Flow sensor transducer with dual spiral wheatstone bridge elements

A flow sensor transducer can measure fluid flow rates as a fluid flows though a channel and under an air bridge. Resistive thermal devices (RTDs) and a heater are on top of the air bridge with two RTDs upstream of the heater and two downstream. The RTDs can be connected in a Wheatstone bridge configuration. A magnetoresistive material that changes its electrical resistance based on its temperature can be used to form the RTDs. The temperature response of magnetoresistive materials, however, can change due to magnetic fields and to the material's magnetic history. Forming the RTDs into a dual spiral structure minimizes the effect of magnetic fields. As such, a magnetoresistive material such as permalloy can be used instead of an expensive material such a platinum. The resulting flow sensor transducer can be formed using standard semiconductor processing techniques and is less expensive than sensors containing platinum.