Modular smart phones have been attracting attention (Fig. 10.1.1) because users can freely customize their phones by purchasing modules and assembling them . The transfer of data between modules is accomplished by non-contact connectors. Because the connection electrodes are not exposed, there is no wear or damage and waterproofing is possible. The methods of constructing non-contact connectors include capacitive coupling, which uses flat plate electrodes , magnetic coupling, which uses coils [2-4], and electromagnetic coupling, which uses transmission-line couplers (TLC) [5-7]. Capacitive and magnetic coupling can be used only for narrowband communication below the resonance frequency (<1GHz). Because impedance varies with frequency, impedance matching is not possible for digital signals that include a wide range of frequency components. For that reason, these couplers can be used for the MIPI D-PHY data rate (1Gb/s), but not for M-PHY (6Gb/s). The TLC, however, can be used for broadband communication (>6GHz). Because the impedance is constant, there is little reflection and digital communication is possible. A data transfer speed of 12Gb/s has been reported for a distance of 1mm between couplers . Thus, full HD (4Gb/s) or 4K (15Gb/s) video data can be transmitted over a small number of lanes.