This paper describes a highly accurate airflow volumetric flowmeter using piezoelectric micromachined ultrasonic transducers (pMUTs) arrays based on transit time. Two pieces of 10by10 multipled aluminum nitride (AlN) pMUTs arrays at resonant frequency of 980 kHz are employed to transmit and receive ultrasonic signals alternately. The dimension of the fabricated 10by10 array is about 3.5 × 3.5 mm ² , so the pMUTs-based flowmeter is able to measure flow rate in a 3D-printed pipe with an inner diameter of 10 mm. An evaluation board TDC1000-TDC7200EVM with resolution in ns is used to excite the transducers and handle the received signal. Leveraging on the high signal to noise ratio (SNR, ~29 dB) of the pMUTs array and excellent resolution (ns) of the evaluation board, the flowmeter has high accuracy. For the reference volumetric flow rate varying from 0-9 L/min in the range of laminar flow, the relative errors of the correctional volumetric flow are within 3%.

Double-threshold method is a typical and simple time-of-flight (TOF) measurement method for time-difference-based ultrasonic flowmeter. Some improvements have been proposed to suppress the cycle-skip phenomenon in double-threshold method. However, there are still some application limitations when the waveform is distorted caused by the environment change, especially the temperature change. This paper proposes a similarity judgment-based double-threshold method to deal with the cycle-skip problem. In this method, time values of three consecutive positive zero-crossing points after the feature point are acquired and five consecutive cycles after the first obtained time are saved. The TOF is automatically selected from three acquired time values according to an adaptive determination function which bases on the similarity between signals from two adjacent measurements. These operations guarantee that the obtained TOF locates on the same positive zero-crossing point in each measurement. The proposed method was validated by both numerical and experimental tests. Comparison between the proposed method and other double-threshold methods shows that the proposed method successfully eliminates cycle-skip phenomenon under different working conditions.

With the extensive applications of biomagnetic signals derived from active biological tissue in both clinical diagnoses and human-computer-interaction, there is an increasing need for approachable weak biomagnetic sensing technology. The inherent merits of giant magnetoresistance (GMR) and its high integration with multiple technologies makes it possible to detect weak biomagnetic signals with micron-sized, non-cooled and low-cost sensors, considering that the magnetic field intensity attenuates rapidly with distance. This paper focuses on the state-of-art in integrated GMR technology for approachable biomagnetic sensing from the perspective of discipline fusion between them. The progress in integrated GMR to overcome the challenges in weak biomagnetic signal detection towards high resolution portable applications is addressed. The various strategies for 1/f noise reduction and sensitivity enhancement in integrated GMR technology for sub-pT biomagnetic signal recording are discussed. In this paper, we review the developments of integrated GMR technology for in vivo/vitro biomagnetic source imaging and demonstrate how integrated GMR can be utilized for biomagnetic field detection. Since the field sensitivity of integrated GMR technology is being pushed to fT/Hz^0.5 with the focused efforts, it is believed that the potential of integrated GMR technology will make it preferred choice in weak biomagnetic signal detection in the future.

A new fluid encapsulation structure, which is characterized by a bubble encapsulating a drop, is reported. It is stably generated from the breakup of a liquid column inside a bubble, which is achieved via the injection of Taylor flow into liquid. A model is constructed to explain the liquid column breakup mechanism. A dimensionless control guidance, which enables the possibility to create different-scale capsules, is provided. The encapsulation stability in external flows is verified, and a method to trigger the release of the encapsulated drop is provided, which supports potential applications with great advantages such as fluid transport.

In this paper, we propose a non-contact ultrasonic liquid flowmeter based on AlN piezoelectric micromachined ultrasonic transducer (PMUT) arrays. Two 10 by 10 PMUT arrays with resonant frequency of 980 kHz in air are mounted outside of a pipe to measure liquid flow without contacting the liquid. An acoustic matching layer is designed to mitigate the loss of sound waves caused by sound reflection. Under excitation of continuous wave, the flow of the liquid can be determined via detecting the phase difference between transmitting and received signals. The measurement range of flow is 0.515 L/min ~ 3.40 L/min and the measurement error is less than 3%. Moreover, an interpolation method is proposed to reduce the signal sampling frequency without obviously affecting the measurement accuracy, which shows potential for further system integration.

The common phenomena of periodic and aperiodic bubbling, which were studied merely in single-phase gas jets, are discovered to exist in submerged gas-liquid jets through a micro-channel. Due to the participation of the liquid input flow which interacts with the gas phase, the periodic and aperiodic bubbling behaviors, as well as the regime transition mechanisms, are quite different from single-phase gas jets. Periodic bubbling is formed by injecting a regular Taylor flow into bulk liquid, in which a special motion of bubbles named “bubble bifurcation” is revealed. Bubbles move into the opposite orientation to the bubbles they touch because unequal contact angles make the bubbles tilt when they detach. The bifurcation process is described by the evolutions of the contact line, bubble centers, and the bifurcation point. The second bifurcation events cause the bubble branches to rotate simultaneously. The difference of periodicity between gas-liquid jets and single-phase gas jets is explained in a dimensionless form as a function of 1/St versus Fr. Aperiodic bubbling including double coalescence, triple, quadruple, and quintuple bubble formation is found to occur at lower gas velocities than single-phase gas jets because of the different mechanism of bubble detachment in which liquid rings make bubbles pitch off before necking. The effect of liquid rings on bubbling period, as well as the disturbance waves spreading over the bubble surface, is explained. Finally, the mechanisms of bubbling losing periodicity are figured out through analyzing the correspondence relationship between the evolutions of bubbling behaviors and the flow regime transitions in the micro-channel with regime boundaries well predicted by corresponding models.