Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?

Validity of the 1984 Interim Guidelines on Airborne Ultrasound and Gaps in the Current Knowledge

ABSTRACT

Airborne ultrasound is used for various purposes both in industrial and public settings, as well as being produced as a by-product by a range of sources. The International Radiation Protection Association (IRPA) published interim guidelines on limiting human exposure to airborne ultrasound in 1984, based on the limited scientific evidence that was available at that time. In order to investigate whether research since 1984 requires the development of revised exposure guidelines we considered (a) within the context of ultrasound exposure the relevance to health of the biological endpoints/mechanisms listed in the IRPA guidelines, (b) the validity of the exposure limits, and (c) whether there are biological endpoints/mechanisms not covered in the guidelines. The analysis of the available evidence showed that the biological endpoints that form the basis of the guidelines are relevant to health and the guidelines provide limits of exposure based on the evidence that was available at the time. However, the IRPA limits and their associated dosimetry were based on limited evidence, which may not be considered as scientifically substantiated. Further, there is no substantiated evidence of biological endpoints/mechanisms not covered by the IRPA guidelines. These two observations could mean that IRPA's limits are too low or too high. Research since the IRPA guidelines has made some improvements in the knowledge base, but there are still significant data gaps that need to be resolved before a formal revision of the guidelines can be made by ICNIRP, including research needs related to health outcomes and improved dosimetry. This statement makes a number of recommendations for future research on airborne ultrasound.

Applying appropriate frequency criteria to advance acoustic behavioural guidance systems for fish

Deterrents that use acoustics to guide fish away from dangerous areas depend on the elicitation of avoidance in the target species. Acoustic deterrents select the optimum frequency based on an assumption that highest avoidance is likely to occur at the greatest sensitivity. However, such an assumption may be unfounded. Using goldfish (Carassius auratus) as a suitable experimental model, this study tested this as a null hypothesis. Under laboratory conditions, the deterrence thresholds of individual goldfish exposed to 120 ms tones at six frequencies (250-2000 Hz) and four Sound Pressure Levels (SPL 115-145 dB) were quantified. The deterrence threshold defined as the SPL at which 25% of the tested population startled was calculated and compared to the hearing threshold obtained using Auditory Evoked Potential and particle acceleration threshold data. The optimum frequency to elicit a startle response was 250 Hz; different from the published hearing and particle acceleration sensitivities based on audiograms. The difference between the deterrence threshold and published hearing threshold data varied from 47.1 dB at 250 Hz to 76 dB at 600 Hz. This study demonstrates that information obtained from audiograms may poorly predict the most suitable frequencies at which avoidance behaviours are elicited in fish.

A non-destructive technique using digital holographic vibrometry and Lamb waves for quality determination of polymer-metal laminates

We used digital holographic vibrometry (DHV) as a non-destructive method to detect debonding areas in laminates made of aluminum and polymer (polylactide, polyvinylidene fluoride or polycarbonate). At low frequencies (up to 30 kHz) \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$A_0$$\end{document}A0 Lamb waves were excited and the amplitude and the phase patterns of the vibration of the sample were simultaneously registered for metal and polymer side of the laminate. Based on these patterns debonding areas in laminates were localized. The transmission properties at low frequencies were also studied in terms of: the frequency range for which regular Lamb waves have been observed, Lamb wave amplitudes and Lamb wave propagation velocity depending on the frequency. We have shown that these properties also change when a defect occures in the laminate. Even when we could not localize the defect it was still possible to detect if a sample was damaged based on the behaviour of the Lamb waves.

Wireless Power Transfer: Systems, Circuits, Standards, and Use Cases

Wireless power transfer provides a most convenient solution to charge devices remotely and without contacts. R&D has advanced the capabilities, variety, and maturity of solutions greatly in recent years. This survey provides a comprehensive overview of the state of the art on different technological concepts, including electromagnetic coupled and uncoupled systems and acoustic technologies. Solutions to transfer mW to MW of power, over distances ranging from millimeters to kilometers, and exploiting wave concepts from kHz to THz, are covered. It is an attractive charging option for many existing applications and moreover opens new opportunities. Various technologies are proposed to provide wireless power to these devices. The main challenges reside in the efficiency and range of the transfer. We highlight innovation in beamforming and UV-assisted approaches. Of particular interest for designers is the discussion of implementation and operational aspects, standards, and safety relating to regulations. A high-level catalog of potential applications maps these to adequate technological options for wireless power transfer.

Investigation of resolution and microphone size for measurements of airborne ultrasound

The growth of ultrasound technologies has entailed the presence of airborne ultrasound emissions in industry and public and private spaces. For occupational safety and health, procedural and technical recommendations are needed that allow measurements to be performed in the field within a short time and with little effort. This study aims to answer two research questions concerning the minimum spatial resolution and microphone size required to determine a spatial distribution of sound pressure levels with sufficient accuracy within a given measurement uncertainty. The investigation focused on high spatial resolution datasets of the airborne ultrasound field of an ultrasonic welding machine acquired using a laboratory measuring system. Based on these datasets, datasets with lower resolutions were generated and measurements with microphones of different sizes were simulated. Subsequently, four different methods of parameterization were applied to the datasets to characterize the airborne ultrasound field with respect to the structure and sound pressure levels. Comparing the parameters of datasets with high precision (high resolution and small microphone size) to those of datasets with reduced precision (lower resolution and larger microphone size) allowed a quantitative assessment of the influence of the reduction in precision. Corresponding recommendations on resolution and microphone size are given.

Possible Effects on Health of Ultrasound Exposure, Risk Factors in the Work Environment and Occupational Safety Review

Ultrasonic waves are mechanical waves with a frequency greater than 20,000 Hz. Ultrasonic waves are emitted by devices that are used in industry or that have a medical or aesthetic purpose. There is growing interest in the effect of ultrasound absorption on the human body, since people's exposure to these acoustic waves has increased considerably in recent years. There are more and more devices that emit ultrasounds used for different sanitary procedures, aesthetic treatments and industrial processes, creating more possibilities of ultrasound noise, and therefore an increased risk of occupational hazard and occupational danger. Experiments on animals have shown damage to internal organs from receiving different ultrasonic frequencies. The main task of this work was to organize and summarize recent studies on ultrasound to reflect the current state of this technique and establish a systematic basis for future lines of research. This work has allowed us to better understand the unknown field of these high frequencies of sound, and highlights the need to carry out more studies on the ultrasound emissions that can be absorbed by the human body to determine how this energy could affect humans by calculating the maximum dose of exposure and developing manuals for the use of ultrasound-emitting equipment to protect the health of workers and all people. It is necessary to develop regulations by public administrations to improve the protection of workers, health professionals, patients and all people in general for better occupational safety, indoor environmental quality and environmental health.

Development of a Personal Ultrasound Exposimeter for Occupational Health Monitoring

Prolonged exposure to airborne ultrasound in a workplace can have a detrimental influence on a worker’s well-being. Given the ever-increasing use of ultrasonic industrial equipment, it is of vital importance—and may also be regulated by law—to monitor ultrasound exposure during a normal workday as part of workplace risk assessment. However, the devices currently utilized exhibit limitations with regard to both their operational frequency and their portability (wearability). In this paper, the first prototype of a high-frequency and ultrasound personal exposimeter is presented in the light of the latest national and international standards governing high-frequency and ultrasonic noise measurement in the field of occupational health monitoring. The prototype was tested in the laboratory environment in order to assess its sound level detection capabilities in both the audible and ultrasonic frequency ranges. Several common industrial scenarios—including an ultrasonic welding machine, an ultrasonic cleaning bath, and a compressed air gun—were simulated in a laboratory environment. For each simulated set-up, a corresponding high-frequency or ultrasonic signal was fed through a specially prepared generation chain. Each experimental scenario was initially surveyed with an ultrasound level meter previously tested up to 100 kHz. This was followed by a measurement with the prototype. For this study, the simulated sound signals varied between 10 kHz and 40 kHz on the frequency scale and between 60 dB and 90 dB in amplitude. The portability of the prototype, which may be required to be worn throughout an entire workday (e.g., 8 h), was also considered. All the experiments were performed on a customized ultrasound measurement set-up within a free-field environment located at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. Results obtained suggest a good agreement between the measurements performed with both devices in the louder areas of the sound fields produced. Because the overall measurement uncertainty is highly dependent on the specificity of the individual measurement set-up and measurement procedure, an uncertainty budget estimated for the prototype considers electro-acoustical contributions only.

A longitudinal, randomized experimental pilot study to investigate the effects of airborne ultrasound on human mental health, cognition, and brain structure

Ultrasound-(US) emitting sources are highly present in modern human environments (e.g., movement sensors, electric transformers). US affecting humans or even posing a health hazard remains understudied. Hence, ultrasonic (22.4 kHz) vs. sham devices were installed in participants' bedrooms, and active for 28 nights. Somatic and psychiatric symptoms, sound-sensitivity, sleep quality, executive function, and structural MRI were assessed pre-post. Somatization (possible nocebo) and phasic alertness increased significantly in sham, accuracy in a flexibility task decreased significantly in the verum condition (indicating hastier responses). Effects were not sustained after p-level adjustment. Exploratory voxel-based morphometry (VBM) revealed regional grey matter (rGMV) but no regional white matter volume changes in verum (relative to placebo). rGMV increased in bilateral cerebellum VIIb/Crus II and anterior cingulate (BA24). There were rGMV decreases in two bilateral frontal clusters: in the middle frontal gyri/opercular part of inferior frontal gyrus (BA46, 44), and the superior frontal gyri (BA4 ,6, 8). No brain-behavior-links were identified. Given the overall pattern of results, it is suggested that ultrasound may particularly induce regional gray matter decline in frontal areas, however with yet unclear behavioral consequences. Given the localization of clusters, candidate behavioral variables for follow-up investigation are complex motor control/coordination, stress regulation, speech processing, and inhibition tasks.Trial registration: The trial was registered at NIH www.clinicaltrials.gov , trial identifier: NCT03459183, trial name: SonicBrain01, full trial protocol available here: https://clinicaltrials.gov/ct2/show/NCT03459183 .

Experimental characterization of high-intensity focused airborne ultrasound fields

High-intensity focused airborne ultrasound fields are increasingly applied in various technical fields, for example, to generate haptic feedback during gesture interaction. Reliable measurement data of sound pressure levels are required to assess potential health hazards to users. Such ultrasound fields pose special challenges for a quantitative characterization. The high sound pressure levels in combination with the higher harmonics generated by nonlinear effects require both a high upper limit of the level linearity range and a wide bandwidth of the measuring chain. Furthermore, small wavelengths and the focusing result in spatially strongly varying sound fields. In the present case, a 40 kHz signal was focused on a single point using a transducer array. Different microphone types were investigated with respect to their suitability for measuring high-power airborne ultrasound fields. A spatial characterization of the ultrasound field in the focal region as well as around an artificial head in a simulated application situation was performed. The microphone measurements were supplemented by measuring the radiation force with a balance and were compared to an analytical model of the sound field distribution. The presented results can contribute to the improvement of measurement technology and support a first assessment of the exposure of potential users.

Review of Audiovestibular Symptoms Following Exposure to Acoustic and Electromagnetic Energy Outside Conventional Human Hearing

Objective: We aim to examine the existing literature on, and identify knowledge gaps in, the study of adverse animal and human audiovestibular effects from exposure to acoustic or electromagnetic waves that are outside of conventional human hearing. Design/Setting/Participants: A review was performed, which included searches of relevant MeSH terms using PubMed, Embase, and Scopus. Primary outcomes included documented auditory and/or vestibular signs or symptoms in animals or humans exposed to infrasound, ultrasound, radiofrequency, and magnetic resonance imaging. The references of these articles were then reviewed in order to identify primary sources and literature not captured by electronic search databases. Results: Infrasound and ultrasound acoustic waves have been described in the literature to result in audiovestibular symptomology following exposure. Technology emitting infrasound such as wind turbines and rocket engines have produced isolated reports of vestibular symptoms, including dizziness and nausea and auditory complaints, such as tinnitus following exposure. Occupational exposure to both low frequency and high frequency ultrasound has resulted in reports of wide-ranging audiovestibular symptoms, with less robust evidence of symptomology following modern-day exposure via new technology such as remote controls, automated door openers, and wireless phone chargers. Radiofrequency exposure has been linked to both auditory and vestibular dysfunction in animal models, with additional historical evidence of human audiovestibular disturbance following unquantifiable exposure. While several theories, such as the cavitation theory, have been postulated as a cause for symptomology, there is extremely limited knowledge of the pathophysiology behind the adverse effects that particular exposure frequencies, intensities, and durations have on animals and humans. This has created a knowledge gap in which much of our understanding is derived from retrospective examination of patients who develop symptoms after postulated exposures. Conclusion and Relevance: Evidence for adverse human audiovestibular symptomology following exposure to acoustic waves and electromagnetic energy outside the spectrum of human hearing is largely rooted in case series or small cohort studies. Further research on the pathogenesis of audiovestibular dysfunction following acoustic exposure to these frequencies is critical to understand reported symptoms.

Does airborne ultrasound lead to activation of the auditory cortex?

As airborne ultrasound can be found in many technical applications and everyday situations, the question as to whether sounds at these frequencies can be heard by human beings or whether they present a risk to their hearing system is of great practical relevance. To objectively study these issues, the monaural hearing threshold in the frequency range from 14 to 24 kHz was determined for 26 test subjects between 19 and 33 years of age using pure tone audiometry. The hearing threshold values increased strongly with increasing frequency up to around 21 kHz, followed by a range with a smaller slope toward 24 kHz. The number of subjects who could respond positively to the threshold measurements decreased dramatically above 21 kHz. Brain activation was then measured by means of magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) and with acoustic stimuli at the same frequencies, with sound pressure levels (SPLs) above and below the individual threshold. No auditory cortex activation was found for levels below the threshold. Although test subjects reported audible sounds above the threshold, no brain activity was identified in the above-threshold case under current experimental conditions except at the highest sensation level, which was presented at the lowest test frequency.

Exposure to High-Frequency Sound and Ultrasound in Public Places: Examples from Zurich, Switzerland

The public is unknowingly exposed to very high-frequency sound (VHFS; 11.2–17.8 kHz) and ultrasound (US; >17.8 kHz) signals in air in public places, as evidenced by previously published reports. The present report provides evidence for the presence of VHFS/US signals in the air at public places in Zurich, Switzerland. The analysis of the signals measured revealed that they: (i) contain one, two or multiple frequencies; (ii) comprise frequencies ranged from 15.5 kHz to 36.0 kHz; (iii) were either quasi constant in their amplitude or exhibit a clear amplitude modulation; and (iv) were in their characteristics (frequencies, modulation, intensity) specific for each place. Based on the signal characteristic it is likely that the signals are generated by public-address voice-alarm (PAVA) systems. The work presented: (i) documents the presence of VHFS/US signals at public places in Zurich, possibly caused by PAVA systems; and should (ii) show that is easily possibly to measure the signals with an affordable measurement equipment as a “citizen scientist”, and stimulate others also to measure and analyse VHFS/US signals with this citizen scientist approach in other cities worldwide. Due to the possible negative health-related effects of a human exposure to VHFS/US signals, further research is needed to document VHFS/US signals at public places and to evaluate biological effects of this exposure with laboratory studies.

Ultrasonic noise measurements in the work environment

In many countries, ultrasonic noise is included in the list of factors harmful to health in the work environment. For the frequency range above 20 kHz, there is no clear and complete information on the factors influencing the result of a measurement of sound pressure level. Moreover, there are no current international standards for performing measurements of ultrasonic noise at work stations. This article presents a possibility for the adaptation of the existing measurement methods [e.g., ISO 9612:2009 (2009)] to the ultrasonic range. In particular, it discusses the requirements for measuring instruments, procedures to be followed while performing measurements, the application of a correction to measurement results, and the determination of measurement uncertainty. The development of a consistent method of ultrasonic noise measurement is of utmost importance in carrying out an assessment and reducing the risk of exposure to this physical factor in the work environment.

Wireless communication between personal electronic devices and hearing aids using high frequency audio and ultrasound

Hearing aids continue to be the main intervention for hearing loss but ease of use and control is of concern due to the small size of these aids. While technological advances in Bluetooth Low Energy have allowed for improved wireless control, in particular between personal electronic devices, its use for communication with hearing aids is problematic due to limited battery life. This paper outlines the implementation of acoustic wireless communication between personal electronic devices and hearing aids using On-Off Keying (OOK) and Frequency Shift Keying (FSK) between the frequencies of 16 and 20 kHz. Reliable communication with bit error rates less than 10^-3 were achieved for OOK with maximum data signalling rates of 50, 35.7, and 27.8 bits per second (bps) obtained over 1, 2, and 3 metres respectively, while FSK provided maximum data signalling rates of 83.3, 50, and 27.8 bps over the same distances.

Public exposure to ultrasound and very high-frequency sound in air

Recent work showing the presence of a new generation of ultrasound (US) sources in public places has reopened the debate about whether there are adverse effects of US on humans, and has identified weaknesses in standards and exposure guidelines. Systems that rely on very high-frequency sound (VHFS) and US include public-address voice-alarm (PAVA) systems (whose operational status is often monitored using tones at ∼20 kHz) and pest deterrents. In this study, sound pressure levels (SPLs) produced by 16 sources that were either publically available or installed in busy public spaces were measured. These sources were identified through a citizen science project, wherein members of the public were asked to provide smartphone recordings of VHFS/US sources. With measurements made in realistic listening positions, pest deterrents were found that produced levels of up to 100 dB SPL at ∼20 kHz, and a hand dryer was found to produce 84 dB SPL at 40 kHz. PAVA systems were found to emit lower levels of up to 76 dB SPL at ∼20 kHz. Pest deterrents measured breach recommended safe listening limits for public exposure for people who are nearby even for relatively short periods.

Potential audibility of ultrasonic signal monitoring of Public Address and Life Safety Sound Systems

Ultrasonic surveillance monitoring, to check the operational integrity of Public Address (PA) and Emergency Communication Systems, has been in existence for over 40 years-particularly in Europe. Since its inception, there has been debate as to the potential audibility that these systems may have. As the vast majority of sound systems engineers and designers have not heard or experienced any effects, it has generally been assumed that the general public do not either. Recently, however, concern has been raised and claims of ill effects have been reported with respect to ultrasonic emissions. There is, however, little or no data as to the ultrasonic sound levels that sound systems actually emit. This paper discusses the results of an initial survey of ultrasound radiated by a sample of some 50 sound systems and compares the results with a number of international standards-there currently being little or no specific guidance. This paper reviews the technology involved, typical emission levels, and concludes by making a number of recommendations to assist with the control of ultrasonic emissions to help mitigate unintended side effects. It is shown that most PA systems generate ultrasonic levels of under 70 dB at normal listener locations.

Effects of very high-frequency sound and ultrasound on humans. Part II: A double-blind randomized provocation study of inaudible 20-kHz ultrasound

Some people have reported symptoms such as nausea, dizziness, and headaches that they attribute to ultrasound (US) emitted by devices in public places. The primary aim of the present study was to investigate whether inaudible US can provoke adverse symptoms compared to a sham presentation, under double-blind conditions. A second aim was to investigate whether the expectation of US being present could provoke adverse symptoms (a nocebo response). The US stimulus was a 20 kHz tone presented continuously for 20 min set to at least 15 dB below the participants' detection threshold, giving a typical sound pressure level (SPL) of 84 dB. No evidence that US provoked symptoms was found, but there was evidence of small nocebo effects. A case study on an individual with high self-reported sensitivity to US gave similar results. The present study did not reproduce the severe symptoms reported previously by some members of the public; this may be due to the SPL or duration of the stimulus, or strength of the nocebo stimulus. These findings cannot be used to predict outcomes from exposures to sounds that are audible to the individual in question, or to sounds with higher SPLs, longer durations, or different frequency content.

Measurements of ultrasonic deterrents and an acoustically branded hairdryer: Ambiguities in guideline compliance

Acoustic radiation from three commercial pest deterrents and two hair dryers were measured in an anechoic chamber. The deterrents were chosen because the frequency range at which they emit the most energy is either in the very high-frequency sound band (11.2-17.8 kHz) or the ultrasound band (greater than 17.8 kHz). These are sources that may be heard by a subset of the general population, with the young typically having better high frequency sensitivity. A hairdryer reported to increase the frequency of the motor noise above the audible hearing range was compared with a standard hairdryer. The outputs of the deterrents are compared against six international regulations and guidelines for audible and ultrasound exposure. Multiple ambiguities in the application of these guidelines are discussed. These ambiguities could lead to a device being considered as in compliance despite unconventionally high levels. Even if a device measured here meets a guideline, actual exposures can exceed those taken here and may therefore breach guidelines if the listener is closer to the device or reflections increase the exposure level.

Assessment of short-term exposure to an ultrasonic rodent repellent device

The objectives of the present study were to investigate the acoustical properties of the very high frequencies and/or ultrasound signals produced by a repellent device and to investigate potential adverse factors as a result of short-term exposure to these signals. Potential adverse effects were evaluated perceptually with 25 young and 25 middle-aged persons, all with normal hearing thresholds, in a quiet room using different outcome measures, including a 15-item survey presented before and immediately after each condition. Spectral analyses showed that, besides emitting frequency modulated sounds in the expected frequency ranges, a faint but audible sound in the 4-5 kHz range was present. On average, a relatively short exposure to the sound produced by a repellent device did not lead to significant adverse effects. Yet, when the signal was perceived, as it was frequently for the younger population at the two lower frequencies settings (12-14 kHz, 25-25 kHz) and with 2 sources emitting, it was considered to be disturbing by several participants. Given the increasing usage of ultrasonic devices as well as the much longer exposure of high frequency and ultrasound in domestic usage, careful consideration and better guidelines are required, especially for those who are most sensitive to sound.

Statistical characterization and modeling of noise effects in near-ultrasound aerial acoustic communications

In this paper, the statistical properties of near-ultrasound acoustic noise in typical indoor environments are investigated. The results indicate that near-ultrasound noise exhibits impulsive behavior and that its first-order probability density functions can be accurately modeled by using a Gaussian mixture or symmetric alpha-stable (SαS) distributions. Furthermore, a practical approach for estimating the parameters of the SαS noise in near-ultrasound aerial acoustic communication receivers is proposed. The problem of modeling memory effects in near-ultrasound acoustic noise is also considered and a simple noise model with memory is proposed based on multiple linear stable processes. The proposed statistical noise models can be used to analyze, simulate, and optimize the performance of various near-ultrasound aerial acoustic communication systems. It is believed that the analysis may contribute to the development of more efficient near-ultrasound aerial communication systems for a range of practical applications.

Measurements of ultrasound from public address and voice alarm systems in public places

Concerns have been raised about potential health effects of public exposure to ultrasound; however, there are few published surveys of measurements taken in public places. Results are presented of measurements taken in a selection of public places including train stations, shopping centres, galleries and museums, and the difficulties of taking measurements with conventional equipment are highlighted. Tones were identified in the 20 kHz third-octave band at 8 of the 14 locations tested; the characteristics of the tones are consistent with their source being Public Address or Voice Alarm systems. The measured results do not exceed existing interim guidelines for public exposure to ultrasound, and existing research suggests that no significant undesirable effects would be anticipated following exposure to ultrasound of this nature for short periods. The measured data may be reviewed against future public exposure guidelines which consider the variation in response across the population and between continuous and pulsed sources.

Uncertainty analysis on free-field reciprocity calibration of measurement microphones for airborne ultrasound

Airborne ultrasound has been used for various purposes, including object detection and pest repellent systems. Recently, it has been used in haptic technology for virtual reality. The safety of exposure to airborne ultrasound has been studied as its use has increased. Although airborne ultrasound cannot be directly perceived by humans, some research has found that exposure to very high sound pressure levels can harm the human body. Thus, quantitative characterization of airborne ultrasound is essential. To contribute to the safe use of airborne ultrasound, this paper established the acoustic standards in Japan in terms of sound pressure from 20 to 100 kHz. This paper evaluates the measurement uncertainty in the free-field reciprocity calibration of quarter-inch condenser microphones, following the document "Guide to the Expression of Uncertainty in Measurement," and describes a few significant uncertainty components, such as deviation from the plane sound field. As a result, it is realized that the expanded uncertainty of 0.3-0.7 dB in a frequency range from 20 to 100 kHz.

Frequency bands for ultrasound, suitable for the consideration of its health effects

It is proposed that the ultrasound frequency spectrum should be divided into three bands in order to facilitate a more rational assessment of its health effects. Whilst statement of the frequencies at the borders of these bands facilitates their definition, it is recognized that these observables vary continuously with frequency and consequently these border frequencies should not be used to rule out the possibility of a given effect occurring. The lowest band, US(A), lies between 17.8 and 500 kHz. In this band acoustic cavitation and its associated forces form the dominant process resulting in biological effects in liquids and soft tissues, whereas health effects from airborne ultrasound have been reported but are far less researched. In the middle band, US(B), between 500 kHz and 100 MHz, temperature rise in tissues becomes the most important biological effect of exposure. The highest band, US(C), covers frequencies above 100 MHz, for which the radiation force becomes an increasingly important biophysical mechanism. A justification for the selection of 17.8 kHz in preference to any other threshold for the lower frequency limit for ultrasound is given.

Ultrasound in air-Guidelines, applications, public exposures, and claims of attacks in Cuba and China

This editorial introduces a Special Issue of the Journal of the Acoustical Society of America, on "Ultrasound in Air." In this Special Issue, one paper covers ways of categorizing the ultrasonic regimes, and three papers cover human effects. One of those three, plus five others, constitute the six papers that report on the measured outputs of commercial devices. Two cover calibration, and the final three papers cover novel applications. This editorial outlines the context in which these papers provide individual studies, including the development of technology and guidelines for safe exposure, and ending with an analysis of what is currently known about claims of sonic attacks on embassy staff in Cuba and China.

Free-field reciprocity calibration of measurement microphones at frequencies up to 150 kHz

Microphones are typically calibrated in a free field at frequencies up to 40 kHz using primary and secondary methods. This upper frequency is sufficiently high as to cover most sound measurement applications related with airborne noise assessment. However, other applications such as measurement of noise emitted by ultrasound cleaning machines, failure detection in aeronautic structures, and the investigation of the perception mechanisms of ultrasound may require that the sensitivity of the microphone is known at frequencies up to 150 kHz. In any of these applications, it is critical to establish a well-defined traceability chain to SI units to support any measurement result. In order to extend the frequency range of absolute free-field calibration, typical reciprocity measurement systems and measurement methods must undergo a series of changes and adaptations which may include using other types of microphones rather than laboratory standard microphones, changing the type of measurement signal, improving the methods for eliminating unwanted reflections from walls, cross-talk, distortion, etc. Herein, a strategy for the changes and adaptations to the existing measurement methodologies, and the determination of the microphone parameters is outlined, the results of its implementation are discussed, and calibrations results are presented and discussed.

Effects of very high-frequency sound and ultrasound on humans. Part I: Adverse symptoms after exposure to audible very-high frequency sound

Various adverse symptoms resulting from exposure to very high-frequency sound (VHFS) and ultrasound (US) have previously been reported. This study aimed to establish whether these symptoms are experienced under controlled laboratory conditions and are specific to VHFS/US. To do this, participants were exposed to VHFS/US (at frequencies between 13.5 and 20 kHz and sound pressure levels between 82 and 92 dB) and to a 1 kHz reference stimulus, both at 25 dB above their hearing threshold. The VHFS/US and reference stimuli were presented 4 times, each time for 3 min, during which participants performed a sustained attention task, rated their symptom severity, and had their galvanic skin response (GSR) measured to assess their level of anxiety. Prior to exposure, participants were assigned either to a symptomatic or an asymptomatic group, based on their prior history of symptoms that they attributed to VHFS/US. In both groups, overall discomfort ratings were higher in the VHFS/US condition than the reference condition. In the symptomatic group only, difficulty concentrating and annoyance were also rated higher in the VHFS/US than the reference condition. No difference between the two stimulus conditions was seen in performance on the attention task or on average GSRs for either group.

Sustainable Consumerism via Context-Aware Shopping

We are living in a world of vast information. The means of the Internet allow access to diverse sources of information, with social media and Internet of Things technologies significantly expanding the informational ecosystem. With the use of social media, it is easy for ‘like-minded' people to group up and initiate movements. One way to articulate such movements is via political consumerism. Users group together and boycott or buycott (boost purchases) for certain products with a concrete collective goal in mind. If, however, the collective goal is vague and abstract, as in the case of sustainability, this bottom-up strategy may lose its popularity and attraction. In this paper, we introduce a new concept of how individual consumers can follow their own understanding of sustainability, while at the same time benefiting from collective and participatory actions. We discuss how the means of ICT can be used to develop political consumerism further to transform individual policies into collective statements.

Wireless Power Transfer to Millimeter-Sized Nodes Using Airborne Ultrasound

We propose the use of airborne ultrasound for wireless power transfer to mm-sized nodes, with intended application in the next generation of the Internet of Things (IoT). We show through simulation that ultrasonic power transfer can deliver 50 [Formula: see text] to a mm-sized node 0.88 m away from a ~ 50-kHz, 25-cm² transmitter array, with the peak pressure remaining below recommended limits in air, and with load power increasing with transmitter area. We report wireless power recovery measurements with a precharged capacitive micromachined ultrasonic transducer, demonstrating a load power of 5 [Formula: see text] at a simulated distance of 1.05 m. We present aperture efficiency, dynamic range, and bias-free operation as key metrics for the comparison of transducers meant for wireless power recovery. We also argue that long-range wireless charging at the watt level is extremely challenging with existing technology and regulations. Finally, we compare our acoustic powering system with cutting edge electromagnetically powered nodes and show that ultrasound has many advantages over RF as a vehicle for power delivery. Our work sets the foundation for further research into ultrasonic wireless power transfer for the IoT.

Comment on 'Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?'

A number of queries regarding the paper 'Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?' (Leighton 2016 Proc. R. Soc. A472, 20150624 (doi:10.1098/rspa.2015.0624)) have been sent in from readers, almost all based around some or all of a small set of questions. These can be grouped into issues of engineering, human factors and timeliness. Those issues (represented by the most typical wording used in queries) and my responses are summarized in this comment.

Synergy of Microfluidics and Ultrasound : Process Intensification Challenges and Opportunities

A compact snapshot of the current convergence of novel developments relevant to chemical engineering is given. Process intensification concepts are analysed through the lens of microfluidics and sonochemistry. Economical drivers and their influence on scientific activities are mentioned, including innovation opportunities towards deployment into society. We focus on the control of cavitation as a means to improve the energy efficiency of sonochemical reactors, as well as in the solids handling with ultrasound; both are considered the most difficult hurdles for its adoption in a practical and industrial sense. Particular examples for microfluidic clogging prevention, numbering-up and scaling-up strategies are given. To conclude, an outlook of possible new directions of this active and promising combination of technologies is hinted.