Study On The Tunability Of Piezoelectric Composite Structures To Elastic Waves And Its Application Design

Synthetic materials/structures with new physical properties have attracted much attention.In the acoustics field,common artificial structures include phononic crystals and acoustic metamaterials.Their elastic parameters are periodically distributed in space,and different acoustic characteristics can be obtained through the doping and mixing proportion of different materials.At present,artificial intelligence has gradually become the trend in new era.At this point,the shortboard effect of the artificial acoustic structure is highlighted,once designed and processed,the acoustic characteristics/functions are fixed and cannot be adjusted,which is not"intelligent".To compensate for this shortcoming,piezoelectric materials have been introduced into artificial structures.Using the piezoelectric effect of the piezoelectric material,the acoustic characteristics of the structure can be controlled by the circuit elements.And the circuit is easy to disassemble,which possess a certain degree of intelligent tunableness.In this paper,the regulation of elastic wave by piezoelectric composite structure is studied,and some adjustable functional devices/structures are designed by using these adjustable properties.Firstly,the influence of the circuit on the dispersion of one-dimensional and two-dimensional piezoelectric periodic structures is studied.Then based on the two-dimensional piezoelectric periodic structure?namely two-dimensional piezoelectric phonon crystal?,two kinds of adjustable functional structures are designed:adjustable composite waveguide and adjustable filter.In the second chapter,we study the influence of external circuit on the dispersion relationship of one-and two-dimensional piezoelectric periodic structures.The results show that the external circuit can generate bandgap in the piezoelectric periodic structure,and the bandgap bandwidth?or frequency of bandgap generation?can be controlled by the value of the circuit element?capacitance/inductance?.The one-dimensional piezoelectric periodic structure is formed by connecting the piezoelectric pole with periodic composite capacitances?C₁ andC₂?.By adjusting₁C and₂C,two adjustable bandgaps of different frequencies can be obtained respectively,and these two bandgaps can also be obtained simultaneously.The two-dimensional piezoelectric periodic structure,which is a standard two-dimensional piezoelectric phonon crystal,is formed by the periodic arrangement of piezoelectric columns in the epoxy.It is shown that the phonon crystal can produce local resonance and form local resonant band gap under the condition of external inductance of piezoelectric column.The width of band and center frequency are also affected by the filling rate.As the filling rate decreases,the bandgap frequency will gradually decrease?exist a minimum value?;As the filling rate approaches zero,the width of bandgap also approaches zero.Based on the two-dimensional piezoelectric phononic crystals,we design some tunable devices in the following chapters.In the third chapter,an adjustable composite waveguide is designed for two-dimensional piezoelectric phononic crystals with a specific filling rate.The waveguide has two advantages:1.By changing the inductance value,the working frequency of the waveguide can be adjusted in a wide frequency range;2.The waveguide can be arbitrarily designed by changing the distribution state of the circuit.We found that when the piezoelectric phonon crystal is not connected to the external circuit?or the external circuit is in the open circuit?,a wide band gap will appear in the higher frequency area.When the external circuit is connected?or the external circuit is closed?,a local resonant pass band can be formed in the band gap by adjusting the value of the inductance.In view of this characteristic of piezoelectric phononic crystals,we only connect an external circuit to a row of piezoelectric columns to obtain a waveguide.At this time,the working frequency of the waveguide can also be regulated by inductance.In addition,the shape of the waveguide can also be designed through different circuit states?open/closed?.The tunable waveguide may have potential applications in acoustic sensors and acoustic signal processing.In the fourth chapter,based on the specific filling rate of two-dimensional piezoelectric phononic crystals,we design a new tunable filter.The greatest advantage of the filter is that the filtering frequency can be adjusted in a wide range,and the filtering effect is remarkable.The filter is composed of piezoelectric phononic crystal waveguide?non-adjustable?and adjustable point defect.The piezoelectric phonon crystals can be locally connected with external circuits to form point defects.Point defect is the core element of filter and has the function of filtering wave and frequency.The working frequency of the filter is the defect state frequency,which can be adjusted by the external inductance.In addition,we also designed an adjustable filter with multiple channels,which can output the wave from different places/paths.Therefore,it can be used as a waveguide switch,as well as waveguide converter/switcher,with certain application prospects.