The manufacture and use of bronze ritual vessels, as far back as the second and the first millennium BC, is an essential tool in maintaining social order and political structure in China’s Shang and Zhou periods, yet the casting techniques that made them have not been well discussed. The core issue is the manufacturing and use of clay moulds. Not only their design and positioning, archaeological studies show that their material property is also a key to the success of casting such products. The present work, among a series research, is mainly focused on the thermal property analysis of the ancient bronze casting moulds and two other contemporary moulds for comparison. Thermal diffusivity is measured with pulsed thermography as a non-destructive method. The results prove that the thermal diffusivity of ancient bronze casting moulds are relatively low which allows liquid bronze to flow for an extended duration, filling all fine patterns and corners. The difference between the three types of moulds are discussed.
Based on metasurface, two beam shapers are designed to modulate the wavefront of the terahertz beam. One of the beam shapers is THz ring-Airy beam generator and the other is THz four-focus lens. Each beam shaper is composed of a serious of C-shaped slot antennas, which can be used to modulate the phase and amplitude of the cross-polarized scattered wave. A THz holographic imaging system is utilized to measure the field of the generated beams. The ring- Airy beam shaper is designed by replacing both the phase and amplitude of its initial electric field with the corresponding antennas. In the experiment, an abrupt focus following a parabolic trajectory is subsequently observed. This method can be expanded to other wavebands, such as the visible band, in which the ring-Airy beam shaper can replace traditional computer-generated holography to avoid undesirable multiple diffraction orders. The phase distribution of the four-focus lens is obtained by using the Yang-Gu amplitude-phase retrieval algorithm and then encoded to the antennas. Both the focusing and imaging properties are demonstrated. A clear image can be obtained with a bandwidth of 110 GHz. This type of transmissive metasurface beam shaper serves as an attractive alternative to conventional diffractive optical elements based on its small size, ease of fabrication, and low cost.
Focusing of terahertz (THz) surface plasmon polaritons (SPPs) excited by linearly and circularly polarized THz radiation is investigated experimentally and theoretically. A high-speed THz-SPPs imaging system is built up to measure both the amplitude and phase of the excited THz-SPPs. For the horizontally polarized THz radiation, the THz-SPPs will be focused in the centre of the semicircular slit and the phase images reveals a π/2 Gouy phase shift though the focal spot of THz-SPPs. With the illumination of vertically polarized THz radiation, the focal spot in the centre will split into two focal spots in the y-direction. For the circularly polarized incident THz radiation, the focal spot of THz-SPPs will shift upward or downward in the y-direction. FDTD simulations are performed and compared with the experimental results. A good agreement between experimental results and simulation results can be found.
Pulsed terahertz reflected imaging technology has been expected to have great potential for the non-invasive analysis of artworks. In this paper, three types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by a pulsed terahertz reflected imaging system. These preset defects include a circular groove, a cross-shaped slit and a piece of “Y-type” metal plate built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. Additionally, three-dimensional analyses have been performed in order to reveal the internal structure of defects. Terahertz reflective imaging can be applied to the defect investigation of the murals.
Based on the localized surface plasmons (LSPs), a series of C-shaped slits antennas are designed to modulate the phase and amplitude of the cross-polarized transmitted wave in THz waveband. By adjusting the structure parameters of the antenna unit, arbitrary phase and amplitude modulation of the cross-polarized THz wave can be obtained. The C-shaped slit antenna units are designed at two operating frequencies f=0.8 THz and f=1.0 THz using a commercial software package (Lumerical Solutions), which is based on the finite-difference time-domain method. According to the simulated results, principles for modulating the phase and amplitude of THz wave are summarized as follows. Firstly, the operating wavelength depends on the effective length of the antenna and the operating wavelength increases as the effective length increases; Secondly, the phase of the cross-polarized wave can be modulated from 0 to 2π by changing the opening angle of the split; Thirdly, the amplitude transmittance of the cross-polarized wave can be changed from the extinction state to the maximum value by rotating the symmetry axis of the C-shaped slit. These principles can be used to direct the design of the field modulator in any other working frequency.
Terahertz time-domain spectroscopy (THz-TDS) imaging technology has been proposed to be used in the non-invasive detection of murals. THz-TDS images provide structural data of the sample that cannot be obtained with other complementary techniques. In this paper, two types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by the terahertz reflected time domain spectroscopy imaging system. These preset defects include a leaf slice and a slit built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. With this THz tomography, different defects with the changes of optical thickness and their relative refractive index have been identified. The application of reflective pulsed terahertz imaging has been extended to the defect detection of the murals.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.