Cost-effective broad-band electrical impedance spectroscopy measurement circuit and signal analysis for piezo-materials and ultrasound transducers

Electrical Tomography Reconstruction Using Reconfigurable Waveforms in a FPGA

The principal objective of this research is to conceive a mobile system based on electrical tomography for subsurface imaging and monitoring in order to enable simultaneous recording of electrical potentials of cardiac and pulmonary activity. For an exploration of excitation waveforms in electrical tomography, specialized hardware is required. As the main principle of tomography is the measurement of electrical perturbations on an unknown object, it is crucial to synchronize excitation and sensing processes in a very precise way for the purpose of acquiring meaningful data. To cope with this problem, an FPGA device is used, with an architecture that allows us to trigger excitation signals and to read sensed data simultaneously via independent processes that share the same clock. In this way, waveform reconfiguration on frequency and shape can be provided and studied. The system is connected to a standard microcontroller SoC with a simple API that allows for IoT capabilities for on-line operation and tracking, given that the design is targeted for in vivo medical monitoring. As a result of the research work, a measuring device was developed, the surface data analyzed and the image was reconstructed using the selected configuration.

An Online Impedance Analysis and Matching System for Ultrasonic Transducers

Electrical impedance matching of ultrasonic transducers is important in optimizing the energy consumption as well as guaranteeing equipment safety for ultrasonic systems in both laboratories and industries. The existing solutions usually rely on expensive instruments to conduct off-line impedance measurements and deploying static impedance matching networks for each specific transducer across a target frequency band. Here, we present an initial prototype of an online impedance analysis and matching system (OIAMS). In this system, an improved voltage-current method and a phase-difference method were integrated for online impedance measurement in real time, and an L-type matching circuit with variable components helped to achieve dynamic impedance matching. A feedback protocol was embedded in a microcontroller to adjust the matching strategies based on dynamic measurements, while the whole system was controlled through a software interface developed on a LabVIEW platform. Online measurement results showed that OIAMS conducted accurate impedance measurements with a relative error within 3.90% for amplitude and 13.11% for phase across the 100% bandwidth of the tested transducers. After matching, the reflected acoustic power of a 1.00-MHz transducer was reduced by over 50%, increasing the generated sound pressure level by over 2.8 dB across its 70% bandwidth.

A Review of Electric Impedance Matching Techniques for Piezoelectric Sensors, Actuators and Transducers

Any electric transmission lines involving the transfer of power or electric signal requires the matching of electric parameters with the driver, source, cable, or the receiver electronics. Proceeding with the design of electric impedance matching circuit for piezoelectric sensors, actuators, and transducers require careful consideration of the frequencies of operation, transmitter or receiver impedance, power supply or driver impedance and the impedance of the receiver electronics. This paper reviews the techniques available for matching the electric impedance of piezoelectric sensors, actuators, and transducers with their accessories like amplifiers, cables, power supply, receiver electronics and power storage. The techniques related to the design of power supply, preamplifier, cable, matching circuits for electric impedance matching with sensors, actuators, and transducers have been presented. The paper begins with the common tools, models, and material properties used for the design of electric impedance matching. Common analytical and numerical methods used to develop electric impedance matching networks have been reviewed. The role and importance of electrical impedance matching on the overall performance of the transducer system have been emphasized throughout. The paper reviews the common methods and new methods reported for electrical impedance matching for specific applications. The paper concludes with special applications and future perspectives considering the recent advancements in materials and electronics.

Reduced graphene oxide–titania based platform for label-free biosensor

A label-free biosensor has been fabricated using a reduced graphene oxide and anatase titania nanocomposite, deposited on indium tin oxide electrode for the specific recognition of Vibrio cholerae.

Design and evaluation of a wearable self-applied therapeutic ultrasound device for chronic myofascial pain

Ultrasound therapy for pain and healing is a versatile treatment modality for musculoskeletal conditions that is used daily in rehabilitation clinics around the world. Our group designed and constructed a wearable, battery-operated, low-intensity therapeutic ultrasound (LITUS) device that patients could self-apply and operate during daily activity for up to 6 h. Thirty patients with chronic trapezius myofascial pain evaluated the LITUS system in a double-blind, placebo-controlled, 10-d study under institutional review board approval. While continuing their prescribed medication regimen, patients with the active device reported on average 1.94× reduction in pain and 1.58× improvement in health relative to placebo devices after 1 h of treatment. Both of these results were statistically significant (p < 0.05) for the first 2 d of the study. Male patients reported the majority of benefit, and there is a sex-treatment confound in the sample. The study indicates that wearable, long-duration LITUS technology improves mobile access to drug-free pain relief.

Comparison between piezoelectric material properties obtained by using low-voltage magnitude frequency sweeping and high-level short impulse signals

Determination of electromechanical piezoceramic material parameters is usually done by fitting the measured input electrical impedance of the piezoceramic sample to the theoretical modelling equation for the input electrical impedance of the unloaded free piezoceramic resonator. The input electrical impedance of the sample is usually measured by using low voltage or current magnitude frequency sweeping signals. In this work, the complex material parameters of piezoceramic samples are determined in the real operating conditions by using the high voltage short impulse excitation signals. The input electrical impedance determined in the impulse mode around thickness extensional vibration mode (TE) and calculated piezoceramic parameters (clamped dielectric permittivity, electromechanical coupling factor, elastic stiffness and piezoelectric constant) are compared to the results obtained by using the low voltage magnitude frequency sweeping signals. When impulse excitation is used, the series resonance frequency is decreased and the input electrical impedance magnitude at series resonance is increased, which means that overall losses included in the piezoceramic parameters are increased. The complex material parameters obtained from the input electrical impedances determined by using the low voltage magnitude sweeping signal and high level short impulse signals are included in the KLM theoretical model describing the piezoceramic sample behaviour around TE mode. Better agreement between measured and theoretically determined current magnitude response around TE mode has been obtained, in the KLM model, when piezoceramic parameters determined by using the impulse signal excitations are included in the modelling. The physical reason for increase of the losses in piezoceramic material could lie in the fact that the ferroelectric domains in the piezoceramic respond harder on very short impulse excitation signals than on continuous frequency sweeping signals which are usually used in determination of piezoelectric material parameters.

Ultrasound-assisted convection-enhanced delivery to the brain in vivo with a novel transducer cannula assembly: laboratory investigation

OBJECT

In convection-enhanced delivery (CED), drugs are infused locally into tissue through a cannula inserted into the brain parenchyma to enhance drug penetration over diffusion strategies. The purpose of this study was to demonstrate the feasibility of ultrasound-assisted CED (UCED) in the rodent brain in vivo using a novel, low-profile transducer cannula assembly (TCA) and portable, pocket-sized ultrasound system.

METHODS

Forty Sprague-Dawley rats (350-450 g) were divided into 2 equal groups (Groups 1 and 2). Each group was divided again into 4 subgroups (n = 5 in each). The caudate of each rodent brain was infused with 0.25 wt% Evans blue dye (EBD) in phosphate-buffered saline at 2 different infusion rates of 0.25 μl/minute (Group 1), and 0.5 μl/minute (Group 2). The infusion rates were increased slowly over 10 minutes from 0.05 to 0.25 μl/minute (Group 1) and from 0.1 to 0.5 μl/minute (Group 2). The final flow rate was maintained for 20 minutes. Rodents in the 4 control subgroups were infused using the TCA without ultrasound and without and with microbubbles added to the infusate (CED and CED + MB, respectively). Rodents in the 4 UCED subgroups were infused without and with microbubbles added to the infusate (UCED and UCED + MB) using the TCA with continuous-wave 1.34-MHz low-intensity ultrasound at a total acoustic power of 0.11 ± 0.005 W and peak spatial intensity at the cannula tip of 49.7 mW/cm(2). An additional 4 Sprague-Dawley rats (350-450 g) received UCED at 4 different and higher ultrasound intensities at the cannula tip ranging from 62.0 to 155.0 mW/cm(2) for 30 minutes. The 3D infusion distribution was reconstructed using MATLAB analysis. Tissue damage and morphological changes to the brain were assessed using H & E.

RESULTS

The application of ultrasound during infusion (UCED and UCED + MB) improved the volumetric distribution of EBD in the brain by a factor of 2.24 to 3.25 when there were no microbubbles in the infusate and by a factor of 1.16 to 1.70 when microbubbles were added to the infusate (p < 0.001). On gross and histological examination, no damage to the brain tissue was found for any acoustic exposure applied to the brain.

CONCLUSIONS

The TCA and ultrasound device show promise to improve the distribution of infused compounds during CED. The results suggest further studies are required to optimize infusion and acoustic parameters for small compounds and for larger molecular weight compounds that are representative of promising antitumor agents. In addition, safe levels of ultrasound exposure in chronic experiments must be determined for practical clinical evaluation of UCED. Extension of these experiments to larger animal models is warranted to demonstrate efficacy of this technique.

Broadband electrical impedance matching for piezoelectric ultrasound transducers

This paper presents a systematic method for designing broadband electrical impedance matching networks for piezoelectric ultrasound transducers. The design process involves three steps: 1) determine the equivalent circuit of the unmatched piezoelectric transducer based on its measured admittance; 2) design a set of impedance matching networks using a computerized Smith chart; and 3) establish the simulation model of the matched transducer to evaluate the gain and bandwidth of the impedance matching networks. The effectiveness of the presented approach is demonstrated through the design, implementation, and characterization of impedance matching networks for a broadband acoustic emission sensor. The impedance matching network improved the power of the acquired signal by 9 times.

Design and characterization of a high-power ultrasound driver with ultralow-output impedance

We describe a pocket-sized ultrasound driver with an ultralow-output impedance amplifier circuit (less than 0.05 ohms) that can transfer more than 99% of the voltage from a power supply to the ultrasound transducer with minimal reflections. The device produces high-power acoustical energy waves while operating at lower voltages than conventional ultrasound driving systems because energy losses owing to mismatched impedance are minimized. The peak performance of the driver is measured experimentally with a PZT-4, 1.54 MHz, piezoelectric ceramic, and modeled using an adjusted Mason model over a range of transducer resonant frequencies. The ultrasound driver can deliver a 100 V(pp) (peak to peak) square-wave signal across 0-8 MHz ultrasound transducers in 5 ms bursts through continuous wave operation, producing acoustic powers exceeding 130 W. Effects of frequency, output impedance of the driver, and input impedance of the transducer on the maximum acoustic output power of piezoelectric transducers are examined. The small size, high power, and efficiency of the ultrasound driver make this technology useful for research, medical, and industrial ultrasonic applications.

Development of a portable therapeutic and high intensity ultrasound system for military, medical, and research use

We have developed a portable high power ultrasound system with a very low output impedance amplifier circuit (less than 0.3 Omega) that can transfer more than 90% of the energy from a battery supply to the ultrasound transducer. The system can deliver therapeutic acoustical energy waves at lower voltages than those in conventional ultrasound systems because energy losses owing to a mismatched impedance are eliminated. The system can produce acoustic power outputs over the therapeutic range (greater then 50 W) from a PZT-4, 1.54 MHz, and 0.75 in diameter piezoelectric ceramic. It is lightweight, portable, and powered by a rechargeable battery. The portable therapeutic ultrasound unit has the potential to replace "plug-in" medical systems and rf amplifiers used in research. The system is capable of field service on its internal battery, making it especially useful for military, ambulatory, and remote medical applications.