THz imaging, THz time domain spectroscopy, THz-TDS, THz tomography, X-ray imaging, physical inspection, authentication, counterfeit detection

1. University of Connecticut
Comparison of THz Imaging with X-Ray
Kiarash Ahi, Navid Asadizanjani, Sina Shahbazmohamadi, Mark
Tehranipoor and Mehdi Anwar
If you want to use these slides, please reference to our work:
K. Ahi, N. Asadizanjani, S. Shahbazmohamadi, M. Tehranipoor, and M. Anwar,
“Terahertz characterization of electronic components and comparison of terahertz
imaging with X-ray imaging techniques,” in . Proc. SPIE 9483, Terahertz Physics,
Devices, and Systems IX: Advanced Applications in Industry and Defense, 94830X
(May 13, 2015).
https://www.researchgate.net/publication/278034592_Terahertz_characterization_of_ele
ctronic_components_and_comparison_of_terahertz_imaging_with_x-
ray_imaging_techniques

2. Overview
 Background and principles of THz pulse generation and detection for
producing THz images
 Experimental Setup in Transmission mode
 Applications of THz radiation in characterization of objects (refractive
indices, absorption coefficients) in Transmission mode
 Producing THz images in transmission mode: Using Attenuation
Coefficient and Time Delay
 Experimental Setup in reflection mode
 Applications of THz radiation in characterization of objects (seeing
the different layers, that floppy disk, blacktopped ICs) in reflection
mode
 THz images in reflection mode: THz tomography
TransmissionmodeReflectionmode

3. Table of content
Classification of counterfeit electronic components; the green ticks
indicates classes which are distinguishable by THz techniques

4. Background and principles of THz pulse generation
and detection for building THz images
The first THz imaging system was introduced less than twenty
years ago, in 1995 by AT&T Bell Laboratories .
Since pulsed femtosecond THz lasers were not commercially
available until just less than two decades ago, THz imaging and
THz spectroscopy have yet to find their roles in wide variety of
applications.
THz techniques can be used for determining the materials in wide
variety of objects from medicines to electronic components.
THz techniques have several advantages over other inspection
and characterization techniques. THz radiation is non-ionizing
and thus not only safer for human in compare to ionizing
techniques like X-ray or gamma inspections but also
nondestructive for electronic components and other objects.

5. THz imaging techniques
Transmission mode
Reflection mode
Images based on
Attenuation
Images based on Phase
(time) delay
Tomogram Images
(based on Phase (time)
delay)

6. Experimental Setup: Transmission mode
Receiver
Transmitter
15 20 25 30 35 40
-1.7
-1.6
-1.5
-1.4
-1.3
-1.2
-1.1
Time Delay[Picoseconds]
DetectedPukse[a.u.] Detected THz pulse after passing an IC
Detected THz pulse where no objects is palced
Time
delay Attenuation

7. THz imaging techniques in transmission mode vs in
reflection mode
(a) THz image of an IC of Figure 4 (a), The left image is obtained in reflection mode and the
right one in transmission mode. (b) Color scale for TH images and the x-ray image of the IC
(c) X-ray and THz images are superimposed.

8. Application: THz imaging techniques in transmission
mode
(a) THz image of an authentic IC of Figure 4 (a) and its x-ray counterpart. (b) THz image of
a counterfeit IC of Figure 4 (a) and its x-ray counterpart. (c) color scale for the THz images.
Asymmetry
Vertical die
Horizontal die

9. The transmitted THz pulse
The received
THz pulse
X-ray
THz imaging techniques in reflection mode:
Tomography

10. THz imaging techniques in reflection mode:
Tomography
(a) THz image of the surface of an IC of Figure 4 (a) obtained in reflection mode. (b) THz
image of the die of the IC obtained in reflection. (c) THz image of the leads of the IC
obtained in reflection. (d) The color scale.

11. THz imaging techniques in reflection mode:
Tomography
(a) THz image of the surface of an authentic IC of Figure 4 (a) and. (b) Its counterfeit counterpart.
The variance of the reflected THz from the surface of the counterfeit IC: 2.70×10-4 a.u.
The variance of the reflected THz from the surface of the authentic IC: 1.17×10-4 a.u:
less than 45% of that of the counterfeit IC
The difference between the peak and the minimum value of the surface for the authentic IC: 0.061 a.u.
The difference between the peak and the minimum value of the surface for the counterfeit IC: 0.076 a.u.:
25% higher than of the authentic IC

12. Conclusions
THz pulse lasers have not been commercially available until only two
decades ago and thus THz techniques need to be developed for
different aspects of science and engineering.
One of the highly promising fields for THz techniques is characterization
and inspection via imaging of inside the objects.
It was also showed that, a wide variety of counterfeit electronic
components are also distinguishable with THz techniques.
THz techniques are fast, economically reasonable, reliable, accessible
for wide variety of consumers, nonhazardous and nondestructive.
Other techniques are mostly destructive, time consuming, hazardous to
personnel, human dependent and thus expensive and with higher errors
while THz is nondestructive, fast, safe for personnel and accurate.