Patent Application
20240146278
The present invention relates generally to the field of non-destructive testing and in particular to Electromagnetic Acoustic Transducers (EMAT).
An EMAT uses an RF (radio frequency) coil of wire energized with AC voltage and a static magnetic field to generate an ultrasonic vibration in an adjacent metallic component. This RF coil of wire acts as an inductor that stores energy in magnetic form that generates an opposing magnetic field in the metallic component. When the generated electromagnetic field on the component interacts with the static magnetic field, the vectorial resultant is a mechanical force in the material of the metallic component in the form of an ultrasonic wave.
In order to build an effective EMAT, the designer needs to take into account the geometry of the RF coil to be able to generate a wave with the desired wavelength, dimensions and shape as well as the characteristics of the EMAT electrical circuit to optimize the amount of energy induced into the part.
One of the challenges in EMAT design is that in addition to the RF coil and the coil cable the component's material composition and structure and its distance to the RF coil—commonly referred as material lift-off—also affect the inductance of the RF coil and as such are part of the EMAT electrical circuit. To compensate for different RF coils, cables, material, and lift-off EMAT circuits are typically joined with transformers and/or capacitors in order to match the impedance of the load (coil) with the source (pulser instrument) which maximizes power transfer and minimizes reflections within the circuit.
Most EMAT systems are often designed for a specific application with fixed impedance matching and will require physically changing circuits to adapt to any change in the EMAT electrical circuit. If physically changing matching components is not possible, the matching is normally a compromise that can work with different EMAT electrical circuits.
This invention relates to a system that can automatically measure the impedance of any EMAT electrical circuit and select the appropriate matching by combining components from a selection of built-in tuning options designed specifically for EMAT coils.
In one aspect of the present invention, a Vector Network Analyzer (VNA) or similar device is used to find the impedance of an EMAT electrical circuit which includes the coil cable, RF coil, material, and lift-off from the material to the coil. The VNA circuit can be connected to the system and send the measured impedance to a processor that will automatically select the appropriate combination of transformer and capacitor values from a second circuit so as to provide the appropriate matching combination.
The matching circuitry includes a multi-tap transformer and selectable capacitors of sufficient values to satisfy the required impedance matching conditions. A set of switches controlled by the processor will select the appropriate transformer taps and capacitor values to properly match the EMAT circuit to the desired impedance.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
The present invention relates to an automatic impedance measurement and impedance matching system to be used with Electromagnetic Acoustic Transducers (EMAT).
An EMAT uses a coil of wire energized with AC voltage and a static magnetic field to generate an ultrasonic vibrations in an adjacent metallic component. The coil of wire acts as an inductor that stores energy in magnetic form that generates an opposing magnetic field in a metallic component. When the field on the part interacts with the static magnetic field, the vectorial resultant is a mechanical force in the material in the form of an ultrasonic wave.
Since the ultrasound is electromagnetically induced into the material, the complete EMAT electrical circuit to be matched with the pulser/receiver includes the RF coil (sensor) cable, the RF coil, and the material being inspected. The distance from the material to the coil (material lift-off) is also relevant since it will affect the amount of energy that is electromagnetically coupled into the part and thus the inductance of the coil itself.
This disclosure refers to a system comprising an electronic circuit that measures the impedance of the EMAT electrical circuit, another electronic circuit with capacitors and inductors that can be combined as needed to match the impedance read by the measuring circuit, and a processor that controls and manages the complete process.
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
