The flow field is one of the key factors that affect the measuring accuracy of ultrasonic gas flowmeters. The present work demonstrates that the designed novel flow conditioner can enhance the measurement accuracy by homogenizing the velocity profile in the acoustic transmission area. The main objective of this study is to reduce the non-uniformity of flow on velocity distribution. To accomplish this objective, a combination of theoretical analysis and numerical simulations is implemented, and the results indicate that the 10:1 aspect ratio rectangular fluid channel is better applied in ultrasonic gas flowmeters. Thus, a Computational Fluid Dynamics (CFD) model of novel flow conditioner based on the 10:1 fluid channel is simulated and validated by an experimental study. The results verify that the ultrasonic gas flowmeter composed of designed flow conditioner can reduce indication errors by up to 6%; moreover, the repeatability of all the tested standard flow rates can meet the national standard and even be enhanced by 0.15%.

In this paper, we propose and fabricated a novel scheme of SOI-based 1$\times$3 coupler with variable splitting ratio. The coupler consists of two cascaded MMI with different sizes, and a wide range of splitting ratios from 1:0.1:1 to 1:18:1 can be achieved by modifying the size of the first-step MMI. Using the structure of cascaded step-size MMI, this kind of device has a compact footprint of below 15 μm$\times$15 μm and simple fabrication process. Meanwhile, the simulation analyses prove that the proposed couplers have a large operation bandwidth above 60 nm and be robust to the fabrication errors. Couplers with several splitting ratios were fabricated and well measured. Based on the measurement results, the splitting ratios of fabricated couplers from 1:0.67:1 to 1:18:1 can be achieved, and stable performance with the transmission efficiencies above 80% can be maintained over 50 nm wavelength range, which is the largest operation bandwidth to the best of our knowledge.

A miniature methane sensor composed of a long ultra-low loss waveguide and a micro-ring resonator filter is proposed with high sensitivity and good selectivity. This sensor takes advantage of the evanescent field to implement methane concentration detection at a near infrared band (1650 nm). In the sensor, two waveguides, a strip waveguide and a slot waveguide, are specially designed and discussed based on three common semiconductor materials, including silica, silicon nitride, and silicon. Through simulations and numerical calculations, we determine that for the strip waveguide, the optimal evanescent field ratio (EFR) is approximately 39.8%, while the resolution is 32.1 ppb using a 15-cm waveguide length. For the slot waveguide, the optimal EFR is approximately 61.6%, and the resolution is 20.8 ppb with a 15-cm waveguide length.

This article presents a diamond nitrogen-vacancy (NV) center-based magnetic field sensor using a voltage-controlled oscillator (VCO) integrated with a filtering antenna. In existing NV-based quantum sensing systems, microwave source and delivery units are implemented by a set of bulky and costly instruments. This limits its practical applications as well as portability. Here, a VCO integrated with the filtering antenna is designed, providing a more uniform, efficient, broadband and lower phase noise microwave field coupling to the NV centers. As a result, the sensitivity and the dynamic range have been improved over the conventional scheme using separate microwave components, such as antennas, transmission lines, and resonators. Moreover, in this work, the optic filter and photodetector are also integrated using the hybrid microwave integrated circuits (HMICs) technique for the first time. This significantly increases the integration level and reduces the cost of the NV-based magnetometers. The experimental results indicate that our VCO integrated filtering antenna achieves a sensitivity of $8.52~\mu \text{T}$ /Hz $^{\mathrm {1/2}}$ and a dynamic range up to 32.73 dB, which are both greatly improved compared to the VCO with a single resonator. This validates the effectiveness of the approach.