Wireless magnetic field sensor employing SAW-transponder

A new wireless interrogable sensor for magnetic field, establishes an alliance of giant magneto-impedance (GMI) sensor and a surface acoustic wave (SAW) transponder device. The basic elements of these sensor units are SAW delay lines connected to an antenna. The second port is operated as a tunable reflector for the SAW. Its acoustic reflectivity depends on the electrical termination. If a serial resonant circuit with the GMI device is used here, the change of the impedance of the GMI due to a magnetic field, yields a sufficient effect for a radio request readout. The sensor unit is passive, it contains no power supply, no semiconductors etc. Thus, they are capable of implementation in a very rough environment, where dust, heat (up to many hundreds of centigrade), electromagnetic interference and mechanical load would cause damage to other types of sensors.