Showing papers on "Acoustic interferometer published in 2017"

Asymmetric absorber with multiband and broadband for low-frequency sound

Abstract: We present the mechanism for the asymmetric absorption of acoustic waves in a two-port transparent waveguide system by shunting detuned Helmholtz resonators (HRs) pairs in cascade. Theoretical analysis, numerical simulations, and experimental measurements verify that sound energy is almost totally absorbed (96.1%) at ∼373 Hz when sound waves are incident from one side while it is largely reflected back from the opposite side by judiciously designed HRs to provide manipulated surface impedance matching/mismatching to that of air at the opposite sides of the waveguide. Thus, asymmetric acoustic absorber is achieved at a low frequency. We have further demonstrated the flexibility of this methodology to get non-reciprocal absorption and reflectance in multiband and broadband. Our design advances the concept of asymmetric acoustic manipulation in passive two-port systems and may enable sound-absorbing devices for more versatile applications.

Acoustic tweezing of particles using decaying opposing travelling surface acoustic waves (DOTSAW)

Abstract: Surface acoustic waves offer a versatile and biocompatible method of manipulating the location of suspended particles or cells within microfluidic systems. The most common approach uses the interference of identical frequency, counter propagating travelling waves to generate a standing surface acoustic wave, in which particles migrate a distance less than half the acoustic wavelength to their nearest pressure node. The result is the formation of a periodic pattern of particles. Subsequent displacement of this pattern, the prerequisite for tweezing, can be achieved by translation of the standing wave, and with it the pressure nodes; this requires changing either the frequency of the pair of waves, or their relative phase. Here, in contrast, we examine the use of two counterpropagating traveling waves of different frequency. The non-linearity of the acoustic forces used to manipulate particles, means that a small frequency difference between the two waves creates a substantially different force field, which offers significant advantages. Firstly, this approach creates a much longer range force field, in which migration takes place across multiple wavelengths, and causes particles to be gathered together in a single trapping site. Secondly, the location of this single trapping site can be controlled by the relative amplitude of the two waves, requiring simply an attenuation of one of the electrical drive signals. Using this approach, we show that by controlling the powers of the opposing incoherent waves, 5 μm particles can be migrated laterally across a fluid flow to defined locations with an accuracy of ±10 μm.

Acoustic levitation of an object larger than the acoustic wavelength

Abstract: Levitation and manipulation of objects by sound waves have a wide range of applications in chemistry, biology, material sciences, and engineering. However, the current acoustic levitation techniques are mainly restricted to particles that are much smaller than the acoustic wavelength. In this work, it is shown that acoustic standing waves can be employed to stably levitate an object much larger than the acoustic wavelength in air. The levitation of a large slightly curved object weighting 2.3 g is demonstrated by using a device formed by two 25 kHz ultrasonic Langevin transducers connected to an aluminum plate. The sound wave emitted by the device provides a vertical acoustic radiation force to counteract gravity and a lateral restoring force that ensure horizontal stability to the levitated object. In order to understand the levitation stability, a numerical model based on the finite element method is used to determine the acoustic radiation force that acts on the object.

Acoustic beam splitting at low GHz frequencies in a defect-free phononic crystal

Abstract: The directional waveguiding in a 2D phononic crystal is simulated based on the analysis of equifrequency contours. This approach is utilized to investigate acoustic beam splitting in a defect-free nanostructure in the low GHz range. We find relaxed limitations regarding the source parameters compared to similar approaches in the sonic regime. Finally, we discuss the possibility to design an acoustic interferometer device at the nanoscale at GHz frequencies.

Detecting acoustic-emission signals with fiber-optic interference transducers

Abstract: Results of the analysis of acoustic-emission signals generated due to ultrasonic waves propagating in a polymer composite material and registered with piezoelectric and fiber-optic sensors are presented. The fiber-optic sensors were arranged into an adaptive interferometer based on using a dynamic hologram formed in a photorefractive crystal. Reducing the setpoint fading has made it possible to improve the noise immunity and sensitivity of the measurement system when using an adaptive interferometer on a photorefractive crystal. Optical fibers in the interferometer’s measurement system served as sensors of ultrasonic waves and were built into a polymer composite material when the sample was manufactured. The sample was a rectangular plate made of a multilayer fiberglass material. It has been discovered that the sensitivity of the adaptive interferometer makes it possible to detect acoustic- emission signals generated by a Hsu–Nielsen source. When determining the speed of sound in the polymer composite material, peculiarities of registering a group wave by fiber-optic sensors have been established that are due to the anisotropy of the medium the wave propagates in and the distributed character of sensor placement in the studied composite material. The wavelet transform has been used to separate the informative component of the wanted signal.

Radio-frequency actuated polymer-based phononic meta-materials for control of ultrasonic waves

Abstract: Radio-frequency (RF) control of an ultrasonic phononic crystal was achieved by encapsulating it in a composite of high k-10% KF-doped BaTiO3 dielectric nanoparticles with poly(N-isopropylacrylamide) (PNIPAm)-based hydrogel. The combination of the nanoparticles and hydrogel produced a composite with elastic properties susceptible to RF actuation. The novel acoustic meta-material enables the regulation of sound waves by electromagnetic waves, which is not possible in a conventional medium as elasto-mechanical waves, and electromagnetic waves do not directly couple. Compared with light waves, radio waves can penetrate deeper into bulk structures and enable the control of propagation of ultrasonic waves through a macroscale phononic crystal. An RF antenna emitting at 318.6 and 422.5 kHz was used to modulate the device in water and ambient air, respectively. An increased transparency of the ultrasonic wave in the material was observed due to an increase in the bandwidth of the modulated device exceeding 8 kHz with a 30-fold increase in the signal modulation at select frequencies. The radio waves induced changes in the transmission and demonstrated the control of ultrasound with applied RF. The synthetic acoustic properties in the resultant meta-material device were actively manipulated through the interaction of electromagnetic waves with the material. Mechanical waves can be controlled by radio waves using a material designed by researchers in the USA and China. Phononic crystals are materials engineered to manipulate sound waves in a desired way. Now, Arup Neogi and co-workers from the University of North Texas and the University of Electronic Science and Technology of China have used a nanoparticle-doped hydrogel to make a phononic crystal sensitive to radio waves — an important development since mechanical waves and electromagnetic waves do not directly interact in nature within conventional materials. The team created an ‘active’ phononic crystal by encapsulating a square lattice of stainless-steel cylinders in a polymer. The polymer contained nanoparticles that are sensitive to radio-frequency electromagnetic waves. The transmission of ultrasonic waves through the material varied depending on the intensity and frequency of an incident radio-frequency signal. Radio-frequency (RF) was used to control ultrasound wave propagating through a phononic crystal based metamaterial device. The tunable metamaterial was realized by interstitially filling the spacing in the phononic crystal with high-k, 10% KF doped BaTiO3 nanoparticles dispersed in poly(N-isopropylacrylamide) (PNIPAM)-based hydrogels. The introduction of high-k nanoparticles enables the hydrogel to have an RF response, thus making a composite with highly variable elastic properties susceptible to RF light. The non-contact mode of applied RF results in a broadening and shift of the transmission spectra resulting in the realization of novel ultrasonic filters and modulators. The RF field also eliminates hybridization and resonance features in the spectra. The metamaterial exhibits tuning of ultrasound waves in both water and air medium.

Nondegenerate Parametric Pumping of Spin Waves by Acoustic Waves

Abstract: The linear and nonlinear interactions between spin waves (magnons) and acoustic waves (phonons) in magnetostrictive materials provide an exciting opportunity for realizing novel microwave signal processing devices and spintronic circuits. Here, we demonstrate the parametric pumping of spin waves by acoustic waves in a ferrimagnet, the possibility of which has long been theoretically anticipated but never experimentally realized. Spin waves propagating in a thin film of yttrium iron garnet—a magnetostrictive ferrimagnet with low spin and acoustic wave damping—are pumped using an acoustic resonator driven at frequencies near twice the spin wave frequency. The observation of a counterpropagating idler wave and a distinct pump threshold that increases quadratically with frequency nondegeneracy are evidence of a nonlinear parametric pumping process consistent with classical theory. This demonstration of acoustic parametric pumping lays the groundwork for developing new spintronic and microwave signal processing devices based on amplification and manipulation of spin waves by efficient, spatially localized acoustic transducers.

Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment

Abstract: . We develop theoretical basics of active experiments with two beams of acoustic waves, radiated by a ground-based sound generator. These beams are transformed into atmospheric acoustic gravity waves (AGWs), which have parameters that enable them to penetrate to the altitudes of the ionospheric E and F regions where they influence the electron concentration of the ionosphere. Acoustic waves are generated by the ground-based parametric sound generator (PSG) at the two close frequencies. The main idea of the experiment is to design the output parameters of the PSG to build a cascade scheme of nonlinear wave frequency downshift transformations to provide the necessary conditions for their vertical propagation and to enable penetration to ionospheric altitudes. The PSG generates sound waves (SWs) with frequencies f1 = 600 and f2 = 625 Hz and large amplitudes (100–420 m s−1). Each of these waves is modulated with the frequency of 0.016 Hz. The novelty of the proposed analytical–numerical model is due to simultaneous accounting for nonlinearity, diffraction, losses, and dispersion and inclusion of the two-stage transformation (1) of the initial acoustic waves to the acoustic wave with the difference frequency Δf = f2 − f1 in the altitude ranges 0–0.1 km, in the strongly nonlinear regime, and (2) of the acoustic wave with the difference frequency to atmospheric acoustic gravity waves with the modulational frequency in the altitude ranges 0.1–20 km, which then reach the altitudes of the ionospheric E and F regions, in a practically linear regime. AGWs, nonlinearly transformed from the sound waves, launched by the two-frequency ground-based sound generator can increase the transparency of the ionosphere for the electromagnetic waves in HF (MHz) and VLF (kHz) ranges. The developed theoretical model can be used for interpreting an active experiment that includes the PSG impact on the atmosphere–ionosphere system, measurements of electromagnetic and acoustic fields, study of the variations in ionospheric transparency for the radio emissions from galactic radio sources, optical measurements, and the impact on atmospheric aerosols. The proposed approach can be useful for better understanding the mechanism of the acoustic channel of seismo-ionospheric coupling.

An improved non-contact thermometer and hygrometer with rapid response

Abstract: Previously (Underwood et al 2015 Meteorol. Appl. 22 830) we reported first tests of a device capable of simultaneous, non-contact, temperature and humidity (NCTAH) measurements in air. The device used an acoustic thermometer and a tuneable diode laser absorption spectrometer (TDLAS), a combination which should be capable of an extremely rapid response to changes in humidity as it does not require moisture in a solid-state matrix to equilibrate with the surrounding air. In this paper we report recent developments of the instrument focussed on reducing its response time so that it can be used as a reference instrument for assessing the response time of conventional humidity sensors. In addition, the interdependence of the temperature and humidity estimates is now accounted for in real-time using an iterative procedure, which eliminates the need for data post-processing. The TDLAS measures water molecule number density based on the transmission of an infrared beam (approximate wavelength 1360 nm) through a 0.6 m path length. The acoustic thermometer is based around a fixed-path acoustic interferometer. The improved NCTAH device now produces estimates of the water molecule number density every 20 ms and the temperature output displays an RC filter-like response, with a time constant of approximately 30 ms. The instrument has been tested in a climatic chamber through a temperature range of −40 °C to +40 °C and a dew point range of −43 °C to +38 °C, at atmospheric pressure, comparing the instrument readings with those from a calibrated hygrometer and four platinum resistance thermometers. In steady-state conditions, the instrument readings are in good agreement with the conventional sensors, with temperature differences less than 1 °C (repeatability 0.1 °C), and humidity differences mostly within 5% of mixing ratio. Under transient conditions, we demonstrate how the instrument can be used to evaluate the response times of conventional sensors.

Transportation control of microfluidic particles using mode switching between surface acoustic waves and plate waves

Abstract: In the past decade, ultrasound acoustofluidics has received increasing interest for its application to serves as a tool for purely mechanical and label-free manipulation of particles and cells in MEMS and biological systems [1–3]. Ultrasound is regarded as one of candidates of the driving forces, in addition to the commonly learned electric, magnatic, optical forces, etc., for tailoring demanded lab-on-a-chip systems. The associated technology is also called acoustophoresis. Earily studies of acoustophoresis typically made use of bulk acoustic waves excited by piezoelectric transducers attached onto a microfluidic channel [4,5]. Constructive interference of the incident waves and reflected waves can build a standing acoustic wave field across the microfluidic channel for the particle manipulation [6]. However, such acoustofluidic devices suffer from the problem of incompatible acoustic impedence of commonly used buliding materials of the microfluidic channels for reflected waves. In recent years, surface acoustic wave (SAW) has been demonstrated as a powerful alternative for bulk acoustic wave in constructing acoustofluidic devices for non-invasive manipulation of particles and cells. For example, SAW based acoustofluidic devices have been utilized to concentrate, separate, transport, enrich, and pattern particles or biological cells for various applications [6–9]. However, SAW based acoustofluidic devices rely on electrodes, which are known as interdigital tranducers (IDTs), properly fabricated on a piezoelectric substrate (e.g. LiNbO3) for generating desired SAWs. Generation of SAWs with desired frequency (or wavelength), amplitude, and acoustic beam width is important for device functionalities. IDT design involves so many parameters to achieve the required properties. For example, different IDT pitches are used to generate SAWs with different wavelengths to build desired standing acoustic wave fields in microfluid. In this work, we present a numerical study of transpotation control of microparticles achieved by mode switching between SAWs and plate acoustic waves (PAWs). The mode switching is based on the electrical excitation by the same IDTs at different input frequencies in a LiNbO3 substrate of finite thickness.

Effects of Acoustic Waves on Buried Tunnel Structures Under an Impact Load

Abstract: In this paper, the transmission and reflection of acoustic waves into and from an underground tunnel are investigated by producing an impact load on the ground and measuring the acoustic pressure levels at different time intervals. For this purpose, a sound detector is placed on the ground and then from an arbitrary location on the surface, acoustic waves are transmitted into the ground from an acoustic source. The pressure levels of acoustic waves transmitted into the tunnel space and reflected back to the ground surface are measured, and the effects of several parameters on the attenuation of acoustic pressure levels of transmitted and reflected sound waves are evaluated. Moreover, the effects of parameters such as soil type, concrete type and thickness, buried depth of the underground structure and also the effect of acoustic absorbers on the transmission, propagation and reflection of acoustic waves into and from the tunnel are investigated. The results obtained indicate that the two parameters of soi...

Observation of sagittal X-ray diffraction by surface acoustic waves in Bragg geometry

Abstract: X-ray Bragg diffraction in sagittal geometry on a Y-cut langasite crystal (La3Ga5SiO14) modulated by Λ = 3 µm Rayleigh surface acoustic waves was studied at the BESSY II synchrotron radiation facility. Owing to the crystal lattice modulation by the surface acoustic wave diffraction, satellites appear. Their intensity and angular separation depend on the amplitude and wavelength of the ultrasonic superlattice. Experimental results are compared with the corresponding theoretical model that exploits the kinematical diffraction theory. This experiment shows that the propagation of the surface acoustic waves creates a dynamical diffraction grating on the crystal surface, and this can be used for space–time modulation of an X-ray beam.

Device for detecting acoustic waves

Abstract: A device for detecting acoustic waves may include a housing having a housing wall with an inner surface, and an acoustic wave sensor provided at least partially inside the housing and configured to detect acoustic waves. The inner surface of the housing wall is made in at least half of its entire area of a thermally insulating material.

Manipulation of Playback Device Response Using an Acoustic Filter

Abstract: An acoustic filter includes holes and is configured to receive sound waves generated by an audio driver of a playback device. The sound waves comprise sound waves of a first frequency that radiate according to a first radiation pattern and sound waves of a second frequency that radiate according to a second radiation pattern that is less directed along an axis of the audio driver than the first radiation pattern. The second frequency is lower than the first frequency. The acoustic filter is configured to attenuate the sound waves of the first frequency so that the attenuated sound waves of the first frequency are emitted from the acoustic filter according to an effective radiation pattern that is less directed along the axis of the audio driver than the first radiation pattern and pass the sound waves of the second frequency in substantial accordance with the second radiation pattern.

Transmission of high-intensity aerial ultrasonic waves by using a straight rigid tube for sound wave transmission

Abstract: In this study, we investigated the transmission and irradiation of aerial ultrasonic waves (frequency: 20 kHz) without attenuation. We proposed a method in which sound waves are transmitted by using a rigid tube to irradiate an object without attenuation. In this report, We transmitted and irradiated high-intensity aerial focused ultrasonic waves with a straight rigid acrylic tube. The results showed that the ultrasonic waves were transmitted with a sound pressure peak generated outside the tube when the inner diameter of the tube was approximately the sound wavelength. When the sound waves were transmitted using a tube with an inner diameter of approximately the sound wavelength, the sound pressure at the radiation end was about 80% of the sound pressure at the incident end. These results clarified that our method can transmit aerial ultrasonic waves while maintaining the sound pressure.

Omnidirectional sound shielding with acoustic metacages

Abstract: Omnidirectional sound barriers are useful for various applications in noise reduction. Conventional sound insulating structures like micro-perforated plates or porous materials prevent the exchange of airflow. Here, we propose the design of an acoustic metacage which can shield acoustic waves from all directions and have the ability of allowing air pass through freely. The mechanism is that the strong parallel momentum along the surface rejects sound regardless of the directions of the incident wave. Structures based on open channels and Helmholtz resonators are designed at an operation frequency of 2.49 kHz with thickness less than half of the wavelength. A prototype is fabricated using 3D printing and further verified experimentally in a waveguide. Simulation and measurement results clearly show that the proposed metacage can shield acoustic waves when the sources are placed either interior or exterior. An average energy decay of more than 10 dB is achieved when a loudspeaker is placed inside the metaca...

Three-parameter liquid sensor based on surface and plate acoustic waves.

Abstract: This work deals with developing the sensor capable to detect viscosity, electric conductivity, and temperature of one and the same micro-liter liquid sample. The sensor is based on surface and plate acoustic waves propagating in LiNbO3 crystal. Properties of the waves and parameter of the sensor are measured and presented.

In principle, it should be possible to measure velocity using a Michelson displacement

Abstract: The VISAR has several desirable characteristics. It is able to measure the velocity of both specular and diffuse surfaces, and it is completely noninvasive. It is capable of measuring a wide range of velocities. The VISAR has a potential bandwidth far in excess of 1 GHz, although most measurements are limited to several hundred megahertz due to the limitation of recording instruments. In addition, since it is a phase sensitive measure­ ment, it is capable of precision far better than one percent. The only other technique for measuring velocities in this range uses a Fabry-Perot interferometer2. The Fabry-Perot technique measures the exceedingly small Doppler shift of reflected laser light to determine the velocity. It is more portable than present VISARs, and requires little analysis to determine the velocity from the data. However, it is not as sensitive or as accurate as the VISAR. This chapter will not discuss the use of Fabry-Perot interferometers for velocity measurements. The reader is invited to refer to the references for an explanation of this technique. The first section of this paper will give the theory of velocity interferometers in general, including a derivation of the phase versus velocity relationship. The next section explains how a VISAR is able to measure the velocity of any surface. A discussion of accuracy and precision of the VISAR is presented in the subsequent section. Experi­ mental apparatus is discussed in the fourth section, and some results will be reported in the following section. The final section will discuss techniques for extending the velocity range. Theory of velocity interferometers In principle, it should be possible to measure velocity using a Michelson displacement interferometer. In this case, the moving part would act as one of the mirrors. However, parts moving with a velocity of several kilometers per second would produce tens of fringe shifts per nanosecond. At present, it is difficult to record such rapid fringe shifts. Streak cameras could be used to record the individual fringe shifts. Because of their limited record length, however, they would be unable to record the velocity over the whole time scale of interest. As is shown below, a velocity interferometer is able to measure velocity over a long time range with high precision. Laser interferometry has been used to determine the velocity in shock wave experiments for over twenty years3' **. Figure 1 is a schematic diagram of a velocity interferometer. Laser light, reflected from a moving target, enters the interferometer. The path lengths of the two legs remain constant, but one leg of the interferometer has an additional time delay, T. Thus, light leaving the interferometer at any given time is composed of two waves of light, each of which left the laser at two different times. The phase difference of the two interfering beams is a function of both the interferometer delay and the velocity of the target. It is possible to determine the velocity by measuring the modula­ tion of the interfering beams. Some controversy has surrounded the derivation of the velocity dependent phase shift of a velocity interferometer. Early derivations were based on the Doppler shift of the reflected light5*6. These were followed by several articles noting corrections7* 8 to earlier works. The derivation in this paper is new, but follows the last most closely by analyzing the history of wavecrests. No approximations will be made unless they lead to a negligible change in the result.

Backward acoustic plate waves: Features of properties and possible applications in microelectronic devices

Abstract: An overview is given of the results of recent and new studies by the authors of this work on topics related to backward acoustic waves of pure-shear type and Lamb type in piezoelectric, crystal, and isotropic plates with free and liquid-loaded surfaces. Various physical mechanisms giving rise to such waves are revealed and quantitatively described by the use of asymptotic expansion of the secular equations and the perturbation theory. The peculiarities of properties of leaky backward waves are considered. The possible applications of backward waves in microelectronic devices (such as sensors et al.) are discussed.

Low-intensity acoustic waves detection using an interferometer

Abstract: We present a device built in fiber optic capable of detecting acoustic signals in water, using a buzzer as the vibration source, this buzzer operates at a frequency range from 3 kHz to 30 kHz. This device operates under the principle of a Sagnac interferometer, where the acoustic waves emitted by the buzzer are detected as a phase modulation in the monitored signal. The measured phase is due to strain experienced by the fiber optic which is caused by the vibrations emitted by the buzzer. The device can detect signals up to 7 cm away from the acoustic source.