Surface Acoustic Wave (SAW) filters based on the acoustoelectric amplification effect have the advantages of high integration and non-reciprocity, and have a wide application prospects in the national defense and commercial fields. At the same time, the research of new materials and structures provides new ideas and directions for the preparation of future highly integrated SAW filter amplifiers. The mechanism of SAW acoustoelectric amplification is introduced in this paper, the commonly used structures of the devices are analyzed, and the performance specifications of some devices are summarized, which have certain reference significance for the application and promotion of SAW filter amplifiers.

The laterally excited bulk wave resonators (XBARs) based on thin film lithium niobate (LN) have both large electromechanical coupling coefficient (K2) and high resonant frequency (f) characteristics, which is expected to fulfill the frequency requirements for 5G applications. However, the single-layer XBAR structure with conventional LN film has poor temperature stability and low temperature coefficient of frequency (TCF). In this paper, a SiO2/LN bilayer structure XBAR with SiO2 temperature compensation layer is proposed, and a finite element model for accurate analysis of the layered structure XBAR is established. The theoretical analysis shows that the first order antisymmetric (A1) Lamb wave is excited as the main mode on this bilayer structure XBAR. High resonant frequency (f ~4.75 GHz) and large electromechanical coupling coefficient (K2~8%) can be obtained by reasonably optimizing the structural parameters configuration, while its temperature stability is also significantly improved (TCF~-36.1×10-6/℃). The TCF is increased by nearly 70×10-6/℃ compared with the single-layer XBAR structure. The study provides a theoretical basis for developing temperature compensated acoustic filter with high-frequency and large bandwidth.

The high integration and high energy density of the RF front-end make the nonlinearity problem in surface acoustic wave (SAW) devices more and more serious. A measurement system of nonlinear signals in RF SAW devices has been set up in this work, and the second harmonic (H2) and third order harmonic (H3) signals of SAW resonators are measured precisely. The measured results are analyzed and the generation mechanisms of nonlinear harmonic signals are discussed. By comparing the fitted simulation result of nonlinear finite element method (FEM) model with the measured results, the influences of the dielectric nonlinearity and the nonlinear effect of acoustic strain on the harmonic generation are verified, which provides an important support for further study on the nonlinear suppression method and design of SAW devices with high linearity.

In the process of designing high frequency surface acoustic wave (SAW) filters, if only the electromagnetic parasitic parameters of the package and the bonding line are considered and the electromagnetic parasitic parameters of the bus bar are ignored, the actual performance of SAW filters will be easily affected by the parasitic parameters of the bus bar, resulting in problems such as large passband ripple and large standing-wave ratio. In this paper, the co-simulation method of the electro-acoustic and electromagnetic is used to design high frequency SAW filter to solve the influence of the parasitic parameters of bus bar on the performance of SAW filter. Based on the proposed method, the filter with the passband insertion loss of less than 1 dB, passband ripple of 0.5 dB, passband standing wave of maximum 2.1,-1.5 dB bandwidth of 75.7 MHz,-3 dB bandwidth of 84 MHz (fractional bandwidth of 4.8%),-30 dB bandwidth of 112 MHz, and the BW-3 dB/ BW-30 dB rectangle factor of 1.33 is developed. The theoretical simulation results of parasitic parameters including the package, bonding wire and bus bar are in good agreement with the experimental test results, indicating the feasibility of using this model to design high-frequency SAW filters.

In this paper, a thin film bulk acoustic wave resonator (FBAR) with a topology of parallel inductors and an external matching circuit was used to realize broadband filtering. A 3D structure simulation of FBAR was performed using Comsol software to extract the curve corresponding to the optimal electrode shape (variable trace pentagon) into the ADS in conjunction with the external matching circuit for band expansion. It was found that the values of inductor Ls in the external matching circuit directly affect the filter bandwidth. After adjustment, the relative bandwidth of 21.15% was achieved at the series resonant frequency of fs=1.97 GHz and parallel resonant frequency of fp=2.03 GHz, which corresponds to a 3 dB bandwidth of 419 MHz and an out-of-band rejection of 11.616 dB at 1 GHz.

The Incredible High Performance (I.H.P.) SAW devices have attracted much attention due to their excellent Q characteristics and temperature stability. In order to develop the wideband filter, the design of a 2-layered I.H.P. SAW substrate structure (Cu electrode/5°Y-rotated LiNbO3 piezoelectric layer/SiO2 function layer/Si substrate) is studied in this paper. Considering the mass loading effects, and combining the distribution characteristics of stress and free charge on the interface between the electrode and the piezoelectric layer, the accurate Finite Element Method and Boundary Element Method (FEM/BEM) is used in the study. Using the continuity boundary condition of the multilayer structure, the composite Green’s function and the admittance of the resonator are calculated accurately. The maximum frequency difference between the resonance point and anti-resonance point is sought to optimize the substrate structure size. The calculation results show that the device with the metallization ratio of 0.5 and structure period (λ/2) of 2 μm has a maximum frequency difference of 138 MHz between the resonant frequency point of 880 MHz and the anti-resonant frequency point of 1 018 MHz when the thicknesses of the function layer, piezoelectric layer and the electrode layer are 0.15λ、0.2λ、0.037 5λ, respectively. The conclusion provides guidance for the design of I.H.P. SAW devices for wideband filters.

With the arrival of 5G communication era, the resonator with high-frequency and ultra wide-bandwith has become an urgent demand of the communication industry. In this paper, a laterally excited bulk acoustic wave resonator (XBAR) with high frequency and ultra wide-bandwidth is designed and fabricated. The resonance frequency of the A1 mode resonator is 5.81 GHz, electromechanical coupling coefficient is up to 39.6% and a Q-3 dB value is 248, and the A3 mode shows a resonance frequency of 17.04 GHz and electromechanical coupling coefficient of 7.0%.The measured temperature coefficient of frequency (TCF) of the A1 and A3 modes of the resonator are -72.6×10-6/℃ and -38.5×10-6/℃, respectively. In addition, a new interdigital electrode (IDT) structure is proposed in this paper, which can suppress the spurious mode and greatly improve the performance of the resonator.

With the development of 5G communication technology, the evolution of communication frequency bands has higher and higher requirements on the performance specifications, package size, and integration of acoustic filters. However, the isolation index is a difficulty point in the design of small-sized surface acoustic wave (SAW) duplexers. This paper studies how to improve the isolation of the duplexer. Based on the Coupling-of-Mode (COM) and the electromagnetic simulation model, a simulation model of the duplexer is established. By improving the topology structure, the common ground inductance and package, etc., finally, the design of a Band 5 duplexer with -60.5 dB of isolation at the Tx end and -50 dB of isolation at the Rx end, small insertion loss has been realized. Comparing with the unimproved duplexer, the isolation of the proposed one has been significantly improved.

Two kinds of thin film heterogeneously stacked resonators based on AlN piezoelectric material and 10% Sc-doped AlN piezoelectric material respectively have been developed in this paper. The effect of Sc doping on the acoustic excitation of the resonator and the frequency-temperature performance of the device are compared and analyzed by the finite element simulation and experiment. The results show that Sc doping may affect the resonant frequency, electromechanical coupling coefficient and corresponding frequency-temperature coefficient (TCF) of the acoustic wave excited by the piezoelectric thin-film stacked resonator, and has different effects on the TCF of the resonant and anti-resonant points of the excited acoustic wave. This work has great application potential in the field of sensors and filters.

Owing to the excellent noise immunity and electromagnetic interference immunity characteristics, balanced filters has become vital key building block in low-noise communication systems in complex spectrum circumstance. In this paper, a balanced bandpass filter with common mode suppression is proposed and designed by using differential/common mode theory, admittance matrix and transmission matrix analysis. The centered frequency of presented balanced filter is located at 1.4 GHz and its fractional bandwidth can reach 74.3%, which cover 2G, GPRS, 3G, and 4G LTE bands. Since two pairs of transmission zeros is introduced separately lower and upper sideband, the developed balanced bandpass filter is of high roll-off rate and sharp shirt. In presented balanced bandpass filter, 10 dB of common mode suppression within differential mode passbands is achieved. The differential mode out of band suppression level is higher than 20 dB, and the circuit size of exploited balanced filter is only occupies 0.17λg×0.17λg.

The one-port resonator and SAW filter were developed by using the SOI substrate with 42°Y-X LiTaO3/SiO2/Si structure and optimizing design such as suppression of the transverse mode. The testing results show that the resonant frequency of resonator is 1.5 GHz, the Bode Q value is as high as 4 000. The center frequency of SAW filter is 1 370 MHz, and the insertion loss is -1.2 dB. The bandwidth of 1 dB is 74 MHz, and the relative bandwidth is 5.4%. The stop-band rejection is more than 40 dB, and the temperature coefficient is better than -9×10-6/℃ at -55~+85 ℃. The product has the characteristics of high frequency, wide bandwidth, low loss, low temperature drift and high stop-band rejection, and its performance specifications are excellent and has good practicability.

In this paper, a small size edge-reflected surface acoustic wave (SAW) IF filter based on a lithium tantalate piezoelectric substrate is modeled and simulated by COMSOL Multiphysics finite element simulation software, and the finite element simulation analysis of the physical fields of solid mechanics and electrostatics is carried out for this SAW filter. At the same time, the effects of electrode material and electrode thickness on the resonant and anti-resonant frequencies of the admittance curves are discussed. It is demonstrated that the electrode thickness can affect the parasitic resonance of the admittance curves. The thickness of the electrode at the weakest resonance in the admittance curves is selected as the optimum thickness of the electrode. Finally, the Al with a thickness of 1.6 μm is chosen as the electrode of the small size SAW filter and the simulation analyses of the transmission responses under different substrate end face positions are carried out. The conventional 2D FEM simulation results show that the device has a center frequency of 126.35 MHz, insertion loss of -2.57 dB, and -3 dB bandwidth of 3.3 MHz when the end face of the substrate edge is 0 from the edge of the IDT. The simulation result has a high matching degree with the response obtained by COM model simulations, which further proves that the reflection of the large dielectric constant substrate end face can be equated to a strongly reflected reflective strip from the perspective of theoretical simulation.

With the increase of the transmission efficiency of the communication system, the bandwidth of the filter is required to be wider and wider. If the conventional SAW filter design technology is used, it will face the problem of high loss or insufficient bandwidth. Based on the development of a series of wideband SAW filters, this paper summarizes the design methods of wideband SAW filters with a relative bandwidth of more than 8% by using LiTaO3 piezoelectric substrate with special technology. These methods include using peripheral inductance and capacitance to increase the difference between the resonant frequency and the anti-resonant frequency of the SAW resonator to improve the bandwidth of the impedance element filter, using multi-mode longitudinal couple resonance structure to increase filter bandwidth, and using dual-pass filter parallel structure to obtain large-bandwidth filter. Each of the described methods has advantages and disadvantages, and the achievable bandwidth is about 9%.

A miniaturized, high out-of-band rejection bandpass filter with three transmissions zeros was proposed in this paper. Three transmission zeros can be introduced into the response of the comb-line filter by using the coupling control. By using the source/load coupling and the spurlines etched on the transmission line, the out-of-band rejection can be reduced, so that the filter can obtain better performance. A miniaturized bandpass filter is designed and fabricated. The simulation results show that the working center frequency and relative bandwidth of the filter designed in this paper are 2.12 GHz and 20%, respectively, and the return loss of the filter is better than 40 dB, insertion loss is less than 0.2 dB, and out-of-band rejection is less than 40 dB. In addition, the filter has the advantages of simple and compact structure and easy processing. The actual test results are basically consistent with the simulation ones.

A physical simulation method for structural thermal deformation based on the macro fiber composites (MFC) is proposed in this paper. The correlation equation between the thermal deformation of the cantilever beam structure and the MFC-driven deformation is established. And it is compared and verified with the finite element simulation. For the composite laminates, aiming at the simulation of the structural thermal deformation, the driving voltage of MFC is inversely calculated by using the optimized method, so as to guide the d MFC riving experiment. The results show that the simulation results are consistent with the theoretical expression for the bending deformation of the homogeneous cantilever beam. The displacement errors of the measuring points between the MFC-driven deformation and thermal deformation are all within 5% for the bending-torsional coupled deformation of the laminate, which verifies the effectiveness of the physical simulation method proposed in the paper.

In this paper, the PVDF/rGO composite films with different mass ratios of reduced graphene oxide (rGO) were prepared by spin-coating method. The layer-by-layer assembly sandwich heterostructure PVDF/rGO (PVDF/rGO-PVDF-PVDF/rGO) piezoelectric nanogenerator (PNG) was manufactured via the layer-by-layer stacking method. The effects of the rGO doping and heterostructre design on the output performance of PNG have been systematically studied. The results showed that the open circuit voltage and short circuit current of the single layer PVDF/rGO composite films PNG were up to 1.76 V and 0.18 μA respectively when the rGO doped mass fraction was 0.4wt%. The open circuit voltage of the PNG with layer-by-layer assembly sandwich-like heterostructure PVDF/rGO0.4-PVDF-PVDF/rGO0.4 was as high as 7.72 V, which was 4.39 times that of the single-layer PVDF/rGO composite PNG, and the short circuit current was as high as 0.69 μA, which was 3.83 times that of single-layer PVDF/rGO composite PNG，which promotes the transfer of electric charge and improves the utilization rate of electric charge. Over 4 000 pressing-releasing cycles tests of the PNG with PVDF/rGO0.4-PVDF-PVDF/rGO0.4 composite layer-by-layer heterostructre have been carried out. The results show that the three-layer heterogeneous structure composite PNG has stable piezoelectric output, which is expected to be widely used in the fields of flexible wearable electronic devices, human-computer interaction and electronic skin.

Targeting the requirement of implantable micropump in the field of biomedicine, in order to increase the output flow rate of micropump under low voltage and miniaturization conditions, a piezoelectric valveless implantable micropump with double-layer pump chamber was designed in this paper. Based on the piezoelectric coupling simulation of the piezoelectric vibrator and the electric-solid-fluid three-phase coupling simulation of the proposed micropump, the validity of the design of the double-layer chamber micropump was verified, and the structural and driving parameters were optimized. The experiments were carried out to verify the feasibility of the results of the coupled simulation and the flow range of the proposed micropump was tested. The results show that the optimal design parameters of the micropump are as follows: the diffusion angle is 30°, the neck width is 300 μm and the height of the upper pump chamber is 100 μm. The net flow of micropump increases with the increase of voltage, and it is suitable for low-frequency drive. The experiments results show that the output flow rate of the double-layer pump chamber piezoelectric valveless micropump is 5.38 times higher than that of the conventional piezoelectric valveless micropump.

A piezoelectric linear actuator based on a double-acting plate stator structure is proposed to address the problem of small output power of existing single-plate piezoelectric actuators and to enrich the form of macro-micro linear actuators. The first-order longitudinal vibration and the second-order bending vibration of the double-acting plate are selected as the operating modes of the actuator, the longitudinal vibration is used to drive the mover to slide and the contact and separation between the driving foot and the mover is realized by the bending vibration. The process of driving the mover forward by the double-acting plate stator is explained and the elliptical trajectory equation of the driving foot and its ellipse forming conditions are derived. The structural dimensions of the stator are optimized to 45.3 mm×11.2 mm×6 mm and the simplification of the two operating modes is realized. An electro-mechanical coupling analysis model of the stator is established, the oscillations of the two-phase operating modes are solved. The frequencies of the two-phase modes are 34 994 Hz and 34 998 Hz respectively. The elliptical trajectory of the stator driving foot is simulated and the voltage regulating and frequency modulation characteristics of the stator are obtained. When the amplitude and frequency of the drive voltage are 250 V and 34 938 Hz, the amplitude of the driving foot along the x and z directions reaches 1.34 μm and 2.73 μm respectively, which is sufficient to drive the movers. The design of the assembly structure of the double-plate actuator has been completed and a three-dimensional assembly model is presented. The actuator is expected to output large speed and power, and has wide application prospects.

The high-speed on-off valve driven by smart materials has better dynamic and static characteristics than the electromagnetic high-speed on-off valve. Aiming at the disadvantage of small output force of traditional cantilever structure piezoelectric bimorph, a pneumatic high-speed on-off valve based on piezoelectric bimorph is studied in this paper, and a simply supported beam structure fixing method is proposed. The fluid structure coupling of the piezoelectric elements is analyzed with the COMSOL. The key structural parameters of the valve are optimized, and the prototype is tested. The experimental result shows that the operating frequency bandwidth reaches 280 Hz, and the maximum flow is 30.7 L/min at the pressure differential of 0.3 MPa.

Based on the requirement of removing water from the surface of the intelligent vehicle vision sensor, a device that uses piezoelectric transducers to excite Lamb waves to drive droplet motion is proposed, and a two-dimensional finite element model of piezoelectric vibrators and elastic plate is established in this paper. First, the frequency analysis of the piezoelectric vibrators under free boundary conditions is performed using COMSOL Multiphysics simulation software. The first 4 order eigenmodes are obtained, and the second order mode has the largest relative displacement of the structure, its characteristic frequency is the resonance frequency. Then, the propagation characteristics of the Lamb wave excited by the piezoelectric vibrator in the plate are analyzed. The results show that the Lamb waves appear to have significant dispersion characteristics in the plate, and the Lamb waves dominated by the A0 mode are excited by changing the piezoelectric vibrator spacing to improve the droplet driving effect. Finally, the feasibility of the Lamb wave driven droplet model is verified by experiments.

In this paper, a frequency up-conversion piezoelectric energy harvester based on a type of spring vibration platform is proposed to solve the problem of low efficiency of low-frequency vibration energy harvesting. The cubic positive correlation between the output power of piezoelectric cantilever beam and the excitation frequency is analyzed, and the reason for harvesting low frequency vibration energy by up-conversion is explained. The Hertzian contact theory is used to analyze the contact-force between the plucking plate and the piezoelectric cantilever beam, and the electromechanical coupling model of the piezoelectric energy harvester with the plucking excitation is established. After comprehensively considering the influencing factors of the overlapping length and the thickness of the plucking plate, the rectangular stainless steel plate with a thickness of 0.1 mm is selected. The experiment shows that the output power of the single-plucking up-conversion V25W piezoelectric cantilever beam can reach 9.6 mW under the excitation of 1g(g=9.8 m/s2） and 5.67 Hz, which has strong low-frequency energy harvesting performance.

In order to investigate the application of direct flexoelectric effect, a model of flexoelectric energy harvester based on the simply supported flexoelectric plate was established. Firstly, the dynamic response of the simply supported plate was derived when subjected to point loading excitation. Secondly, according to the direct flexoelectric effect, the energy harvesting theory induced by the dynamic strain gradient is established, and the expression of output voltage and power at both ends of the external load resistance are derived. Finally, the effects of different parameters, such as mode shape, point loading excitation location, flexoelectric patch size, thickness and location, and loading resistance and so on, on the output voltage and power were analyzed. The results show that the output power of the flexoelectric energy harvesting was affected by different vibration mode, patch location, flexoelectric patch thickness and so on. The analysis results have practical significance for optimizing the energy output of the flexoelectric electrical energy harvester with plate structure.

The electromechanical impedance (EMI) method is one of the hot research fields of structural health monitoring (SHM) technology. However, in practical applications, the impedance signal measured by EMI method will be disturbed by temperature, resulting in misjudgment of damage. Firstly, the reason for the change of impedance caused by temperature is analyzed theoretically. Then, taking the typical PZT-5H ceramic sensor in EMI method as the research object, the influence of temperature on the characteristics of PZT impedance is tested and analyzed. It is found that the frequency shift of impedance peak is linear with temperature, and the influence of temperature on the peak frequency shift is closely related to frequency. Further, combined with the variation law of frequency offset and amplitude, the temperature effect correction model of structural health monitoring based on the mechanical impedance method is established. The results lay a foundation for reducing the influence of ambient temperature on the impedance characteristics of PZT.

The monitoring of environmental vibration is very important for the safe operation of the equipment. The perception of environmental vibration information can be realized by using piezoelectric vibration energy harvester, and then the safe operation status of the equipment can be monitored wireless through intelligent information processing methods. Combining the wireless sensing with deep learning, on the basis of fully studying the output signal characteristics of piezoelectric vibration energy harvester, an optimized convolutional neural network model is proposed to identify the abnormal vibration patterns of the environment. The intelligent sensing wireless monitoring sensor node is designed and implemented. When the system works, the sensor node can monitor the environmental vibration and temperature information and alarm the abnormal events. The test results show that the wireless transmission distance exceeds 100 m,the sensor node can realize real-time monitoring of the environmental vibration events, the alarm time is less than 5 s, and the accuracy of environmental vibration pattern recognition can reach 95.7%. The node can monitor the ambient temperature and give an accurate alarm for abnormal combustion events in less than 3.7 s. The node has a wide application prospect in fields target monitoring and other occasions.

A high sensitivity optical fiber temperature sensor based on Mach-Zehnder interferometer(MZI) and dimethyl silicone oil(DSO) is introduced in this paper. The sensor consists of MZI and DSO filled on its surface. The MZI consists of single-mode fiber-tapered no-core fiber-single-mode fiber. After the DSO is filled, the resonant peak of MZI shifts a little to the right. The ambient temperature is measured by tracking the change of MZI resonant peak wavelength with temperature. The temperature sensitivity of the sensor is -97.7 pm/℃, while the temperature sensitivity of MZI without DSO is -50.1 pm/℃. The sensitivity of the sensor is increased by about 1.95 times. The sensor has the advantages of simple structure, easy fabrication, low cost and high sensitivity, and has a certain application prospects.

In order to improve the sensitivity and linearity of the sensor, it is proposed to change the surface roughness of the optical fiber and the type of probe. Firstly, the D-type optical fiber with rough surface is prepared by the self-built wheel optical fiber side polishing system, and then one end of the optical fiber is coated with a layer of Ag film, which can be used as a mirror, so as to obtain the D-type optical fiber probe. Finally, when detecting the sensing characteristics of the probe, it is found that the change of the refractive index of the measured solution will cause the absorption of different energy, which will change the optical power received by the optical power meter. A series of experiments results show that the prepared D-type optical fiber sensor not only has very strong stability, but also has very good linearity. In particular, the sensitivity and linear correlation coefficient of the sensor with polishing loss of 18 dB are as high as 66.02 dB/RIU and 99.58%, respectively. The measurement and calculation of the accuracy of refractive index show that the accuracy can be as high as 0.000 04. The results show that the sensing structure has the potential to be widely used in biochemical sensing (such as COVID-19 pandemic) and real-time monitoring of environmental pollution.

Aiming at the need for high-precision error compensation, higher application accuracy and faster startup speed of the fiber optic platform system, the article takes the error characteristics such as the lever arm error of the accelerometer, time asynchronous error of the inertial instruments, the installation error and the scale factor error into account, the two-level calibration Kalman filter equation is established. The Kalman filtering method is used to identify the error parameters, and the method is simulated and verified by experiments. The simulation and experimental results show that the designed system-level calibration algorithm can estimate all error parameters and has higher application performance, which is of great significance to improve the application accuracy of the high-precision fiber optic platform system.

The semicircular canal is an angular displacement sensing organ in human vestibular system. In this paper, based on the geometric size, mechanical properties and internal structure of human semicircular canal, a bionic angular acceleration sensor with similar structure size and working mechanism as human semicircular canal is designed and fabricated by using the sensor with symmetrical electrode metal-core PVDF fiber (SMPF). At the same time, an experimental system is built to verify the sensing theoretical model of bionic semicircular canal sensor. The experimental results show that the working mechanism of the sensor is basically consistent with the derivation results of the mathematical model. The bionic sensor outputs electrical signals with corresponding amplitudes under different acceleration stimuli. Through the frequency sweep experiment, it is confirmed that the natural frequency of the system is about 10 Hz, which can be used for the motion detection of human head.

A double ridged horn antenna with trapezoidal grooves is proposed in this paper. The trapezoidal groove structure is introduced into the aperture plane and the outer side wall, which can effectively suppress the current on the outer wall of the horn, so as to reduce the sidelobe of the horn antenna. The horn wall of antenna is designed as hollow structure, which reduces the weight of antenna. The antenna adopts the 3D printing technology, which effectively solves the problems of difficult processing and poor consistency in traditional methods. The simulated and measured results show that the proposed antenna design can effectively improve the antenna gain. The antenna gain is higher than 10.32 dBi and the return loss is lower than -10 dB at the operating frequency band of 5~ 10 GHz and the peak gain reaches 14.61 dBi at 9.6 GHz. Adopting the hollow structure design of the antenna wall can reduce the antenna mass by 74%. The test results are basically consistent with the simulation ones.

A millimeter wave differential phase shifter working at 30~32 GHz is proposed in this paper. Its size is 30 mm×18 mm×0.127 mm. The phase shifter is designed on the basis of a microstrip line and consists of a central circular ring and a pair of split resonant rings (SRR). The optimization of S-parameter in the operational frequency band is realized by changing the radius of the central ring. Taking the transmission phase of the reference line as the standard, the differential phase shifts of 22.5°, 45°, and 90° are sequentially realized by changing the radius of the SRRs. The return loss of this phase shifter is less than -10 dB, the insertion loss is better than 1.4 dB, and the simulated maximum phase deviation is less than 5° at the designed frequency range. Moreover, the proposed structure is simple and convenient to fabricate. The reliability of the simulation result is verified by the sample test.

The airborne ultrasound can be used to remove the moisture at room temperature, which has outstanding advantages for drying heat-sensitive fruits. This paper investigates the microflow phenomenon the airborne ultrasound during the drying process based on the finite element simulation software and experiments. The effect of airborne ultrasound on the microstructure of apple slices and the effect of the ultrasonic power on the moisture content of fruit during the drying process are studied. The result shows that the tissue porosity of apple after airborne ultrasound drying treatment are significantly enlarged, which is beneficial to the diffusion of moisture inside the apple, at the same time, the airborne ultrasound drying can better maintain the microstructure of the sample. Compared with the apple slices without ultrasound treatment, the moisture content of the apple slices after airborne ultrasound treating has been reduced significantly, and the drying rate can rapidly increase in a short time. The above-mentioned results have reference value for understanding the mechanism of airborne ultrasound drying.