Prototype Transducer Research Articles

Dual-Mode Intracranial Catheter Integrating 3D Ultrasound Imaging and Hyperthermia for Neuro-oncology: Feasibility Study

In this study, we investigated the feasibility of an intracranial catheter transducer with dual-mode capability of real-time 3D (RT3D) imaging and ultrasound hyperthermia, for application in the visualization and treatment of tumors in the brain. Feasibility is demonstrated in two ways: first by using a 50-element linear array transducer (17 mm x 3.1 mm aperture) operating at 4.4 MHz with our Volumetrics diagnostic scanner and custom, electrical impedance-matching circuits to achieve a temperature rise over 4 degrees C in excised pork muscle, and second, by designing and constructing a 12 Fr, integrated matrix and linear-array catheter transducer prototype for combined RT3D imaging and heating capability. This dual-mode catheter incorporated 153 matrix array elements and 11 linear array elements diced on a 0.2 mm pitch, with a total aperture size of 8.4 mm x 2.3 mm. This 3.64 MHz array achieved a 3.5 degrees C in vitro temperature rise at a 2 cm focal distance in tissue-mimicking material. The dual-mode catheter prototype was compared with a Siemens 10 Fr AcuNav catheter as a gold standard in experiments assessing image quality and therapeutic potential and both probes were used in an in vivo canine brain model to image anatomical structures and color Doppler blood flow and to attempt in vivo heating.

Dual-Mode Intracranial Catheter Integrating 3D Ultrasound Imaging and Hyperthermia for Neuro-oncology: Feasibility Study

In this study, the performances of one-dimensional and two-dimensional least-squares strain estimators (LSQSE) are compared. Furthermore, the effects of kernel size are examined using simulated raw frequency data of a widely-adapted hard lesion/soft tissue model. The performances of both methods are assessed in terms of root-mean-squared errors (RMSE), elastographic signal-to-noise ratio (SNRe) and contrast-to-noise ratio (CNRe). RMSE analysis revealed that the 2D LSQSE yields better results for phased array data, especially for larger insonification angles. Using a 2D LSQSE enabled the processing of unfiltered displacement data, in particular for the lateral/horizontal strain components. The SNRe and CNRe analysis showed an improvement in precision and almost no loss in contrast using 2D LSQSE. However, the RMSE images for different kernel sizes revealed that the optimal 2D kernel size depends on the region-of-interest and showed that the LSQ kernel size should be limited to avoid loss in resolution.

A thermoacoustic device for sound reproduction

Many current research efforts focus on alternative electroacoustic transduction devices having no moving parts, in order to achieve sufficient audio performance from compact solid state devices. Thermoacoustic loudspeakers are transducers based on the conversion of A/C current signals to thermal energy, causing a local fluctuation of air pressure which generates acoustic waves. A thermoacoustic actuator does not involve any movement of solid components in order to generate an acoustic wave and it is based on a mechanism of a "virtual" piston produced by vibrating air molecules via alternating heat transfer to the medium. This work examines such novel and alternative audio transduction technologies based on a novel hybrid thermoacoustic transducer prototype which was developed at the University of Patras through the cooperation between Audio and Acoustic Technology Group and Solid State Physics Laboratory. This hybrid solid state device without moving parts is based on the thermoacoustic method of sound reproduction and preliminary measurements of its performance are presented. The theoretical principles of these systems are also simulated, resulting into comparisons with the measured performance of the prototype.

A Linear Variable Differential Capacitive Transducer for Sensing Planar Angles

A linear variable differential capacitive transducer for the measurement of planar angles (from 0deg to 360deg) is presented in this paper. The sensor part of the transducer is made of parallel plates of standard and easy-to-fabricate shapes, and the signal-conditioning electronics are realized, employing a couple of simple relaxation oscillators. The output of the transducer is only dictated by a pair of dc reference voltages, and hence, high accuracy and linearity over the entire range (from 0deg to 360deg) are easily obtained by the use of precision dc reference voltages. Detailed analysis indicates that the sensitivity of the transducer is minimal for variations in different parameters. Experimental results obtained on a prototype transducer that has been built and tested establish the efficacy of the proposed transducer. The worst-case error of the prototype transducer is found to be less than 0.1%.

선형 전기접촉으로 계측해상도가 향상된 저항성 변위센서

Although variable resistance displacement transducer is widely applied for its technical simplicity, electrical point contact limits measurement resolution (precision). The present study introduced roller shaped structure for electrical line contact. Proto-type transducer was developed and measurement characteristics were compared with a commercialized product. When the displacement was varied with steps of 5 mm, 1 mm, and down to 0.1 mm, the correlation coefficient between resistance and displacement decreased lower than 0.9 in the commercialized product while the proto-type transducer maintained values higher than 0.99. Therefore, the measurement resolution was enhanced by approximately 10 times. Since manufacturing also seemed easier, the present results would enable more accurate and less expensive manufacturing of variable resistance displacement transducer.

Development of a flextensional transducer for high resolution seismic imaging

Piezoelectric transducers are considered as potential sources for geophysical applications such as 4D monitoring or shallow subsurface survey, which require high repeatability and precise control of the emitted signal. However, the use of piezoelectric sources is limited by their low power and narrow bandwidth. Flextensional transducers are compact, high power, low frequency, wide‐band projectors used in underwater acoustics. The design, fabrication and test of a flextensional transducer for high resolution seismic imaging are presented in this paper. Circuit modeling is used to discuss the general properties of piezoelectric sources radiating in the ground. Finite element simulations (ATILA code) are conducted to design a wide band 500–1500 Hz flextensional transducer. On‐site tests are performed for a typical configuration of shallow subsurface survey. The prototype transducer is compared to a weight drop which constitutes a well‐known seismic source. By taking advantage of the source repeatability and using specific signal processing, it is found that the flextensional transducer is equivalent to weight drop ranging from 300 to 1300 J. Bandwidth is increased by 200 to 300%, leading to a significant improvement of image resolution.

A New Integrated Ultrasound System for Shockwave Lithotripsy

Inline ultrasound monitoring requires good image quality for accurate stone localization, as well as low shockwave shadowing and a robust transducer. In general, conventional transducers designed for another purpose, such as abdominal scanning, are employed. The distance between the transducer and the SWL focus can be varied by a mechanical drive. The drawback is reduced fragmentation at short distances and poor imaging at long distances. This paper introduces a new approach using a specially designed transducer without a mechanical drive. A transducer prototype with optimized beam focusing (B-K Medical, Herlev, Denmark) was integrated into a modified Compact Delta II therapy head (Dornier MedTech, Wessling, Germany). Image quality was tested at two clinical sites, where 40 kidney and 14 ureteral stones were treated. The shockwave was characterized by model stone tests and fiberoptic hydrophone measurements. Both kidney and ureteral stone treatments could be monitored reliably. Despite the long distance to the SWL focus, the transducer could be operated with relatively high frequencies (3.5-6 MHz), so that high image resolution was obtained. Model stone tests yielded the same fragmentation as the standard Compact Delta II without a transducer. This study shows that the concept of an integrated transducer distant from the shockwave focus is feasible. Transducer elevation, which is accompanied by shockwave shadowing and early transducer failure, is avoided by employing a dedicated transducer design.

Two-dimensional finite element method simulation of a four-quadrant transducer prototype machine considering skewed slots

A four-quadrant transducer (4QT) electric machine is an integrated electric machine used for hybrid electric vehicles. In this article a 4QT prototype machine that is radially integrated by two permanent-magnet synchronous machines is analyzed. Skewed slots are adopted for the two machines, and the multislice two-dimensional time-stepping finite element method is used to calculate the performance. The dividing method of the 4QT, the choice of calculated cutplanes and the determination of the number of slices are discussed. The no-load and load performance of the 4QT are calculated. The 4QT prototype machine was tested. The tested no-load line-to-line back electromotive force curves are in good agreement with the calculated ones, which verifies the feasibility of the proposed method.

Influence of saturation and saliency on the inductance of a four-quadrant transducer prototype machine

An inductance determination method that can be based on both experiments and calculations is discussed in this paper. The inductances of a four-quadrant transducer (4QT) prototype machine were measured and calculated with the two-dimensional time-stepping finite-element method (FEM), and the measured and calculated results are in good agreement. It is found that the d- and q-axis inductances are different, and the inductances obtained from the phase and line voltage are also different for both the two machines of the 4QT prototype machine. Analysis shows that the differences are caused by the saliency and d-axis saturation. Although there is little saliency for the double rotor machine (DRM), the two kinds of the inductance differences of the DRM are more serious than that of the stator machine (SM). This is because of the higher level of the d-axis saturation of the DRM. The inductances obtained from the phase voltage at very low frequency are recommended as final results for both experiments and calculations.

Proapoptotic BID Is an ATM Effector in the DNA-Damage Response

The "BH3-only" proapoptotic BCL-2 family members are sentinels of intracellular damage. Here, we demonstrated that the BH3-only BID protein partially localizes to the nucleus in healthy cells, is important for apoptosis induced by DNA damage, and is phosphorylated following induction of double-strand breaks in DNA. We also found that BID phosphorylation is mediated by the ATM kinase and occurs in mouse BID on two ATM consensus sites. Interestingly, BID-/- cells failed to accumulate in the S phase of the cell cycle following treatment with the topoisomerase II poison etoposide; reintroducing wild-type BID restored accumulation. In contrast, introducing a nonphosphorylatable BID mutant did not restore accumulation in the S phase and resulted in an increase in cellular sensitivity to etoposide-induced apoptosis. These results implicate BID as an ATM effector and raise the possibility that proapoptotic BID may also play a prosurvival role important for S phase arrest.

A chloroform transducer based on sPS-δ-coated quartz-crystal microbalance for gaseous environment

A prototype of a quartz-crystal microbalance-based transducer is proposed for in-situ measurements of very low chloroform activity in a gaseous environment. The sensing element consists of an innovative semicrystalline form of syndiotactic polystyrene sprayed as a thin film on the piezoelectric quartz electrode of the microbalance. Chloroform sorption and desorption in the film give rise to a mass variation, implying a related shift in the resonance frequency of the quartz. Results of static and dynamic metrological characterization of the transducer prototype at varying chloroform concentration and temperature in a gaseous environment are reported. Satisfactory sensitivity, repeatability, and dynamic hysteresis are highlighted.

Numerical investigation of dual-frequency HIFU pulsing for lithotripsy

As an alternative to traditional shock-wave lithotripsy, high-intensity focused ultrasound (HIFU) is currently being investigated for its capability to comminute renal calculi. Because current data indicate that cavitation plays a role in both stone comminution as well as collateral tissue damage, the cavitation effects of HIFU treatment strategies are investigated numerically. In particular, numerical simulations are designed to model the response of bubbles to acoustic excitations generated by a prototype, dual-frequency HIFU transducer for lithotripsy. The prototype transducer is capable of producing both high- (∼4-MHz) and low-frequency (∼100-kHz) outputs, while the bubble dynamics are modeled by the Gilmore equation for a single spherical bubble subject to diffusion. Numerical simulations are currently ongoing to investigate the effects of the relative phase between high and low-frequency pulses. Initial results demonstrate that the simultaneous application of high and low-frequency pulses can generate maximum pressures several orders of magnitude higher than high-frequency pulses alone.

Sensitivity of reflection transducers

This article discusses the sensitivity of new high-speed optical transducers for measuring acoustic transients propagating in water. These devices are based upon the measurement of reflectance at a solid–water interface using a probe beam, perturbations in reflected intensity being brought about by the changes in pressure from an acoustic transient traversing the boundary. It is found that the sensitivity of such transducers is highly dependent not only upon the angle of incidence of the probe beam used to measure reflectance, but also the divergence of the probe beam and the acoustic properties of the transducer material. This results in a trade off between obtaining high spatial resolution and high sensitivity with such a transducer, and higher sensitivities give rise to a more nonlinear response. The fabrication and calibration of a robust prototype transducer made out of perspex is discussed and initial experimental results measuring acoustic transients associated with laser cavitation are shown. High spatial resolution and sensitivity were achieved by focusing the probe beam onto the interface at an angle which was slightly smaller than the critical angle. Finally, a transducer with yet higher sensitivity fabricated out of glass is demonstrated, allowing the study of smaller amplitude rarefaction waves.

Technical feasibility of a three-axis force transducer for measuring pressure and friction on the model die surface — prototype development

A new transducer for measuring normal and shear stress in physical modelling was designed and tested. From many methods of contact stress measurements, a local approach based on pin load cell was chosen. The sensing element employed was a stack of piezoelectric plates which measured three components of the force directly. The design process included a study of piezoelectricity in various materials, designing a prototype transducer and choosing an appropriate electronic circuit. The piezoelectric stack and the whole transducer were tested using a calibration rig capable of applying the normal and tangential force independently. Calibration results confirmed the suitability of the adopted concept and provided guidelines for proper design of the final transducer. In particular, a new calibration procedure was proposed which took into account interactions between the measured force components.

Compact piezoelectric transducers for lithotripsy

Self-focusing piezoelectric transducers are widely used in extracorporeal shockwave lithotripsy. This application demands high focal pressure pulse amplitudes, small focal beamwidths and large penetration depths, which results in large transducers with typical dimensions of 350-mm focal distance and 500-mm diameter. Against the background of the development of smaller and therefore more economical devices it is still desirable to reduce the transducer size but keep the acoustic properties. This can be achieved only by an increased initial pressure amplitude at the transducer surface. Since the single piezoelectric elements are driven close to their electrical limit, a different mechanical design is necessary. Piezoelectric elements placed in a layered manner on both sides of a spherical cap could provide a significant increase of the pressure pulse amplitude generated at the transducer surface. Three-dimensional FEM simulations of the transducer structure including all important design parameters, like the electrical drive for both sides, show the ability of generating higher amplitudes by keeping similar pulse shapes. Measurements made on a prototype transducer with a diameter of 270 mm and a focal distance of 200 mm show comparable results to the standard single-layered design regarding peak focal pressure amplitude and spatial amplitude distributions.

Blood flow noise transducer for detecting intracranial vascular deformations

A transducer using PVDF film, which is placed on the eyelid, has been designed to measure intracranial blood flow noise, called “bruit”, as a screening test for detecting intracranial vascular deformations such as aneurysms, stenosis, and malformations. First, the mechanical impedance of the eye was measured. Then, the transducer performance on the eye was evaluated in terms of sensitivity versus frequency while varying the parameters of the transducer components. The prototype transducer fabricated had a sensitivity of −76dB(0dB=1V/(dyn/cm2)) at frequencies of up to around 1, 000Hz. It was successfully used in a neurosurgical clinic to measure the bruit signals, and was proved to be effective for detecting cerebral aneurysms and stenosis.

Intracardiac ultrasound scanner using a micromachine (MEMS) actuator

Catheter-based intracardiac ultrasound offers the potential for improved guidance of interventional cardiac procedures. The objective of this research is the development of catheter-based mechanical sector scanners incorporating high frequency ultrasound transducers operating at frequencies up to 20 MHz. The authors' current transducer assembly consists of a single 1.75 mm by 1.75 mm, 20 MHz, PZT element mounted on a 2 mm by 2 mm square, 75 mum thick polyimide table that pivots on 3-mum thick gold plated polyimide hinges. The hinges also serve as the electrical connections to the transducer. This table-mounted transducer is tilted using a miniature linear actuator to produce a sector scan. This linear actuator is an integrated force array (IFA), which is an example of a micromachine, i.e., a microelectromechanical system (MEMS). The IFA is a thin (2.2 mum) polyimide membrane, which consists of a network of hundreds of thousands of micron scale deformable capacitors made from pairs of metallized polyimide plates. IFAs contract with an applied voltage of 30-120 V and have been shown to produce strains as large as 20% and forces of up to 8 dynes. The prototype transducer and actuator assembly was fabricated and interfaced with a GagePCI analog to digital conversion board digitizing 12 bit samples at a rate of 100 MSamples/second housed in a personal computer to create a single channel ultrasound scanner. The deflection of the table transducer in a low viscosity insulating fluid (HFE 7100, 3M) is up to +/-10 degrees at scan rates of 10-60 Hz. Software has been developed to produce real-time sector scans on the PC monitor.

Contactless linear position transducer based on reluctance variation

A novel form of electromagnetic transducer for continuous position sensing in linear drive systems is described. The transducer relies on a repetitive variation of inductance with position caused by the change of reluctance between moving and static saliences of a magnetic circuit. The novelty feature of the transducer is seen in terms of its design which is distinguished by a simple cylindrical modular form and allows a large sensing range. The transducer's accuracy and sensitivity are independent of the sensing range. The investigations presented are focused on studying the magnetic circuit design and the excitation of the transducer, with the aim to accomplish a linear relationship between the transducer output and position. A consideration of the effects of core losses and motional EMF on the transducer output has been made. Results obtained with an experimental prototype transducer are included.

A study on the design of a shear wave ultrasonic transducer considering the effect of the side layer

Most researches on the design of ultrasonic transducers deal with the optimal design of matching and backing layers. The importance of the side layer has not been noticed so much and detailed investigation into its effect has been done quite rarely even though it plays a vital role in the proper operation of a shear wave transducer. The effect of the side layer structure and its material properties is analyzed with three-dimensional finite element method, and based on the results, a shear wave transducer with highest sensitivity is designed. The same procedure can also be applied to the design of a wideband transducer. The validity of the design is verified through comparison with experimental data with a prototype transducer constructed following the design values.

Sapphire high-Q low temperature transducer for resonant bar gravitational wave antennas

A very high quality factor sapphire dielectric resonator transducer is shown to be an extremely sensitive readout device for a resonant bar gravitational wave antenna. The transducer has the possibility of allowing operation below the standard quantum limit. Tests on a prototype transducer with quality factor up to Q ⋍ 4 × 10 8 are described.