Craig N. Dolder

A simple resonator technique for determining the acoustic properties of fish schools

Acoustic resonators have been used for decades to measure material properties, but only recently have they been applied to determine the effective medium properties of largely inhomogeneous materials. One-dimensional resonators can be used in both a laboratory and field setting to determine the speed and attenuation of acoustic waves through fish schools. Artificial arrays of fish schools are placed in a one-dimensional resonator. After correcting for elastic waveguide effects, the resonances give effective phase speeds and attenuations. The application of this technique to artificial arrays of fish, and how it can be applied to live fish in both a laboratory setting and deployed in the sea will be discussed.

Multi-frequency modes in dispersive media

A common phenomenon in acoustics is the existence of multiple eigenfunctions (mode shapes) corresponding to the same eigenvalue (frequency), which is known as degeneracy. In highly dispersive media the opposite can occur, whereby a single eigenfunction corresponds to multiple eigenvalues. Several ways to visualize the source of, and interpret the physical meaning of, this phenomenon are presented. Instances of this phenomenon occurring in analytical models and experiments are used as examples.

A scavenger hunt using ultrasonic geocaches

Sound is commonly used for either communication or navigation. An ultrasonic scavenger hunt was designed that does both and is designed to raise awareness about acoustics. This scavenger hunts utilizes ultrasonic geocaches to both give information to the participants and educate them on topics including, the fact that sound may not be audible, the concept of hearing loss, other animals hear at different frequencies, and general facts from the hosting event. The geocaches use the frequency band above typical human hearing but still within the bandwidth of most personal electronics, 20 kHz–22 kHz. This band can be picked up by common smartphones and tablets and viewed using free spectrogram applications. The maximum sound pressure level output by the geocache devices falls below maximum public exposure recommendations but the signal is still visible on a spectrogram. The scavenger hunt was trialed at a science engagement event at the University of Southampton with over 6000 in attendance.Sound is commonly used for either communication or navigation. An ultrasonic scavenger hunt was designed that does both and is designed to raise awareness about acoustics. This scavenger hunts utilizes ultrasonic geocaches to both give information to the participants and educate them on topics including, the fact that sound may not be audible, the concept of hearing loss, other animals hear at different frequencies, and general facts from the hosting event. The geocaches use the frequency band above typical human hearing but still within the bandwidth of most personal electronics, 20 kHz–22 kHz. This band can be picked up by common smartphones and tablets and viewed using free spectrogram applications. The maximum sound pressure level output by the geocache devices falls below maximum public exposure recommendations but the signal is still visible on a spectrogram. The scavenger hunt was trialed at a science engagement event at the University of Southampton with over 6000 in attendance.

Adverse effects of very high-frequency sound and ultrasound on humans

For many years, workers have reported adverse symptoms resulting from exposure to very high-frequency sound (VHFS) and ultrasound (US), including annoyance, dizziness and difficulty concentrating. Recent work showing the presence of a new generation of VHFS/US sources in public places has reopened the debate about whether adverse effects can be caused by exposure to VHFS/US. Our field measurements of VHF/US sources in public places have identified devices producing up to 100 dB SPL at 20 kHz. Nearly all of the sources measured, including those in places occupied by tens of millions of people each year, are likely to be clearly audible to many young people. We have conducted two studies. The first looked at adverse symptoms resulting from exposure to audible VHFS/US, and the second was a double-blind study of adverse symptoms resulting from exposure to inaudible VHFS/US. In each study, both symptomatic participants, who reported previously experiencing symptoms, and asymptomatics participants, who did not, were tested. We found evidence that symptoms were produced by exposure to audible VHFS/US but not by inaudible sound. It is possible that the substantial effects reported for inaudible VHFS/US exposure were not reproduced because of ethical restrictions on stimulus level and duration.

Impulse scattering from clouds of acoustically coupled gas bubbles in fluids

To calculate the impulse response of a bubble cloud in a compressible medium, a methodology is developed that incorporates multiple scattering effects between bubbles and coherent interactions of their individual scattered fields. This method is based on a perturbation theory, and provides for an approximate solution formulated by adding a perturbation to the mathematical description of a linear problem. The solution is defined as a power series, where the first term of the expansion corresponds to the solution of a linear uncoupled equation. The convergence of the expansion is determined by the parameters of the physical bubbles and the acoustic interactions. The model is successfully applied to describe experimental measurements of a model bubble cloud response in a shallow freshwater environment.

Teaching ultrasound in air

The use of ultrasonics sensors in laboratory exercises and robotics has become popular in recent years. That is, however, only one avenue for exploring the world of inaudible sound that is around us. This talk discusses exercises to interact with the ultrasonic world surrounding us using smartphones, computers, and tablets. Messages can be sent through analog or digital means and the very concept of what is inaudible varies significantly from one person to another. The use of ultrasound is not limited to range finding but also spans communication and art.

Using one-dimensional waveguide resonators to measure phase velocities in bubbly liquids

Resonator techniques can be successfully used to extract effective medium properties from dispersive materials. However, in some cases the dispersion can cause modes to repeat. If repeated modes are not taken into account, the useful range of the resonator technique is limited. A resonance tube containing tethered balloons is used to create a dispersive effective medium. Resonator measurements show that modes do repeat. Direct measurement of the mode shapes allows exploitation of all longitudinal radially symmetric modes and expands the frequency range of the technique. A theoretical model is also used to predict when modes repeat. For the presented data set this method increases the measurement range from below 160 Hz to 3000 Hz excluding the stop band where resonances are damped. A means to account for non-ideal resonator boundary conditions often found in highly dispersive systems is discussed.

Exposure measurements for ultrasound in air

Everyday we are exposed to a world of sounds that we do not hear. Many of the sounds come on the edge of our hearing range and some are even audible to a small part of the population. This presentation relates experimental measurements of sound exposures in the high-frequency regime that we are not intended to hear. There has been recent speculation about whether the regulations in the near-audible (or audible for a small population) regime are sufficient. Whether it is annoyance or some other mechanism that affects some part of the population is unknown, but this data present an idea of what exposure we receive at the edge of our hearing range.

Ultrasonic activated stream cleaning of a range of materials

Despite decades of routine use (starting from the industrial setting but now also with domestic products available), ultrasonic cleaning faces technical challenges that have never been overcome, and the root of many of these lies with an understanding of the interaction between the bubble population and the sound field. Ultrasonically Activated Stream (UAS) technology is designed to produce ultrasonic cleaning, and in this paper it does so for scenarios for which an ultrasonic cleaning bath would be unsuitable, e.g., removing key contaminants (such as biofilms) from delicate substrates (tissues, etc.), without damaging that substrate.

Data supporting the paper "The acoustic bubble: Ocean, cetacean and extraterrestrial acoustics, and cold water cleaning"

Data supporting the paper Leighton T.G. (2016) The acoustic bubble: Ocean, cetacean and extraterrestrial acoustics, and cold water cleaning. Journal of Physics: Conference SeriesThe data consist of four video files in mp4 format showing cleaning mascara off a file, hand cleaning, cleaning Vaseline (petroleum jelly) on top of lipstick off a piece of tile, and a computer animation of the StarStream device attaching on a standard water bottle.