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Electromagnetic acoustic transducers (EMATs) are non-contact, ultrasonic transducers that are usually kept within 5 mm from the sample surface to obtain a sufficient signal-to-noise ratio (SNR). One important issue associated with operation on a ferromagnetic plate is that the strong attraction force from the magnet can affect measurements and make scanning difficult. This paper investigates a method to generate fundamental, symmetric Lamb waves on a ferromagnetic plate. A coil-only, low-weight, generation EMAT is designed and investigated, operating at lift-offs of over 5 mm. Another design of an EMAT is investigated using a rectangular magnet with a much higher lift-off than the coil, of up to 19 mm. This results in a much lower force between the EMAT and sample, making scanning the EMAT much easier.
Jianpeng He; Steve Dixon; Samuel Hill; Ke Xu. A New Electromagnetic Acoustic Transducer Design for Generating and Receiving S0 Lamb Waves in Ferromagnetic Steel Plate. Sensors 2017, 17, 1023 .
AMA StyleJianpeng He, Steve Dixon, Samuel Hill, Ke Xu. A New Electromagnetic Acoustic Transducer Design for Generating and Receiving S0 Lamb Waves in Ferromagnetic Steel Plate. Sensors. 2017; 17 (5):1023.
Chicago/Turabian StyleJianpeng He; Steve Dixon; Samuel Hill; Ke Xu. 2017. "A New Electromagnetic Acoustic Transducer Design for Generating and Receiving S0 Lamb Waves in Ferromagnetic Steel Plate." Sensors 17, no. 5: 1023.
Lei Kang; Chao Zhang; Steve Dixon; Hui Zhao; Samuel Hill; Menghan Liu. Enhancement of ultrasonic signal using a new design of Rayleigh-wave electromagnetic acoustic transducer. NDT & E International 2017, 86, 36 -43.
AMA StyleLei Kang, Chao Zhang, Steve Dixon, Hui Zhao, Samuel Hill, Menghan Liu. Enhancement of ultrasonic signal using a new design of Rayleigh-wave electromagnetic acoustic transducer. NDT & E International. 2017; 86 ():36-43.
Chicago/Turabian StyleLei Kang; Chao Zhang; Steve Dixon; Hui Zhao; Samuel Hill; Menghan Liu. 2017. "Enhancement of ultrasonic signal using a new design of Rayleigh-wave electromagnetic acoustic transducer." NDT & E International 86, no. : 36-43.
Guided wavesinspection is a well-established method for the long-range ultrasonicinspection of pipes. Guided waves, used in a pulse-echo arrangement, can inspect a large range of the pipe from a single point as the pipe structure carries the waves over a large distance due to the relatively low attenuation of the wave modes. However, the complexity of the dispersion characteristics of these pipe guided wave modes are well known, and can lead to diffculty interpreting the obtained results. The torsional family of guided wave modes are generally considered to have much simpler dispersion characteristics; especially the fundamental T(0,1) mode, which is nominally non-dispersive, making it particularly useful for guided waveinspection. Torsional waves have been generated by a circumferential ring of transducers to approximate an axi-symmetric load to excite this T(0, 1) mode. Presented here is a new design of Electromagnetic Acoustic Transducer (EMAT) that can generate a T(0, 1) as a single transducer, rather than a circumferential array of transducers that all need to be excited in order to generate an axisymmetric force. The EMAT consists of a periodic permanent magnet array and a single meander coil, meaning that the excitation of the torsional mode is greatly simplified. The design parameters of this new EMAT are explored, and the ability to detect notch defects on a pipe is demonstrated.
Samuel Hill; Steve Dixon; Sri Harsha Reddy K.; Prabhu Rajagopal; Krishnan Balasubramaniam. A new electromagnetic acoustic transducer design for generating torsional guided wave modes for pipe inspections. AIP Conference Proceedings 2017, 1 .
AMA StyleSamuel Hill, Steve Dixon, Sri Harsha Reddy K., Prabhu Rajagopal, Krishnan Balasubramaniam. A new electromagnetic acoustic transducer design for generating torsional guided wave modes for pipe inspections. AIP Conference Proceedings. 2017; ():1.
Chicago/Turabian StyleSamuel Hill; Steve Dixon; Sri Harsha Reddy K.; Prabhu Rajagopal; Krishnan Balasubramaniam. 2017. "A new electromagnetic acoustic transducer design for generating torsional guided wave modes for pipe inspections." AIP Conference Proceedings , no. : 1.
The use of phased array methods are commonplace in ultrasonic applications, where controlling the variation of the phase between the narrowband emitters in an array facilitates beam steering and focusing of ultrasonic waves. An approach is presented here whereby emitters of alternating polarity arranged in a one-dimensional array are pulsed simultaneously, and have sufficiently wide, controlled bandwidth to emit a two-dimensional wave. This pulsed approach provides a rapid means of simultaneously covering a region of space with a wave-front, whereby any wave that scatters or reflects off a body to a detector will have a distinct arrival time and frequency. This is a general wave phenomenon with a potential application in radar, sonar, and ultrasound. The key result is that one can obtain a smooth, continuous wave-front emitted from the array, over a large solid angle, whose frequency varies as a function of angle to the array. Analytic and finite element models created to describe this phenomenon have been validated with experimental results using ultrasonic waves in metal samples.
Steve Dixon; Samuel Hill; Yichao Fan; George Rowlands. The wave-field from an array of periodic emitters driven simultaneously by a broadband pulse. The Journal of the Acoustical Society of America 2013, 133, 3692 -3699.
AMA StyleSteve Dixon, Samuel Hill, Yichao Fan, George Rowlands. The wave-field from an array of periodic emitters driven simultaneously by a broadband pulse. The Journal of the Acoustical Society of America. 2013; 133 (6):3692-3699.
Chicago/Turabian StyleSteve Dixon; Samuel Hill; Yichao Fan; George Rowlands. 2013. "The wave-field from an array of periodic emitters driven simultaneously by a broadband pulse." The Journal of the Acoustical Society of America 133, no. 6: 3692-3699.