Terahertz sensors can solve the above problems, because terahertz waves can penetrate opaque materials, such as cloth, paper, wood and plastic, and the defects of these objects can be visualized by tens of billions of hertz. Terahertz technology can detect the characteristics of imaging and measure the characteristics of material components, and realize the detection of various objects.
The electromagnetic spectrum of terahertz wave is between microwave and infrared wave, with the wavelength range of 1mm ~ 100mm and the frequency range of 300GHz~3THz 3 THz. Compared with X-ray energy, THz wave is non-invasive and non-ionizing because of its extremely low photon energy.
Terahertz system has two modes: continuous wave and pulse wave. Pulse wave system obtains material information by sending a frequency band, while continuous wave system can only obtain information by a single frequency. Terahertz system uses transmitter and single point detector to obtain the frequency profile of the measured object surface. By moving these single-point detectors, two-dimensional linear scanning and three-dimensional array scanning are carried out, so as to obtain two-dimensional and three-dimensional frequency profiles of the measured object.
In the terahertz system in automation application, the measured object enters the field of view of the sensor through the conveyor belt, and the terahertz light wave is transmitted through the coaxial cable of the Vega control box, and the received high-frequency waveform is captured and processed by the photoelectric mechanical delay system. After the signal is digitized, it is transmitted to the standard PLC controller through Ethernet or other ship speed protocols. In the test, the time domain waveform can be used to characterize the thickness of the product, and the frequency spectrum can be used to identify the type of polymer used.
When detecting the thickness of opaque plastic or rubber bottles and tubes, it is necessary to adopt non-contact and non-invasive detection technology. The non-contact and non-invasive terahertz measurement system provided by Vega has a measurement accuracy as high as 10um. It has the characteristics of low energy, strong absorption and resonance of various biological macromolecules, small attenuation of penetrable substances and high signal-to-noise ratio. It can be used in national defense, medical care, scientific research and many other fields, and has great market value.
In many plastic sorting systems, materials can be sorted by detecting the near infrared electromagnetic spectrum of plastic materials. Near-infrared technology is only effective when detecting light-colored plastics. If the plastic sheet is black, dark or painted, near infrared absorption and near infrared separation are ineffective. These problems can be solved by using terahertz continuous system, and the amplitude of terahertz signal can be used for detection.
Terahertz has high frequency and short wavelength, high signal-to-noise ratio in time domain spectrum and low transmission loss in smoke and dust environment. It can penetrate the wall and scan the interior of the house, which is an ideal technology for enemy-seeking imaging in complex battlefield environment. With the help of THz's unique "wall-penetrating technology", three-dimensional imaging of "behind the wall" objects can detect weapons, camouflage personnel and display tanks, artillery and other equipment hidden in the dust, thus clearing the fog of the battlefield.
In recent years, with the rapid development of ultrafast laser technology, the excitation light source of terahertz pulse is more stable and reliable, which creates conditions for further research of terahertz spectroscopy technology. At the same time, the research of terahertz radiation sources and detectors with various mechanisms is also developing rapidly, which lays the foundation for the application of terahertz technology in national defense, aerospace, communication and other fields, and makes terahertz technology have broad application prospects.