Patent ID: 7392704

Claim:
An acceleration sensor comprising: a housing member; a spring member attached to said housing member, said spring member having freedom in at least one direction of acceleration to be detected; a magnetic field generation member with weight fixed to said spring member; and at least one magnetic field detection sensor attached to said housing member to face said magnetic field generation member with weight, each magnetic field detection sensor being provided with at least one pair of multi-layered magnetoresistive effect elements each including a magnetization fixed layer and a magnetization free layer, a magnetized direction of said magnetization fixed layers being fixed to a direction parallel to the direction of acceleration to be detected, said magnetic field generation member with weight including at least one permanent magnet that provides a closed magnetic loop, said at least one pair of multi-layered magnetoresistive effect elements being arranged in the closed magnetic loop to receive magnetic field substantially perpendicular to a lamination plane of the multi-layered magnetoresistive effect elements when no acceleration is applied, wherein said at least one permanent magnet that provides a closed magnetic loop comprises a pair of permanent magnets arranged in parallel to each other so that their surfaces facing the respective magnetic field detection sensors have different magnetic polarities with each other.