Figure 1: The experimental configuration for a transmission (Tr) mode measurement, with a TB slice between two US transducers - one as Tr the US signal and the other - for its reception (Rec).
C [m/sec] |
T [µsec] |
X [mm] |
|
1493 |
5.56 |
8.3 |
Slice 1 |
1533 |
9.13 |
14 |
Slice 2 |
Table 1: Thicknesses X of samples No. 1 and 2 and the calculated propagation tine and SOS for each one of them. The difference between the assessed SOS is 2.6%.
Note:
In was found that the sides of slice No.3, where the US transducers are attached,
are not flat* as in slices 1 and 2, causing to difficulties to perform an accurate measurement.
Flat - for producing a good contact with the US transducer, thus no (or negligible) loss while transmitting or receiving the US signal.
Sample Thickness |
Relative Time Delay |
p-p amplitude of the Received Signal |
mm |
μsec |
Volt |
4.5 |
Ref. |
0.08 |
8.3 |
3 |
0.04 |
14 |
6 |
0.025 |
Table 2: Relative Time Delay and p-p amplitude of the Rec signal, as a function of slice thickness, which are related to the attenuation of the
US signal along the path in the TB sample.
Assumption: The Tr signal was the same in all the measured cases. Therefore, the received signal from the 2nd sample was attenuated to about its half (relative to the first sample) where to the 3rd one ‑ almost to its quarter. These results are according to the sample thicknesses.
Frequency |
pulses per burst (ppb) |
No. pf TB samples |
Spectral response analysis |
Attenuation vs. frequency |
Remarks |
5 |
1 |
3 |
-HF SL in noise. |
Slice 4.5 cm: |
Higher attenuation prop, to sample thickness.
|
5 |
3 |
3 |
As above |
Similar to above. |
As above |
5 |
3 |
3 |
As above |
Slice 4.5 cm: |
As above |
Table 3: Summary of the experiments with the 3 samples, at fUS = 5 MHz and for 1, 3 and 6 pulses/burst. Here were measured (i) Signal amplitude vs time; (ii) Attenuation vs. frequency; and there were assessed (iii) Spectra distribution vs. frequency and (iv) SOS.
US Frequency [GHz] |
Pulse per burst |
Amplitude [dB] vs. time [μsec] |
Spectral Response |
4 |
1 |
Received US signal is wider |
LF, Sl att: (-20) to (-30) dB |
4 |
3 |
Received US signal is wider |
LF, SL att.: (-10) to (-20) dB |
4 |
6 |
Received US signal is wider |
LF, SL att.: (-20) to (-40) dB |
5 |
1 |
Distorted signal |
LF, SL att: (-40) |
5 |
3 |
Distorted signal |
LF SL & Ctrl. Freq. att.: (-30 to (-50) dB |
5 |
6 |
Distorted signal |
LF SL: (-20) to (-40) dB |
6 |
1 |
Distorted signal |
LF, SL att.: (-40) |
6 |
3 |
Distorted signal |
LF SL & Ctrl. Freq. att.: (-30) to (-50) dB |
6 |
6 |
Distorted signal |
LF SL att.: (-20) to (-40) dB |
Table 4: Summary of Experiment No.2: Tr and Rec US signals and their analysis (Amplitude vs. time and Spectral response)
Figure 1: The experimental configuration for a transmission (Tr) mode measurement, with a TB slice between two US transducers - one as Tr the US signal and the other - for its reception (Rec).
Figure 2: Block Diagram of the Electronic System.
Figure 3: Transmission of 5 MHz, 1 pulse/burst, in the upper plot. In the lower plot, are presented 3 received signals, referring to the 3 slices with different thicknesses: green - slice 1 (4.5 mm), red - slice 2 (14 mm), blue - slice 3 (8.3 mm).
Note:
* It is expected that the received amplitude from slice No.2 (14mm) would be smaller than from slice No.3 (8.3mm) - presumably caused by a slightly different setups of the measuring system (i.e. the TB surfaces where the US transducers are attached, were not smooth enough, thus causing to a loss of energy). This situation repeats with 3 and 6 pulses/burst.
Figure 4: Attenuation vs. frequency fUS = 5 MHz, and Tr of 1 pulse/burst.
Notes:
(i) At higher frequencies the attenuation is higher. The attenuation, in dB, is
closely linear with frequency, in the range of ~0.2 106 Hz to ~4.5 106 Hz.
(ii) The attenuation of slice no. 2 (blue) of 8.3 mm, is higher than of slice no. 3
(red)of 14 mm, an anomaly already observed and explained in Figure 3.
Figure 5: The upper plot described the Tr signal of 6 pulses/burst at fus = 5MHz. The lower plot describes the Rec signals, as they refer to different attenuations in these slices i.e., Blue - slice 1 (8.3 mm), Red slice 2 (14 mm) and Green - slice 3 (4.5 mm).
Note:The red slice (thickness = 14 mm), does not contain in its ReC signal all the 6 pulses; and the Rec signal is completely distorted
Figure 6: Spectral response of Tr and Rec signals, for fUS = 5 MHz, 6 pulses/burst, for the 3 samples: Blue - slice 1 (8.3 mm), Red - slice 2 (14 mm) and Green - slice 3 (4.5 mm).
Note:
(i) The higher side-lobes (SL) in the Rec spectral response, are highly attenuated,
while the main lobe and the lower frequencies SL are attenuated by ~ 25 dB,
thus, they are observable and are able to provide carried information.
(ii) The Lower SL are attenuated by ~20 dB, on average.
(iii) The main lobe is attenuated by ~25 dB.
Figure 7: The Tr and Rec signals at 5 MHz, 1 pulse/burst. The Rec signal is broader.
Figure 8: Spectral response of Tr and Rec signals, at 5 MHz, 1 pulse/burst.
Note:
Frequencies higher than ~1 MHz are attenuated by 40 to 50 dB; similarly, the main lobe - thus they are submerged in noise and only the LF
SL is attenuated by ~20 dB and is well observed.
Figure 9: The Tr and Rec signals vs. time, at fUS = 5MHz, 6 pulses/burst. The Rec signal is very distorted.
Figure 10: Spectral responses of Tr and Rec signals, at fUS = 6 MHz, 3 pulses/burst.
Note:
(i)The high frequency (HF) SL are attenuated more than 75 dB,
(ii)The central frequency (f = 6 MHz) - by 50 dB and
(iii) The LF SL by ~ 25 dB.
Figure 11: The Tr and Rec signals vs. time, at fUS = 6 MHz, 6 pulses/burst. The Rec signal is very distorted.
Tables at a glance
Figures at a glance