Andrew Feeney

Smart cymbal transducers with nitinol end caps tunable to multiple operating frequencies

Cymbal flextensional transducers have principally been adopted for sensing and actuation and their performance in higher power applications has only recently been investigated. Nitinol is a shape-memory alloy (SMA) with excellent strain recovery, durability, corrosion resistance, and fatigue strength. Although it has been incorporated in many applications, the implementation of nitinol, or any of the SMAs, in power ultrasonic applications is limited. Nitinol exhibits two phenomena, the first being the superelastic effect and the second being the shape-memory effect (SME). This paper assesses two cymbal transducers, one assembled with superelastic nitinol end caps and the other with shape-memory nitinol end caps. Characterization of the nitinol alloy before the design of such transducers is vital, so that they can be tuned to the desired operating frequencies. It is shown this can be achieved for shape-memory nitinol using differential scanning calorimetry (DSC); however, it is also shown that characterizing superelastic nitinol with DSC is problematic. Two transducers are assembled whose two operating frequencies can be tuned, and their dynamic behaviors are compared. Both transducers are shown to be tunable, with limitation for high-power applications largely being associated with the bond layer.

An ultrasonic orthopaedic surgical device based on a cymbal transducer

An ultrasonic orthopaedic surgical device is presented, where the ultrasonic actuation relies on a modification of the classical cymbal transducer. All current devices consist of a Langevin ultrasonic transducer with a tuned cutting blade attached, where resonance is required to provide sufficient vibrational amplitude to cut bone. However, this requirement restricts the geometry and offers little opportunity to propose miniaturised devices or complex blades. The class V flextensional cymbal transducer is proposed here as the basis for a new design, where the cymbal delivers the required vibrational amplitude, and the design of the attached cutting insert can be tailored for the required cut. Consequently, the device can be optimised to deliver an accurate and precise cutting capability. A prototype device is presented, based on the cymbal configuration and designed to operate at 25.5kHz with a displacement amplitude of 30μm at 300V. Measurements of vibrational and impedance responses elucidate the mechanical and electrical characteristics of the device. Subsequent cutting tests on rat femur demonstrate device performance consistent with a commercial Langevin-based ultrasonic device and show that cutting is achieved using less electrical power and a lower piezoceramic volume. Histological analysis exhibits a higher proportion of live cells in the region around the cut site for the cymbal device than for a powered sagittal or a manual saw, demonstrating the potential for the ultrasonic device to result in faster healing.

Vibration characterisation of cymbal transducers for power ultrasonic applications

A Class V cymbal flextensional transducer is composed of a piezoceramic disc or ring sandwiched between two cymbal-shaped shell end-caps. These end-caps act as mechanical transformers to convert high impedance, low radial displacement of the piezoceramic into low impedance, large axial motion of the end-cap. The cymbal transducer was developed in the early 1990s at Penn State University, and is an improvement of the moonie transducer which has been in use since the 1980s. Despite the fact that cymbal transducers have been used in many fields, both as sensors and actuators, due to its physical limitations its use has been mainly at low power intensities. It is only very recently that its suitability for high amplitude and high power applications has been studied, and consequently implementation in this area of research remains undeveloped. This paper employs experimental modal analysis (EMA), vibration response measurements and electrical impedance measurements to characterise two variations of the cymbal transducer design, both aimed at incorporation in ultrasonic cutting devices. The transducers are fabricated using the commercial Eccobond 45LV epoxy adhesive as the bonding agent. The first cymbal transducer is of the classic design where the piezoceramic disc is bonded directly to the end-caps. The second cymbal transducer includes a metal ring bonded to the outer edge of the piezoceramic disc. The reason for the inclusion of this metal ring is to improve the mechanical coupling with the end-caps. This would therefore make this design particularly suitable for power ultrasonic applications, reducing the possibility of debonding at the higher ultrasonic amplitudes. The experimental results demonstrate that the second cymbal design is a significant improvement on the more classic design, allowing the transducer to operate at higher voltages and higher amplitudes, exhibiting a linear response over a practical power ultrasonic device driving voltage range. The results also show that the device can be accurately tuned using finite element modelling and that the cymbal exhibits a modal response as predicted by the finite element models.

Differential scanning calorimetry of superelastic Nitinol for tunable cymbal transducers

Recent research has shown that estimations of the transformation temperatures of superelastic Nitinol using differential scanning calorimetry can be inaccurate, in part, due to the residual stress in the material. Superelastic Nitinol is selected as the end-cap material in a tunable cymbal transducer. The differential scanning calorimetry accuracy is initially probed by comparing transformation temperature measurements of cold-worked superelastic Nitinol with the same material after an annealing heat treatment, administered to relieve stresses from fabrication. The accuracy is further investigated through a study of the vibration response of the cymbal transducer, using electrical impedance measurements and laser Doppler vibrometry to demonstrate that the change in resonant frequencies can be correlated with the transformation temperatures of the Nitinol measured using differential scanning calorimetry. The results demonstrate that differential scanning calorimetry must be used with caution for superelastic Nitinol, and that an annealing heat treatment can allow subsequent use of differential scanning calorimetry to provide accurate transformation temperature data.

The Dynamic Performance of Flexural Ultrasonic Transducers

Flexural ultrasonic transducers are principally used as proximity sensors and for industrial metrology. Their operation relies on a piezoelectric ceramic to generate a flexing of a metallic membrane, which delivers the ultrasound signal. The performance of flexural ultrasonic transducers has been largely limited to excitation through a short voltage burst signal at a designated mechanical resonance frequency. However, a steady-state amplitude response is not generated instantaneously in a flexural ultrasonic transducer from a drive excitation signal, and differences in the drive characteristics between transmitting and receiving transducers can affect the measured response. This research investigates the dynamic performance of flexural ultrasonic transducers using acoustic microphone measurements and laser Doppler vibrometry, supported by a detailed mechanical analog model, in a process which has not before been applied to the flexural ultrasonic transducer. These techniques are employed to gain insights into the physics of their vibration behaviour, vital for the optimisation of industrial ultrasound systems.

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 endcaps, thereby forming a dual-resonance transducer. The second employs transducer endcaps 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 or stress dependence of the Nitinol endcaps. 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 paper, two viable dual-resonance cymbal transducers are designed and characterized and compared to illustrate the advantages and disadvantages of the two different approaches.

Ultrasonic compaction of granular geological materials

HighlightsUltrasonic compaction of four granular geological materials is presented.Physical characteristics are identified using laser diffraction analysis and SEM.The operational variables are studied, including strain rate and ultrasonic amplitude.Physical characteristics of the materials are shown to affect compaction. Abstract It has been shown that the compaction of granular materials for applications such as pharmaceutical tableting and plastic moulding can be enhanced by ultrasonic vibration of the compaction die. Ultrasonic vibrations can reduce the compaction pressure and increase particle fusion, leading to higher strength products. In this paper, the potential benefits of ultrasonics in the compaction of geological granular materials in downhole applications are explored, to gain insight into the effects of ultrasonic vibrations on compaction of different materials commonly encountered in sub‐sea drilling. Ultrasonic vibrations are applied, using a resonant 20 kHz compactor, to the compaction of loose sand and drill waste cuttings derived from oolitic limestone, clean quartz sandstone, and slate‐phyllite. For each material, a higher strain for a given compaction pressure was achieved, with higher sample density compared to that in the case of an absence of ultrasonics. The relationships between the operational parameters of ultrasonic vibration amplitude and true strain rate are explored and shown to be dependent on the physical characteristics of the compacting materials.

Flow measurement based on two-dimensional flexural ultrasonic phased arrays

Transit-time flow measurement is a technology which has been increasingly utilized in recent years, in industries such as petrochemical, water, and gas. In general, this method of flow measurement employs two ultrasonic transducers, one situated upstream, and the other downstream. The fluid flow is then characterized via transmission and detection of ultrasound using the transducers. However, there are notable limitations of the transit-time method, including drift of the propagation direction of the ultrasonic beam. This is termed the sound drift effect. This paper reports on the latest developments of ultrasonic phased arrays, which are a potentially robust and economic solution to compensating for this sound drift effect. The design and fabrication of phased arrays is discussed, and experimental flow measurement results are reported, utilizing flow rates from 0 to 2500 m3/h. The results show that the compensation of the sound drift effect has been achieved, demonstrating the feasibility of phased array...

Dynamic characteristics of flexural ultrasonic transducers

The flexural ultrasonic transducer is a robust and inexpensive device which can be used as either a transmitter or receiver of ultrasound, commonly used as proximity sensors or in industrial metrology systems. Their simple construction comprises a piezoelectric disc bonded to a metal cap, which is a membrane that can be considered as a constrained plate. Flexural transducers tend to be driven with a short voltage burst of several cycles at a nominal resonant frequency, in one of two vibration modes. The physics of their vibration response has not been thoroughly reported, and yet an understanding of their operation is essential to optimise application. The vibration behaviour of a flexural transducer can be discretised into three principal zones, comprising a build-up to steady-state, steady-state, and a natural decay, or ring-down. This discretisation can be used to develop mathematical interpretations of the flexural transducer response. Through a combination of experimental methods including laser Doppler vibrometry, and the development of a mechanical analog model, the response mechanisms of flexural transducers are investigated.The flexural ultrasonic transducer is a robust and inexpensive device which can be used as either a transmitter or receiver of ultrasound, commonly used as proximity sensors or in industrial metrology systems. Their simple construction comprises a piezoelectric disc bonded to a metal cap, which is a membrane that can be considered as a constrained plate. Flexural transducers tend to be driven with a short voltage burst of several cycles at a nominal resonant frequency, in one of two vibration modes. The physics of their vibration response has not been thoroughly reported, and yet an understanding of their operation is essential to optimise application. The vibration behaviour of a flexural transducer can be discretised into three principal zones, comprising a build-up to steady-state, steady-state, and a natural decay, or ring-down. This discretisation can be used to develop mathematical interpretations of the flexural transducer response. Through a combination of experimental methods including laser Dopp...

HiFFUTs for high temperature ultrasound

Flexural ultrasonic transducers have been widely used as proximity sensors and as part of industrial metrology systems. However, there is demand from industry for these transducers to have the capability to operate in both liquid and gas, at temperatures of 100-200°C and higher, significantly greater than those tolerated by current flexural transducers. Furthermore, flexural transducers tend to be designed for operation up to around 50 kHz, and the ability to operate at higher frequencies will open up new application and research areas. A limitation of current flexural transducers is the electromechanical driving element, usually a lead zirconate titanate piezoelectric ceramic, which experiences significantly reduced performance as temperature is increased. This investigation proposes a new type of flexural transducer, the HiFFUT, a high frequency flexural ultrasonic transducer, comprising a bismuth titanate ceramic for operation at high temperatures, that could be replaced by another suitable high Curie ...