A polarimetric millimeter-wave radar imaging technique is proposed to remotely detect, localize, and wirelessly read a novel additively manufactured passive sensor composed of a microfluidic channel filled with liquid metal Galinstan. Very high variation of the radar-cross section of the sensor to small variations of the level of Galinstan in the channel is obtained. Indeed, at the radar-to-sensor distance of 2.4 m, the measured radar echo level of the sensor varies by 4.5 dB when the level of Galinstan changes by 1 mm. This sensitivity is higher than those previously reported in the literature for wireless and passive sensors of the same class. Moreover, the localization technique of the sensor is successfully achieved for only three false detections on 75 measurements in cluttered environments from radar-tosensor distances up to 15 m.