Terahertz imaging for multiple reflectors using time-domain correlating synthesis method

Abstract

We had proposed a correlating synthesis method for terahertz imaging using a pulse reflection mode terahertz time-domain spectrometry system. The efficiency of the method for improving the resolution and eliminating fake images was verified by numerical simulations and experiments with two metal cylinders. However, an artifact image between the two reflectors is markedly shown. Moreover, the multi-reflection and the influence of echo distortion caused by the directivity of the terahertz beam have not been discussed. For application of imaging complicated target, this paper addresses following issues: 1) multi-reflection between reflectors, as well as the effect of the direction of polarization of terahertz wave; 2) distortion of echo signals from targets distributed in a broader area, as well as the effect of concave lenses. Finally, the efficiencies of these proposals are verified by an imaging experiment with five metal cylinders.

Terahertz wave imaging using time domain iterative shrink threshold method

“…In previous works, we demonstrated a correlating synthesis (CS) method and its efficiency in improving imaging resolution. [15][16][17][18][19][20][21] Instead of linear summation of back projected signals shown in Eq. ( 3), the CS method emphasizes the correlations between back projections by introducing multiplications, as shown in Eq.…”

Terahertz reflection imaging using virtual arrays and MUSIC in a synthetic aperture array

“…[6][7][8][9][10][11][12][13][14] Synthetic aperture arrays (SAAs) using unfocused beams are promising candidates to increase the spatial resolution of terahertz images while reducing the restrictions on target placement. [15][16][17][18][19][20][21][22][23][24][25][26] SAAs can obtain a substantially large aperture by moving the transmitting and/or receiving antennas, making it possible to scan the beam and reduce the beamwidth by signal processing. SAA has been widely used in various applications, including radar and ultrasonic sensing.…”

“…21) Toh showed the effectiveness of correlating synthesis method proposed in ultrasonic field measurement for THz-TDS reflection imaging. [22][23][24] SAA is also needed for time reversal terahertz imaging. [18][19][20] Three-dimensional terahertz imaging using SAA has also been investigated.…”

THz wave imaging through layered dielectric using correlating synthesis method

“…Moreover, experimental imaging result using five metal cylinders verified the effect of broadening the imaging area by introducing a pair of concave lenses in front of the transmitter and the receiver. 30) However, all the experiments in our previous works were performed in air with no obstacle between the target and the THz setup, although detection or inspection of invisible objects is more important in a practical application. Considering the reflecting properties of THz waves, imaging metal targets behind a dielectric obstacle can be regarded as a realistic example.…”