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Materials with high and broadband absorption characteristics in the terahertz (THz) range are desirable for many applications. In this paper, we propose, fabricate and experimentally demonstrated a wafer-scale vertically aligned carbon nanotube (VACNT) array for broadband THz wave absorption. The effects of VACNT parameters on the absorption performance are investigated within the THz and infrared spectra using the Maxwell-Garnett theory, revealing that the absorption in the THz range can be greatly enhanced by suitable selections of the length, volume fraction and vertical alignment factor of CNTs. A VACNT array with an average CNT length of ∼600 μm is fabricated on a 4-inch silicon substrate. Experimental results measured by a THz time-domain spectroscopic system show an average power absorptance of ∼98% from 0.3 to 2.5 THz, and agree well with the numerical modelling. This device can be used as a cost-effective near-perfect absorber across the THz and infrared regions for thermal emission and imaging, electromagnetic interference shielding, stealth and energy harvesting applications. This work was partially supported by the National Key R&D Program of China (Grant No. 2018YFC0603301), the National Natural Science Foundation of China (Grant No. 61801185), and HUST Key Innovation Team Foundation for Interdisciplinary Promotion (Grant No. 2016JCTD102). We thank Kejia Wang and Yue Song at the Wuhan National Laboratory for Optoelectronics at HUST for their assistance in THz-TDS measurements.

High-precision seismic sensors are key components in geophysical applications. Traditional seismic sensors apply levelling systems to avoid overload by the gravity projection, introducing additional volume, weight and cost. In this paper, we design, fabricate and experimentally demonstrate a levelling-free single-axis in-plane seismic sensor based on MEMS technology. Three kinds of capacitive sensors are integrated into one chip. Two encoder-like area-varying capacitive displacement sensors work alternatively to avoid the inflection points, enabling the seismic sensor to work linearly in arbitrary attitudes with a high sensitivity and an angle sensor selects the working array from the two arrays and measures the angle between the sensitive direction and gravity direction at the same time. In order to calibrate the scale factor, a gap-varying capacitive displacement sensor is integrated to measure the spacing. By the combination of these capacitive sensors, the micromachined seismic sensor is able to work in arbitrary attitudes with a resolution of better than 50 ng/√Hz at 1 atmosphere. Assembling three seismic sensors along axes orthogonal to each other, a three-axis seismic measurement system can be constructed. This system has successfully detected a MS7.0 earthquake at 2017-08-08 (UTC time), which happened in Sichuan Province (1000 km away), and another MS6.6 earthquake happened about 10 h later in Xinjiang Province (2700 km away). Being low cost and low power, this nano-g MEMS seismic sensor provides an alternative solution for geophysical applications.

TianQin-1 is a mission in the TianQin project, which uses a single satellite to demonstrate the maturity of the key technology for the space-based gravitational wave detection. The spaceborne laser in the TianQin-1 mission consists of a self-developed DBR one and a commercial RIO one. The DBR laser is also developed as a pumping source for the main NPRO laser in the final solution of TianQin. The two lasers were mutual backups and both passed the environment performance verification. The on ground results showed that the self-developed DBR laser could provide a stable output of 18 mW with a drift of 0.6 mW/h. Meanwhile, the internal temperature was controlled at the mK level. The results of in-orbit experiments show that the DBR laser works well as a direct source of the laser interferometer. The overall displacement resolution and the noise floor of the interferometer was approximately 25 pm and 30 pm/√Hz at 0.1 Hz, respectively, better than the goals of the TianQin-1 mission.

Tilt sensors have been widely used in many applications, such as instrumentation leveling, oil drilling and structural health monitoring. With the rapid development of the micro-electromechanical system (MEMS) technology, MEMS accelerometer-based high-performance tilt sensors are capable of replacing conventional tilt sensors in most of application fields. High-sensitivity MEMS resonant accelerometers (MRAs) are fully qualified for tilt sensing. However, MRA chips have to be vacuum packaged and require complex circuits; therefore, they are difficult to be miniaturized and commercialized. In this case, this paper introduces a commercial-oriented capacitive MEMS accelerometer for tilt sensing with both high-resolution and compact size. The proposed MEMS sensor utilizes simplified fabrication processes, the area-change-based capacitive displacement transducer and the capacitance-to-voltage conversion application specific integrated circuit (ASIC) for low-cost, high-sensitivity, low power consumption and miniaturization. The developed MEMS sensor has a package dimension of 14 mm × 14 mm × 3.6 mm with a single +5 V power supply and analog voltage output. Several evaluation experiments have been conducted with the results showing that the developed MEMS tilt sensor has a full measurement range of ±180°, a linear measurement range of ±30° with a nonlinearity of ±2.8%, a sensitivity of 33.6 mV/°, a noise floor of 2 × 10−4°/√Hz, a bandwidth of 100 Hz and an angle resolution of 7 × 10−4° with an integral time of 0.5 s. Compared with other commercial MEMS tilt sensors, the proposed sensor has a better resolution, a lower noise floor, a larger bandwidth, a lower power consumption and a smaller package. The simplified fabrication process and high performance suggest the developed MEMS tilt sensor is promising to be competitive in the market.

Diamagnetism as a fundamental physical phenomenon is commonly existed in many materials, such as water and even human body. Since the Nobel Prize laureate Prof. Geim successfully demonstrated the flying frog in 1997, diamagnetic levitation has attracted significant research interests due to the advantages of simple structure, stable and passive levitation without power consumption. There are several applications based on diamagnetic levitation, including container-less crystal growth, weightless fluid dynamics, low friction bearings, magnet rotors, energy harvesters and also inertial sensors. However, the developed diamagnetic levitation based inertial sensors cannot meet the low-frequency response and high sensitivity requirements of geophysical applications. This paper introduces a prototype of a diamagnetic levitation based inertial sensor which includes the diamagnetic levitation system and the optical displacement transducer. The proof mass is a floating magnet which is lifted by a fixed magnet above and sandwiched by two pyrolytic graphite sheets for stable levitation. A high precision optical displacement transducer has been developed with a noise floor of 2 nm/√Hz@0.5 Hz and 0.1 nm/√Hz@10 Hz at atmosphere and room temperature. The fundamental frequency of the levitation system was measured as 0.65 Hz, giving an acceleration noise floor of 20 ng/√Hz@0.5 Hz (3.4 ng/√Hz@0.5 Hz in theory). Benefitting on the excellent sensitivity and low-frequency responses, earth tremor peaks at 0.2∼0.3 Hz and 2∼3 Hz have been observed using this inertial sensor. The proposed inertial sensor is promising to be used for high-sensitivity vibration monitoring, seismic imaging and other geophysical applications.

Area-changed capacitive displacement transducers have been widely applied in micro-electro-mechanical-system (MEMS) sensors such as sandwich-type MEMS accelerometers to detect in-plane displacement with a high sensitivity. The cross-axis disturbance could result in out-of-plane displacement of the proof mass, which brings a gap variation of sensing capacitor electrodes and lead to an undesirable variation of the accelerometer’s scale factor. In order to solve this problem, this paper presents a novel method to improve out-of-plane robustness of an Area-changed capacitive displacement transducer in a MEMS accelerometer. An on-chip capacitor, sensitive to the out-of-plane displacement of proof mass, was integrated as the feedback capacitor of the charge amplifier. Thus, the influence of the out-of-plane displacement on the scale factor caused by cross-axis disturbance is compensated. The method was verified by theoretical calculation, simulation and experiments. The results indicated that the cross-sensitivity of the MEMS accelerometer with an on-chip feedback capacitor was less than 1/3 of that with off-chip feedback capacitor when acceleration was applied on the out-of-plane direction. Besides, the noise floor of the accelerometer maintained at 60 ng/√Hz regardless of the on-chip or off-chip feedback capacitors.

Flexible micro-supercapacitors (MSCs) are promising candidates as miniaturized power sources and energy storage components for next generation wearable electronic devices. Herein, we report a low-temperature-operated ( ~ 80∘C) direct fabrication method for the realization of flexible MSCs. To demonstrate the capability of the fabrication method, a flexible MSC based on zinc oxide (ZnO) nanorod/titanium (Ti)/titanium nitride (TiN) core-shell nanostructures and metallic interdigits on a polyethylene terephthalate (PET) substrate was fabricated, with no additional transfer procedure required. The as-produced MSC exhibits increased power (432 W kg−1) and energy (0.24 Wh kg−1) densities, when compared to those of ZnO nanorod based or ZnO seed layer/Ti/TiN based devices. The capacitance retention is over 98 % after 5000 cycles, showing an excellent stability. The flexibility of the MSC is tested by bending the device from 0∘ to 180∘, demonstrating nearly identical electrochemical properties for all bending angles. With such a low temperature environment, the proposed fabrication strategy can be applied to other material networks to further improve the performance of MSCs. This method potentially allows for mass production due to its low fabrication complexity, paving the way for the direction fabrication of on-chip MSCs for flexible and wearable devices.

We amplified the geomagnetic influence on torsion pendulum experiment by producing an additional horizontal magnetic field, and obtained the dissipation, which is proportional to B 2 in the disc-shaped torsion pendulum experiment. The geomagnetic influence should be considered due to the inelasticity correction in G measurement in high Q-factor torsion pendulum experiments.  2001 Elsevier Science B.V. All rights reserved.