# Mobility, Citizens, Innovation and Technology in Digital and Smart Cities
## 3 Cities Transportation Trends
### Electric Based Transportation Systems
#### 3.3.2 Superconducting Based Technologies  
Certainly, one of the most promising technologies of this century is the advent of superconducting materials [111; 112; 113]. These have unique physical properties that will propel human beings to understand and produce technologies with lower levels of interference and noise in their vicinity. Among them, a Superconducting Quantum Interference Device (SQUID) [114] allows measurement of very small magnetic fields, with magnitude detection on the order of \(10^{-15}T\). These sensors also have high sensitivity in relation to the amplification of electrical or light signals. Conventional electronics, which use semiconductor and ferromagnetic materials, have already reached a satisfactory sophistication so far. However, certain problems can only be solved with the advent of superconductors, by using Josephson junctions in components such as SQUID. This extremely sensitive sensor allows the magnetic flux to be transduced into measurable electrical signals. This device is so sensitive that it can capture the magnetic field of human hearts and brains with great precision, perhaps this explains the great rise of superconductors in medical areas. When it comes to small-scale applications, superconductors are being used in biomedicine, metrology, geophysics, digital processing, devices and sensors [115; 116; 117]. As far as superconducting sensors are concerned, superconductors are already being used in various areas of human knowledge, from physicians, astronomers, to the military [118; 119; 120]. A widely publicized application of SQUID is magnetoencephalography, a technique that allows for mapping the magnetic fields generated by the brain activities through sensors that work in conjunction with SQUIDs. By promoting greater robustness in quantum technologies, superconductors will bring a real scientific revolution in different areas, such as emerging transportation systems [121]. The latter face challenges that will be circumvented, such as fuel economy, environmental issues, overcoming the increased demand, among others. With the advent of superconductors applied for this area, different sectors related to transportation may see its benefits [122], such as high-speed trains; boat propulsion systems; and high-powered aircraft engines. Although significant applications in electronic devices are still difficult because of the need for operation at low temperature, superconducting materials are already under development in very high integration circuits [123]. By reducing the dimensions of the components' thermal dissipation is limited, requiring it to be cooled by liquid nitrogen or even liquid helium. In relation to efficient superconducting electric motors, they have been inserted into some specific transports, giving rise to a new generation of turbines, coils and, consequently, electric transport, airplanes, trains, cars and ships [124; 125; 126; 127]. An example of transport in which the superconductors are employed refers to the Maglev train [128; 129]; this levitates on the rails counting, basically, only with the resistance of the air-like force of friction. Thus, Maglev trains are faster than conventional trains because they float about ten inches above the rails on a \"magnetic mattress\" for a lower cost and greater safety than a conventional train. These are listed as one of the best means of transport for futuristic cities [130], and can reach speeds of the order of 600 km/h, mainly due to the elimination of conventional wheels, making the friction no longer a huge barrier. Of course, this technology will also receive attention with the recent advent of SC [131; 132], which has been promoting researchers to idealize insights about possible future projects [133]. With regard to storage, there is still no efficient method for large volumes of electricity. The Superconductive Magnetic Energy Storage (SMES) [134] is a promising technology that has been applied in different transportation systems [135].