A novel ultrasonic horn atomizer is developed for the purpose of obtaining small size droplets at a large flow rate. The
ultrasonic horn has a non-monotonically decreasing cross sectional area to provide a large atomizing surface. Consisting
of two horns and one actuator section, the 301 kHz atomizer nozzle is made of {100} silicon wafer with its axis aligned
in the <100> direction to minimize the length. Two PZT plates are adhered to each side of the actuator section to provide
driving power. This device atomizes the liquid film on its nozzle tip to generate droplets. It is capable of atomizing more
than 350 μl/min water into droplet. The mean diameter of droplet is 9.61 μm and the size distribution is quite narrow.
The atomizing mechanism is based on the capillary wave on liquid surface. Once the wave amplitude exceeds the critical
value, the motion of surface liquid becomes unstable and releases droplets. Therefore, driving at resonant frequency is
the most effective way for atomizing. Dimension deviation combined with different kind of liquid to be atomized causes
resonant frequencies of nozzles changed from time to time. Due to the high Q nature of nozzles, atomizing performance
will drop drastically once the driving frequency is different from its resonant frequency by very little amount. Therefore,
a feedback circuit is designed to tracking resonant frequency automatically instead of adjusting driving frequency
manually. Comparing the atomizing performance between the open loop system and the closed loop system, significant
improvement is obtained.
When the thickness of a plane structure is much smaller than its other characteristic lengths, a plate model is more realistic than a beam model. For a thin piezoelectric layer fully coated with metal electrodes on its top and bottom surfaces, the internal electric field is simple and easy to model. Therefore, it is advantageous to derive a piezoelectric composite plate model based on e-form constitutive equations. This approach is adopted to develop a mathematical model of Kirchhoff–Love type for a plate composed of a piezoelectric layer and a metal layer. To develop a method for calculating the loaded-circuit voltage between the top and bottom electrodes is one of the major tasks of this paper. The electric power generated from piezoelectric layer is found by modal analysis. Top and bottom electrodes of the piezoelectric layer are shorted for calculating resonant frequencies and mode shapes. Once these two electrodes are connected to an external circuit load, boundary conditions of top and bottom surfaces become nonhomogeneous. Superposition of short-circuit modes and one particular field constitutes the nonhomogeneous solution. A composite plate composed of a 0.3mm thick copper layer and a 0.2mm thick PZT-5A layer is investigated. The cantilever plate of 25mm in length is base-excited near the first resonant frequency. When connected to a circuit with certain load impedance, more than 80% efficiency of power generation can be achieved.
There are five kinds of plane waves in a general piezoelectric solid, three of them are quasi-acoustic waves and the other
two are quasi-electromagnetic waves. When these plane waves propagate from interior of a half space to the solidvacuum
interface, electromagnetic waves in vacuum are induced. For the same input power, the power of EM waves in
the free space induced by quasi-acoustic waves is much smaller than that induced by quasi-electromagnetic waves. That
is, the EM waves are hardly to be generated mechanically in piezoelectric materials. Piezoelectric superlattice formed by
intervallic polarizing oppositely along one direction can have significant coupling between phonon and photon in the
vicinity of the first Brillouin zone center. Since the acoustic energy and electromagnetic energy of polaritons in the
piezoelectric superlattice can be very close, the free space EM waves excited by polaritons can be expected. LiNbO3 is
adopted as an example. Once LiNbO3 is polarized intervallic oppositely, the power ratio increases significantly. The free
space electromagnetic field coupled with polaritons can extend very far from the solid -vacuum interface.
A superlattice is formed in a piezoelectric substrate by intervallic polarizing oppositely along one direction. Wave
propagation in this structure is studied with plane-wave expansion method. The polariton behavior in the superlattice is
obtained by solving Newton's equations of motion and Maxwell's equations simultaneously. Significant coupling
between mechanical and electromagnetic energy occurs in the vicinity of the center of the first Brillouin zone. At the
frequency bands of strong coupling, part of the excitation electromagnetic energy will convert into mechanical energy in
the superlattice or radiating into free space as EM waves. By measuring the S parameters, the coupling behavior is
observed and the frequency bands corresponding to different kinds of energy conversion can be identified.
This paper compares the simulation results with the experimental results of impedance analysis and longitudinal vibration measurement of micro-fabricated 0.5 MHz silicon-based ultrasonic nozzles. Impedance analysis serves as a good diagnostic tool for evaluation of longitudinal vibration of the nozzles. Each nozzle is made of a piezoelectric drive section and a silicon-resonator consisting of multiple Fourier horns each with half wavelength design and twice amplitude magnification. The experimental results verified the simulation prediction of one pure longitudinal vibration mode at the resonant frequency in excellent agreement with the design value. Furthermore, at the resonant frequency, the measured longitudinal vibration amplitude gain at the nozzle tip increases as the number of Fourier horns (n) increases in good agreement with the theoretical value of 2n. Using this design, very high vibration amplitude at the nozzle tip can be achieved with no reduction in the tip cross sectional area. Therefore, the required electric drive power should be drastically reduced, decreasing the likelihood of transducer failure in ultrasonic atomization.
Due to the coupled mechanical and electrical properties, piezoelectric materials are widely adopted for sensing purpose. In order to predict the device behavior in the design phase, many finite element tools were developed. However, most of the elements did not concern about the equipotential nature of sensor electrodes and the equipotential constraint has to be imposed in the structure level. This paper develops a composite plate element that the equipotential condition of electrode is ensured automatically. The element is displacement-electric potential type that can model elastic plates bonded with piezoelectric sensing layer. The formulations of displacement and electric potential fields are based on Mindlin plate model and the element is deduced from Hamilton's principle. In order to model physical behavior reasonably, different power series are assigned to displacements and electric potential respectively. Employing penalty function method imposes the equipotential condition on element electrode. Thus the element has the capability to analyze deformation, natural frequencies, and electrical signal efficiently. Patch tests are carried on different problems whose analytic solutions are available. In static constant stress situations, these tests show that the element correctly finds out the displacements, stresses, and electric potential. The excellent convergent rate of the natural frequencies demonstrates it is also good for dynamic analysis.
Wafer bonding is an important fabrication step for some MEMS devices. ALignment of device patterns is vital for a successful bonding. When anisotropic wet etching is employed to fabricate microstructures on single crystal silicon wafers, the same mask may result in different etched patterns on different wafers. If the wafer pair for bonding are not matched well, the position and orientation of device patterns cannot be aligned simultaneously. This article presents a method for position and orientation alignment of the device patterns on wafer pairs. An offset angle indicating mark and a self-aligning bonding fixture are developed to satisfy the alignment requirement. The photomask for wet anisotropic etching contains patterns of indicating marks and wafer cutting targets. The indicating marks provide information of offset angles between device patterns and crystal planes after wet etching. Wafer pairs for bonding are matched with offset angles, depending on the device configuration. Simultaneously align the position and orientation is possible for the matched wafer pairs. Wafers are cut with the guide of cutting targets to ensure they have the same size. The bonding fixture consists of a steel frame and a pair of flat glass plates. The steel frame has a rectangular opening where the wafer pair are sandwiched between the glass plates. The wafer cutting process is the major source of misalignment in this bonding method.
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