An Electromagnetic Sensor for the Autonomous Running of Visually Impaired and Blind Athletes (Part II: The Wearable Device)

Marco Pieralisi, Valentina Di Mattia, Valerio Petrini, Alfredo De Leo, Giovanni Manfredi, Paola Russo, Lorenzo Scalise, Graziano Cerri
2017 Sensors  
Currently, the availability of technology developed to increase the autonomy of visually impaired athletes during sports is limited. The research proposed in this paper (Part I and Part II) focuses on the realization of an electromagnetic system that can guide a blind runner along a race track without the need for a sighted guide. In general, the system is composed of a transmitting unit (widely described in Part I) and a receiving unit, whose components and main features are described in this
more » ... aper. Special attention is paid to the definition of an electromagnetic model able to faithfully represent the physical mechanisms of interaction between the two units, as well as between the receiving magnetic sensor and the body of the user wearing the device. This theoretical approach allows for an estimation of the signals to be detected, and guides the design of a suitable signal processing board. This technology has been realized, patented, and tested with a blind volunteer with successful results and this paper presents interesting suggestions for further improvements. directly on the ground perimeter of a standard athletic track (400 m length), generating two magnetic fields that can be detected by a coil (the receiver) worn by the runner. Therefore, the overall system is composed of a transmitting unit-whose main features were reported in Part I of this paper-and a receiving unit, whose design and realization will be discussed in this paper. It is worth noting that when designing a device to be worn during sport or in general physical activity, it is necessary to account for specific requirements such as comfort, weight, and ease of use. This is especially important when athletes are affected by visual disabilities. The results of a recent user-focused assessment conducted among visually impaired and blind volunteers [7] highlighted the requirements for electronic travel aids where the main issues were related to the physical characteristics and appearance of the devices. Users wanted devices which were unobtrusive, inconspicuous, and easy to carry. Blind people preferred discrete devices that were not eye-catching and alienating, but small, light-weight, and preferably consisted of a single unit. Moreover, many users considered hands-free operation to be extremely useful, and provided different modes of outputs (e.g., tactile or auditory). Currently, most wearable magnetic sensors proposed in the literature or available in the market [8, 9] can satisfy the main requirements listed above, especially in terms of reduced weight and dimensions. However, in order to provide these characteristics, it is necessary to work at high frequencies (beyond the MHz range). This is a critical point, because-as explained in Part I of this paper [10]-for the running-track system, the frequency f = 100 kHz was chosen as a trade-off working frequency because it satisfied important system requirements, but was also high enough to induce a sufficient voltage in the receiving sensor whilst still being able to provide a uniform current along the whole cable. Since none of the existing sensors were suitable as magnetic sensors for the running-track system, an ad hoc wearable device has been designed and realized. Our design is a flat loop composed of 40 turns, and can be worn as a belt. The two magnetic fields generated by the transmitting unit induce different electromotive forces in the flat loop sensor. Basically, the signal processing unit connected to the sensor calculates the difference between the two voltages, and allows information about the position of the user inside the lane to be delimited by the two wires. If the value of the difference overcomes a certain threshold, it means that the athlete is getting too close to one of the borderlines and the unit generates a vibrational signal to warn the user. It must be emphasized that the proposed device was designed for athletes in training; and the present system is not applicable for road marathons, since two long wires need to be placed along the entire marathon path. An alternative electromagnetic system [11] has been proposed for these types of events, or other innovative GPS-based devices could be investigated. The paper is divided as follows: In Section 2, an overview of the theoretical considerations for designing the receiving magnetic sensor is provided; in Section 3, the receiving unit and all its features are described; and in Section 4, the first tests carried out in collaboration with a blind runner are shown and discussed. A final discussion and some conclusions will be reported in Section 5. An appendix at the end of the paper will provide the mathematical details concerning the theoretical model proposed in Section 2.
doi:10.3390/s17020381 pmid:28212348 pmcid:PMC5335952 fatcat:h3hbdhvpbngozakl4m57ejtr6a