A method and a system having a sensor for detecting legs of a person in a monitored zone having protected fields and for releasing a function of a vehicle, having a control and evaluation unit for evaluating the protected fields, wherein the sensor is configured to generate at least two protected fields, wherein a first protected field detects at least a part of a first leg of the person, wherein a second protected field detects at least a part of a second leg of the person, the control and evaluation unit is configured to determine whether at least a part of a first leg of the person was detected in the first protected field and at least a part of a second leg of the person was detected in the second protected field, and to transmit at least a release signal to the vehicle and thus to release the function when at least a part of a first leg of the person was detected in the first protected field and at least a part of a second leg of the person was detected in the second protected field, wherein the sensor is a time of flight sensor wherein at least one light transmitter transmits a light signal and at least one light receiver receives a signal reflected or remitted by the person, and the control and evaluation unit is configured to evaluate the received signal on the basis of the time of flight and to form object determination signals.

A magnetorheological fluid includes: a first metal magnetic particle having an average particle diameter of 5 m or more; a second metal magnetic particle having an average particle diameter of 500 nm or less; and an ionic liquid having a cationic group and an anionic group, in which the cationic group is one or more selected from the group including a quaternary ammonium ion, an imidazolium ion, a pyridinium ion, and a phosphonium ion, and the anionic group is one or more selected from the group including a tetrafluoroborate ion, a hexafluorophosphate ion, a trispentafluoroethyl trifluorophosphate ion, and a bis(trifluoromethanesulfonyl)amide ion.

A magnetorheological fluid includes: a first metal magnetic particle having an average particle diameter of 5 m or more; a second metal magnetic particle having an average particle diameter of 500 nm or less; and an ionic liquid having a cationic group and an anionic group, in which the cationic group is one or more selected from the group including a quaternary ammonium ion, an imidazolium ion, a pyridinium ion, and a phosphonium ion, and the anionic group is one or more selected from the group including a tetrafluoroborate ion, a hexafluorophosphate ion, a trispentafluoroethyl trifluorophosphate ion, and a bis(trifluoromethanesulfonyl)amide ion.