Langevin Ultrasonic Transducer Research Articles

Dynamic stability of a nitinol Langevin ultrasonic transducer under power and current tracking conditions

The Langevin transducer is widely used in medical and industrial ultrasonics, typically comprising a piezoelectric ceramic stack preloaded between two end-masses. A principal operational challenge is that, depending on the target application or operational environment, piezoelectric ceramics commonly experience elevated temperatures promoting nonlinear dynamic behaviours, often reducing operational performance. Transducers can be operated via burst excitation to mitigate this, but such methods can have limited efficacy, particularly at elevated temperatures. A novel emergent approach is the incorporation of shape memory Nitinol into the transducer, where its temperature-dependent microstructural phase transformations can compensate for changes in the mechanical properties of the piezoelectric ceramics. However, the ability to maintain dynamic stability under power and current tracking, common methods used to ensure stability of Langevin transducers in practical applications, remains unknown. In this research, a cascaded Nitinol Langevin transducer is used to demonstrate its practical application potential. Dynamic stability is assessed whilst power and current levels are tracked in operation. Stable operating frequency, electrical impedance, and vibration amplitude are shown, using a combination of methods including electrical impedance analysis and laser Doppler vibrometry. This research demonstrates the practical application of Langevin transducers incorporating shape memory materials, including with dynamic stability at elevated temperatures.

An analytical model of ultrasonic transducers considering acoustic losses of contact surfaces

In this paper, a continuum electromechanical model of a Langevin ultrasonic transducer is developed considering acoustic losses of contact surfaces. The calculated energy losses between components of a transducer are considered as loss modulus of backing and matching parts. Considering the losses, the calculated vibrations amplitude of the transducer is matched to measured values. In addition, the calculated frequency response of the electrical admittance of the transducer is in good agreement with experimental results. The errors of calculated resonant frequency, anti-resonance frequency and amplitude of vibrations compared to the experimental results are 0.02%, 0.03%, 4.5% respectively. The values of the electrical admittance in the resonant and anti-resonant frequency have errors of 2.7%, 9.5% compared to empirical results. The developed model, fixes the drawback of previous models to anticipate amplitude of vibrations and the frequency response of the electrical admittance of ultrasonic transducers.

Study on heat pipe heat dissipation of high-power ultrasonic transducer

In order to solve the problems of frequency shift, efficiency decline and life shortening caused by temperature rise in the working process of high-power ultrasonic transducer, the technology of heat pipe is employed for enhancing heat dissipation of the ultrasonic transducer. A new type of high-power transducer with heat pipe heat dissipation (HPUT) is proposed in this study. The heat pipe radiator adopts the form of a copper–water-composite wick, and installs straight fins on the condensation section to enhance heat dissipation. Six heat pipe radiators are embedded in the front cover plate of the transducer close to the piezoelectric ceramic and evenly arranged along the circumference of the transducer. The vibration characteristics, radiated sound field characteristics and heat dissipation characteristics of the HPUT are compared with those of traditional Langevin ultrasonic transducer (TLUT) through simulations and experiments. Results manifest that compared with the TLUT, the HPUT has much lower operation temperature (reduced by 60% in this study), much smaller resonant frequency shift (reduced by 75% in this study) and the higher vibration amplitude (increased by 25% in this study). This study will contribute to the development of high-power ultrasonic transducer which has potential application value in many industrial fields.

Investigation of the nonlinear phenomena of a Langevin ultrasonic transducer caused by high applied voltage

In the field of power ultrasound, Langevin ultrasonic transducers (LUTs) usually operate at a large displacements output power by applying high voltages. However, empirically, a LUT exhibits nonlinearities such as amplitude jumping and peak hysteresis for high voltages in actual operations. The nonlinearities would reduce the efficiency and output accuracy of an LUT. In this research, the burst-mode method was used to measure the longitudinal vibration velocity of the LUT, which gradually decreased with time after the excitation voltage was turned off. The equivalent mechanical losses and equivalent spring constants were determined using the velocity attenuation rate and resonant frequency and they were found to be the linear functions of velocity, helping to develop a novel nonlinear model. This model contained two quadratic nonlinear terms based on the linear model. Furthermore, the developed nonlinear model was analyzed using the Lagrangian method as well as the multiscale method, which confirmed that the model was effective in describing the nonlinear behavior. It was also found that the frequency-amplitude curve bent when the nonlinear term was taken into account, which resembled the nonlinear phenomenon tested experimentally. From a physical point of view, this bending was meaningful because it led to the formation of multi-valued response regions with jumping phenomena. Additionally, according to the obtained results, the maximum value of the system response was independent of the degree of nonlinearity of the system.

Development of an Accurate Resonant Frequency Controlled Wire Ultrasound Surgical Instrument.

Our developed wire ultrasound surgical instrument comprises a bolt-clamped Langevin ultrasonic transducer (BLUT) fabricated by PMN-PZT single crystal material due to high mechanical quality factor and electromechanical coupling coefficient, a waveguide in the handheld instrument, and a generator instrument. To ensure high performance of wire ultrasound surgical instruments, the BLUT should vibrate at an accurate frequency because the BLUT’s frequency influences hemostasis and the effects of incisions on blood vessels and tissues. Therefore, we implemented a BLUT with a waveguide in the handheld instrument using a developed assembly jig process with impedance and network analyzers that can accurately control the compression force using a digital torque wrench. A generator instrument having a main control circuit with a low error rate, that is, an output frequency error rate within ±0.5% and an output voltage error rate within ±1.6%, was developed to generate the accurate frequency of the BLUT in the handheld instrument. In addition, a matching circuit between the BLUT and generator instrument with a network analyzer was developed to transfer displacement vibration efficiently from the handheld instrument to the end of the waveguide. Using the matching circuit, the measured S-parameter value of the generator instrument using a network analyzer was −24.3 dB at the resonant frequency. Thus, our proposed scheme can improve the vibration amplitude and accuracy of frequency control of the wire ultrasound surgical instrument due to developed PMN-PZT material and assembly jig process.

Numerical design and analysis of a langevin power ultrasonic transducer for acoustic cavitation generation

This paper presents the design and analysis of a Langevin Ultrasonic Transducer for Acoustic Cavitation Generation (LUTACG) operating under acoustic load. When an ultrasonic transducer is used with acoustic loads its Impedance-Frequency-Phase (IFP) characteristics change. The changes produced in its frequency response are very large and require a readjustment in the control of the resonance frequency as well as the magnitude of the voltage. In this work, a study of the effects of the load type on the impedance-phase relation is made. Experimental tests to study the changes produced in the frequency response were performed in air, water and transformer oil. The different factors that should be taken into consideration in the numerical simulation for a good mechanical-acoustic design are analyzed. Characteristics such as geometry, acoustic impedance, resonance frequency and phase which the ultrasonic transducer and sonotrode must have for proper operation under an acoustic load are analyzed. A simple and economical method is used for the electrical characterization of the transducer. An analysis of the effect of the acoustic impedance between the different interfaces and as they affect the acoustic efficiency of the transducer is made.

Heat transfer enhancement in an annulus under ultrasound field: A numerical and experimental study

Abstract This paper presents experimental and numerical studies of heat transfer enhancement of water in an annulus under ultrasonic waves and fluid flow. An experimental setup is designed and built from two concentric pipes and a bolted Langevin ultrasonic transducer with a frequency of 25.7 kHz stuck to the inner pipe. Two new solvers are developed in OpenFOAM software and a numerical simulation is carried out to model the effect of both acoustic streaming and fluid flow on heat transfer and flow field. There are good agreements between the experimental and numerical results. Experimental results show that increasing the Reynolds number decreases the effect of acoustic streaming as compared to the effect of fluid flow on heat transfer and flow field. As a result, heat transfer enhances about 87% and 25% for Reynolds numbers of 32 and 674, respectively, at the transmitted acoustic power of 100 W. Numerical simulation is used to find the reason of heat transfer enhancement under ultrasonic waves, and results show that the cross-flow generated by circulations due to acoustic streaming is responsible for heat transfer augmentation.

Experimental and numerical study on heat transfer enhancement using ultrasonic vibration in a double-pipe heat exchanger

Heat transfer enhancement of double-pipe heat exchanger in the presence of ultrasonic vibrations is experimentally and numerically studied. A novel experimental setup made of two concentric pipes is constructed and a bolted Langevin ultrasonic transducer is used for applying the ultrasonic vibrations to the inner pipe with a frequency of 26.7 kHz. The numerical simulation is carried out by OpenFOAM software to clarify the reason for heat transfer enhancement. The effects of hot and cold fluid flow rates and acoustic power on heat transfer and pressure drop are studied in this work. The performance of heat exchanger is investigated by comparing the overall heat transfer coefficient and pressure drop with and without the influence of ultrasonic vibrations. Results show that using ultrasonic vibration is more effective at low fluid flow rates. As a result, heat transfer enhances about 60% for both cold and hot fluid flow rates of 0.5 L/min, while heat transfer enhancement is equal to 20% for cold and hot fluid flow rates of 1 and 1.5 L/min, respectively, at the transmitted acoustic power of 120 W. Numerical results demonstrate that the cross-stream flows generated by propagation of ultrasonic waves into the cold fluid are responsible for heat transfer enhancement.

Evaluation of mechanical and electric power losses in a typical piezoelectric ultrasonic transducer

In this paper, contributions of the mechanical and electric power losses have been studied in a typical piezoelectric ultrasonic transducer under free conditions. The losses in a Langevin ultrasonic transducer can be divided into three parts: dielectric loss of piezoelectric, structural damping loss of the transducer’s mechanical components, and losses due to the friction of contact surfaces. In order to estimate dielectric losses, loss factor or tanδ of the piezoelectric ceramic have been measured. Dielectric power loss is obtained by calculating the electrical energy stored in a piezoelectric and using the loss factors. The structural damping of the mechanical components of the transducer is calculated using the mechanical quality factors of each component. The factors have been measured using the standard modal tests. Structural power losses are obtained by calculating the elastic energy stored in each component and using the mechanical quality factors. Based on the calculations for the transducer with the resonance frequency of 20 kHz, under free conditions, the input power is 532 W, the total structural power loss at the resonance frequency is 221.82 W, the dielectric power loss is 15 W, and the power loss due to friction is 184.18 W.

Characterization of the acoustic field generated by a horn shaped ultrasonic transducer

A horn shaped Langevin ultrasonic transducer used in a single axis levitator was characterized to better understand the role of the acoustic profile in establishing stable traps. The method of characterization included acoustic beam profiling performed by raster scanning an ultrasonic microphone as well as finite element analysis of the horn and its interface with the surrounding air volume. The results of the model are in good agreement with measurements and demonstrate the validity of the approach for both near and far field analyses. Our results show that this style of transducer produces a strong acoustic beam with a total divergence angle of 10°, a near-field point close to the transducer surface and a virtual sound source. These are desirable characteristics for a sound source used for acoustic trapping experiments.

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.

An analytical model of a longitudinal-torsional ultrasonic transducer

The combination of longitudinal and torsional (LT) vibrations at high frequencies finds many applications such as ultrasonic drilling, ultrasonic welding, and ultrasonic motors. The LT mode can be obtained by modifications to the design of a standard bolted Langevin ultrasonic transducer driven by an axially poled piezoceramic stack, by a technique that degenerates the longitudinal mode to an LT motion by a geometrical alteration of the wave path. The transducer design is developed and optimised through numerical modelling which can represent the geometry and mechanical properties of the transducer and its vibration response to an electrical input applied across the piezoceramic stack. However, although these models can allow accurate descriptions of the mechanical behaviour, they do not generally provide adequate insights into the electrical characteristics of the transducer. In this work, an analytical model is developed to present the LT transducer based on the equivalent circuit method. This model can represent both the mechanical and electrical aspects and is used to extract many of the design parameters, such as resonance and anti-resonance frequencies, the impedance spectra and the coupling coefficient of the transducer. The validity of the analytical model is demonstrated by close agreement with experimental results.

Designing a Hollow Langevin Transducer for Ultrasonic Coring

A number of architectures for a hollow Langevin ultrasonic transducer are proposed and evaluated. One of these is optimised by finite element modelling and is then manufactured and analysed experimentally. The preload on the transducer ceramics is increased and the effect on the performance is measured. At maximum preload the results of an experimental modal analysis are used to determine the natural frequency and response of both the operating longitudinal mode and unwanted bending modes. The performance of the hollow transducer is compared to a solid commercial transducer containing the same volume of piezoceramic material. The efficiency is shown to be comparable. Higher ultrasonic displacement amplitudes are achieved with the hollow transducer although a lower Q-factor is found.

Finite element analysis and optimization of a single-axis acoustic levitator

A finite element analysis and a parametric optimization of single-axis acoustic levitators are presented. The finite element method is used to simulate a levitator consisting of a Langevin ultrasonic transducer with a plane radiating surface and a plane reflector. The transducer electrical impedance, the transducer face displacement, and the acoustic radiation potential that acts on small spheres are determined by the finite element method. The numerical electrical impedance is compared with that acquired experimentally by an impedance analyzer, and the predicted displacement is compared with that obtained by a fiber-optic vibration sensor. The numerical acoustic radiation potential is verified experimentally by placing small spheres in the levitator. The same procedure is used to optimize a levitator consisting of a curved reflector and a concave-faced transducer. The numerical results show that the acoustic radiation force in the new levitator is enhanced 604 times compared with the levitator consisting of a plane transducer and a plane reflector. The optimized levitator is able to levitate 3, 2.5-mm diameter steel spheres with a power consumption of only 0.9 W.

Investigation of Electrical Transient Behavior for Ultrasonic Transducer in on/off Cycles

This paper investigates a theoretical analysis of electrical transient responses of a bolt-clamped Langevin ultrasonic transducer (BLT) and its verifications based on simulations and experiments during on/off transient states immediately after turning on/off. The simulations are determined by a power electronic simulator originally designed for power converters and motor drives. The responses include the open-circuit voltage, the terminal current, the motional current and the mechanical power loss. A linear equivalent circuit model with the initial conditions is stated first. This model is used to derive the responses characterized by simple closed-form equations. The off transient state as specified by the initial conditions regarding switching-off time of an ac sine source for the drive of the BLT is related to cyclic behavior. The derived responses are further checked by simulations and experiments. To obtain the experiments, a test system which contains an ac power supply, a digital oscilloscope and a control switch is needed. Finally, characteristics of the responses and effects of switching-on/off times of the ac sine source on the characteristics are discussed. The characteristics comprise the dc/ac time constants and the maximum/minimum wave amplitudes for the BLT during on/off transient states.

Study on the multifrequency Langevin ultrasonic transducer

Langevin ultrasonic transducers are widely used in high-power ultrasonics and underwater sound. In ultrasonic cleaning, a matching metal horn rather than a metal cylinder is used as the radiator in order to enhance the radiating surface and improve the acoustic matching between the transducer and the processed medium. To raise the effect of ultrasonic cleaning, the standing wave in the cleaning tank should be eliminated. One method to eliminate the standing wave in the tank is to use the multifrequency ultrasonic transducer. In this paper, the Langevin ultrasonic horn transducer, with two resonance frequencies, is studied. The transducer consists of two groups of piezoelectric ceramic elements: the back metal cylinder, the middle metal cylinder and the front matching metal horn. The vibrational modes of the transducer are analysed, and resonance frequency equations of the transducer in the half-wave and the all-wave vibrational modes are derived. According to the resonance frequency equations, transducers with two resonance frequencies are designed and made. The resonance frequencies, the effective electromechanical coupling coefficients and the equivalent electric impedances of the transducers are measured. It is shown that the measured resonance frequencies are in good agreement with the computed results, and the transducer can be excited to vibrate at two resonance frequencies, which correspond to the half-wave and the all-wave vibrational modes of the transducer.