Ultrasonic flowmeters play an important role in industrial production, aerospace and other fields. In this paper, a high-precision ultrasonic flowmeter based on the cross-correlation method is designed, and the commercial finite element software COMSOL Multiphysics 5.6 is used to simulate the propagation process of ultrasonic waves during flow measurement, and the implementation process of the cross-correlation algorithm is simulated by Python language. The flowmeter adopts the cross-correlation algorithm to improve the measurement accuracy of ultrasonic time of flight and adopts the method of combining FPGA and an embedded microprocessor to improve operation efficiency. In order to verify the performance of the flowmeter, we tested the flowmeter on the National Institute of Metrology and the self-built test platform, using the still water dragging method, the dynamic volume method and the field comparison method, respectively. The results show that the flowmeter has the ability to test the flow under the condition of high flow velocity (26 m/s) and a pipe diameter in the range of DN6~DN1600, that the absolute value of the relative indication error does not exceed 0.815% and that the repeatability does not exceed 0.150%. The designed ultrasonic flowmeter has high measurement accuracy, good repeatability, strong stability and a wide application range.

Surface acoustic wave (SAW) devices are widely used in many fields such as mobile communication, phased array radar, and wireless passive sensor systems. With the upgrade of mobile networks, the requirements for the performance of SAW devices have also increased, and high-frequency wideband SAW devices have become an important research topic in communication systems and other application fields. In this paper, a theoretical study for the realization of a layered SAW filter based on a new SiO₂/IDT/128°YX-LiNbO₃/diamond/silicon layered structure using the modeling software COMSOL Multiphysics is presented. The effects of lithium niobate (LiNbO₃), an interdigital transducer (IDT), and SiO₂ thin films on the evolution of the phase velocity, electromechanical coupling coefficient (k²), and temperature coefficient of frequency were studied by employing a finite element method simulation. Furthermore, a longitudinal coupling resonator filter was designed. To investigate the SAW characteristics of the filter, a transient analysis was conducted to calculate the electrical potential and particle displacement under the resonance condition and to analyze the frequency response. The study concluded that this new multilayer structure can be applied to design and manufacture a variety of high-frequency and wideband SAW filters with a temperature compensation function, for operation above the GHz range.

Low temperature measurement is crucial in deep space exploration. Surface acoustic wave (SAW) sensors can measure temperature wirelessly, making them ideal in extreme situations when wired sensors are not applicable. In this study, 128° YX LiNbO₃ was first introduced into low temperature measurements for its little creep or hysteresis in cryogenic environments and affordable price. The finite element method was utilized to raise the design efficiency and optimize the performance of SAW sensors by comparing the performance with different interdigital transducer (IDT) structure parameters, including the height of electrodes, pairs of IDTs, reflecting grid logarithm and acoustic aperture. Once the parameters were changed, a novel design of high-performance SAW temperature sensors based on 128° YX LiNbO₃ with double electrode transducers was obtained, of which the Q value could reach up to 5757.18, 4.2-times higher than originally reported. Low temperature tests were conducted, and the frequency responsiveness of SAW sensors was almost linear from −100 °C to 150 °C, which is in good agreement with the simulation results. All results demonstrate that double electrode transducers are considerably efficient for performance enhancement, especially for high-Q SAW sensors, and indicate that LiNbO₃ substrate can be a potential high-performance substitute for cryogenic temperature measurements.

Capacitive micromachined ultrasound transducers (CMUTs) have broad application prospects in medical imaging, flow monitoring, and nondestructive testing. CMUT arrays are limited by their fabrication process, which seriously restricts their further development and application. In this paper, a vacuum-sealed device for medical applications is introduced, which has the advantages of simple manufacturing process, no static friction, repeatability, and high reliability. The CMUT array suitable for medical imaging frequency band was fabricated by a silicon wafer bonding technology, and the adjacent array devices were isolated by an isolation slot, which was cut through the silicon film. The CMUT device fabricated following this process is a 4 × 16 array with a single element size of 1 mm × 1 mm. Device performance tests were conducted, where the center frequency of the transducer was 3.8 MHz, and the 6 dB fractional bandwidth was 110%. The static capacitance (29.4 pF) and center frequency (3.78 MHz) of each element of the array were tested, and the results revealed that the array has good consistency. Moreover, the transmitting and receiving performance of the transducer was evaluated by acoustic tests, and the receiving sensitivity was −211 dB @ 3 MHz, −213 dB @ 4 MHz. Finally, reflection imaging was performed using the array, which provides certain technical support for the research of two-dimensional CMUT arrays in the field of 3D ultrasound imaging.

The capacitive micromachined ultrasonic transducer (CMUT), as a new acoustic-electric conversion element, has a promising application prospect. In this paper, the structure of the vacuum capacitive micromachined ultrasonic transducer is presented, and its performance-influencing factors are investigated. Firstly, the influencing factors of the performance parameters of the vacuum CMUT are analyzed theoretically based on the circular plate model and flat plate capacitance model, and the design principles of the structural parameters of the CMUT cell are proposed. Then, the finite element simulation software COMSOL Multiphysics is used to construct CMUT cell models with different membrane materials, membrane shapes, membrane radius thicknesses, and cavity heights for simulation verification. The results show that both the membrane parameters and the cavity heights affect the performance parameters of the Vacuum CMUT. In order to improve the efficiency of the CMUT, materials with low bending stiffness should be selected, and the filling factor of the membrane should be increased. In order to achieve high-transmission sound pressure, a smaller radius thickness and a larger cavity height should be selected. To achieve high reception sensitivity, a larger membrane radius thickness and a smaller cavity height should be selected. In order to obtain high fractional bandwidth, a larger membrane radius thickness should be selected. The results of this paper provide a basis for the design of Vacuum CMUT cell structure.

CMUT based on micro-electro-mechanical systems technology has a significant advantage that traditional piezoelectric ultrasonic transducers do not have, and has become the mainstream transducer for the new generation of ultrasound imaging systems. In this paper, the state equation is deduced and the analysis model is established in SIMULINK environment based on the lumped parameter system model of the CMUT micro-unit. Through the state equation-SIMULINK model, the influence of the parameters such as the DC bias voltage, the amplitude, frequency and period number of the AC excitation signal on the radiation characteristics is analyzed comprehensively. These results provide the important theoretical basis and reference for further optimization of structural design and application testing in the future.