Magnetostrictive EMAT for in-motion inspection of railroad wheels
This disclosure relates to the inspection of train wheels while mounted on a train that is moving on a railroad track. A magnetostrictive EMAT transducer is built using an RF Coil, a static biasing magnetic field, and a strip of highly magnetostrictive material. This magnetostrictive EMAT transducer is subsequently attached to a rail on the track so the wheel tread of the moving train can contact and apply downward pressure on the magnetostrictive EMAT transducer. A mechanism under the transducer provides enough counterforce to pressure-couple the transducer with the tread of the wheel. Once the transducer is ultrasonically coupled with the wheel, an ultrasonic instrument sends a pulse to the transducer generating a Shear Horizontal wave that travels circumferentially following the tread body. The Shear Horizontal wave generated with this magnetostrictive strip EMAT transducer penetrates deep into the wheel tread and permits detection of both surface and internal defects.
1. A system for detecting surface and internal defects on the tread of a rail wheel riding on a railroad track comprising:
a magnetostrictive EMAT transducer that generates Shear Horizontal waves by means of a magnetostrictive strip;
an attachment that connects the magnetostrictive EMAT transducer to a railroad track so the tread of the wheel of a moving train makes contact and applies downward pressure on the magnetostrictive strip so as to momentarily pressure couple the strip to the wheel of the train as it rolls on the track using at least one spring;
an ultrasonic instrument connected to the magnetostrictive EMAT transducer to pulse it and receive and record the ultrasonic signals.
2. The system of claim 1 , wherein the magnetostrictive EMAT transducer comprises the following elements:
a strip section of magnetostrictive material positioned on the surface of the transducer that contacts the wheel;
at least one RF Coil that generates eddy currents on the strip section of magnetostrictive material;
a static biasing magnetic field which in combination with the eddy currents generated by the RF Coil induces ultrasonic Shear Horizontal waves on the strip section of magnetostrictive material.
3. The system of claim 1 , wherein the magnetostrictive EMAT transducer is mounted on an actuator that can be adjusted to provide the desired amount of counter pressure to mechanically couple the ultrasonic energy from the transducer to the wheel.
4. The system of claim 2 , wherein the strip section of magnetostrictive material is made out of Nickel, Cobalt, alloys of FeCo, alloys of FeNi, alloys of FeAl, alloys of FeGa, Terfenol-D, or another material that exhibits high magnetostriction.
5. The system of claim 2 , wherein a thin layer of malleable material is adhered on top of the strip section of magnetostrictive material to enhance coupling with the wheel tread.
6. The system of claim 2 , wherein the static biasing magnetic field is generated with one or more permanent magnets.
7. The system of claim 2 , wherein the static biasing magnetic field is generated with one or more electromagnets.
8. The system of claim 2 , wherein the strip section of magnetostrictive material has been permanently magnetized and does not require a permanent magnet or electromagnet to create the static biasing magnetic field.
9. The system of claim 2 , wherein the RF coil used for transmitting the Shear Horizontal waves is the same as the one receiving the Shear Horizontal waves in a pulse-echo configuration.
10. The system of claim 2 , wherein the RF coil used for transmitting the Shear Horizontal waves is separate from the one receiving the Shear Horizontal waves in a pitch-catch configuration.