#### Location

La Jolla, CA

#### Start Date

1-1-1998 12:00 AM

#### Description

It is well known that using progressively lower frequencies in eddy current detection permits deeper penetration into conductive samples since the skin depth increases as the inverse square root of the frequency. Since the signal of interest is produced by Faraday’s Law, the amplitude of the signal voltage is proportional to the excitation frequency. This fact limits the use of normal eddy current techniques as frequency decreases. This paper presents a method of detecting the field due to the induced eddy currents rather than its time derivative, so that at least the “return” portion of the signal is not proportional to frequency.

#### Book Title

Review of Progress in Quantitative Nondestructive Evaluation

#### Volume

17A

#### Chapter

Chapter 4: NDE Sensors and Fields

#### Section

Electromagnetic Sensors

#### Pages

1039-1042

#### DOI

10.1007/978-1-4615-5339-7_134

#### Copyright Owner

Springer-Verlag US

#### Copyright Date

January 1998

#### Language

en

#### File Format

application/pdf

Detection of Deep Flaws in Aluminum Structure with Magneto-Resistive Sensors

La Jolla, CA

It is well known that using progressively lower frequencies in eddy current detection permits deeper penetration into conductive samples since the skin depth increases as the inverse square root of the frequency. Since the signal of interest is produced by Faraday’s Law, the amplitude of the signal voltage is proportional to the excitation frequency. This fact limits the use of normal eddy current techniques as frequency decreases. This paper presents a method of detecting the field due to the induced eddy currents rather than its time derivative, so that at least the “return” portion of the signal is not proportional to frequency.