多孔Nafion膜离子聚合物金属复合材料的制备及性能

离子聚合物金属复合材料(IPMC)是一种新型人工肌肉材料。传统IPMC的含水率较低,其电致动性能较差。文中采用微粒浸析法,利用纳米四氧化三铁粒子成功制备了多孔Nafion膜。多孔Nafion膜含水率是普通Nafion膜的2.5~4.3倍,并且随着纳米粒子含量的增加,含水率不断增大。多孔Nafion膜IPMC的输出位移、应变能密度(能量转换效率)和稳定工作时间分别是普通Nafion膜IPMC的1.6~2.5倍、2.8~4.8倍和1.7~2.1倍。总之,Nafion膜中多孔结构的存在提高了IPMC的电致动性能。

Lensless Fourier-transform terahertz digital holography for real-time full-field phase imaging

With the development of continuous-wave terahertz(THz) sources and array detectors, the pursuit of highfidelity real-time imaging is receiving significant attention within the THz community. Here, we report a real-time full-field THz phase imaging approach based on lensless Fourier-transform THz digital holography.A triangular interferometric layout is proposed based on an oblique illumination of 2.52 THz radiation, which is different from other lensless holographic configurations at other frequencies. A spherical reference beam is generated by a reflective parabolic mirror with minor propagation loss. The complex-valued images are reconstructed using a single inverse Fourier transform of the hologram without complex calculation of the diffraction propagation. The experimental result for a Siemens star validates the lateral resolution of-46 μm in the diagonal direction. Sub-pixel image registration and image stitching algorithms are applied to enlarge the area of the reconstructed images. The dehydration process of an aquatic plant leaf(Hottonia inflata) is monitored for the first time, to the best of our knowledge, at the THz band. Rapid variations in water content and morphology are measured with a time interval of 0.6 s and a total time of 5 min from a series of reconstructed amplitude and phase images, respectively. The proposed method has the potential to become a powerful tool to investigate spontaneous phenomena at the THz band.

Continuous-wave terahertz diffraction tomography for measuring three-dimensional refractive index maps

Three-dimensional(3D)refractive index(RI)distribution is important to reveal the object’s inner structure.We implemented terahertz(THz)diffraction tomography with a continuous-wave single-frequency THz source for measuring 3D RI maps.The off-axis holographic interference configuration was employed to obtain the quantitative scattered field of the object under each rotation angle.The 3D reconstruction algorithm adopted the filtered backpropagation method,which can theoretically calculate the exact scattering potential from the measured scattered field.Based on the Rytov approximation,the 3D RI distribution of polystyrene foam spheres was achieved with high fidelity,which verified the feasibility of the proposed method.

Continuous-wave terahertz in-line holographic diffraction tomography with the scattering fields reconstructed by a physics-enhanced deep neural network

Diffraction tomography is a promising,quantitative,and nondestructive three-dimensional(3D)imaging method that enables us to obtain the complex refractive index distribution of a sample.The acquisition of the scattered fields under the different illumination angles is a key issue,where the complex scattered fields need to be retrieved.Presently,in order to develop terahertz(THz)diffraction tomography,the advanced acquisition of the scattered fields is desired.In this paper,a THz in-line digital holographic diffraction tomography(THz-IDHDT)is proposed with an extremely compact optical configuration and implemented for the first time,to the best of our knowledge.A learning-based phase retrieval algorithm by combining the physical model and the convolution neural networks,named the physics-enhanced deep neural network(PhysenNet),is applied to reconstruct the THz in-line digital hologram,and obtain the complex amplitude distribution of the sample with high fidelity.The advantages of the PhysenNet are that there is no need for pretraining by using a large set of labeled data,and it can also work for thick samples.Experimentally with a continuous-wave THz laser,the PhysenNet is first demonstrated by using the thin samples and exhibits superiority in terms of imaging quality.More importantly,with regard to the thick samples,PhysenNet still works well,and can offer 2D complex scattered fields for diffraction tomography.Furthermore,the 3D refractive index maps of two types of foam sphere samples are successfully reconstructed by the proposed method.For a single foam sphere,the relative error of the average refractive index value is only 0.17%,compared to the commercial THz time-domain spectroscopy system.This demonstrates the feasibility and high accuracy of the THz-IDHDT,and the idea can be applied to other wavebands as well.

Binary diffractive lens with subwavelength focusing for terahertz imaging

The converging lens is one of the key components in high-resolution terahertz imaging.In this Letter,a binary diffractive lens is proposed for the scanning imaging system working at 278.6 GHz,in which a convergent beam with a waist diameter of0.65 mm is generated,and 1 mm lateral imaging resolution is realized.This low-cost terahertz lens,constituted by concentric rings with different radii,is optimized by stimulated annealing algorithm and fabricated by three-dimensional printing.Compared with the conventional transmissive convex lens,higher resolution and enhanced imaging quality are achieved via smaller focal spot of the illumination beam.This type of lens would promote terahertz imaging closer to practical applications such as nondestructive testing and other scenarios.

Dynamic full-field refractive index distribution measurements using total internal reflection terahertz digital holography

Massive usage scenarios prompt the prosperity of terahertz refractive index(THz RI) measurement methods.However, they are very difficult in measuring the full-field dynamical RI distributions of either solid samples without a priori thickness or liquid samples. In this study, we propose total internal reflection THz digital holography and apply it for measuring RI distributions for both solid and liquid samples dynamically. An RI measurement model is established based on an attenuated total reflection prism with a pitching angle. The pitching angle and the field of view can be numerically calculated from the spectrogram of the off-axis Fresnel hologram,which solves the adjustment of the visually opaque prism irradiated by the invisible THz beam. Full-field RI distributions of the droplets of solid-state soy wax and distilled water are obtained and compared with THz time-domain spectroscopy. The evaporation of an ethanol solution droplet is recorded, and the variation of the RI distribution at the sample–prism interface is quantitatively visualized with a temporal resolution of 10 Hz. The proposed method greatly expands the sample range for THz RI measurements and provides unprecedented insight into investigating spontaneous and dynamic THz phenomena.