Patent ID: 7609054

Claim:
A method for detecting magnetic particles entrained in a fluid provided in a channel gap formed in a channel base material supported on at least a portion of a substrate at a sensor location where a magnetic field sensor is also supported on at least a portion of said substrate but without said channel base material being across said magnetic field sensor from said substrate so as to form sides of an extended opening therein at said sensor location that extends past said magnetic field sensor in at least one direction to thereby form an extended said channel gap in said channel base material across from at least a portion of said sensor location, there being a first electrical conductor supported on said substrate positioned at least in part at said sensor location so as to be in direct contact with at least some surface of said magnetic field sensor and a second electrical conductor supported on said substrate positioned at least in part along, and between projections of said sides of, said channel gap in a region thereof adjacent to, but separated from, said magnetic field sensor, said method comprising: introducing said fluid with said magnetic particles entrained therein into said channel gap so as to be present at said sensor location; supplying a selected first electrical current in said first electrical conductor and said magnetic field sensor while monitoring that voltage occurring across said magnetic field sensor; supplying a selected second electrical current in said second electrical conductor; and supplying a magnetic field from a source other than said magnetic particles in a selected direction such that said magnetic field is present in said channel gap.