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  7. Fujitsu Develops Terahertz-Band Imaging Method Speeding Up Material Inspections 25-Fold

September 12, 2011
Fujitsu Laboratories Ltd.

Fujitsu Develops Terahertz-Band Imaging Method Speeding Up Material Inspections 25-Fold

Makes interiors of objects visible; safer than X-rays, can be applied to a wider range of materials

Kawasaki, Japan, September 12, 2011 — Fujitsu Laboratories Limited today announced that it has developed a technology that will speed inspections that use terahertz-band imaging by a factor of 25. Terahertz waves, which can penetrate non-metallic materials such as paper, plastic, and textiles for nondestructive inspections, hold the promise of showing an accurate picture of a subject, revealing hidden materials through non-destructive inspections, and making an object's interior visible. Existing terahertz-wave inspection methods have only been able to measure a part of a substance per exposure. Obtaining a complete picture of a target object has required incrementally shifting the target between repeated exposures, resulting in a time-consuming process.

Fujitsu Laboratories has developed a new optical element that obviates the need for moving the target, measuring 30 millimeters both horizontally and vertically, by reducing its inspection time from 34 minutes to 1 minute and 21 seconds - speeding up the process by a factor of 25. As a result, this new technology has potential applications in airport security, inspecting narcotics in envelopes, and inspecting electronic devices.

Background

Terahertz waves have a wavelength of approximately 0.3 mm, lying on the spectrum of electromagnetic radiation between light waves and radio waves, and can penetrate non-metallic substances such as paper, plastic, and textiles. Similar to how objects look different under X-rays and visible light, the use of terahertz waves reveals objects in a different way. A specific item can be identified by its characteristic spectrum (a "fingerprint spectrum") under terahertz waves. As well, compared to X-rays, terahertz waves are deemed safe for people. On the other hand, as terahertz-wave imaging has far been a time-consuming process, it has had a limited range of applications. However by taking advantage of the ability to make visible what had been invisible, the use of terahertz waves holds promise in applications that make the inside of objects visible. This includes customs inspections without the need to open luggage or packages, inspections of the contents of envelopes, inspections of adulterants in foodstuffs, and quality inspections of electronic devices.

Figure 1. Relationship between electromagnetic wavelengths and frequencies

Larger View

Figure 2. Comparison of bands used in imaging

Figure 3. Spectrographic image obtained using terahertz-band imaging

Larger View

Technological Issues

The problem with terahertz-band imaging has been the time required to scan the contents of carry-on luggage, for example.

Terahertz waves are not visible to the eye and cannot be photographed. As shown in Figure 4, an electro-optical crystal(1) makes it possible for variations in the strength of a terahertz wave to be photographed indirectly, by modulating them to changes in the light intensity of a probe light. It has been proposed that inspection methods using these crystals could be accelerated by exposing the target object to terahertz waves at the same time that it is exposed to an angled probe light. By taking advantage of the time difference between the penetrating terahertz wave and the probe light, the time waveform of the penetrated target material could be instantly obtained.

However as this process can only receive information on one direction of the substance from one exposure, it is not possible to measure the complete substance in one exposure. To obtain a complete picture requires incrementally shifting the substance between repeated measurements.

Figure 4. Existing measurement technique

About the New-Developed Technology

To measure the object without moving it, Fujitsu Laboratories developed an improvement to the technique using a terahertz wave and angled probe light beam in which a newly-developed graduated mirror array with multiple levels is placed in the light beam. As this technique produces results equivalent to those obtained when taking multiple exposures with incremental movements between each, it becomes possible to perform an inspection with just one exposure.

Figure 5. Newly developed measurement technique

Results

Fujitsu Laboratories researched terahertz-band imaging using this graduated mirror array and found that measurement times were 25 times faster, reducing the time frame from the previous 34 minutes to 1 minute and 21 seconds, for targets measuring 30 millimeters horizontally and vertically. This new technology has the promise to accelerate airport-security inspections, inspections for narcotics in envelopes, and electronic-device inspections.

Future Plans

Fujitsu Laboratories is continuing to work on even faster methods, with an eye towards commercialization around 2014, and is proceeding with development for applications in manufacturing inspections.


Glossary and Notes

Electro-optical crystal:
A crystal whose optical refractivity varies with the intensity of terahertz waves incident upon it. The crystal modulates a probe light beam shone upon it, effectively modulating the terahertz waves into changes in intensity in the probe light beam, which can be recorded by a camera.

About Fujitsu Laboratories

Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited, Fujitsu Laboratories Limited is one of the premier research centers in the world. With a global network of laboratories in Japan, China, the United States and Europe, the organization conducts a wide range of basic and applied research in the areas of Next-generation Services, Computer Servers, Networks, Electronic Devices and Advanced Materials. For more information, please see: http://jp.fujitsu.com/labs/en/.

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