A physiological sensor apparatus for measuring at least one physiological parameter, and for controlling the positioning of a sensing surface against a human tissue receiving surface, comprising: said sensing surface; an electroactive polymer structure adapted to deform in response to an application of an electrical signal, to thereby manipulate a positioning of the sensing surface; and a controller , adapted to: provide an electrical signal composed of superposed actuation signal and AC sensing signal to the electroactive polymer structure , the actuation signal for stimulating a deformation of the electroactive polymer structure to thereby manipulate the sensing surface to apply an actuation force to the receiving surface, and the AC sensing signal for facilitating pressure sensing and having an AC frequency belonging to a harmonic of either a resonance or anti-resonance frequency of the electroactive polymer structure ; monitor an impedance exhibited by the electroactive polymer structure over time, to thereby provide an indication of a returning force exerted on the electroactive polymer structure by the receiving surface over time, and adjust a magnitude of the applied actuation signal in dependence upon the measured impedance and/or the returning force to thereby adjust the positioning of the sensing surface against the receiving surface. said sensing surface; an electroactive polymer structure adapted to deform in response to an application of an electrical signal, to thereby manipulate a positioning of the sensing surface; and a controller , adapted to: provide an electrical signal composed of superposed actuation signal and AC sensing signal to the electroactive polymer structure , the actuation signal for stimulating a deformation of the electroactive polymer structure to thereby manipulate the sensing surface to apply an actuation force to the receiving surface, and the AC sensing signal for facilitating pressure sensing and having an AC frequency belonging to a harmonic of either a resonance or anti-resonance frequency of the electroactive polymer structure ; monitor an impedance exhibited by the electroactive polymer structure over time, to thereby provide an indication of a returning force exerted on the electroactive polymer structure by the receiving surface over time, and adjust a magnitude of the applied actuation signal in dependence upon the measured impedance and/or the returning force to thereby adjust the positioning of the sensing surface against the receiving surface. provide an electrical signal composed of superposed actuation signal and AC sensing signal to the electroactive polymer structure , the actuation signal for stimulating a deformation of the electroactive polymer structure to thereby manipulate the sensing surface to apply an actuation force to the receiving surface, and the AC sensing signal for facilitating pressure sensing and having an AC frequency belonging to a harmonic of either a resonance or anti-resonance frequency of the electroactive polymer structure ; monitor an impedance exhibited by the electroactive polymer structure over time, to thereby provide an indication of a returning force exerted on the electroactive polymer structure by the receiving surface over time, and adjust a magnitude of the applied actuation signal in dependence upon the measured impedance and/or the returning force to thereby adjust the positioning of the sensing surface against the receiving surface. <EOS>