Research on micro-sized acoustic bandgap structures (original) (raw)
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Microfabricated VHF acoustic crystals and waveguides
Sensors and Actuators A: Physical, 2008
Microfabricated acoustic crystals have been designed and experimentally verified. The acoustic crystals are realized by including tungsten (W) scatterers in a SiO 2 matrix. Wide frequency ranges where acoustic waves are forbidden to exist (acoustic bandgaps, ABG) are formed due to the large acoustic impedance and mass density mismatch between W and SiO 2. The acoustic crystal structures are fabricated in a 7-mask process that features integrated aluminum nitride piezoelectric couplers for interrogating the devices. Acoustic crystals in a square lattice have been measured at 67 MHz with greater than 30 dB of acoustic rejection and bandwidths exceeding 25% of the midgap. Single and multimode acoustic waveguides have been realized by defecting the acoustic crystals through removal of a subset of the W scatterers. These waveguides achieve relative transmission of up to 100% for the propagating modes.
Physical Review E, 2002
The propagation of acoustic waves in a two-dimensional composite medium constituted of a square array of parallel copper cylinders in air is investigated both theoretically and experimentally. The band structure is calculated with the plane wave expansion ͑PWE͒ method by imposing the condition of elastic rigidity to the solid inclusions. The PWE results are then compared to the transmission coefficients computed with the finite difference time domain ͑FDTD͒ method for finite thickness composite samples. In the low frequency regime, the band structure calculations agree with the FDTD results indicating that the assumption of infinitely rigid inclusion retains the validity of the PWE results to this frequency domain. These calculations predict that this composite material possesses a large absolute forbidden band in the domain of the audible frequencies. The FDTD spectra reveal also that hollow and filled cylinders produce very similar sound transmission suggesting the possibility of realizing light, effective sonic insulators. Experimental measurements show that the transmission through an array of hollow Cu cylinders drops to noise level throughout frequency interval in good agreement with the calculated forbidden band.
Hypersonic phononic crystal for surface acoustic waves
2010 IEEE International Ultrasonics Symposium, 2010
A phononic crystal exhibiting a band gap in the near-gigahertz frequency range for surface acoustic waves was fabricated in a lithium niobate substrate. Reflection and transmission properties of the sample were characterized both electrically and optically, by means of embedded broadband interdigital transducers and optical heterodyne interferometry, respectively. Measurements performed for (XZ) propagating surface waves show the existence of a band gap between 660 and 900 MHz. Optical measurements confirm that the phononic crystal behaves as a perfect mirror for waves propagating at frequencies within the band gap. Outside the band gap, transmission can be observed for frequencies below, but also above the forbidden frequency range, hence showing that losses experienced by high frequency surface acoustic waves, i.e. for modes located beyond the sound line, can be partially overcome.
Evidence for complete surface wave band gap in a piezoelectric phononic crystal
Physical Review E, 2006
A complete surface acoustic wave band gap is found experimentally in a two-dimensional square-lattice piezoelectric phononic crystal etched in lithium niobate. Propagation in the phononic crystal is studied by direct generation and detection of surface waves using interdigital transducers. The complete band gap extends from 203 to 226 MHz, in good agreement with theoretical predictions. Near the upper edge of the complete band gap, it is observed that radiation to the bulk of the substrate dominates. This observation is explained by introducing the concept of the sound line.
Designing a Ultrasound Coupler on a Phononic Crystal Platform
We are reporting the design of a new ultrasound coupler with the operating frequency of ~28.69 MHz, by means of coupling a W1 waveguide to a ring resonator based on a 2-D phononic crystal (PnC) platform. The 2-D PnC is composed of a periodic array of infinitely long cylindrical rods of steel, arranged in a square lattice of constant a 0 =6 µm, in air background. The radii of the steel rods are r 0 =0.42a 0 =2.52 µm. Mechanical waves propagating through this particular PnC are of acoustic types, experiencing a 10-MHz wide phononic bandgap within the frequency range of 25 MHz≤ f ≤ 35 MHz. The PnC based W1 waveguide that can be made by removing a row of rods in a straight line guides an acoustic mode within the phononic bandgap. The PnC ring resonator that is assumed to be made by removal of the rods from the periphery of a square of side lengths L=3a 0 =18 µm. Simulations are done by employing plane wave expansion (PWE) and finite element (FE) methods.
Observation of surface-guided waves in holey hypersonic phononic crystal
Applied Physics Letters, 2011
We observe experimentally the propagation of surface-guided waves in a hypersonic phononic crystal, both in the radiative and nonradiative regions of the spectrum. Combining electrical measurements in reflection and transmission as well as optical maps of the surface displacement, a band gap extending from 0.6 to 0.95 GHz is identified in a square lattice array of 1 m radius air holes milled in lithium niobate. The optical measurements reveal the transmission of surface-guided waves above the band gap, well inside the sound cone.
Ultra high frequency (UHF) phononic crystal devices operating in mobile communication bands
2009 IEEE International Ultrasonics Symposium, 2009
Recently phononic crystal slabs operating in the very high frequency (VHF) range have been reported and have gained interest for RF signal processing. This paper reports phononic crystal slabs and devices operating in the commonly used GSM-850 and GSM-900 cellular phone bands, representing nearly an order of magnitude increase in operating frequency compared to the state-of-the-art. Phononic crystals centered at 943 MHz are formed by arranging 1.4 µm diameter W rods in a square lattice with a pitch of 2.5 µm inside a 1.85 µm thick suspended SiO 2 membrane. The resulting phononic crystal has a bandgap width of 416 MHz or 44% and a maximum bandgap depth of 35 dB. Waveguide devices formed by placing defects in the phononic lattice have also been realized with propagation frequencies of 780 and 1060 MHz.
Waveguide-Based Phononic Crystal Micro/Nanomechanical High-$Q$ Resonators
Journal of Microelectromechanical Systems, 2000
In this paper, we report the design, analysis, fabrication, and characterization of a very high frequency phononic crystal (PnC) micro/nanomechanical resonator architecture based on silicon PnC slab waveguides. The PnC structure completely surrounds the resonant area, and the resonator is excited by a thin aluminum nitride-based piezoelectric transducer stack directly fabricated on top of the resonator. This architecture highly suppresses the support loss of the resonator to the surroundings while providing mechanical support and electrical signal delivery to the resonator. Qs as high as 13 500 in air at a frequency of ∼134 MHz with a motional resistance of ∼600 Ω and 35-dB spurious-free range of ∼20 MHz are obtained. Comparing the Q of this resonator with the previously reported lateral bulk acoustic wave resonators with a similar stack of layers confirms the support loss suppression in this architecture.