###### Abstract  
The interactions between paralyzed individuals with severe physical disabilities and smart infrastructure need to be facilitated, and the tongue-computer interface (TCI) provides an efficient and feasible solution. By attaching a permanent magnet (PM) on the apex of the tongue, the real-time tongue motion tracking can be switching to solve a nonlinear inverse magnetic problem. This paper presents a proof-of-concept prototype TCI system utilizing a combined \(T\)-type PM marker for potential environment control. The introduction of the combined \(T\)-type PM promotes the anisotropy of the magnetic field distribution. A comprehensive calibration method for the sensing system is proposed to figure out the bias in the magnetic moment of the PM marker and the sensing axis rotation of the sensors. To address the influence of initialization in solving the overdetermined inverse magnetic problem, an adaptive Levenberg-Marquardt algorithm is designed utilizing real-time measurements. Bench-top experiments were carried out based on a high-precision three-dimensional (3D) translation platform, and the feasibility of the proposed TCI system in magnetic localization accuracy and efficiency is fully assessed. The mean localization error is 1.65 mm with a mean processing time of 65.7 ms, and a mean improvement of 54.7% can be achieved compared with a traditional LM algorithm. s 2018 8 2498 298 2018 298 2018 298 2018 298 2018 298 2018 298 2018 298 2018 298 2018 298 2018 298 2018 298 2018 298 2018 298 2018 2018 298 2018 2018 2018 2018 2018 2018 2018 2018  
including movements of tongue [4], eyeball [5; 6], head [7], facial muscle activity [8], and even brain activity signals [9; 10; 11; 12]. Among the body-function based ATs, the tongue-computer interface (TCI), tracking intraoral tongue motions, takes advantage of physiological property and has become a new trend [4; 13]. The tongue is a muscular organ in the mouth with supplemental and flexibility. The redundancy of its muscle fibers offers the tongue with high resistance to fatigue. Besides, five out of the 12 pairs of cranial nerves can control tongue motions, which could protect tongue movements from paralyzation. The interface based on the controllable tongue becomes a promising communication channel between the individuals with severe disabilities and the environment. There are two categories of TCIs: the indirect detecting method and direct detecting method. The former type indirectly identifies the tongue motion by sensing other kinds of physiologic signals induced by the tongue movements. Several TCI-based ATs employ electromyography (EMG) signals detected in the oral cavity [14] or on the neck [15] to help individuals access a computer [7; 16] using the limited commands classified from certain tongue motions. Tongue-movement ear pressure signals induced by impulsive tongue actions has been developed; however, training may require a long time [17; 18]. Brain-computer interface (BCI)-based TCI [19] measures the electric responses related to glossokinetic potentials on the scalp, and are related to certain tongue motions, involving a sense of touch inside the mouth. To promote the system safety and comfort and avoid external contamination, non-contact sensors, including magnetic sensors and photoelectric sensors, are widely taken for direct intraoral tongue tracking [4; 13; 20; 21; 22]. Compared with other non-contact TCIs, permanent magnet (PM)-based interfaces, taking advantages of wirelessness, the similar magnetic permeability of the human body with the free space, and high safety without side effects or biomechanical reaction, employ a passive magnetic source without power supply, and can provide higher magnetic fields in a smaller form factor [23]. All of these features make it more suitable to perform tracking tasks related to the human body. In recent years, approaches have been proposed by attaching a magnet or ferromagnetic marker on the apex of the tongue, and both intraorally [13; 21] and out orally [4; 24; 25] sensing systems are designed.