Modified Mach–Zender laser interferometer for probing bulk acoustic waves

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

Meltaus

Pensala

et al. 2012

Aalto University publication series DOCTORAL DISSERTATIONS 112/2014 © Kimmo Kokkonen AbstractThe research summarized in this dissertation focuses on the development of a heterodyne scanning laser interferometer and of data-analysis techniques for the characterization and analysis of the surface vibration fields in microacoustic devices and test structures.The heterodyne laser interferometer enables a phase-sensitive, absolute-amplitude detection of the out-of-plane component of a surface vibration field, with a minimum detectable amplitude of less than a picometer, while the lateral resolution is better than 1 micrometer. The instrument features a flat frequency response up to 6 GHz.The phase-sensitive absolute-amplitude data enables the visualization of the actual wave behavior in electromechanical components and test structures, but more importantly, it is the basis for further analysis. The research instrument is applied to the study of electroacoustic devices based on surface acoustic wave (SAW) and bulk acoustic wave (BAW) technologies. Two novel SAW devices are studied in detail: a phononic crystal (PnC) structure and a scattering structure resulting in a random wave field. PnCs are acoustic metamaterials that can provide engineered material properties. The laser interferometric measurements were amongst the first to directly characterize the wave interaction with the PnC. SAW slowness curves of an anisotropic substrate material are extracted by measuring and analyzing the scattered random wave field. Data analysis methods are developed further in the context of BAW research by experimentally addressing two important aspects of device design: the correct operation of the acoustic reflector used to confine the energy in the resonator, and investigation of the role of the dispersion and standing wave resonances to the spurious responses often observed in high-Q resonators. Fourier transform techniques are used for selective visualization of wave fields and for the extraction of the dispersion characteristics of the plate-waves. The dispersion data are then further used to analyze the transfer characteristics of an acoustic reflector and to study the properties of lateral eigenresonances and the lateral energy confinement in detail.The research described in this thesis provides a detailed characterization of the operation of SAW and BAW devices and effects within, highlighting and further developing the experimental characterization capabilities and data-analysis methods.Keywords laser interferometry, microacoustics, surface acoustic waves, bulk acoustic waves Tiivistelmä Väitöskirjatyö käsittelee heterodyne-tyyppisen laserinterferometrin sekä interferometrin tuottaman datan analyysitekniikoiden kehittämistä pintavärähtelykenttien karakterisoimiseksi ja analysoimiseksi mikroakustisissa komponenteissa ja testirakenteissa.Työssä rakennettu heterodynelaserinterferometri mahdollistaa pintavärähtelyiden vaiheherkät absoluuttiamplitudimittaukset aina 6 GHz taajuuteen asti. Laitteisto kykenee värähtely-kenttien k...

“…Interferometers have gained popularity as the optical detection method of choice and several setups have been published [21][22][23][24][25][26][27][28][29][30][31][32][33].…”

Section: Optical Characterization Of Surface Vibrationsmentioning

confidence: 99%

Measurement of evanescent wave properties of a bulk acoustic wave resonator [Letters]

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

Meltaus

Pensala

et al. 2012

“…[1][2][3][4][5][6][7] Laser interferometry is a noncontact optical method that enables direct measurement of wave fields in an acoustic component. It has been also used to characterize the plate-wave dispersion properties in thin-film BAW resonators ͑see, e.g., Refs.…”

mentioning

confidence: 99%

Characterization of energy trapping in a bulk acoustic wave resonator

Applied Physics Letters

Meltaus

Pensala

et al. 2010

Acoustic wave fields both within the active electrode area of a solidly mounted 1.8 GHz bulk acoustic wave resonator, and around it in the surrounding region, are measured using a heterodyne laser interferometer. Plate-wave dispersion diagrams for both regions are extracted from the measurement data. The experimental dispersion data reveal the cutoff frequencies of the acoustic vibration modes in the region surrounding the resonator, and, therefore, the energy trapping range of the resonator can readily be determined. The measured dispersion properties of the surrounding region, together with the abruptly diminishing amplitude of the dispersion curves in the resonator, signal the onset of acoustic leakage from the resonator. This information is important for verifying and further developing the simulation tools used for the design of the resonators. Experimental wave field images, dispersion diagrams for both regions, and the threshold for energy leakage are discussed.

“…To develop better components that have their operation based on mechanical vibrations, it is important to be able to directly study the actual vibration fields. Consequently, optical setups based on various techniques [1][2][3][4][5][6][7][8] have been developed in order to facilitate noncontact vibration measurements that do not disturb the device operation.…”

mentioning

confidence: 99%

Scanning heterodyne laser interferometer for phase-sensitive absolute-amplitude measurements of surface vibrations

Applied Physics Letters

Kaivola

2008

We describe a scanning heterodyne interferometer for imaging surface vibrations with a wide frequency range, with current electronics, up to 6GHz. The heterodyne operation facilitates measurement of absolute amplitude and phase of the surface vibration without calibration. Currently, the setup allows detection of vibration amplitudes down to ∼1pm with a lateral resolution of <1μm. The interferometer is designed to accommodate the different sample types, e.g., surface and bulk acoustic wave devices and micromechanical resonators. The absolute-amplitude and phase information allows for a thorough characterization of surface vibrations in such components and provides direct information of the vibration fields not obtainable via electrical measurements.