Mixed sensor

The invention provides a mixed sensor. The mixed sensor is composed of a superconducting ring and a superconducting gradient coil. The superconducting ring is a square loop (7) with a retracting part (8); the superconducting ring is composed of the square loop (7) and the retracting part (8); the retracting part (8) is located at one edge of the square loop (7); the retracting part (8) and other three edges of the square loop (7) are located on the same plane; and one edge of the square loop with the retracting part is connected with the other three edges to form the superconducting ring. The superconducting ring is vertically arranged in a magnetic field to be detected; and the superconducting gradient coil is parallel to the retracting part of the superconducting ring and is distributed at one side of the retracting part of the superconducting ring. The superconducting gradient coil is composed of a receiving coil and a compensation coil which are located on the same plane. Each turn of coil of the receiving coil and the compensation coil is wound in the same direction; winding directions of the receiving coil and the compensation coil are opposite; the receiving coil and the compensation coil have the equal diameter and equal number of turns; and the receiving coil and the compensation coil are connected through double stranded wires.