Small Transducer Research Articles

Experimental analysis of the feasibility of low-cost piezoelectric diaphragms in impedance-based SHM applications

Structural health monitoring (SHM) systems with damage detection based on the electromechanical impedance (EMI) method have received attention in recent decades because of the simplicity of the methodology, which is based on the use of small and lightweight piezoelectric transducers that operate simultaneously as sensors and actuators. Typically, the piezoelectric transducers used in the EMI method have been thin PZT (lead zirconate titanate) ceramics, which can be cut into different sizes and shapes. In this study, an experimental analysis of the feasibility of low-cost piezoelectric diaphragms, commonly known as buzzers, for damage detection based on the EMI method is presented. Diaphragms of different sizes were evaluated in aluminum beams, and the experimental results were compared with those obtained from a conventional PZT ceramic. Four types of experiments were performed: sensitivity estimation using the pencil lead break (PLB) method, analysis of the ability to detect structural damage using conventional impedance signatures and damage indices, analysis of temperature effects, and determination of the long-term reproducibility of the results. The results indicate that a conventional PZT ceramic and a diaphragm of similar size have similar reproducibilities and sensitivities to damage and temperature effects.

Low power electronic interface for electrostatic energy harvesters

This paper presents design and simulation of a power electronic interface circuit for MEMS electrostatic energy harvesters. The designed circuit is applicable to highly miniaturized electrostatic harvesters with small transducer capacitances below 10 pF. It is based on comb- drive harvesters with two anti-phase capacitors that are connected as charge pumps and uses a flyback-path scheme. Controlled activation and deactivation of sub-circuits, some by help of clocking, were exploited to reduce power consumption down to 1.03 μW. Net power generation can be achieved with as low initial voltage as 3.0 V.

Low-Dose Molecular Ultrasound Imaging with E-Selectin-Targeted PBCA Microbubbles.

Our objective was to determine the lowest diagnostically effective dose for E-selectin-targeted poly n-butyl cyanoacrylate (PBCA)-shelled microbubbles and to apply it to monitor antiangiogenic therapy effects. PBCA-shelled microbubbles (MBs) coupled to an E-selectin-specific peptide were applied in mice carrying MLS or A431 carcinoma xenografts scaling down the MB dosage to the lowest level where binding could be examined with a 18-MHz small animal ultrasound transducer. Differences in E-selectin expression in the two carcinoma xenografts were confirmed by enzyme-linked immunosorbent assay (ELISA). In addition, MLS tumor-bearing mice under antiangiogenic therapy were monitored using E-selectin-targeted MBs at the lowest applicable dose. Therapy effects on tumor vascularization were verified by immunohistological analyses. The minimally required dosage was 7 × 10(7) MBs/kg body weight. This dosage was sufficient to enable E-selectin detection in high E-selectin-expressing MLS tumors, while low E-selectin-expressing A431 tumors required almost 2.5-fold higher doses. At the dose of 7 × 10(7) MBs/kg body weight, a decrease in E-selectin MB binding under antiangiogenic therapy could be assessed (being significant after 3 days of treatment; p < 0.0001), which was in line with the significant drop in E-selectin-positive area fractions that was found histologically (p < 0.05). Molecular ultrasound imaging with our E-selectin-targeted MB and therapy monitoring was possible down to a dose of 7 × 10(7) MBs/kg body weight (equates to 66 μg PBCA/kg and 4.6 mg PBCA/70 kg). Improvements in choice of targets, MB composition, and other MB detection methods may improve sensitivity and lead to reliable detection results of clinically transferrable MBs at even lower dosage levels.

Dosimetry systems based on Gallium Nitride probe for radiotherapy, brachytherapy and interventional radiology

Our studies focus on dedicated dosimetry systems based on the Gallium Nitride (GaN) probe for Quality Assurance and patient safety in radiotherapy, brachytherapy and interventional radiology. The small size GaN transducer in the probe has high radioluminescence (RL) yield and rapid RL signal response for real time measurements. Preliminary prototypes of dedicated systems were tested in clinical conditions for external beam radiotherapy, brachytherapy and interventional radiology. The obtained pre-clinical results appear favorable and encouraging: in radiotherapy, GaN RL response has not significant dependence on the main influence parameters, excepted for the field size. In brachytherapy, using an instrumented phantom with integration of GaN probes allows real time verification of planned treatments. In interventional radiology, skin dose measurements using GaN probe based dosimeters show consistent results with those from a reference dosimeter.

Analysis of a Non-resonant Ultrasonic Levitation Device

In this study, a non-resonant configuration of ultrasonic levitation device is presented, which is formed by a small diameter ultrasonic transducer and a concave reflector. The influence of different levitator parameters on the levitation performance is investigated by using a numerical model that combines the Gor‘kov theory with a matrix method based on the Rayleigh integral. In contrast with traditional acoustic levitators, the non-resonant ultrasonic levitation device allows the separation distance between the transducer and the reflector to be adjusted continually, without requiring the separation distance to be set to a multiple of half-wavelength. It is also demonstrated, both numerically and experimentally, that the levitating particle can be manipulated by maintaining the transducer in a fixed position in space and moving the reflector in respect to the transducer.

A 44–93- $\mu\hbox{s}$ 250–400-mV 0.18- $\mu\hbox{m}$ CMOS Starter for DC-Sourced Switched-Inductor Energy Harvesters

Although microsystems can replenish batteries and energize modules with ambient energy without having to store much energy on board, on-chip photovoltaic cells and thermoelectric generators generate 50-400 mV, which is usually not sufficiently high to operate transistors. Although stacking cells is possible, the tradeoff in power is ultimately unfavorable because small transducers output little power. Thankfully, transformers can boost millivolt voltages but not without a significant toll on space. Motion-propelled microelectromechanical system switches can also start a harvester but only in the presence of vibrations. Moreover, although 50-300-mV ring and LC oscillating networks can charge batteries, initialization requires 1-15 ms. The prototyped 0.18-μm CMOS oscillating starter presented here draws power from 250-450 mV to charge 100 pF to 0.32-1.55 V in 44-92 μs. In the steady state, the cost of the starter to the direct-current-sourced harvester it supports is only a 1.8% drop in the power conversion efficiency.

Asynchronous compressed beamformer for portable diagnostic ultrasound systems.

State-of-the-art portable ultrasound imaging systems employ a small transducer array and a low carrier frequency to fit stringent constraints on power and form factor, and this tends to compromise the ultrasound imaging quality. In this paper, we present a low-complexity low-power asynchronous compressed beamformer (ACB) for portable diagnostic ultrasound. The proposed ACB integrates asynchronous sampling and compressive sensing (CS), and is capable of reducing data conversion power and handling a large data volume at the mixed-signal interface. A high-rate continuoustime ternary encoding (CT-TE) scheme eliminates the need for interpolation filters and coordinate rotation digital computer (CORDIC) units typically used in a conventional architecture. A split-projection least squares (SPLS) signal reconstruction algorithm is applied that replaces high-cost nonlinear signal recovery with a series of low-complexity and independent linear problems. Experiments with measured ultrasound data demonstrate the proposed ACB architecture, and the SPLS reconstruction algorithm achieves 9-fold data compression compared with Nyquist sampling.

Sonographically guided therapeutic injections in the meniscoid lesion in patients with anteromedial ankle impingement syndrome.

We describe a sonographically guided technique to perform therapeutic injections for anteromedial ankle impingement syndrome. Scans are carried out using a high-frequency small footprint linear array transducer, positioned along the anteromedial aspect of the tibiotalar joint. A 25 gauge needle is advanced under direct sonographic guidance into the "meniscoid lesion" (area of scarring), and a standardized therapeutic mixture is injected extra-articularly. Image-guided injections have a positive influence on clinical decision making by improving patient management, increasing the accuracy of diagnosis, and decreasing patient pain. Sonography allows confirmation of correct injection placement, resulting in increased accuracy and more successful patient outcomes. Therapeutic, Level V, Expert Opinion.

Speech Intelligibility and Subjective Evaluation of Music Playback of Sound Transducers with Glass and Wooden Membrane

Novel state-of-the-art designer loudspeaker solutions offer “invisible audio” applications by applying a relatively small transducer onto glass or wooden plates, surfaces such as windows, tables, doors etc. Although manufacturers promise high quality transmission and good technical parameters, reliable measurement data do not exist. In our former evaluation, the SolidDrive system with glass membrane of different shapes, sizes, fixation methods was analyzed using vibration analysis, acoustic measurements and numerical simulations in COMSOL/FEM. This paper presents experimental results of standardized speech intelligibility measurements as well as subjective evaluation of the system.

Nonlinear acoustic properties of ex vivo bovine liver and the effects of temperature and denaturation

Thermal ablation by high intensity focused ultrasound (HIFU) has a great potential for the non-invasive treatment of solid tumours. Due to the high pressure amplitudes involved, nonlinear acoustic effects must be understood and the relevant medium property is the parameter of nonlinearity B/A. Here, B/A was measured in ex vivo bovine liver, over a heating/cooling cycle replicating temperatures reached during HIFU ablation, adapting a finite amplitude insertion technique, which also allowed for measurement of sound-speed and attenuation. The method measures the nonlinear progression of a plane wave through liver and B/A was chosen so that numerical simulations matched the measured waveforms. To create plane-wave conditions, sinusoidal bursts were transmitted by a 100 mm diameter 1.125 MHz unfocused transducer and measured using a 15 mm diameter 2.25 MHz broadband transducer in the near field. Attenuation and sound-speed were calculated using a reflected pulse from the smaller transducer using the larger transducer as the reflecting interface. Results showed that attenuation initially decreased with heating then increased after denaturation, the sound-speed initially increased with temperature and then decreased, and B/A showed an increase with temperature but no significant post-heating change. The B/A data disagree with other reports that show a significant change and we suggest that any nonlinear enhancement in the received ultrasound signal post-treatment is likely due to acoustic cavitation rather than changes in tissue nonlinearity.

Comparative analysis of small versus large transducers for high-frequency ultrasonic testing of breast cancer

High-frequency ultrasound (20–80 MHz) has been found to be sensitive to margin pathology from breast cancer surgery. In order to improve the resolution and sensitivity of this method, transducers are needed that have smaller piezoelectric elements than those currently in use. This study's purpose was to determine if small-element transducers (Blatek, 50 MHz, diameter &amp;lt;2 mm) produce similar results as those from large-element transducers (Olympus NDT, 50 MHz, 6.35-mm diameter). Pulse-echo and through-transmission measurements were performed on bovine heart tissue and 10 phantom specimens containing chopped nylon fibers and polyethylene microspheres. The density of peaks in the ultrasonic spectra of the small or mini transducers (MT) paralleled those of the large transducers (LT) in the bovine tissue, with higher peak densities associated with connective tissue and lower peak densities with muscle tissue. The MT data from the phantoms showed greater variance than the LT data, indicating that the MT were more sensitive to the heterogeneous wavefields arising from microsphere scattering. Additional in vivo testing is currently being performed on breast tumors grown in mice treated with Avastin. Small-element transducers may ultimately provide in vivo cancer detection in margins, allowing more precise excision of cancerous tissue and thus eliminating follow-up surgeries.

The effect of crosstalk in a circular transducer array on ultrasound transmission tomography of breast

Various types of undesirable crosstalk can occur in ultrasonic arrays consisting of a number of elementary piezoelectric transducers. Crosstalk is a result of deficiency in electrical or mechanical isolation between array elements. It is a function of proximity between piezoelectric transducers of the array or between connections. Small piezoceramic transducers tightly located inside of a circle (cylinder or sphere in 3-D systems) are mostly used for in vivo ultrasound tomography imaging of breast tissue. This means that proper switching of transducers makes it possible to quickly acquire tomographic transmission and reflection data for all directions around the object. A problem with such arrangements is the occurrence of crosstalk, which introduce specific errors to measurement data. Transmission and reflection tomographic images reconstructed based on ultrasonic measurements with crosstalk are distorted in a characteristic way. This work analyzes the effect of crosstalk in a circular transducer array on ultrasound transmission tomography imaging—especially, when used for examination of breast tissue.

Side-polished fiber as a sensor for the determination of nematic liquid crystal orientation

The orientation change of nematic liquid crystal (NLC) has been the essential mechanism for various high sensitive sensors. In this paper, a side-polished fiber (SPF) is proposed to sense the orientation change of NLC. We successfully designed the liquid crystal cell embedded with a SPF that enabled us to mechanically rotate the orientation of NLC on the polished surface of the SPF. Our experimental results showed that the orientation change of NLC can indeed be sensed by monitoring the output optical power transmitted through the SPF. The increment of the transmitted optical power through the SPF was measured as large as 28.10dB with the mechanical rotation from 0° to 90°. Within the angle range from 0° to 30°, the response was almost linear. The average response slope was about 0.359dB/°, which indicated relatively high sensitivity. These experimental results indicate that SPF can be used to determine the orientation change of NLC. In particular, there exists a possibility that a SPF overlaid with NLC on its polished surface can potentially be made into a small transducer of a biosensor.

Dynamic Characterization of a Piezoelectric Actuated Cantilever Beam Using Energetic Parameters

This article aims to examine, in experimental terms, some new research opportunities on the dynamic behavior of the mechanical systems with piezoelectric actuation, using the energetic parameters evolution (especially the electric active power or real power as well) captured from the supply circuit of the actuator. The study is carried out on an experimental setup that consists of an aluminium cantilever beam having two small thickness PZT piezoelectric plate transducers glued close-by the rigidly fixed end on each side of the beam. Using some new theoretical and experimental approaches developed for these purposes there is undertaken the computer assisted monitoring of the energetic parameters from the piezoelectric transducers supply circuit. The transducers are used as sensors and actuators as well. The research focuses on the possibility to describe some essential dynamic phenomena, such as vibration modes characterization, resonance, modal damping using negative power actively and passively generated, and the dynamics of transient regimes. Some results are similar to those already obtained on a cantilever beam actuated with a voice-coil (Lorentz force) actuator.

Modal Sensitivity and Selectivity of Small, Rectangle-Shaped Piezoelectric Transducers Used as Sensors and Actuators in Active Vibroacoustic Control Systems

The paper focuses on some issues regarding the utilization of small rectangle-shaped piezoelectric transducers as both sensors and actuators in active vibration and vibroacoustic control systems of beam, plate and panelled structures with arbitrary (non-homogeneous) boundary conditions. A new form of description of a simple proportional active control system with multiple independent feedback loops is proposed. The modal sensitivity functions of sensors and the modal selectivity functions of actuators are introduced to describe their ability for sensing and exciting specific structural modes of the structures. Basing on the assumed form of cost function and the derived equations of control system the influence of the modal characteristics of transducers on the stability of the system and on the performance of the active control is analyzed. The results of analytical solutions and numerical simulations are compared with the results of the experiments carried out on various beam and plate structures made up of aluminium or composite materials including the actual materials used in aviation, proving usefulness of the presented approach.

Development of Hand Gesture Controlled Electrolarynx

The feasibility of using a motion sensor to replace a conventional electrolarynx(EL) user interface was explored. Forearm motion signals from MEMS accelerometer was used to provide on/off and prosody control. The small transducer was placed against the throat using support bandage. A battery operated ARM-based small control unit was developed and placed on the wrist. The control unit can convert the tilt angle into the pitch frequency. Speech generation was tested with various forearm movements, and then a simple and small action was chosen to control the device. A simple comparison study has been made with well-trained normal speakers. Results of the study showed that the prototype system was able to produce the pitch patterns similar to those in natural utterances.

Variation of Pinch and Grip Force Between Different Size Transducers

Work-related musculoskeletal disorders affect a large percentage of diagnostic medical sonographers. Ultrasound transducer design has been identified as a major contributing factor to hand and wrist strains. The purpose of this study was to determine if the design of the ultrasound transducer affects the amount of pressure exerted by the hands of the sonographer to achieve a quality scan. The study also aimed to determine if the amount of pressure exerted on the transducer relates to the subjective pain level reported by the sonographer. The study found that the average maximum pressure and average force exerted was higher when scanning with a small transducer compared with a large transducer, and the thumb typically exerted a much greater pressure and force. Sonographers reported pain during the scan trials, as well as throughout their typical workdays, leisure pursuits, and daily activities.

Acoustic Doppler velocity measurement system using capacitive micromachined ultrasound transducer array technology

This paper describes the design, fabrication, modeling, and characterization of a small (1 cm(2) transducer chip) acoustic Doppler velocity measurement system using microelectromechanical systems capacitive micromachined ultrasound transducer (cMUT) array technology. The cMUT sensor has a 185 kHz resonant frequency to achieve a 13° beam width for a 1 cm aperture. A model for the cMUT and the acoustic system which includes electrical, mechanical, and acoustic components is provided. Furthermore, this paper shows characterization of the cMUT sensor with a variety of testing procedures including Laser Doppler Vibrometry (LDV), beampattern measurement, reflection testing, and velocity testing. LDV measurements demonstrate that the membrane displacement at the center point is 0.4 nm/V(2) at 185 kHz. The maximum range of the sensor is 60 cm (30 cm out and 30 cm back). A velocity sled was constructed and used to demonstrate measureable Doppler shifts at velocities from 0.2 to 1.0 m/s. The Doppler shifts agree well with the expected frequency shifts over this range.

Opening of the blood-brain barrier with an unfocused ultrasound device in rabbits

The blood-brain barrier (BBB) is a major impediment to the intracerebral diffusion of drugs used in the treatment of gliomas. Previous studies have demonstrated that pulsed focused ultrasound (US) in conjunction with a microbubble contrast agent can be used to open the BBB. To apply the US-induced opening of the BBB in clinical practice, the authors designed an innovative unfocused US device that can be implanted in the skull and used to transiently and repeatedly open the BBB during a standard chemotherapy protocol. The goal of this preliminary work was to study the opening of the BBB induced by the authors' small unfocused US transducer and to evaluate the effects of the sonications on brain parenchyma. Craniectomy was performed in 16 healthy New Zealand White rabbits; epidural application of a single-element planar ultrasonic transducer operating at 1 MHz was then used with a pulse-repetition frequency of 1 Hz, pulse lengths of 10-35 msec, in situ acoustic pressure levels of 0.3-0.8 MPa, and sonication for 60-120 seconds. SonoVue was intravenously injected during the US applications, and opening of the BBB was determined by detecting extravasation of Evans blue dye (EBD) in brain tissues, quantitative measurement of EBD with UV-visible spectrophotometry, and contrast enhancement after Gd injection in 4.7-T MRI. A histological study was performed to determine adverse effects. An opening of the BBB was observed over a large extent of the US beam in the brain corresponding to in situ pressures of greater than 0.2 MPa. The BBB opening observed was highly significant for both EBD (p < 0.01) and MRI Gd enhancement (p < 0.0001). The BBB opening was associated with minor adverse effects that included perivascular red blood cell extravasations that were less than 150 μm in size and not visible on MR images. Moderate edema was visible on FLAIR sequences and limited to the extent of the sonication field. The results demonstrate that the BBB can be opened in large areas of the brain in rabbits with low-power, pulsed, and unfocused US with limited damage to healthy tissue.

COMPUTER-AIDED PROTOTYPING OF INTERDIGITAL TRANSDUCERS FOR THE STRUCTURAL HEALTH MONITORING OF PLANAR STRUCTURES

In recent years an intensive research activity into the application of guided waves (GWs) for structural health monitoring (SHM) can be observed. For instance, Lamb waves (LWs) have shown a great potential in monitoring of thin, planar structures. However, due to the dispersive and multimodal nature of the LWs, their snapshots can consist of many pulses even for an intact structure, which makes damage detection very complex. Moreover, small PZT transducers, most commonly used in SHM systems, act normally as omni-directional wave sources; therefore, dense or sparse transducers networks are required for damage localization. Some of the above-mentioned drawbacks of single PZT emitters and sensors can be overcome using interdigital transducers (IDT) designed to excite and sense a single, selected mode. The mode-tuning is performed by changing the span of finger electrodes to match the wavelength of the excited mode for the selected frequency. An IDT is a directional source, therefore, it generates a wave steered to the direction perpendicular to the electrodes. The width of the excited main lobe can be determined by the length of the electrodes. Since many parameters of the IDTs influence the LWs propagation, techniques for the simulation of the wave excitation and propagation are needed. In the paper, numerical tools for the computer aided design and virtual prototyping of the IDTs are presented. The simulation technique is based on the frequency-dependent transfer function of the structure, and due to its computational efficiency it can be used for fast testing of IDTs’ performance and for preliminary transducer design for further finite element simulations, and prototyping.