Characterisation of Nitinol for the Design of Tuneable Transducers

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A comparison of two configurations for a dual-resonance cymbal transducer

The ability to design tuned ultrasonic devices that can be operated in the same mode at two different frequencies has the potential to benefit a range of applications, such as surgical cutting procedures where the penetration through soft then hard tissues could be enhanced by switching the operating frequency. The cymbal transducer has recently been adapted to form a prototype ultrasonic surgical cutting device that operates at a single frequency. In this paper, two different methods of configuring a dual-resonance cymbal transducer are detailed. The first approach relies on transducer fabrication using different metals for the two end-caps, thereby forming a dual-resonance transducer. The second employs transducer end-caps composed from a shape memory alloy, superelastic Nitinol. The resonance frequency of the Nitinol transducer depends on the phase microstructure of the material, switchable through the temperature and/or stress dependency of the Nitinol end-caps. The vibration response of each transducer is measured through electrical impedance measurements and laser Doppler vibrometry, and finite element analysis is used to show the sensitivity of transducer modal response to the fabrication processes. Through this research, two viable dual-resonance cymbal transducers are designed and characterised, and compared to illustrate the advantages and disadvantages of the two different approaches

Nitinol Cymbal Transducers for Power Ultrasonics Applications

The effects of shape memory alloy phenomena such as superelasticity and thermal phase change on the dynamic response of a cymbal transducer incorporating two Nitinol end-caps has not been studied into detail. The experimental results, using both vibration response and electrical impedance measurements, demonstrate that the use of Nitinol as the end-cap material for a cymbal transducer can impose significant effects on the vibration response. The understanding of the effect Nitinol has on the vibration response of a cymbal transducer provides future opportunities to design a power ultrasonic cymbal transducer that can operate with two different and selectable vibration behaviours, which is particularly appealing in a range of applications, including ultrasonic cutting devices that are required to penetrate more than one material

Dynamics characterisation of cymbal transducers for power ultrasonics applications

A class V cymbal flextensional transducer is composed of a piezoceramic disc sandwiched between two cymbal-shaped shell end-caps. Depending on the type of piezoceramic, there exists a maximum voltage that can be reached without depolarisation, but also, at higher voltage levels, amplitude saturation can occur. In addition, there is a restriction imposed by the mechanical strength of the bonding agent. The effects of input voltage level on the vibration response of two cymbal transducers are studied. The first cymbal transducer has a standard configuration of end-caps bonded to a piezoceramic disc, whereas the second cymbal transducer is a modified design which includes a metal ring to improve the mechanical coupling with the end-caps, to enable the transducer to operate at higher voltages, thereby generating higher displacement amplitudes. This would allow the transducer to be suitable for power ultrasonics applications. Furthermore, the input voltages to each transducer are increased incrementally to determine the linearity in the dynamic responses. Through a combination of numerical modelling and experiments, it is shown how the improved mechanical coupling in the modified cymbal transducer allows higher vibration amplitudes to be reached

Optimisation of a cymbal transducer for its use in a high-power ultrasonic cutting device for bone surgery

The class V cymbal is a flextensional transducer commonly used in low-power ultrasonic applications. The resonance frequency of the transducer can be tailored by the choice of end-cap and driver materials, and the dimensions of the end-caps. The cymbal transducer has one significant limitation which restricts the operational vibration amplitude of the device. This is the limit imposed by the mechanical strength of the bonding agent between the metal end-cap and the piezoceramic driver. Therefore, when there is an increase in the input power or displacement, the stresses in the bonding layer can lead to debonding, thereby rendering the cymbal transducer ineffective for high-power ultrasonic applications. In this paper, several experimental analyses have been performed, complemented by the use of Abaqus/CAE finite element analysis, in order to develop a high-power ultrasonic cutting device for bone surgery using a new configuration of cymbal transducer, which is optimised for operation at high displacement and high input power. This new transducer uses a combination of a piezoceramic disc with a metal ring as the driver, thereby improving the mechanical coupling with the metal end-cap

The high frequency flexural ultrasonic transducer for transmitting and receiving ultrasound in air

Flexural ultrasonic transducers are robust and low cost sensors that are typically used in industry for distance ranging, proximity sensing and flow measurement. The operating frequencies of currently available commercial flexural ultrasonic transducers are usually below 50 kHz. Higher operating frequencies would be particularly beneficial for measurement accuracy and detection sensitivity. In this paper, design principles of High Frequency Flexural Ultrasonic Transducers (HiFFUTs), guided by the classical plate theory and finite element analysis, are reported. The results show that the diameter of the piezoelectric disc element attached to the flexing plate of the HiFFUT has a significant influence on the transducer's resonant frequency, and that an optimal diameter for a HiFFUT transmitter alone is different from that for a pitch-catch ultrasonic system consisting of both a HiFFUT transmitter and a receiver. By adopting an optimal piezoelectric diameter, the HiFFUT pitch-catch system can produce an ultrasonic signal amplitude greater than that of a non-optimised system by an order of magnitude. The performance of a prototype HiFFUT is characterised through electrical impedance analysis, laser Doppler vibrometry, and pressure-field microphone measurement, before the performance of two new HiFFUTs in a pitch-catch configuration is compared with that of commercial transducers. The prototype HiFFUT can operate efficiently at a frequency of 102.1 kHz as either a transmitter or a receiver, with comparable output amplitude, wider bandwidth, and higher directivity than commercially available transducers of similar construction

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Language evolution as a constraint on conceptions of a minimalist language faculty

PhD ThesisLanguage appears to be special. Well-rehearsed arguments that appeal to aspects of language acquisition, psycholinguistic processing and linguistic universals all suggest that language has certain properties that distinguish it from other domain general capacities. The most widely discussed theory of an innate, modular, domain specific language faculty is Chomskyan generative grammar (CGG) in its various guises. However, an examination of the history and development of CGG reveals a constant tension in the relationship of syntax, phonology and semantics that has endured up to, and fatally undermines, the latest manifestation of the theory: the Minimalist Program. Evidence from language evolution can be deployed to arrive at a more coherent understanding of the nature of the human faculty for language. I suggest that all current theories can be classed on the basis of two binary distinctions: firstly, that between nativist and non-nativist accounts, and secondly between hypotheses that rely on a sudden explanation for the origins of language and those that rely on a gradual, incremental picture. All four consequent possibilities have serious flaws. By scrutinising the extant cross-disciplinary data on the evolution of hominins it becomes clear that there were two significant periods of rapid evolutionary change, corresponding to stages of punctuated equilibrium. The first of these occurred approximately two million years ago with the speciation event of Homo, saw a doubling in the size, alongside some reorganisation, of hominin brains, and resulted in the first irrefutable evidence of cognitive behaviour that distinguishes the species from that of our last common ancestor with chimpanzees. The second period began seven to eight hundred thousand years ago, again involving reorganisation and growth of the brain with associated behavioural innovations, and gave rise to modern humans by at least two hundred thousand years ago. ii I suggest that as a consequence of the first of these evolutionary breakthroughs, the species Homo erectus was endowed with a proto-‘language of thought’ (LoT), a development of the cognitive capacity evident in modern chimpanzees, accompanied by a gestural, and then vocal, symbolic protolanguage. The second breakthrough constituted a great leap involving the emergence of advanced theory of mind and a fully recursive, creative LoT. I propose that the theory outlined in the Representational Hypothesis (RH) clarifies an understanding of the nature of language as having evolved to represent externally this wholly internal, universal LoT, and it is the latter which is the sole locus of syntax and semantics. By clearly distinguishing between a phonological system for semiotic representation, and that which it represents, a syntactico-semantic LoT, the RH offers a fully logical and consistent understanding of the human faculty for language. Language may have the appearance of domain specific properties, but this is entirely derived from both the nature of that which it represents, and the natural constraints of symbolic representation

Venting in the comparative study of flexural ultrasonic transducers to improve resilience at elevated environmental pressure levels

The classical form of a flexural ultrasonic transducer is a piezoelectric ceramic disc bonded to a circular metallic membrane. This ceramic induces vibration modes of the membrane for the generation and detection of ultrasound. The transducer has been popular for proximity sensing and metrology, particularly for industrial applications at ambient pressures around 1 bar. The classical flexural ultrasonic transducer is not designed for operation at elevated pressures, such as those associated with natural gas transportation or petrochemical processes. It is reliant on a rear seal which forms an internal air cavity, making the transducer susceptible to deformation through pressure imbalance. The application potential of the classical transducer is therefore severely limited. In this study, a venting strategy which balances the pressure between the internal transducer structure and the external environment is studied through experimental methods including electrical impedance analysis and pitch-catch ultrasound measurement. The vented transducer is compared with a commercial equivalent in air towards 90 bar. Venting is shown to be viable for a new generation of low cost and robust industrial ultrasonic transducers, suitable for operation at high environmental pressure levels

Avoiding bias in reconstructing the largest observable scales from partial-sky data

Obscuration due to Galactic emission complicates the extraction of information from cosmological surveys, and requires some combination of the (typically imperfect) modeling and subtraction of foregrounds, or the removal of part of the sky. This particularly affects the extraction of information from the largest observable scales. Maximum-likelihood estimators for reconstructing the full-sky spherical harmonic coefficients from partial-sky maps have recently been shown to be susceptible to contamination from within the sky cut, arising due to the necessity to band-limit the data by smoothing prior to reconstruction. Using the WMAP 7-year data, we investigate modified implementations of such estimators which are robust to the leakage of contaminants from within masked regions. We provide a measure, based on the expected amplitude of residual foregrounds, for selecting the most appropriate estimator for the task at hand. We explain why the related quadratic maximum-likelihood estimator of the angular power spectrum does not suffer from smoothing-induced bias.Comment: 8 pages, 8 figures. v2: replaced with version accepted by PRD (minor amendments to text only