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Frequency-filtered images. r-ω space results. (a) Straight waveguide at 322 MHz (row 1) and 482 MHz (row 2). Columns 1 and 2: maps of the experimental and simulated A = |Fω(r, ω)|, together with sections (vertical curves) through the centre of the waveguide. Columns 3 and 4: A cos ϕ. Column 4 includes cross sections in a vertical plane running through the waveguide centres. Both the simulation and experimental data are normalized, with identical scales at the two frequencies in each case. (b) The same for the L waveguide. Cross sections are based on lines or planes though the centre of the waveguide.
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Control of sound in phononic band-gap structures promises novel control and guiding mechanisms. Designs in photonic systems were quickly matched in phononics, and rows of defects in phononic crystals were shown to guide sound waves effectively. The vast majority of work in such phononic guiding has been in the frequency domain, because of the impor...
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Strongly confined waveguiding is one of the main applications of phononic crystals that can be achieved at any frequency and scale. Phononic crystal waveguides replace the cladding of classical homogeneous waveguides by a crystal possessing a complete phononic bandgap. We review the different material systems used to implement phononic crystal wave...
We demonstrate the switching behavioral differences between lossy and nearly lossless edge-mode propagation by non-Hermitian modulation based on the phononic band design of a C3v symmetric, two-dimensional (2D) phononic crystal with a unit cell composed of three air-filled circular holes in polydimethylsiloxane (PDMS). We numerically show that stro...
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Citations
... Zhang 19 created three novel arrays to expand the BG of local resonance, which formed a WG and might be more suitable for noise reduction of railway or highway vehicles compared with the conventional PnC plate. Sun 20 and Otsuka 21 identified the BG and eigenmode of the model by calculating the dispersion relation and displacement field of PnC. They designed the L-shaped WG using defects. ...
... The micro-patterning of two-dimensional phononic crystals on the sample surface has permitted demonstration of the mastering of phonon propagation on the surfaces. It enabled, for instances, the observation of caustics, [53] of negative refraction, [54] or the guiding of ultrasound waves along micron guides in rows of lacunas in two-dimensional phononic crystals [55]. ...
In this article we first present the foundations of ultrafast photoacoustics, a technique where the acoustic wavelength in play can be considerably shorter than the optical wavelength. The physics primarily involved in the conversion of short light pulses into high frequency sound is described. The mechanical disturbances following the relaxation of hot electrons in metals and other processes leading to the breaking of the mechanical balance are presented, and the generation of bulk shear-waves, of surface and interface waves and of guided waves is discussed. Then, efforts to overcome the limitations imposed by optical diffraction are described. Next, the principles behind the detection of the so generated coherent acoustic phonons with short light pulses are introduced for both opaque and transparent materials. The striking instrumental advances, in the detection of acoustic displacements, ultrafast acquisition, frequency and space resolution are discussed. Then secondly, we introduce picosecond opto-acoustics as a remote and label-free novel modality with an excellent capacity for quantitative evaluation and imaging of the cell's mechanical properties, currently with micron in-plane and sub-optical in depth resolution. We present the methods for time domain Brillouin spectroscopy in cells and for cell ultrasonography. The current applications of this unconventional means of addressing biological questions are presented. This microscopy of the nanoscale intra-cell mechanics, based on the optical monitoring of coherent phonons, is currently emerging as a breakthrough method offering new insights into the supra-molecular structural changes that accompany cell response to a myriad of biological events.
... Studying PC cavity modes by imaging at GHz frequencies is of broad interest, notably in sensing and telecommunications; at such frequencies, time-resolved methods are effective in revealing acoustic eigenmode field patterns in real space and -space [42][43][44][45][46]. Here we use a time-resolved optical pump-probe technique to image the 2D acoustic field in a microscopic PC-slab cavity in the range ∼0.1-1 GHz. ...
... While keeping the pump spot fixed, the probe spot is scanned across the sample to generate images of the 2D acoustic wave field evolution over an area of ∼120 × 120 μm 2 in the -plane, allowing animations of the surface motion to be obtained at acoustic frequencies up to ∼1 GHz. The approach is similar to that used for previous PC imaging studies, making use in our case of two probe pulses at an interval of 300 ps to monitor the out-of-plane surface particle velocity [43][44][45]. The use of two probe pulses allows a differential measurement, resulting in the imaging of the out-of-plane velocity rather than the displacement. ...
... The -space plots of Fig. 3(b) are closely related to constantfrequency surfaces in the dispersion relation [42,44,45]. At 80 MHz, Bloch harmonics are clearly seen as faint rings surrounding the central bright ring. ...
We extend gigahertz time-domain imaging to a wideband investigation of the eigenstates of a phononic crystal cavity. Using omnidirectionally excited phonon wave vectors, we implement an ultrafast technique to experimentally probe the two-dimensional acoustic field inside and outside a hexagonal cavity in a honeycomb-lattice phononic crystal formed in a microscopic crystalline silicon slab, thereby revealing the confinement and mode volumes of phonon eigenstates-some of which are clearly hexapole in character-lying both inside and outside the phononic-crystal band gap. This allows us to obtain a quantitative measure of the spatial acoustic energy storage characteristics of a phononic crystal cavity. We also introduce a numerical approach involving toneburst excitation and the monitoring of the acoustic energy decay together with the integral of the Poynting vector to calculate the Q factor of the principal in-gap eigenmode, showing it to be limited by ultrasonic attenuation rather than by phonon leakage to the surrounding region.
... 7 PnCs were used widely to help high-end engines reduce vibration, high-rise buildings reduce wind vibration, and provided a vibration-free environment for ultra-finishing and precision instruments within a precise frequency range. [8][9][10][11][12][13] At present, the bandgap generation mechanism of PnCs mainly includes the Bragg scattering mechanism and local resonance mechanism. [14][15][16] The application of PnCs depends greatly on the width of the bandgap, so it is of great significance to design a structure with a wide bandgap. ...
This paper proposed a two-dimensional composite square lattice structure containing two kinds of inclusions (polymethylmethacrylate and T2 copper). To maximize the relative widths of the gaps between the adjacent energy bands of the phononic crystals (PnCs), an improved multi-parameter genetic algorithm was adopted in this paper. The material distribution and ligament sizes were considered simultaneously by ternary encoding and binary encoding. The propagation wave behaviors of the composite lattice structures were studied by the finite element method. The effects of different lattice shapes and other relevant influencing parameters on the bandgaps were discussed. The results showed that the lattice shape, ligament width, and material density affect the width and the location of the bandgaps, and the effectiveness of the proposed method was demonstrated by a transmission spectrum experiment.
... All-optical time-resolved two-dimensional (2D) imaging techniques for surface acoustic waves up to GHz frequencies have been the subject of much attention over the last two decades [14][15][16][17][18][19][20][21][22][23]. These techniques make use of light pulses with picosecond temporal durations to generate the acoustic waves and to image the acoustic wavefield as a function of time and 2D spatial position. ...
... Spatiotemporal Fourier analysis yields constant frequency images and access to the 2D wavevector and acoustic amplitude as a function of frequency, allowing the extraction of the dispersion relation. Many GHz frequency studies have concentrated on imaging 1D and 2D phononic crystals [16][17][18][19][20][21][22]24], but to our knowledge a systematic study of phonon refraction at boundaries after point-source excitation in a 2D phononic crystal has not been presented. Neither has a quantitative interpretation of such phenomena been forwarded. ...
We exploit a time-resolved ultrafast optical technique to study the propagation of point-excited surface acoustic waves on a microscopic two-dimensional phononic crystal in the form of a square lattice of holes in a silicon substrate. Constant-frequency images and the dispersion relation are extracted, and the latter measured in detail in the region around the phononic band gap. Mode conversion and refraction at the interface between the phononic crystal and surrounding non-structured silicon substrate is studied at constant frequencies. Symmetric phonon beam splitting, for example, is shown to lead to a striking Maltese-cross pattern when phonons exit a square region of phononic crystal excited near its center.
... This ranges from quantum entanglement 3,4 to topological states 5,6 and negative refraction 7 . The ability to engineer phononic spectra gave rise to applications such as phononic shielding in ultracoherent mechanical resonators [8][9][10][11] , wave guiding 12,13 or thermal management 14 . Due to the much lower propagation speed of phonons compared to photons or electrons, PnCs are also promising candidates for quantum information technology based on guiding and storing mechanical motion, especially on length scales too small for photonic approaches 6,[15][16][17][18] . ...
We present a tunable phononic crystal which can be switched from a mechanically insulating to a mechanically conductive (transmissive) state. Specifically, in our simulations for a phononic lattice under biaxial tension (σxx = σyy = 0.01 N m−1), we find a bandgap for out-of-plane phonons in the range of 48.8–56.4 MHz, which we can close by increasing the degree of tension uniaxiality (σxx/σyy) to 1.7. To manipulate the tension distribution, we design a realistic device of finite size, where σxx/σyy is tuned by applying a gate voltage to a phononic crystal made from suspended graphene. We show that the bandgap closing can be probed via acoustic transmission measurements and that the phononic bandgap persists even after the inclusion of surface contaminants and random tension variations present in realistic devices. The proposed system acts as a transistor for MHz-phonons with an on/off ratio of 105 (100 dB suppression) and is thus a valuable extension for phonon logic applications. In addition, the transition from conductive to isolating can be seen as a mechanical analogue to a metal-insulator transition and allows tunable coupling between mechanical entities (e.g. mechanical qubits).
... [23,24] One of the earliest implementations of a phononic waveguide for SAW was achieved by managing line defects in phononic crystals made by periodic arrays of holes in a solid matrix. [25] A subsequent design demonstrated a phononic waveguide integrated with IDTs on a piezoelectric lithium niobate substrate. [26] However, only straight waveguiding was demonstrated, leaving arbitrary guiding to be explored. ...
Phononic crystals (PnCs) exhibit acoustic properties that are not usually found in natural materials, which leads to the possibility of new devices for the complex manipulation of acoustic waves. In this article, a micron‐scale phononic waveguide constructed by line defects in PnCs to achieve on‐chip, tightly confined guiding, bending, and splitting of surface acoustic waves (SAWs) is reported. The PnC is made of a square lattice of periodic nickel pillars on a piezoelectric substrate. The PnC lattice constant, pillar diameter, and pillar height are set to 10, 7.5, and 3.2 µm, respectively, leading to a complete bandgap centered at 195 MHz. Interdigitated transducers are monolithically integrated on the same substrate for SAW excitation. The guiding, bending, and splitting of SAWs in the phononic waveguide are experimentally observed through measurement of the out‐of‐plane displacement fields using a scanning optical interferometer. The combination of destructive interference due to the Bragg bandgap and the interaction of the propagating wave with the pillars around the channel results in a tight confinement of the displacement field. The proposed phononic waveguides demonstrate the feasibility of precise local manipulation of SAW that is essential for emerging frontier applications, notably for phonon‐based classical and quantum information processing.
... 2) To control acoustic waves, phononic crystals (PnC) in particular have attracted much attention in the past few decades because they can influence the propagation behavior of sound waves by means of flexible design methodologies based on different shapes, dimensions, and materials. PnC has been applied to waveguides, 3) filters, 4) energy harvesters, 5) vibration isolators, 6) and, notably, sensors, [7][8][9][10][11][12][13] showing great potential. Sensors based on PnC show advantages of high sensitivity, quality factor and target selectivity. ...
We propose a high sensitivity biosensor based on a GHz phononic crystal (PnC) waveguide, and demonstrate its operation by numerical simulations. The geometry consists of a micron-scale freestanding PnC silica waveguide plate with embedded Au nanopillars for bioparticle attachment, the PnC plate lying between two groups of periodic metal strips for GHz Lamb-wave acoustic generation and detection with ultrashort light pulses. By precise choice of the waveguide defect width, this biosensor is designed to work using a single, isolated waveguide mode. We study the influence of the waveguide defect width on the acoustic dispersion and transmission of this mode. Bioparticle attachment is simulated by investigation of the Au nanopillar mass loading, and is shown to shift the waveguide transmission peak to lower frequencies. We thereby demonstrate femtogram detection, showing that our approach provides a new methodology for label-free ultra-sensitive biosensing.
... The introduction of defects provides new ideas to manipulate waves, and to design and manufacture novel acoustic devices with phononic crystals, and has attracted widespread attention. Linear lines * Corresponding authors. of defects [12][13][14], as the most commonly used guidance mechanism, are thus formed to channel waves at selected frequencies in the band gap with strong confinement [15,16], promising a variety of potential applications [17][18][19] such as sensing [20][21][22][23][24][25], filtering [26], or waveguiding [14,27,28]. ...
We study numerically and experimentally acoustoelastic wave propagation in a two-dimensional phononic metaplate consisting of a periodic array of cups sitting on a thin epoxy plate that is perforated with cross holes. When all cups are filled with water, the metaplate possesses a complete band gap. Reconfigurable coupled-resonator acoustoelastic waveguides (CRAEWs) are created by locally emptying certain cups, thus introducing local resonances that are evanescently coupled. Straight and 90° bent periodic waveguides are considered, together with an aperiodic chain of 11 coupled resonators. The aperiodic chain has no definite spatial periodicity but supports collective resonances resulting from the coupling of nearest resonators. Lamb waves are experimentally excited by a piezoelectric patch and received by a scanning optical vibrometer. Experimental results for acoustoelastic wave propagation along both periodic and aperiodic CRAEWs are compared to a three-dimensional finite element model taking fluid–structure interaction into account. The propagation of confined acoustoelastic waves in the 90° bent waveguides and the collective resonances of the aperiodic chain of defected resonators are observed experimentally. Reconfigurability are realized based on the coupling of acoustoelastic waves in a phononic metaplate. Our results show plenty of potential possibilities for the practical design of reconfigurable and programmable elastic wave devices.
... A phononic crystal (PnC) is a promising platform that enables acoustic phonons to be guided and trapped in a tiny wavelength-scale acoustic cavity and waveguide [21][22][23][24][25][26][27]. Individual cavities are efficiently and finely driven and thereby can be used to control magnetic elements embedded in a PnC circuit. ...
Establishing a way to control magnetic dynamics and elementary excitations (magnons) is crucial to fundamental physics and the search for novel phenomena and functions in magnetic solid-state systems. Electromagnetic waves have been developed as means of driving and sensing in magnonic and spintronics devices used in magnetic spectroscopy, non-volatile memory, and information processors. However, their millimeter-scale wavelengths and undesired cross-talk have limited operation efficiency and made individual control of densely integrated magnetic systems difficult. Here, we utilize acoustic waves (phonons) to control magnetic dynamics in a miniaturized phononic crystal micro-cavity and waveguide architecture. We demonstrate acoustic pumping of localized ferromagnetic magnons, where their back-action allows dynamic and mode-dependent modulation of phononic cavity resonances. The phononic crystal platform enables spatial driving, control and read-out of tiny magnetic states and provides a means of tuning acoustic vibrations with magnons. This alternative technology enhances the usefulness of magnons and phonons for advanced sensing, communications and computation architectures that perform transduction, processing, and storage of classical and quantum information.
