Invited Speakers

Functional ultrasound imaging (fUS) is a powerful neuroimaging tool that can measure brain-wide vascular signals linked to neuronal activity with high spatial and temporal resolution. Focusing on fundamental neuroscience applications, I will highlight some of the recent technical advancements of fUS used in our laboratory, including the ability to image the entire mouse brain while manipulating specific neuronal circuits with optogenetics. I will show the potential of fUS for advancing our understanding of the neural basis of behavior as fUS is one of the few methods that allows for real-time imaging of activity deep in the brain of behaving animals. Finally, I will discuss the challenges and limitations of fUS that must be overcome to fully unlock its potential for neuroscientists.

Without the right intra-operative imaging, removing tumors in a human brain or spine feels like operating in the dark. All while carrying the pressure of the fine line between removing ‘too much’ or ‘too little’, with all the life-altering consequences for the patients in question. A new technique called functional ultrasound (fUS) imaging has the potential to shine further light on this problem to revolutionize these neurosurgical procedures: fUS not only enables discrimination between tumor and healthy tissue based on vascular morphology, but also allows for real-time monitoring of brain functionality. In this talk I will describe our efforts of bringing the fUS technique from lab bench to a new clinical modality including our choices and implementation in data processing, integration within the surgical workflow and validation against techniques such as fMRI and Electro-cortical Stimulation Mapping (ESM). 

Ultrasound continues to expand into an increasing number and diversity of applications. Polymer-based capacitive micromachined ultrasonic transducers (polyCMUTs) were invented at UBC to provide a fast and effective way to produce new transducer designs. By providing a wide design space to work in, polyCMUTs open the door to custom solutions for different applications. The design space includes a range of frequencies and form factors including flexible arrays, transparent arrays, and matrix arrays; all made in-house with low-toxicity materials and processes. These capabilities are being exploited in a multi-institutional program “Mend the Gap”, where polyCMUTs are used to guide and monitor a new injectable biomaterial that is being tested to facilitate healing and regeneration of broken neural circuitry. These capabilities are also being exploited in a multi-institutional program “In Utero”, where polyCMUTs are used in measurement and monitoring during gestational development to predict and prevent stillbirth.  A common theme in these and other research projects is to develop custom low-cost easy-to-use solutions so that the benefits of ultrasound are available wherever and whenever it is needed.

Blood flow plays a key role in the developing human heart from it starts beating at gestational week five. Altered and abnormal hemodynamics at any stage during fetal life or after birth may lead to remodeling of the heart and development of disease. Of all live births, almost 1% of the babies are born with a congenital heart disease. In one-quarter of the cases, the heart disease is severe and the baby need intervention during the first year of life. To image blood flow and evaluate cardiac function, ultrasound has been the physicians’ best tool for 50 years. However, the inherent limitations in the conventional ultrasound imaging methods make the sonographer’s experience and ability to interpret findings significant factors in detecting defects. Now, new methods for more in-depth and detailed analysis of cardiovascular blood flow are emerging with the advent of high-frame-rate imaging. The new techniques can be used to visualize complex and fast-varying blood flow and study short-lived cardiac events. In this talk, fundamental clinical and technical imaging challenges in pediatric and fetal imaging will be presented, and current clinical state of the art imaging technology will be demonstrated. Both the opportunities of new pathophysiological knowledge and diagnostic tools, and the inherent challenges of high-frame-rate imaging will be discussed. 

The author has been involved in the design and delivery of several measurement systems based on piezo electric and electromagnetic acoustic ultrasonic transducers that are in widespread commercial use (1000s of units). With the help of practical examples such as temperature, viscosity and wall thickness measurements this talk will touch on some of the key aspects that need to be considered when optimizing non-destructive evaluation (NDE) and structural health monitoring (SHM) systems. The talk will focus on showing how the SNR is one of the key parameters that affects the uncertainty with which a particular measurand can be determined. The use of signal processing techniques such as coded excitation to maximize signal SNR will be discussed. Furthermore, topics such as configuring the sensor to maximize its sensitivity to changes in the properties of the measurand and corrections for conflicting influences such as temperature cross sensitivities with viscosity and thickness measurements will be presented. Throughout, practical examples related to an industrial application will be used to illustrate the subject matter.

High temperature ultrasonic transducers have been demanded for some industrial applications, such as process monitoring and structural health monitoring of power/chemical plant. However, there are difficulty to realize such ultrasonic transducers by many reasons, such as space limitation, couplant degradation, complex shapes of monitoring surfaces, backing material degradation/delamination, etc.

Ultrasonic transducers made by sol-gel composites could be one of the solutions. The mixture of ferroelectric powders and sol-gel solution is deposited as a film on the target surface, and it becomes porous sol-gel composite film after thermal treatments. Sol-gel composite ultrasonic transducers do not require couplant nor backing material, it could be applied on complex geometry if spray coating methos is chosen. Therefore it could operate very high temperatures, for example around 1000°C if lithium niobate is used as ferroelectric powder phase material.

In this presentation, we highlight results from our developments of advanced NDE technologies which enable zero-defect mass production of bonded joints through the integration of AI into real-time ultrasonic process monitoring systems. We will discuss use cases, including the implementation of resistance spot weld process monitoring using a deep learning approach which analyzes ultrasonic B-scans via semantic segmentation in real time. Our AI can assess throughout the weld process various weld properties including e.g. the amount of nugget penetration into each sheet in the stack up. These assessments are fed back to an adaptive weld controller so it can always produce high-quality welds that match production-level requirements.

Nondestructive evaluation using nonlinear ultrasonic guided waves combines the advantages of long propagation distances and ability to interrogate otherwise inaccessable regions in structures provided by guided waves with the sensitivity of nonlinear ultrasonics. The novelty of nonlinear ultrasonics is that the analyzed signal propagates at a frequency other than the driving frequency of the waves’ generator. Essentially, material nonlinearity or interaction with discontinuities causes distortion to the finite amplitude waves that is detectable in the frequency domain. Thus, an ideal nondestructive evaluation application is detection of precursors to fatigue, creep, and thermally induced material degradation based on microstructural evolution associated with dislocation structures, precipitate distributions, and grain morphology for example. After highlighting some of the foundational concepts of nonlinear ultrasonic guided waves, recent applications utilizing harmonic generation and wave mixing will be given: second harmonic generation of symmetric Lamb waves, third harmonic generation of shear-horizontal (SH) waves, mixing of SH and Lamb waves to generate back-propagating secondary waves at the difference frequency, and fully noncontact Rayleigh wave second harmonic generation.

Dennis Gabor invented the hologram for electromagnetic waves to refine electron microscope images. However, the hologram can also be applied to longitudinal pressure waves. It is then possible to project pressure images. The acoustic hologram thereby simplifies an otherwise cumbersome technology involving many transducers and permits the most sophisticated pressure images to be projected to date. Since sound waves can also exert forces, the acoustic hologram can thus be used for actuation and assembly, especially at small scales. I will describe work to realize the first fully connected 3D hologram, as well as its use to assemble matter into 3D objects in “one shot”. Recent work to obtain dynamic holograms, as well as fast methods to record pressure patterns will be presented. The talk will also discuss potential applications of acoustic holograms for the assembly of cells and opportunities for tissue engineering.

In the last ten years, significant breakthroughs such as layered SAW devices and laterally-excited bulk acoustic resonators have arisen to address the 5G band stringent requirements. Particularly, Bulk Acoustic Wave (BAW) devices based on single crystal piezoelectric LiNbO₃ and LiTaO₃ films have been emerged as promising candidates for wide bandwidth filters in the sub-6 GHz range. In these materials, the polarization of the acoustic wave, its velocity and its electromechanical coupling coefficient can be adjusted by a proper choice of the crystal orientation. 

In this review paper, we will briefly recall from an historical perspective the development of BAW resonators based on single crystal LiNbO₃ and LiTaO₃ films. Then we will address the design and fabrication of Film Bulk Acoustic Resonator (FBAR) and Solidly Mounted Resonator (SMR) based on such films, providing some thoughts for necessary improvements with regard to issues such as quality factors, temperature coefficient of frequency, spurious modes mitigation or power handling. Finally, recent experimental results will be also presented. 

Bulk and Surface Acoustic Wave (BAW and SAW) devices are key devices in mobile communications. Requirements for a higher frequency, wider bandwidth (BW), higher Q, lower temperature coefficient of frequency (TCF), and/or less spurious characteristic never end. To answer such requirements, the combination of a piezoelectric thin plate and a support substrate of a different material has appeared as enabling technology. In this talk, 3 kinds of new devices are presented.

Scaling electromechanical devices to the bandwidths and center frequencies of emerging communications standards requires innovations in both the materials and device structures. We report on the synthesis of low stress and highly scandium alloyed, aluminum scandium nitride (AlScN) thin films for applications in high frequency electromechanical resonators, filters, and signal processors. Utilizing the combination of an optimized process gas mixture and a gradient seed layer, we show the synthesis of AlScN films with up to 37% Sc alloying on Si substrates and 42% Sc alloying on SiC substrates. The films are free of anomalously oriented grains (AOGs), have low average stress (< 100 MPa), exhibit X-ray diffraction omega-scan FWHM of approximately <1.3°, and have rms surface roughness < 0.8 nm. We report on the formation of bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices operating at frequencies of 4 GHz and above in these films that exhibit Q factors approaching 1000 and electromechanical coupling from 5-23%. We discuss the scaling trends of achievable coupling and Q factor with increasing operating frequency. 

Ultrafast ultrasound imaging (UUI) is revolutionizing our diagnostic approach at the patient’s bedside. Thanks to the technical developments of the last years and the clinical proofs of concept obtained, cardiologists are becoming more and more interested in the benefits of this imaging technique. The use of specific acquisition or post-processing modes has given us access to new quantitative metrics for the anatomical or functional analysis of the cardiovascular system. Indeed, ultrafast ultrasound imaging now allows us to analyze the structure of the myocardium (stiffness or fiber orientation), its perfusion (coronary flow), or the blood flow in the cardiac cavities in a quantitative way (vector flow imaging or blood speckle tracking). Progressively, we are witnessing a complete paradigm shift in the use of ultrasound in cardiology and vascular medicine. During my presentation, I will share my experience as a cardiologist facing daily clinical challenges, and I will provide my insights on how clinical and fundamental researchers can work in concert for the benefit of the patient.

50+ years of Moore's law and related advances in nanofabrication have taught us how to make nanoscale objects routinely. But getting information (both classical and quantum) efficiently into and out of these (deeply sub-wavelength) nanoscale objects remains an unsolved problem in general. This is especially true when there is more than one material or signal modality (either frequency or information carrier: light, sound and microwaves) involved. 

Elastic metamaterials enable unprecedented control over acoustic waves in solids, including periodicity-driven or subwavelength wave attenuation, waveguiding, wave focusing, negative refraction, and other interesting phenomena. The predicted dynamic properties of the metamaterials made of polymers can however be altered by the mechanical behavior of the constituent materials due to the presence of intrinsic viscous losses. Comprehensive understanding of the influence of the losses on the dynamics of polymer elastic metamaterials has not been achieved yet which makes a burden for the practical applications of these materials and complicates the prediction of their functionalities. In the first part of this talk, we discuss the influence of linear viscoelastic material behavior on wave attenuation in polymer metamaterials which are produced by conventional manufacturing techniques and reveal (non)resonance wave scattering. For this, we estimate the accuracy of commonly used mechanical models to model viscoelastic behavior of polymers in comparison with experimental data. In the second part, we consider additively manufactured meta-structures and estimate the influence of the 3D-printed microstructure and a manufacturing method on the macroscopic dynamics of several types of elastic metamaterials.

The use of wearable electronic devices that can acquire vital signs from the human body noninvasively and continuously is a significant trend for healthcare. The combination of materials design and advanced microfabrication techniques enables the integration of various components and devices onto a wearable platform, resulting in functional systems with minimal limitations on the human body. Physiological signals from deep tissues are particularly valuable as they have a stronger and faster correlation with the internal events within the body compared to signals obtained from the surface of the skin. In this presentation, I will demonstrate a soft ultrasonic technology that can noninvasively and continuously acquire dynamic information about deep tissues and central organs. I will also showcase examples of this technology's use in recording blood pressure and flow waveforms in central vessels, monitoring cardiac chamber activities, and measuring core body temperatures. The soft ultrasonic technology presented represents a platform with vast potential for applications in consumer electronics, defense medicine, and clinical practices.

Key requirements for easy and wide-range applicability of an Ultrasonic Structural Health Monitoring (SHM system include high selectivity and accuracy in damage detection and localization, low hardware complexity and low power consumption for in-situ, real time operation. These features are not simultaneously available in present-days SHM systems as they represent cutting-edge challenges for state-of-the-art research. A major limitation is due to the fact that inspections are typically implemented through phased arrays featuring a large number of piezoelectric transducers. The weight penalty and maintenance concerns associated with such a large number of transducers have to be addressed for widespread field deployment of SHM systems. To this aim, a possible solution is in the shaping of the piezoelectric transducer electrodes to achieve the capability of steering the ultrasonic beam by simply controlling the central frequency of the actuated pulse. This solution enables the imaging of large 2D areas by actuating just two signals. Some recent realizations of Frequency steerable transducers will be presented, together with the electrode shapes design methodology and the signal processing techniques which can be applied on the acquired signals. 

Pulsed lasers are routinely used to optically excite and optically detect ultrasounds in a broad frequency range from MHz up to THz. This laser ultrasonics technique perfectly fits the needs for non-contact, non-invasive, non-destructive mechanical probing of samples of mm to nm sizes. Though well established for decades, this technique is limited by optical damage to the sample and consequently, rather weak ultrasonics pressures well above kbars can be excited. The laser-excitation of high-pressure ultrasounds i.e. shock waves is possible but, since the sample gets irrevocably damaged after each shot, it implies single-shot measurements with low reproducibility and poor signal-to-noise of the data. In the context of strain engineering of materials, alternative optical techniques enabling the excitation of high amplitude strains in a non-destructive optical regime are seeking. In this talk, I will present a methodology for the excitation of non-destructive shock waves, at high-repetition rate, limited only by the mechanical strength of the sample. Our technique for the excitation of non-destructive shock waves in the 10 kbar pressure range, is based on the spatio-temporal superposition of numerous laser-excited nanosecond acoustic waves for Surface Acoustic Waves (SAWs) or Bulk Acoustic Waves (BAWs) amplification, well below laser damage to the sample.

Current super resolution imaging is conducted using ultrasound contrast agents with a sparse distribution of bubbles. The sparse targets make the acquisition time long in the range of 1 to 10 minutes, and therefore demands accurate motion correction over a long time. The employment of contrast agents also demands a mechnical index below 0.2 to not disrupt the bubbles. A new method using erythrocytes as targets: SURE (SUper Resolution ultrasound imaging using Erythrocytes) was developed to alleviate these problems. Perfused tissues contain an abundance of targets, and the full clinical acoustic pressure range can be used. The method was investigated using data from kidneys for a number of Sprague-Dawley rats acquired using  a Verasonics Vantage 256 scanner and a 10 MHz linear array GE L10-18i probe with a recursive and interleaved synthetic aperture sequence. The SURE images are consistently obtained in a few seconds for all rats scanned with a resolution of 25 to 50 micrometers determined by Fourier ring correlation, and the vasculature is consistent with that visualized by ex vivo micro-CT scans of the kidneys. SURE demands no injection of intravenous contrast agents and can use the full pressure and intensity range allowable in medical ultrasound, making the method easily translatable to clinical use.

The number of applications involving implanted medical devices is growing. Safe and secure communications with these devices remains an important problem. Ultrasound provides a safe, secure, robust and high data rate alternative to electromagnetic communications. We have been developing in body devices that interact with ultrasonic scanners to provide diagnostic information and developing high data rate, ultrasonic communication protocols for in body devices. Here, we describe efforts to develop in body devices: radiological clips with ultrasound identification (USID) and a wireless capsule endoscopy that uses ultrasound to communicate images outside the body.   
We have developed an active radiological clip that transmits a unique USID signal based on pseudonoise (PN) codes when imaged with ultrasound. The clip ID is superimposed on a B-mode image for display providing improved visibility and tagging of multiple specific tissues. In a second device, we implemented an OFDM receiver with Xilinx ZCU106 development and TI AFE58JD48EVM evaluation boards, which provided 16 channels of 125 MSPS, 16-bit A/D converters. The ultrasound signal was transmitted using a single sonomicrocrystal through a 6-cm slab of pork belly and received with IP103 array. Maximum ratio combining were utilized to improve receiver performance.
For the first device, clips with six different USID tags were successfully visualized on B-mode images using an ultrasonic scanner. For the second device, we were able to successfully stream 25 secs of 4k video through 6 cm of pork belly. Specifically, an 8.3 Mbps error-free payload data rate was achieved with the proposed communication scheme.  
 

Ultrasound Localization Microscopy (ULM) can map the vasculature at large depth with unprecedented resolution by localizing millions of injected microbubbles in hundreds of thousands of images acquired over a few minutes but remains mostly limited to the generation of static images because of long acquisition times. Dynamic Ultrasound Localization Microscopy (DULM) enables the generation of movies of periodic phenomena at ULM resolution of the vasculature by using a combination of enhanced image formation and processing techniques to drastically increase the number of microbubbles that can be detected in each image. Examples of application for the mapping of pulsatility in the brain and the dynamics of the intramyocardial blood flow in 2D+t and 3D+t will be shown. Specifically, we will describe how the detection of microbubbles directly in space time along with novel aberration correction algorithms and a motion invariant Lagrangian beamforming approach can be used to increase the concentration of microbubbles in DULM with a limited degradation in spatial resolution.

GHz ultrasonic (US) imaging has the potential for imaging objects at very high resolutions while measuring elasticity and density, which are hard to measure with other imaging approaches. However, US imaging and Surface Acoustic Microscopy at GHz frequencies have been limited to laboratories and niche applications. Recent advances in thin film piezoelectric AlN and AlScN enable monolithic integration of BAW transducers onto CMOS circuitry. This capability lends itself to controlling GHz US waves and pulses within the silicon die. US wave diffraction and pulse control can be used for information transfer, imaging and allow computation of Fourier Transforms (FT). We have integrated arrays of GHz pixels to enable real-time imaging of samples in contact with imaging chips from a startup (Geegah Inc.) An imager chip with a 128x128 array of 50x50um AlN thin-film transducer pixels operating @ 1.85 GHz has been used to image thin liquid films, bacteria collections, CMOS dies, and other objects. A GHz US metalens has been implemented, enabling US FT using wave propagation properties, often used in optics. Unlike optics, the much smaller acoustic velocities, smaller wavelengths, and low frequencies allow the detection of the amplitude and phase of the resulting FT in a small space with gains readily available from current CMOS nodes. The two examples of US imaging and FT for computation acceleration pave the way for inexpensive devices realizing GHz US devices for the masses.