TeTechS Blog-Hidden Object Detection with Terahertz Sensors

Hidden Object Detection with Terahertz Sensors

Posted by Daniel Hailu on Monday, 29 September 2014 in Terahertz

http://www.tetechs.com/blog/latest

After the Columbia disaster in 2003, NASA grounded the space shuttles for more than a year as it worked on new safety protocols to ensure that such a tragedy would not happen again. As part of the preparations for the Return to Flight mission, the Agency required a method for detecting potentially hazardous defects in the external tank’s sprayed-on insulating foam prior to launch. The solution NASA Langley Research Center scientists suspected was a new imaging technology called terahertz imaging that had the potential to accurately find flaws in the foam on the external tank. Terahertz wavelengths can be used to see through many materials and reveal defects like cracks, voids, and density variations. They can be used to image or as an anomaly detector, or both at the same time. Hidden object or defects inside opaque structures can be seen using Terahertz waves. For example a hidden glue gel inside a plastic enclosure is observed to change through absorption the Terahertz wave generated and detected by Terahertz sensors. As seen in this video, the hidden gel that is behind an opaque barrier and can not be seen by a visible nor IR camera becomes visible in the Terahertz frequency range.

There has been intense interest in the use of millimetre wave and terahertz technology for the detection of concealed weapons, hidden metallic as well as non-metallic objects, explosives and other threats. Radiation at these frequencies is safe, penetrates barriers and has short enough wavelengths to allow discrimination between objects. In addition, many solids including explosives have characteristic spectroscopic signatures at terahertz wavelengths which can be used to identify them.

In many cases, real-time or video rate images with sub-millimeter resolution are required to see small defects or hidden objects. Strong Terahertz sources are required for these imaging applications, which are currently expensive and bulky. While low-cost and room temprature detectors are required for imaging and sensing. These challenges have to be overcome in order for Terahertz technology to be widely adapted by industry.   

TeTechS blog -Terahertz Imaging and Spectroscopy for Food Inspection

http://www.tetechs.com/blog/index.php/categories/listings/terahertz

Terahertz Imaging and Spectroscopy for Food Inspection

Posted by Daniel Hailu on Tuesday, 18 February 2014 in Terahertz

TeRecent advances in Terahertz (THz) technology have enabled various applications in food inspection and quality control of powders and food.  THz technologies do have some limitations in food inspection application, one of which is that THz is strongly absorbed by water. While this actually offers an advantage when using THz for quality control of powders, this makes the transillumination of some food products with water content such as meat impossible. The second limitation is imposed by metal layers in food packages: as soon as the thickness of such a metal layer is more than a few microns, THz waves cannot pass the barrier.

Despite these limitations there are still many scenarios in which food products can benefit from a THz inspection system.  One example is using THz imaging to reveal potentially hazardous inclusions in chocolate bars.  While metallic contaminations are easily detected by conventional quality control systems using X-ray, dielectric contaminations are often hard to find due to similar densities or lack of contrast.  When the physical contrast between the material and the contamination is slight existing approaches such as ultrasonic or X-ray scans may fail, so that certain types of inclusions, e.g. plastic and wood splinters, etc. remain undetected.  However, such contaminations can still present serious health risks for consumers.

In contrast to X-ray systems, THz scans do not only consider the amplitude but also phase information. Due to the fact that the dielectric contrast mechanisms are much more pronounced at THz frequencies, hidden inclusions can be reliably revealed in THz images.  In the figure an image is shown of a chocolate bar contaminated with a buried glass splinter, a stone and a piece of metal, is depicted. It can be seen that the contaminants can be clearly detected.  

Another promising application of THz technology lies in the area of quality control of packaged goods.  Terahertz radiation can be used to detect production faults in flexible plastic packages.  Relying on the large difference between the absorption coefficients of plastic and water (for water-filled channel defects) and on the refraction index difference between plastic and air (for air-filled channel defects), the technique consists of focusing and scanning a terahertz beam on the sealed area of the package, followed by detection of the transmitted signal.

Compared with traditional methods, such as visual and ultrasound inspection, this technique can be applied to optically opaque packages and does not require immersion in a matching liquid. The detection limit (the minimum size of a detectable defect) depends on the conveying speed. The results show that THz system has the potential for application in an actual production line for real-time inspection. In the near future, THz system may be used for real-time inspection in actual production line.

TeTechS blog-Terahertz Technology for Microelectronic Package Fault Isolation and Failure analysis

Terahertz Technology for Microelectronic Package Fault Isolation and Failure analysis

Posted by Daniel Hailu on Friday, 13 December 2013 in Terahertz

http://www.tetechs.com/blog/index.php/entry/terahertz-technology-for-microelectronic-package-fault-isolation-and-failure-analysis

Electro-optical terahertz pulse reflectometry (EOTPR), an electro-optical system driven by an ultrafast laser source, was introduced recently to isolate faults and detect defects in advanced IC packages.  The steadily growing complexity of integrated-circuit (IC) technology is pushing the available inspection and fault-analysis tools to their limits.  Among the nondestructive methods, time-domain reflectometry (TDR) is considered to be an exceptionally fast method for fault detection in electronic packages.  The EOTPR system provides 10 μm in distance accuracy that can be used to localize package-level open and short failures non-destructively.  Today’s TDR systems are generally all-electronic and use a step or pulse generator and a high-bandwidth oscilloscope as the main components.  The electromagnetic signal is transmitted through a high-frequency cable and a probe tip to the device under test (DUT).  Every discontinuity at the transmission path within the DUT causes a part of the injected signal to be reflected.  By monitoring these reflections in the time domain, it is possible to detect structural defects and distinguish functional from defective structures.  Terahertz technology enables high resolution fault isolation in advanced semiconductor packages and 3D imaging in integrated circuit devices.  An EOTPR system was used to determine the location of open and short failures and to identify impedance variations in a series of package substrates.  The experimental results demonstrate the higher accuracy of the EOTPR system in determining the distance to defect compared to traditional time-domain reflectometry systems.  

(Source TeraView:  Using Terahertz pulses for fault analysis)

A first femtosecond-laser-driven optoelectronic TDR system for fault isolation was recently introduced by Intel (Santa Clara, CA).  With this system, a substantial improvement over all-electronic systems was achieved with τrise = 5.7 ps. However, a main bottleneck within this system, which prevents utilizing the full benefits of optoelectronic sub-picosecond-range switching speeds is brought about due to the waveguide and probe components that are required for signal transmission between the optoelectronic pulse-generation and detection devices and the DUT.  Frequencies above 110 GHz are not transmitted by these components, and hence the majority of resolution power is lost within the TDR system.  Nagel et al., Opt. Expr., 19, 12509–12514 (2011) and using Terahertz reflectometry imaging to find faults in silicon chips have recently demonstrated this bottleneck can now be effectively eliminated by novel micromachined probe tips applied for broadband photoconductive (PC) pulse generation and detection immediately at the DUT.  A TDR signal rise time of τrise = 1.1 ps has been achieved by this advanced optoelectronic system.  In contrast to earlier configurations, the probes can also be used in a contact-free mode through capacitive probe/waveguide coupling.

TeTechS starts terahertz blog

My Note: I found, yet another THz blog, this one on the TeTechS webpage, and I am sharing one of the posts below. 
http://www.tetechs.com/blog/

Terahertz Imaging is viable alternative to X-ray for Dental Imaging

Posted by Daniel Hailu on Thursday, 08 August 2013 in Terahertz

The terahertz (THz) region of the electromagnetic (EM) spectrum has several advantages for skin cancer detection, dental imaging, and pharmaceutical applications. Continuous wave (CW) and pulsed THz transmission-mode and reflection-mode imaging with nonionizing and noninvasive properties for tooth imaging are considered an alternative modality to X-ray imaging. Dental imaging application of THz imaging exploits the change in the refractive index between dental caries and enamel and/or dentine tissues. Dental caries or tooth decay is the most common human disease, and there is currently no sensitive or accurate means for detecting it using X-rays in its early stages, when tissue damage can be minimized or even reversed. The shortfalls of existing clinical tools are compounded by the fact that some dentists do not regularly assess patients for caries with X-rays owing to fears associated with exposure to ionizing radiation. One needs to go the dentist every six month to reduce exposure to ionizing radiation.These fears are even more serious when it comes to children.

Terahertz rays use for tooth imaging have been in the news for more than a decade. Terahertz rays are viable option for in vivo imaging of dental carries.Interest in biomedical applications has been increasing since the first introduction of THz pulsed imaging (TPI) in 1995 by Hu and Nuss. Their THz images of porcine tissue demonstrated a contrast between muscle and fats. This initial study promoted later research on the application of THz imaging to other biological samples. THz pulsed imaging actually can be viewed as an extension of the THz-Time domain spectroscopy (TDS) method. T-rays have longer wavelength than X-rays resulting in less scattering when passing through tooth samples.Terahertz imaging offers a non-invasive non-ionising alternative to x-rays and additionally provides higher contrast in clinical diagnosis.

THz imaging involves in vivo imaging of the tooth to examine surface features and employs reflection geometry THz probe used for THz reflection from the outer layer of enamel. Terahertz Pulsed Imaging system is one such system that distinguishs between the different types of tissue in a human tooth; detect caries at an early stage in the enamel layers of human teeth and monitor early erosion of the enamel at the surface of the tooth . Caries are a result of mineral loss from enamel, and this causes a change in refractive index within the enamel. The change in refractive index means that small lesions, smaller than those detected by the naked eye, can be detected. However, in practice THz imaging systems are large and cumbersome - even structures as obvious as teeth can make a challenging target. In this respect THz imaging is still some way off offering a non-ionizing alternative to X-rays in dentistry.But the design of compact THz sources and detectors such as photoconductive antennas at 800 nm and 1550 nm, which can come close to tooth, along with the advantage of THz imaging to detect early onset of decay and enamel erosion, material characterization and use of improved THz TDS 3D imaging techniques based on radar techniques make it possible for a viable tool for dentists.