Design of multi-frequency acoustic kinoforms

Complex diffraction limited acoustic fields can be generated from a single element transducer using inexpensive 3-D printable acoustic kinoforms. This is extremely promising for a number of applications. However, the lack of ability to vary the field limits the potential use of this technology. In this work, this limitation is circumvented using multi-frequency acoustic kinoforms for which different acoustic fields are encoded onto different driving frequencies. An optimisation approach based on random downhill binary search is introduced for the design of the multi-frequency kinoforms. This is applied to two test cases to demonstrate the technique: a kinoform designed to generate the numerals “1,” “2,” and “3” in the same plane but at different driving frequencies, and a kinoform designed to generate 3 sets of eight foci lying on a circle with a driving-frequency-dependent radius. Field measurements from these samples confirmed that multi-frequency acoustic kinoforms can be designed that switch between different arbitrary, pre-designed, acoustic field patterns in the target plane by changing the driving frequenc

Stackable acoustic holograms

Acoustic holograms can be used to form complex distributions of pressure in 3D at MHz frequencies from simple inexpensive ultrasound sources. The generation of such fields is vital to a diverse range of applications in physical acoustics. However, at present, the application of acoustic holograms is severely hindered by the static nature of the resulting fields. In this work, it is shown that by intentionally reducing the diffraction efficiency of each hologram, it is possible to create stackable acoustic holograms that can be repositioned to reconfigure the combined acoustic field. An experimental test-case consisting of two holograms, each designed to generate a distinct distribution of acoustic foci, is used to demonstrate the feasibility of this approach. Field scans taken for four different positions of the two holograms confirm that the individual patterns for each hologram can be arbitrary translated relative to one another. This allows for the generation of a much greater range of fields from a single transducer than could be created using a single hologram

Binary Volume Acoustic Holograms

In recent years, high-resolution additive manufacturing has enabled a diverse range of low-cost methods for ultrasonic wave-front shaping. Acoustic holograms, in particular, allow for the generation of arbitrary diffraction-limited acoustic fields at megahertz frequencies from single-element transducers. These are phase plates that function as direct acoustic analogs to thin optical holograms. In this work, it is shown that, by using multiple polymer three-dimensional (3D) printing, two-material (binary) acoustic analogs to "thick"or volume optical holograms can also be generated. First, an analytic approach for designing a volume hologram that diffracts a set of input fields onto a desired set of output fields is briefly summarized. Next, a greedy-optimization approach based on random downhill binary search able to account for the constraints imposed by the chosen fabrication method is introduced. Finally, an experimental test case designed to diffract the field generated by a 2.54-cm planar lead zirconate titanate (PZT) transducer onto eight distinct patterns dependent on the direction of the incident field is used to validate the approach and the design method. Field scans of the eight target fields demonstrate that acoustic analogs of optical volume holograms can be generated using multipolymer printing and that these allow the multiplexing of distinct fields onto different incident field directions

Control of broadband optically generated ultrasound pulses using binary amplitude holograms

In this work, the use of binary amplitude holography is investigated as a mechanism to focus broadband acoustic pulses generated by high peak-power pulsed lasers. Two algorithms are described for the calculation of the binary holograms; one using ray-tracing, and one using an optimization based on direct binary search. It is shown using numerical simulations that when a binary amplitude hologram is excited by a train of laser pulses at its design frequency, the acoustic field can be focused at a pre-determined distribution of points, including single and multiple focal points, and line and square foci. The numerical results are validated by acoustic field measurements from binary amplitude holograms, excited by a high peak-power laser

Single Pulse Illumination of Multi-Layer Photoacoustic Holograms for Patterned Ultrasound Field Generation

A new method for the creation of patterned, focused, optically generated acoustic fields using a single optical pulse is introduced. This utilises multi-layer `holograms' composed of several spatially separate absorbing layers. Each layer is individually patterned so as to focus at a set of targeted points. To create the patterns, a ray-tracing model was implemented to calculate the impulse response of pixels within each absorbing layer to a set of targeted points. An optimisation approach was then used to find the optimal pattern for each layer to create a field evenly focused at each of the target points. The method was validated using both numerical simulations and acoustic field measurements. It was demonstrated that a 3×3 array of acoustic foci could be generated from a 3-layer hologram using a single laser pulse

Generating arbitrary ultrasound fields with tailored optoacoustic surface profiles

Acoustic fields with multiple foci have many applications in physical acoustics ranging from particle manipulation to neural modulation. However, the generation of multiple foci at arbitrary locations in three-dimensional is challenging using conventional transducer technology. In this work, the optical generation of acoustic fields focused at multiple points using a single optical pulse is demonstrated. This is achieved using optically absorbing surface profiles designed to generate specific, user-defined, wavefields. An optimisation approach for the design of these tailored surface profiles is developed. This searches for a smoothly varying surface that will generate a high peak pressure at a set of target focal points. The designed surface profiles are then realised via a combination of additive manufacturing and absorber deposition techniques. Acoustic field measurements from a sample designed to generate the numeral “7” are used to demonstrate the design method

VALIDATION OF SAFETY CLIMATE FACTORS: A FIRST LOOK AMONG NURSES IN NIGERIA

Purpose – The primary aim of this paper is to validate safety climate factors (management commitment to safety, safety training, safety rules and procedures, safety communication and workers’ involvement in safety) among nurses in select Nigerian healthcare facilities. Design/methodology/approach – A survey of 149 nurses of primary and secondary healthcare facilities in South-south Nigeria was carried out with the use of self-reported measures to obtain data on safety climate factors. The partial least squares structural equation modeling (PLS-SEM) technique was used in ascertaining the validity of the factors in study. Findings – In the present study, it was found that the reliability and validity of the factors were significant notwithstanding that this is a first long among the respondents of the study. Research limitations/implications – Generalizing the findings of this study may be limited to the location from which the respondents are drawn. Also, the present study validated existing safety climate factors, hence did not permit a correlational, causal or longitudinal inferences. Practical Implications – The study highlights some of the most important safety climate factors needed that could determine attendant safety-related behaviours in the healthcare setting. Originality/value – Existing literature indicates the absence of safety climate research in the Nigerian healthcare industry and especially among nurses. Also, as nurses are routinely exposed to occupational hazards and attendant accidents and injuries, this study brings to light the most critical safety climate factors that should be worthy of note in possibly ensuring the safety and health of nurses in the Nigerian healthcare system. Keywords Nigeria, safety climate, nurses, healthcare Paper type Research pape

Measurement of the ultrasound attenuation and dispersion in 3D-printed photopolymer materials from 1 to 3.5 MHz

Over the past decade, the range of applications in biomedical ultrasound exploiting 3D printing has rapidly expanded. For wavefront shaping specifically, 3D printing has enabled a diverse range of new, low-cost approaches for controlling acoustic fields. These methods rely on accurate knowledge of the bulk acoustic properties of the materials; however, to date, robust knowledge of these parameters is lacking for many materials that are commonly used. In this work, the acoustic properties of eight 3D-printed photopolymer materials were characterised over a frequency range from 1 to 3.5 MHz. The properties measured were the frequency-dependent phase velocity and attenuation, group velocity, signal velocity, and mass density. The materials were fabricated using two separate techniques [PolyJet and stereolithograph (SLA)], and included Agilus30, FLXA9960, FLXA9995, Formlabs Clear, RGDA8625, RGDA8630, VeroClear, and VeroWhite. The range of measured density values across all eight materials was 1120–1180 kg · m−3, while the sound speed values were between 2020 to 2630 m · s−1, and attenuation values typically in the range 3–9 dB · MHz−1· cm−1

Investigating the effect of thickness and frequency spacing on multi-frequency acoustic kinoforms

The generation of complex diffraction limited acoustic fields from a simple planar transducer is possible using cheap 3-D printable kinoforms. This approach is extremely promising for several areas of physical acoustics. However, one drawback is that the acoustic field generated from a given kinoform is fixed, limiting flexibility. In this work, multi-frequency acoustic kinoforms are investigated as a means to circumvent that limitation. These are kinoforms designed to generate different distributions of pressure at a target depth when driven at particular design frequencies. An optimisation approach based on direct search for the design of these structures from a set of input frequencies and target distributions is briefly described. The effect of different parameters of the kinoform on the performance are then established. These include the maximum thickness, frequency spacing and target depth. It is found that the maximum thickness has to be limited to avoid significant aberrations, the frequency spacing should be maximised within the usable bandwidth of the transducer, and the optimal thickness is influenced by the choice of target depth. The thin phase approximation is also shown to be increasingly inaccurate for increasing element thicknesses