Seat Occupancy and Belt Detection in Removable Seats via Inductive Coupling

Seat Belt Reminder (SBR) systems are effective in avoiding deaths and injuries in traffic accidents. However, their implementation can be unpractical in removable vehicle seats because of the difficulty in wiring the associated sensors, e.g. a seat occupancy sensor and a seat belt detector, to an electronic control unit (ECU). This paper proposes the use of inductive links to avoid wiring the sensors. Both sensors, which can be roughly modeled as switches, form part of a secondary resonant network. Their state (open- or short-circuit) is attained by estimating the resonance frequency of the equivalent input resistance of a primary network inductively coupled to the secondary network. Attending to the possible states of the sensors, four different resonant frequencies result. Because the application is space-constrained, small coils have been used. Commercial ferrite-core models were selected in order to achieve high coil inductance and quality factor. Furthermore, computer simulations showed the higher coupling factor achieved with respect to that achieved with air-core coils. Experimental tests were carried out using an impedance analyzer and commercial sensors for seat occupancy and belt detection. Detection was feasible at distances up to 2 cm between the primary and secondary coils.