Experimental Demonstration and Circuitry for a Very Compact Coil-Only Pulse Echo EMAT.

Dirk Rueter

doi:10.3390/s17040926

Abstract

This experimental study demonstrates for the first time a solid-state circuitry and design for a simple compact copper coil (without an additional bulky permanent magnet or bulky electromagnet) as a contactless electromagnetic acoustic transducer (EMAT) for pulse echo operation at MHz frequencies. A pulsed ultrasound emission into a metallic test object is electromagnetically excited by an intense MHz burst at up to 500 A through the 0.15 mm filaments of the transducer. Immediately thereafter, a smoother and quasi “DC-like” current of 100 A is applied for about 1 ms and allows an echo detection. The ultrasonic pulse echo operation for a simple, compact, non-contacting copper coil is new. Application scenarios for compact transducer techniques include very narrow and hostile environments, in which, e.g., quickly moving metal parts must be tested with only one, non-contacting ultrasound shot. The small transducer coil can be operated remotely with a cable connection, separate from the much bulkier supply circuitry. Several options for more technical and fundamental progress are discussed.

Highlights

Electromagnetic acoustic transducers (EMATs) are contactless ultrasound transducers for metallic test objects [1]
A conventional EMAT usually consists of a radio frequency (RF) induction coil and a bulkier permanent magnet or electromagnet [2] (Figure 1a)
The ultrasound intensity in the aluminum metal is proportional to the square of the RF Lorentz forces; it is proportional to the square of the present bias field and the induced RF eddy current in the target plane

Summary

Introduction

Electromagnetic acoustic transducers (EMATs) are contactless ultrasound transducers for metallic test objects [1]. The aim and novelty of this practical contribution is to: (a) demonstrate contact-less ultrasound emission and subsequent ultrasound echo detection within a single, simple, compact copper coil without a permanent magnet or a separate electromagnet; and (b) modify the required setup and circuitry in a potentially maintenance-free solid-state design, without the disadvantages of high voltage and spark gaps. This transducer coil should be operational through a cable and remote from much bulkier (and more sensitive, not suitable for a narrow and hostile environment) supply electronics.

The spiralspiral coil coil was made from a

Emission Pulses

Echo Signals on Long and Short Time Scales

MHz is about

MHz used as aistarget

Discussion