Laws of formation of grating lobes in the acoustic field of electromagnetic-acoustic transducers as a linear array of unidirectional conductors

- Increase in the gap between the inductor and tested object decreases the level of grating lobes and narrows the main lobe.
- Increase in the frequency decreases the angle of appearance of grating lobes and increases their amplitude.
- Decrease in the linear array spacing on a fixed aperture leads to the decrease in the level of grating lobes.
- Decrease in the transducer quality factor (increase in the passband) leads to the decrease in the level of grating lobes.
- The opposite influence of design parameters of the EMAT on the amplitude of grating and side lobes is observed.

Investigation of acoustic fields of transducers is the important stage of development of techniques and means of ultrasonic testing. Appearance of grating lobes in the acoustic field of phased array is possible, thus leading to misinterpretation of testing results. The paper proposes the model of an electromagnetic acoustic (EMA) transducer represented as a linear array of unidirectional conductors with current. The influence of the design features and excitation parameters of this transducer on formation of grating lobes is investigated. It is shown that the amplitude of grating lobes is mainly determined by the gap between the inductor and the testing object, the operating frequency of the transducer, pulse character of excitation and the aperture, number and parameters of unit elements of the inductor. The necessity of searching for a compromise between achieving the required sensitivity and the absence of grating lobes is stated. The obtained results can be applied when developing the design of EMA transducers with optimization of the gap, aperture, number and parameters of the inductor elements to achieve the required directional pattern.