Mode Transducer Research Articles

Theoretical analysis and experiment verification in improvement of the new micro contour mode ultrasound transducer

Commercialized micro ultrasonic transducer generally adopts thickness mode to produce ultrasound radiation of thickness direction. The miniaturization of low-frequency transducer is a problem due to frequency inversely proportional to thickness of transducer. A new micro contour mode ultrasound transducer is proposed for satisfying miniaturization design. Theory analysis, FEM analysis and experimental investigation are carried out to verify the principle and improve the sound field distribution of contour mode transducer. Three kinds of contour transducers with width 300 μm, 600 μm, and 900 μm are fabricated and the reflecting house is added to improve lateral resolution. The performance is evaluated by electrical impedance, pulse-echo response tests and B-mode imaging tests with a 25 µm tungsten wire phantom. The corresponding experiment result of center frequency, −6 dB bandwidth and sensitivity are 4.1 MHz@37 %@4.5Vpp, 2.5 MHz@37 %@3.4Vpp, and 1.8 MHz@29 %@2.0Vpp respectively. Wire phantom imaging showed the lateral resolution has been markedly promoted with reflecting house. Compared with traditional thickness mode transducer, the proposed transducer can achieve smaller size with simplifying fabricated structure. It has a good application prospect in the fields of intervention image and therapy.

Smart structural health monitoring (SHM) system for on-board localization of defects in pipes using torsional ultrasonic guided waves

Most reported research for monitoring health of pipelines using ultrasonic guided waves (GW) typically utilize bulky piezoelectric transducer rings and laboratory-grade ultrasonic non-destructive testing (NDT) equipment. Consequently, the translation of these approaches from laboratory settings to field-deployable systems for real-time structural health monitoring (SHM) becomes challenging. In this work, we present an innovative algorithm for damage identification and localization in pipes, implemented on a compact FPGA-based smart GW-SHM system. The custom-designed board, featuring a Xilinx Artix-7 FPGA and front-end electronics, is capable of actuating the PZT thickness shear mode transducers, data acquisition and recording from PZT sensors and generating a damage index (DI) map for localizing the damage on the structure. The algorithm is a variation of the common source method adapted for cylindrical geometry. The utility of the algorithm is demonstrated for detection and localization of defects such as notch and mass loading on a steel pipe, through extensive finite element (FE) method simulations. Experimental results obtained using a C-clamp for applying mass loading on the pipe show good agreement with the FE simulations. The localization error values for experimental data analysed using C code on a processor implemented on the FPGA are consistent with algorithm results generated on a computer running Python code. The system presented in this study is suitable for a wide range of GW-SHM applications, especially in cost-sensitive scenarios that benefit from on-node signal processing over cloud-based solutions.

Conformable Shear Mode Transducers from Lead‐Free Piezoelectric Ceramic Coatings: An Innovative Ultrasonic Solution for Submerged Structural Health Monitoring

AbstractShear mode‐guided ultrasonic waves are highly regarded for submerged or subterranean structural health monitoring (SHM), owing to their non‐dispersive feature and minimized acoustic energy loss when in contact with liquid or solid. High‐performance shear mode ceramic ultrasonic transducers with robustness and cost‐effectiveness are highly demanded for underwater or underground SHM applications, especially in harsh environments. However, the implementation of discrete shear mode piezoelectric ceramic ultrasonic transducers is hindered by the inconsistency with manual installation, lack of conformability on curved surfaces, and unreliable acoustic coupling between the transducers and the structure. Here, direct‐write conformable shear mode ultrasonic transducers made from piezoelectric lead‐free ceramic coatings, which are in situ produced on steel structures by a scalable thermal spray process, are proposed. The obtained lead‐free lithium‐doped potassium sodium niobate (KNN‐LN) ceramic coatings exhibit a high effective shear piezoelectric strain coefficient (d24, f) above 60 pm V−1 in a broad frequency range from 100 Hz to 200 kHz. The resulting conformable shear mode KNN‐LN ceramic coating transducers successfully showcase the functions of exciting and detecting stable shear mode ultrasonic wave signals with operation temperature exceeding 200 °C and demonstrate reliable capability in defect detection in both air and liquid environments.

A Whole W-Band Multi-Polarization Horn Antenna Based on Boifot-Type OMT.

A wideband multi-polarized square-horn antenna based on an orthogonal mode transducer (OMT) is developed for working in the whole W-band in this paper. The designed antenna is capable of radiating multiple polarization modes as horizontal polarization (HP) and vertical polarization (VP) when as single-port excitation and left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) when as dual-port excitation, owing to the characteristic of the OMT with the transmitting of orthogonally polarized waves. A CNC-layered fabrication approach is proposed, which means that the antenna prototype integrating with a Boifot-type OMT, turning waveguide, twisting waveguide and phase shifter is divided into three layers along the vertical direction to be fabricated based on computerized numerical control (CNC) technology. In the design, the turning waveguide and twisting waveguide are employed to achieve plane consistency of the antenna branch ports. Furthermore, a phase shifter is designed to compensate the orthogonally polarized waves, which can keep the phase of the orthogonally polarized waves consistent in a wideband frequency range from 75 GHz to 110 GHz. A prototype is fabricated and measured to verify the performance of the proposed multi-polarization antenna, and the measured results agree well with the simulation ones. In the whole W-band, the value of return loss is better than 10 dB of all polarization modes, and the value of AR of the LHCP and RHCP is below 3.5 dB. The maximum gain of the antenna reaches up to 18.8 dBi at 110 GHz. In addition, regarding the layered structure, the possible layered assembly error analysis is discussed, which verifies the feasibility of the layered machining for this antenna.

A CNC-Machined WR-2.2 Band Orthogonal Mode Transducer for a Radiometer

A CNC-Machined WR-2.2 Band Orthogonal Mode Transducer for a Radiometer

Mesoscopic Monitoring of Human Skin Explants Viscoelastic Properties

The investigation of the mechanical properties of skin is of great interest for monitoring physiological and pathological changes in the cutaneous barrier function for dermatological and cosmetic issues. Skin constitutes a complex tissue because of its multi-layered organisation. From a rheological point of view, it can be considered to be a soft tissue with viscoelastic properties. In order to characterise ex vivo mechanical properties of skin on the mesoscopic scale, a biosensor including a thickness shear mode transducer (TSM) in contact with a skin explant was used. A specific experimental set-up was developed to monitor continuously and in real-time human skin explants, including the dermis and the epidermis. These were kept alive for up to 8 days. Skin viscoelastic evolutions can be quantified with a multi-frequency impedance measurement (from 5 MHz to 45 MHz) combined with a dedicated fractional calculus model. Two relevant parameters for the non-destructive mesoscopic characterisation of skin explants were extracted: the structural parameter αapp and the apparent viscosity ηapp. In this study, the validity of the biosensor, including repeatability and viability, was controlled. A typical signature of the viscoelastic evolutions of the different cutaneous layers was identified. Finally, monitoring was carried out on stripped explants mimicking a weakened barrier function.

PZT-based high-temperature ultrasonic dual mode transducer applicable to cubic-anvil apparatus for sound velocity measurement

The ultrasonic transducer is an indispensably critical component for sound velocity measurement. With the increasing demand of high-temperature ultrasonic dual mode transducer applicable to cubic-anvil apparatus, where experiments of high-pressure and high-temperature sound velocity are routinely conducted, a PZT-based ultrasonic dual mode transducer was presented in this study. It was made of a sandwich of two PZT piezoceramic wafers, the upper one generating P-waves and the lower one generating S-waves. The transducer was directly bonded onto a WC anvil of cubic-anvil apparatus using high-temperature adhesive, and then heated in an oven while measuring the bottom echoes from the WC anvil. The results showed that the high-temperature transducer could work up to 140 °C. The transducer features low cost, easy fabricating, and highquality signals, and so we believe it is useful for sound velocity measurement at high temperatures in cubic-anvil apparatus.

A High-Efficiency W-Band Power Combiner Based on the TM₀₁ Mode in a Circular Waveguide

A high-efficiency W-band 12-way power combiner system based on the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode in a circular waveguide has been presented in this study. It is a radial structure composed of three elements: a circular waveguide TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> -mode transducer, an isolated 12-way radial power combiner, and amplifier modules. The measured passive combining efficiency is observed to be greater than 89.5% over the range of 85–100 GHz. The isolation between the inputs is better than 10 dB, with a maximum back-to-back return loss of 13 dB. By using 12 GaN monolithic microwave integrated circuit (MMIC) 2-W power amplifiers, the active combiner system produces a maximum power output of up to 22 W with an average combining efficiency of 81.7% within the band of 92–97 GHz. The power-added efficiency within the operating band has been measured to be up to 20.8%.

A Broadband Radial Power Combiner Using a Dipole Antenna-Based TM Mode Transducer

A TM01 mode transducer based on dipole antenna is proposed to design a broadband and low-loss radial power combiner at Ka-band (26.5–40 GHz). It is an essential component in the radial power combiners to convert the electromagnetic modes between rectangular and circular waveguides. The latter feeds the cylindrical cavity in TM01 mode of which the fields exhibit a circular symmetry. The proposed TM01 mode transducer consists of the dipole antenna, microstrip, and probe on a dielectric substrate. It is an in-line mode transducer. In other words, the rectangular and circular waveguides are aligned along the same axis of wave propagation. Therefore, it does not require the waveguide components such as tee junctions, steps, and bends which are normally used in the traditional mode transducers and increase the complexity, size, and loss of entire power combiner. The eight-way radial junction is also designed using a cylindrical cavity, where the rectangular waveguides are placed along the circumference of the cylindrical cavity. The dimensions of each component are determined based on the full-wave electromagnetic simulations. The designed eight-way radial power combiner consisting of the TM01 mode transducer and radial junction is fabricated in four-split blocks by mechanical machining. In the measurements, the proposed power combiner exhibits a broadband and low-loss performance under a compact size while maintaining the magnitude and phase balances between the eight ports.

Direct observation of capillary waves due to high frequency ultrasound and their relation to atomized droplets

Ultrasonic atomization has been studied and used in applications for decades, but a mechanistic understanding of droplet production does not exist at a quantitative level. Early work seemed to indicate that droplet size follows from the driving frequency according to Kelvin's equation. The underlying assumptions in this model do not hold at larger frequencies, and the model relies on a fitting parameter that has not been consistent across experimental studies. Additionally, modern experiments often indicate multi-modal droplet size distributions further complicating the physics. It is difficult to experimentally measure relevant quantities like capillary wavelength because of the time and length scales involved and the fact that the phenomenon occurs at a free liquid surface. We use a high speed digital holographic microscope, the only one of its kind in the world, to image the liquid surface—in full 3D and real time—fast enough to resolve capillary waves generated by 5–50 MHz ultrasound. We extract from this data the spectrum of capillary wavelengths and then compare these to droplet size distributions measured with laser diffraction particle sizing. Both thickness mode and surface acoustic wave lithium niobate transducers are included as well as a range of frequencies in each case. It is shown that droplet size does depend directly on capillary wavelength, but that capillary wavelength is not related to the driving frequency in a simple way.

Ultra-low noise L-band cryogenic astronomical receiver for the FAST telescope

This paper presents an ultra-low noise L-band radio astronomical cryogenic receiver for the Five-hundred-meter Aperture Spherical radio Telescope (FAST) telescope. The development of key low noise microwave parts of coupling low noise amplifier (Coupling-LNA) and conical quad-ridge orthogonal mode transducers (OMT) and reasonable system integration achieve outstanding performance of receiver. It covers the frequency range of 1.2 GHz to 1.8 GHz. Novel cryogenic Coupling-LNAs with low noise, large return loss, high dynamic range and the function of coupling calibration signals are developed for the proposed receiver. Amplification and coupling function circuits are integrated as a single Coupling-LNA with full noise temperature of 4 K at the physical temperature of 15 K. Its return loss is more than 18 dB, and output 1 dB compression power is +5 dBm. A cryogenic dewar is fabricated to provide 55 K and 15 K cryogenic environment for OMT and Coupling-LNAs, respectively. The receiver’s system noise temperature is below 9 K referred to feed aperture plane. Benefiting from optimal design and precise mechanical treatment, good scattering performance of OMT and equalized radiation patterns of horn are achieved with an antenna efficiency above 75%.

Energy conversion models and characteristics under various inner connections of a novel packaged piezoelectric transducer for pavements

The piezoelectric effect in piezoelectric transducers converts the mechanical energy into electrical energy to supply power to road facilities. The piezoelectric transducer designed in the 3–3 piezoelectric mode has been widely studied due to the consideration of power generation performance and load-bearing requirements. However, the conservative design of some external packages and the lack of theory in the internal connection design are two deficiencies of existing research on 3–3 piezoelectric mode transducers. Given the shortcoming of packages cannot make full use of the compressive properties of piezoelectric ceramics which weakens the energy conversion ability of the piezoelectric transducers, a novel piezoelectric transducer with full-pressure packaging was designed. For the lack of theoretical and systematic research on the spatial arrangement and electrical connection of piezoelectric materials inside piezoelectric transducers, from a theoretical point of view, the energy conversion models of piezoelectric transducers in four connection modes: stacked series, stacked parallel, array series, and array parallel were derived. Subsequently, through model verification tests, the influence of the four connection modes on the energy conversion characteristics of the piezoelectric transducer was systematically studied. Finally, the effect of connection mode on energy conversion was explained in a unified manner. Five methods of promoting the energy conversion of piezoelectric transducers were proposed. The study indicated that the connection mode affected the energy conversion of the piezoelectric transducer. Specifically, the maximum energy conversion potential of the piezoelectric transducer is only affected by the spatial arrangement. The electrical connection method determines the matching resistance, which can facilitate the piezoelectric transducer to exert the maximum energy conversion potential. In the stacked type, the peak energy conversion monotonously increases with the number of stacked layers, whereas the array type exhibits the opposite trend. Regardless of the spatial arrangement of the piezoelectric materials, when piezoelectric ceramics are connected in series, the optimal value of resistance increases with the number of piezoelectric ceramics, and the opposite is true when the connection is made in parallel. The normalization analysis pointed out that the connection mode affects the energy conversion of the piezoelectric transducer can be summarized as the volume index of the piezoelectric ceramic group affects its energy conversion. A larger ratio of height to diameter of the piezoelectric ceramic group can improve the energy conversion of the transducer. This article provides ideas for the packaging design of piezoelectric transducers and a theoretical reference for the design of internal piezoelectric ceramic connection methods.

3-D Printed Directional Couplers in Circular Waveguide

The design of an additively manufactured circular waveguide 3-dB hybrid directional coupler is proposed and demonstrated. Asymmetric corner radius perturbations at the in-plane orthogonal junction of the four waveguides along with curvilinear inductive posts designed to interact with the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode of the circular waveguide are used to facilitate directivity and isolation. Capacitive waveguide perturbations at each of the four ports provide impedance matching. The proposed design is engineered to operate within V-band from 57 to 64 GHz and provide both 10-dB isolation and return loss and a 90° phase difference between the direct and coupled ports. A commercially available stereolithography (SLA) printer is used to fabricate the hybrid coupler as well as the rectangular-to-circular tapered mode transducers and the thru, reflect, line (TRL) calibration components required for experiments. The printed couplers are metallized using an electroless silver plating process by a closed-loop bidirectional multiport pump-driven fluidic system. Results from the experiment and the simulation are provided.

Evolution of some newer flextensional transducer designs

Flextensional transducers, such as the classic oval Class IV, have provided a means for magnified high output at low frequencies from a small size, when compared with Tonpilz piston transducers. We present here a transition to other newer flextensional types and shapes, such as the cylindrical Trioid and LCAT transducers and the piston cantilever mode transducer, CMX. We will show that these transitions came about after a flextensional X-spring design was realized. Although the X-spring was originally conceived to increase the output and also lower the resonance frequency of Tonpilz piston transducers, it also turned out to provide a significant means for the development of newer flextensional transducer designs. Examples of these newer designs and their operation, as well as an initially unexpected improved lower frequency performance from an array of CMX transducers, will be presented. [Work supported in part by Office of Naval Research.]

A Compact 3-D Printed Asymmetric Orthogonal Mode Transducer

In this article, a compact 3-D-printed orthogonal-mode transducer (OMT) is proposed. Unlike conventional OMT that uses long extended transition for port matching, the proposed design uses embedded fences and novel short tapered triangular prism (TTP) to replace such long transition. In this way, the size of the OMT can be reduced. The TTP effectively improves the matching of the perpendicularly transverse port without affecting the performance of the port aligned with the common port. The fence acts as a polarizer grid to further reduce the reflection of incident waves back into the input port. The return loss and isolation of the very compact OMT are better than 16 and 40 dB, respectively, from 2.65 to 3.2 GHz. Considering the complicated geometry of the proposed OMT, 3-D metal printing technology is adopted as the fabrication method. The measurement results agree well with the simulation results.

Evaluation of Additive Manufacturing Techniques Applied to a Waveguide Mode Transducer

This article presents a detailed comparison between the classic manufacturing technology by computer numerical control (CNC) and the disruptive additive manufacturing (AM) technology by means of selective laser sintering (SLS). Three different implementations of a mode transducer from the TE10 rectangular waveguide mode into the TM01 circular waveguide mode at Ku-band have been manufactured, each one using a different technology. Their experimental performances are compared with respect to effective conductivity, insertion and return losses, weight, cost, and delivery time. The first technology under analysis was high precision milling by CNC using aluminum. The second one was AM-SLS using AlSi10Mg aluminum alloy powder. Finally, the third one was also SLS, but using CuNi2SiCr, an alloyed copper-material with electrical conductivity after precipitation hardening of 23 MS/m. In order to verify the theoretical simulations, a back-to-back arrangement using two transducers was measured in all three cases. A detailed comparison and a final table highlighting the advantages and drawbacks found for each technology are presented, which can be used as a reference for other similar waveguide components.

Portable acoustofluidic nebulizer

The field of acoustofluidics studies the effects of acoustic waves transferred from piezoelectric solids to small volumes of fluid. The phenomenon of acoustofluidic atomization has been studied for several decades now, and one of its major proposed applications is in pulmonary drug delivery. It is well known that droplets in the 1 to 5 μm range are optimal for lung delivery. High-frequency, oriface-free, acoustic vibration has been shown to produce droplets in narrow size distributions including this range. Until now, this technology has not been practical for point-of-care. We have created the first portable acoustofluidic nebulizer as a proof of concept for this application. This device has been enabled by improved transducer design that can now be driven by standard COTS (commercial off-the-shelf) integrated circuits for efficient frequency-synthesis and power-delivery in the 5-25 MHz, 0.5–2 W range. We use a thickness mode transducer with reduced dimensions and incorporate an on-board resonance search algorithm in order to obtain a true thickness mode acoustic wave. We supply fluid from a wick in contact with the edge of the transducer and promote wetting of the surface via fine abrasion in order to obtain continuous atomization from a thin film. Our device nebulizes 0.1 ml/min of water in the critical 1 to 5 μm diameter range using a standard 3.7 V, rechargeable, lithium-ion battery.

Additive Manufacturing of a High-Performance $Q$ -Band Circular TE01 Mode Flared-Type Transducer

This letter presents a $Q$ -band mode transducer based on a slowly flared structure to convert the rectangular TE10 mode into the circular TE01 mode, with an excellent performance in return loss level and conversion purity, overcoming the main issues of this kind of structures: its manufacturing complexity and high cost. They have been tackled by means of the additive manufacturing technology using selective laser sintering, especially well-suited for this problem allowing a single part suitable for high-power applications. The prototype shows a minimum return loss level of 20 dB in the whole $Q$ -band. Measurements have been carried out using four different angles to connect two equal transducers in a back-to-back configuration (0°, 45°, 90°, and 180°). Furthermore, in spite of the expected roughness of the laser sintering, a measured converting efficiency higher than 82% in a 41% relative frequency bandwidth has been achieved. Therefore, the experimental results validate both the proposed geometry and the technology used for its implementation.

Dielectric and piezoelectric properties of Pb[(Mg1/3Nb2/3)0.52(Yb1/2Nb1/2)0.15Ti0.33]O3 single-crystal rectangular plate and beam mode transducers poled by alternate current poling

The dielectric, piezoelectric and physical properties of the [001]-oriented rectangular plate and beam mode of Pb[(Mg1/3Nb2/3)0.52(Yb1/2Nb1/2)0.15Ti0.33]O3 (PMN-PYbN-PT) ternary single crystals (SC) poled by alternate current poling (ACP) were investigated. The dielectric permittivity and average piezoelectric coefficient d33 were 6800 and 2490 pC/N, respectively, for the rectangular plate sample after ACP, which were 31% and 41% larger than those of the same sample after conventional direct current poling. The highest value of d33 reached 2750 pC N−1. The dielectric loss was reduced by 31%; nevertheless, the d33 improved after ACP. The beam mode electromechanical coupling factor () was 91% by using ACP, showing the highest value among all relaxor-PT SC systems reported so far. The regular periodic stripe domains were observed in ACP samples, showing high domain wall density and uniform domain size. This work demonstrates that the high performance after ACP is an effective method of improving the relaxor-PT SC transducers.

Compact Symmetric Opposed Port Orthomode Transducer

This letter presents an innovative design for a compact orthogonal mode transducer (OMT). The proposed OMT is a T-shaped junction with two symmetrical output ports. Two coupling elements, a ridge and a resonant cavity, have been included in the OMT design, resulting in low $S_{11}$ scattering parameter and high isolation between orthogonal signals. The proposed design has been simulated for 6.5 GHz and prototyped with machined aluminum components, using a computer numerical control machine. Electromagnetic (EM) CAD model and prototype have been analyzed for the frequency range of 5.925–7.125 GHz. The OMT bandwidth is slightly greater than 18.4%, with $S_{11}$ and isolation values below −22 and −37 dB respectively, obtained from prototype measurement. Moreover, the proposed OMT design presents a reduced size and low–wind-exposure area, which is a relevant feature when operating in outdoor dual-radio setup, resulting in a low-cost and easy manufacturing device.