Terahertz and millimeter waves penetrate various dielectric materials, including plastics, ceramics, crystals, and concrete, allowing terahertz transmission and reflection images to be considered as a new imaging tool complementary to X-Ray or Infrared. Terahertz imaging is a well-established technique in various laboratory and industrial applications. However, these images are often two-dimensional. Three-dimensional, transmission-mode imaging is limited to thin samples, due to the absorption of the sample accumulated in the propagation direction. A tomographic imaging procedure can be used to acquire and to render three-dimensional images in the terahertz frequency range, as in the optical, infrared or X-ray regions of the electromagnetic spectrum. In this paper, after a brief introduction to two dimensional millimeter waves and terahertz imaging we establish the principles of tomography for Terahertz Computed tomography (CT), tomosynthesis (TS), synthetic aperture radar (SAR) and time-of-flight (TOF) terahertz tomography. For each technique, we present advantages, drawbacks and limitations for imaging the internal structure of an object.

https://hal.archives-ouvertes.fr/hal-00968839/document

Review of Terahertz Tomography Techniques

The present disclosure provides three-dimensional (3D) printing methods, apparatuses, and systems using, inter alia, a controller that regulates formation of at least one 3D object (e.g., in real time during the 3D printing); and a non-transitory computer-readable medium facilitating the same. For example, a controller that regulates a deformation of at least a portion of the 3D object. The control may be in situ control. The control may be real-time control during the 3D printing process. For example, the control may be during a physical-attribute pulse. The present disclosure provides various methods, apparatuses, systems and software for estimating the fundamental length scale of a melt pool, and for various tools that increase the accuracy of the 3D printing.

Accurate three-dimensional printing

The present disclosure provides three-dimensional (3D) printing methods, apparatuses, systems and/or software to form one or more three-dimensional objects, some of which may be complex. The three-dimensional objects may be formed by three-dimensional printing using one or more methodologies. In some embodiments, the three-dimensional object may comprise an overhang portion, such as a cavity ceiling, with diminished deformation and/or auxiliary support structures.

Three-dimensional printing of three-dimensional objects

Three-dimensional (3D) terahertz (THz) imaging or THz tomography has recently proven to be useful for nondestructive testing of industrial materials and structures In place of previous imaging techniques such as THz pulsed/continuous-wave radar and THz computed tomography, we propose a THz optical coherence tomography using photonics- and electronics-based THz sources, and demonstrate thickness measurement and tomographic imaging in frequency regions from 400 to 800 GHz

Terahertz imaging based on optical coherence tomography [Invited]

Terahertz imaging is being applied to non-destructive inspection and chemical analysis. The main advantage of this approach is that electromagnetic waves at terahertz frequencies can penetrate non-conductive materials and also provide the material’s spectral response. The application of terahertz imaging is rapidly spreading to fields such as the evaluation of industrial materials and pharmaceutical products, examination of works of art, investigation of cultural assets, quality control in manufacturing processes, diagnosis of buildings, detection of dangerous objects, biomedical diagnostics and more. This paper describes imaging methods which use terahertz pulses and terahertz camera technology. In addition, interesting applications are introduced from the view point of practical use.

Terahertz Imaging: Widespread Industrial Application in Non-destructive Inspection and Chemical Analysis

We have developed the “3D Imaging Analysis System” that uses terahertz waves, the world's first such system for practical applications. This system has an unprecedented capability for nondestructive three-dimensional spectroscopic analysis of the spatial distribution of constituents.

3D Imaging and analysis system using terahertz waves

We have developed a three-dimensional spectroscopic imaging system that uses terahertz waves and is based on transmission computed tomography. Using this system, we demonstrate transmission three-dimensional computed tomography imaging of high refractive index objects, with identification of chemical components, by analyzing spectroscopic information.

3D Spectroscopic computed tomography imaging using terahertz waves

An electromagnetic wave measurement device includes an electromagnetic wave outputter that outputs an electromagnetic wave having a frequency equal to or more than 001 THz and equal to or less than 100 THz toward a device under test An electromagnetic wave detector detects the electromagnetic wave which has transmitted through the device under test A relative position changer changes a relative position of an intersection of an optical path of the electromagnetic wave transmitting through the device under test and the device under test, with respect to the device under test, so that the intersection is at a predetermined relative position due to the refraction of the electromagnetic wave by the device under test A characteristic value deriver derives a characteristic value of the electromagnetic wave based on a detection result of the electromagnetic wave detector, the characteristic value being associated with the predetermined relative position

Electromagnetic wave measuring apparatus, measuring method, program and recording medium

Novel Nondestructive Imaging Analysis for Catalyst Washcoat Loading and DPF Soot Distribution Using Terahertz Wave Computed Tomography

It is getting significant to identify the fault location in advanced IC packaging technology. However, challenges have been posed to precisely determine the fault location in the failure analysis process, which is difficult to be handled by the conventional electronic based time domain reflectometry. In this work, we developed a time-domain reflectometry technology with extremely small distance-to-fault measurement error less than 50 μm, which includes X-ray length measuring error, by introducing pulsed terahertz probing signal to Quad Flat Package.

Shigeki Nishina

Papers

3D Imaging and analysis system using terahertz waves

3D Spectroscopic computed tomography imaging using terahertz waves

Electromagnetic wave measuring apparatus, measuring method, program and recording medium

Novel Nondestructive Imaging Analysis for Catalyst Washcoat Loading and DPF Soot Distribution Using Terahertz Wave Computed Tomography

Failure analysis of LSI interconnection by terahertz time-domain reflectometry