Electro-Magnetic Acoustic Transducer / FOD system (EMAT/FOD)

By combining FOD and magnetic, metal thickness is measured. According to Flemming law, EMAT generates vibration into metal, where FOD sensor detects such vibration frequency. The strongest frequency is corresponding to metal thickness.

　

Metal thickness as d, wavelength of ultrasonic as λ, when the following formula is fulfilled, resonance occurs,

(n : integral)

Then reformulated as below,

Meanwhile, FOD sensor can detect in-plane vibration of metal, thus FOD can detect above resonant frequency and amplitude easily.
EMAT (Electromagnetic Acoustic Transducer) is used as heat-proof ultrasonic exciter by Lorenz force. Where Lorenz force as F, eddy current as J, magnetic force as B, the following formula

By using F, ultrasonic wave is generated into metal, and voltage frequency is swept. At a certain thickness, ultrasonic comes into resonance and obtains the maximum amplitude, which is thickness-correlated.

Item
Material		Carbon steel, Stainless steel etc
	Range	5〜30mm
Spec	Resolution	±0.1mm
	Condition	Atmospheric
	temperature	0-200 degrees Celsius

Technical features

Conventional thickness measurement is 1) Time-based inspection 2) Shutdown inspection at accessible temperature by measuring one point to another 3) employment of much human power and time. By EMAT/FOD system, 1) Continual monitoring of thickness at important fixed points, 2) Permanent sensor probes inside the insulation 3) On-line monitoring even under high temperature operation 4) Cost savings from scaffolding, insulation disassemble and reassemble work

Applicable area

- Piping (elbow also) and pressure vessels