Dandan Wen

As a benchmark apparatus for small-angle precision measurements, enhancing the measurement accuracy of autocollimators has always been a focal point of industry attention. However, there are currently no reports on the investigation of the impact that internal aperture processing quality has on measurement precision and accuracy. This paper integrates the general Hough transform image recognition and localization algorithm to analyze the mechanisms inducing measurement uncertainty and error in autocollimators caused by defects in the optical stop aperture. A method utilizing femtosecond laser (FSL) processing of the crosshair aperture is proposed to compensate for the traditional optical stop aperture roughness. Compared to conventional machining, this method reduces the autocollimator measurement uncertainty by 31.6% and 48.1% in the yaw and pitch angle directions, respectively, and decreases the measurement root mean square (RMS) error by 35.9% and 41.8%, respectively.

A calibration and measurement method based on an autocollimator and a manual turntable are proposed to calibrate the mounting error of a three-axis microelectromechanical system (MEMS) gyroscope in a wearable inertial measurement unit (IMU). In this system, with extension of the angle range of the autocollimator to ±9° and setting the mutual orthogonal structure of the two autocollimators, the measurement angle range of the MEMS gyroscope mounting error and the evaluation reference of the three-axis attitude angle data are obtained respectively, and the common data acquisition serial port between the autocollimator camera and the IMU host computer is built. As a result, the acquisition time is synchronized between the two systems. Additionally, the angular rate reading value of the MEMS gyroscope is integrated by time to unify the reading value scale between the calibration system and the MEMS gyroscope. This method is further compared with the traditional precision three-axis angular rate output turntable calibration method, and the accuracy deviation of the MEMS gyroscope mounting error after calibration is less than 0.3%. This method helps facilitate the development of inertial sensing calibration techniques toward traceability, which significantly reduces and simplifies laboratory equipment costs and maintenance requirements.

Flexible polymer-based magnetoelectric (ME) materials have broad application prospects and are considered as a new research field. In this article, FeCoSiB thin films were deposited on poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) substrate by DC magnetron sputtering. The structure of PVDF-TrFE/FeCoSiB heterostructure thin films was similar to 2-2. Under a bias magnetic field of 70 Oe, the composites have a dramatically increased ME voltage coefficient as high as 111 V/cm⋅Oe at a frequency of about 85 kHz. The piezoelectric coefficient of PVDF-TrFE thin films is 34.87 pC/N. The surface morphology of PVDF-TrFE thin films were studied by FESEM, and the results of XRD and FTIR showed that the β-phase of PVDF-TrFE thin films was dominant. Meanwhile, the effects of different heating conditions on the crystallization and piezoelectric properties of PVDF-TrFE films were also studied. The flexible ME heterojunction composite has a significant ME voltage coefficient and excellent piezoelectric properties at room temperature, which allows it to be a candidate material for developing flexible magnetoelectric devices.

Microwave-absorbing materials have attracted increased research interest in recent years because of their core roles in the fields of electromagnetic (EM) pollution precaution and information security. In this paper, microwave-absorbing material NiFe-layered double hydroxide (NiFe-LDH) was synthesized by a simple co-precipitation method and calcined for the fabrication of NiFe-mixed metal oxide (NiFe-MMO). The phase structure and micromorphology of the NiFe-LDH and NiFe-MMO were analyzed, and their microwave-absorbing properties were investigated with a vector network analyzer in 2–18 GHz. Both NiFe-LDH and NiFe-MMO possessed abundant interfaces and a low dielectric constant, which were beneficial to electromagnetic wave absorption, owing to the synergistic effect of multi-relaxation and impedance matching. The optimum reflection loss (RL) of NiFe-LDH and NiFe-MMO was −58.8 dB and −64.4 dB, respectively, with the thickness of 4.0 mm in the C band. This work demonstrates that LDH-based materials have a potential application in electromagnetic wave absorption.