up to 350 km/h" became official, it appeared as if the track brake could no longer be of use for this purpose. It was not until passenger train speeds exceeded 140 km/h and a friction-independent brake system became necessary that the plans for the track brake were brought out again and the design improved. To improve the contact surfaces with the rail, articulated magnets were developed and patented. Active principle and functionality The main component of the magnetic track brake is the brake magnet. Following the principle of an electromagnet, it consists of a coil wound around an iron core, which is enclosed by horseshoe-shaped magnets. Direct current is passed through this magnet coil, generating a magnetic field. This causes an attractive force between the brake magnet with the pole shoes attached to it and the rail. The pole shoes are pressed onto the rail, and the resulting friction converts the kinetic energy of the movement into heat (dissipation) until the kinetic energy is consumed or the brake is deactivated. Magnetic track brakes must also work safely in the event of a contact line failure. The braking system must therefore be designed in such a way that, in the event of a power failure, a supply from the vehicle's batteries is guaranteed at all times. Rigid magnets Rigid magnets contain a single steel core running the entire length of the magnet body, with pole shoes located on the underside as wear parts. Rigid magnets are typically used for streetcars, where they are usually suspended in a low position. Suspension The suspension is responsible for holding the switched-off magnet above the rail. In the event of braking, the magnet automatically attracts itself to the rails against the effect of the suspension springs. After switching off, the springs of the suspension pull the magnet back into the readiness position. Driver The drivers are responsible for the transmission of the brake force from the magnet to the bogie. It takes place via tie bars or driver towers. Tie