**7. References**


using the suggested signal processing, a gearbox was installed in the test rig system. Misalignment was created by twisted case caused by arc-welding to fix the base and bearing inner race fault is generated by severe misalignment. To identify the sensing ability of the AE, vibration signal was acquired through accelerometer and compared to the AE signal. Also, to find the advantage of the proposed signal processing method, it was compared with

According to the experiment result, AE sensor can detect the fault earlier than an accelerometer because of high sensitivity and in the power spectrum, the harmonics of the rotating speed and the gear mesh frequency clearly occurred. Misalignment was observed and bearing faults were also detected in the early fault stage. The proposed envelope analysis is worked to evaluate the faults and indicated the faults frequencies, rotating speed,

For the detection of the crack growth on the shaft, a cracked shaft was installed on the test rig, and the crack was seeded by wire-cutting with 0.5 mm depth. The cracked shaft was lifted 6.5 mm by the lifting tool. The AE signals were transformed by FFT to create the power spectrums, and in the spectrums several peaks were occurred by the crack growth. Along the growth of the crack, the characteristic of the power spectrum was changed and

In the power spectrum, it was shown that the harmonic components of the rotating speed and bearing cage frequency were excited by the crack growth as shown in the Fig. 6, especially on the 3X (28.6Hz) and 31Hz. And the AE signal caused by the crack growth is generated on the whole ultrasonic frequency range; the initial crack could be detected using the PAC-Energy on wavelet level 1 to 4, and after that, it could be presented on wavelet level 5 until the fracture of the shaft. Therefore, in this paper, it could be shown that the crack growth in rotating machinery is able to be considered and to be detected; in addition,

Therefore, the proposed signal processing method that is the envelope analysis intercalated DWT using Daubechies mother function between BPF and wave rectification can be shown

This work has been supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and

Burrus, C.S., Gopinath, R.A. & Guo, H. (1997). *Introduction to wavelet and wavelet transforms:* 

Douglas, H. & Pillay, P. (2005). The impact of wavelet selection on transient motor current

Hatch, C.T. & Bently, D.E. (2002). *Fundamentals of Rotating Machinery Diagnostics*, Bently

signature analysis, *Proceedings of 2005 IEEE International Conference on Electric Machines and Drives*, ISBN 0780389875; 978-078038987-8, San Antonio, TX, May

*A Primer*, Prentice-Hall, ISBN 0134896006, Upper Saddle River, NJ.

Pressurized Bearing Press, ISBN 0-9714081-0-6, Minden, NV.

sideband of BPFI, gear mesh frequency and harmonics, explicitly.

PAE-Energy can be used to detect the early detection of the crack.

Technology (2011-0013652) and the 2nd Phase of Brain Korea 21.

to provide better result than traditional envelope analysis.

traditional envelope analysis.

displayed different frequencies.

**6. Acknowledgment** 

**7. References** 

2005.


**9** 

*Austria* 

**Compensation of Ultrasound Attenuation in** 

*1Christian Doppler Laboratory for Photoacoustic Imaging and Laser Ultrasonics,* 

Photoacoustic imaging is a non-destructive method to obtain information about the distribution of optically absorbing structures inside a semitransparent medium. It is based on thermoelastic generation of ultrasonic waves by the absorption of a short laser pulse inside the sample. From the ultrasonic waves measured outside the object, the interior distribution of absorbed energy is reconstructed. The ultrasonic waves, which transport information from the interior to the surface of the sample, are scattered or absorbed to a certain extent by dissipative processes. The scope of this work is to quantify the information loss which is equal to the entropy production during these dissipative processes and thereby to give a principle limit for the spatial resolution which can be gained in photoacoustic imaging. This theoretical limit is compared to experimental data. In this book chapter stateof-the-art methods for modeling ultrasonic wave propagation in the case of attenuating media are described. From these models strategies for compensating ultrasound attenuation are derived which may be combined with well-known reconstruction algorithms from the

Section 2 gives a short description of photoacoustic imaging, especially photoacoustic tomography, and the available image reconstruction algorithms to reconstruct the interior structure from the detected ultrasound signal at the sample surface. Beside small point-like detectors also large detectors, so called integrating detectors are used for photoacoustic tomography. The latter ones require different image reconstruction algorithms. Spatial resolution is an essential issue for any imaging method. Therefore we describe the

Section 3 is dedicated to acoustic attenuation. The spatial resolution in photoacoustic imaging is limited by the acoustic bandwidth. To resolve small objects shorter wavelengths with higher frequencies are necessary. For such high frequencies, however, the acoustic attenuation increases. This effect is usually ignored in photoacoustic image reconstruction but as small objects or structures generate high frequency components it limits the minimum detectable size, hence the resolution. Several models for acoustic attenuation, especially used for ultrasound propagation in biological tissue, are compared with

**1. Introduction** 

experimental data.

non-attenuating case for photoacoustic imaging.

influencing factors of the resolution in photoacoustic tomography.

P. Burgholzer1,2, H. Roitner1,2, J. Bauer-Marschallinger1,2,

*2Research Center for Non Destructive Testing (RECENDT),* 

*3Institute of Physics, Karl-Franzens-University Graz* 

**Photoacoustic Imaging** 

H. Grün2, T. Berer1,2 and G. Paltauf3

