# An Improved Hilbert-Huang Transform for Vibration-Based Damage Detection of Utility Timber Poles
## 5 Results and Discussion
### Improved HHT
#### 5.3.3 Instantaneous Frequency Analysis Using Improved HHT
the Unserviceable Pole 3 (from Figure 19) are found to be bigger than that of the serviceable pole case. Standard deviation values are also relatively high for the Unserviceable Pole 3. Figure 17: Hilbert spectrum of IMF1 for A90C1, Serviceable Pole 1 including all 4 tests. Figure 20 shows the instantaneous frequencies of dominant IMFs for A0R2 sensor, Unserviceable Pole 1 using improved HHT. IMF1, IMF2, and IMF3 are found to be dominant for A0R2 sensor using correlation coefficient method. Another major finding from this figure is that instantaneous amplitude of IMF1 is significantly higher than instantaneous amplitude of IMF1 for the serviceable pole case from Figure 16. This phenomenon is observed for sensors in the radial directions which contains highest energy since the hammer impact was made in the radial direction (horizontal). Similarly, instantaneous amplitude of IMF1 for A0R2 are studied for all three serviceable poles and three unserviceable poles. Figure 21 illustrates the instantaneous amplitude of IMF1 for A0R2 considering all six poles used in this study. From this figure, it is clearly observed that instantaneous amplitudes of three unserviceable poles for A0R2 sensor are significantly higher than that of three serviceable poles. This finding is observed for all six poles and for all four repeats which reassures the accuracy and consistency of the study. Figure 22 shows the instantaneous amplitude of IMF1 for A0R1 considering all six poles. From this figure, it is  
Figure 19: Bar chart showing frequency range of dominant IMFs, average frequency of each IMF and standard deviation for 12 accelerometers, Unserviceable Pole 3. Figure 18: Bar chart showing frequency range of dominant IMFs, average frequency of each IMF and standard deviation for 12 accelerometers, Serviceable Pole 1.  
apparent that A0R1 yield the same conclusion (as for A0R2) on considering instantaneous amplitude as damage sensitive feature. However, A0R1 for Unserviceable Pole 1 does not follow this trend. This is related to an error in capturing data during the field testing. To further elaborate this, Figure 23 shows the time vs. acceleration data and their frequency spectrum from A0R1 of Unserviceable Pole 1. From this figure, it is observed that amplitude of A0R1 is very low compared to A0R2 due to connection problem during field testing. As a result, A0R1 did not capture any data while testing Unserviceable Pole 1. Figure 21: Instantaneous amplitude of IMF1 for A0R2 considering 3 serviceable poles and 3 unserviceable poles. Figure 16.0 Instantaneous frequencies of dominant IMFs for A0R2 Unserviceable Pole 3 using improved HHT. For this study, instantaneous amplitude of 0.02 obtained from IMF1 of A0R1 and A0R2 (from Figures 21 and 22) is considered as the threshold point to differentiate unserviceable poles from serviceable ones. This observation was consistent for all four repeats as well. Therefore, it can be concluded that instantaneous amplitude will increase according to the severity of damage. If instantaneous amplitude of dominant IMFs is noticed to be increased significantly over time during routine inspection, pole condition can be considered to worsen, and adequate steps should be taken in order to avoid pole failure. Such a finding is vital for condition assessment utility timber poles.