Wireless recording of the calls of Rousettus aegyptiacus and their reproduction using electrostatic transducers

Bats are capable of imaging their surroundings in great detail using echolocation. To apply similar methods to human engineering systems requires the capability to measure and recreate the signals used, and to understand the processing applied to returning echoes. In this work, the emitted and reflected echolocation signals of Rousettus aegyptiacus are recorded while the bat is in flight, using a wireless sensor mounted on the bat. The sensor is designed to replicate the acoustic gain control which bats are known to use, applying a gain to returning echoes that is dependent on the incurred time delay. Employing this technique allows emitted and reflected echolocation calls, which have a wide dynamic range, to be recorded. The recorded echoes demonstrate the complexity of environment reconstruction using echolocation. The sensor is also used to make accurate recordings of the emitted calls, and these calls are recreated in the laboratory using custom-built wideband electrostatic transducers, allied with a spectral equalization technique. This technique is further demonstrated by recreating multi-harmonic bioinspired FM chirps. The ability to record and accurately synthesize echolocation calls enables the exploitation of biological signals in human engineering systems for sonar, materials characterization and imaging

Characterization of a CMUT Array

Ultrasound transducers are used in a broad range of applications covering from underwater communications to medical imaging and treatment. The ultrasonic transducer determines the key specifications such as resolution, sensitivity and signal to noise ratio. The capacitive micromachined ultrasonic transducer (CMUT) has emerged as an alternative to standard piezoelectric transducers due to advanced microelectronics fabrication technology and methods. Comparing to piezoelectric transducers, the CMUT is superior to it\u27s competitor with higher acoustic bandwidth, higher sensitivity and greater coupling with the acoustic medium. Design, fabrication, and characterization of a capacitive micromachined ultrasonic transducer (CMUT) array have been presented along this thesis. The array is designed to operate in the frequency range of 113-167 kHz. The CMUT array is fabricated using an SOI based fabrication technology and includes 6x6 CMUTs. Necessary test setups and readout circuitry is designed in order to carry out the characterization process. Static analysis results are verified with Wyko optical profilometer, Agilent LCR meter and SEM analysis. Dynamic characterizations are done with Polytec MSA-4 laser Doppler vibrometer. An efficient and low noise capacitive readout circuit is designed using transimpedance amplifier scheme with 75 kilo ohm gain and fabricated on a PCB. The developed analytical models, FEA and experimental results are in very good agreement to exhibit accuracy of the design methodology

医用超音波における散乱体分布の高解像かつ高感度な画像化に関する研究

Ultrasound imaging as an effective method is widely used in medical diagnosis andNDT (non-destructive testing). In particular, ultrasound imaging plays an important role in medical diagnosis due to its safety, noninvasive, inexpensiveness and real-time compared with other medical imaging techniques. However, in general the ultrasound imaging has more speckles and is low definition than the MRI (magnetic resonance imaging) and X-ray CT (computerized tomography). Therefore, it is important to improve the ultrasound imaging quality. In this study, there are three newproposals. The first is the development of a high sensitivity transducer that utilizes piezoelectric charge directly for FET (field effect transistor) channel control. The second is a proposal of a method for estimating the distribution of small scatterers in living tissue using the empirical Bayes method. The third is a super-resolution imagingmethod of scatterers with strong reflection such as organ boundaries and blood vessel walls. The specific description of each chapter is as follows: Chapter 1: The fundamental characteristics and the main applications of ultrasound are discussed, then the advantages and drawbacks of medical ultrasound are high-lighted. Based on the drawbacks, motivations and objectives of this study are stated. Chapter 2: To overcome disadvantages of medical ultrasound, we advanced our studyin two directions: designing new transducer improves the acquisition modality itself, onthe other hand new signal processing improve the acquired echo data. Therefore, the conventional techniques related to the two directions are reviewed. Chapter 3: For high performance piezoelectric, a structure that enables direct coupling of a PZT (lead zirconate titanate) element to the gate of a MOSFET (metal-oxide semiconductor field-effect transistor) to provide a device called the PZT-FET that acts as an ultrasound receiver was proposed. The experimental analysis of the PZT-FET, in terms of its reception sensitivity, dynamic range and -6 dB reception bandwidth have been investigated. The proposed PZT-FET receiver offers high sensitivity, wide dynamic range performance when compared to the typical ultrasound transducer. Chapter 4: In medical ultrasound imaging, speckle patterns caused by reflection interference from small scatterers in living tissue are often suppressed by various methodologies. However, accurate imaging of small scatterers is important in diagnosis; therefore, we investigated influence of speckle pattern on ultrasound imaging by the empirical Bayesian learning. Since small scatterers are spatially correlated and thereby constitute a microstructure, we assume that scatterers are distributed according to the AR (auto regressive) model with unknown parameters. Under this assumption, the AR parameters are estimated by maximizing the marginal likelihood function, and the scatterers distribution is estimated as a MAP (maximum a posteriori) estimator. The performance of our method is evaluated by simulations and experiments. Through the results, we confirmed that the band limited echo has sufficient information of the AR parameters and the power spectrum of the echoes from the scatterers is properly extrapolated. Chapter 5: The medical ultrasound imaging of strong reflectance scatterers based on the MUSIC algorithm is the main subject of Chapter 5. Previously, we have proposed a super-resolution ultrasound imaging based on multiple TRs (transmissions/receptions) with different carrier frequencies called SCM (super resolution FM-chirp correlation method). In order to reduce the number of required TRs for the SCM, the method has been extended to the SA (synthetic aperture) version called SA-SCM. However, since super-resolution processing is performed for each line data obtained by the RBF (reception beam forming) in the SA-SCM, image discontinuities tend to occur in the lateral direction. Therefore, a new method called SCM-weighted SA is proposed, in this version the SCM is performed on each transducer element, and then the SCM result is used as the weight for RBF. The SCM-weighted SA can generate multiple B-mode images each of which corresponds to each carrier frequency, and the appropriate low frequency images among them have no grating lobes. For a further improvement, instead of simple averaging, the SCM applied to the result of the SCM-weighted SA for all frequencies again, which is called SCM-weighted SA-SCM. We evaluated the effectiveness of all the methods by simulations and experiments. From the results, it can be confirmed that the extension of the SCM framework can help ultrasound imaging reduce grating lobes, perform super-resolution and better SNR(signal-to-noise ratio). Chapter 6: A discussion of the overall content of the thesis as well as suggestions for further development together with the remaining problems are summarized.首都大学東京, 2019-03-25, 博士（工学）首都大学東

Ultrasonic guided waves in composite plates: a study of interface bond condition and material properties determination with broadband focused air-coupled ultrasounds

This work is focused on two important aspects of the study of the composite materials: characterization of interface bonding in layered composites and evaluation of elastic material properties in air-coupled experiments.;The characterization of interface condition in a layered composite is critical to understand the behavior of the material under various stress situations. A closed disbond, alternatively known as zero-volume disbond or kissing-disbond (KSD) is difficult to detection by conventional normal-incidence ultrasonic nondestructive evaluation (NDE) methods. Such undetected defect may be dangerous because it can produce a significant decrease in structural integrity or lead to a catastrophic failure under certain loading conditions. We have successfully demonstrated a new technique for KSD detection in carried-to-completion experiments involving various artificially created defects.;The dependence of the modes of the propagating wave in a plate on the elastic material properties has motivated us to develop a method suitable for rapid non-contact reconstruction of the guided waves spectra. To overcome the weak and inefficient generation of ultrasonic waves in air of conventional transducers and to achieve the desired wide angular spread of the acoustic beam in air, we employed capacitive foil transducers and designed focusing devices. Measurements of the acoustic pressure profile of the transducers have been performed in both planar and focused configurations and compared with our computationally efficient received voltage model.;We exploited our custom broadband focused air-coupled system and a synthetic aperture scan technique to produce, in one line scan with only one incident angle, an almost complete spectrum of the Rayleigh-Lamb waves of various engineering materials subject to a 700-kHz frequency and 16° angular bandwidth limitation of the transducers. A pulse-compression method along with a fast data acquisition and processing capability allowed us to perform rapid reconstruction and evaluation of the guided waves spectra. Tests of our method on numerous materials showed excellent agreement with theoretical predictions.*;*This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat

Simultaneous measurement for material parameters using self-mixing interferometry

Material related parameters such as Young’s modulus and internal friction are important for mechanical and material engineering. These parameters play key roles in the material performances. It has been a great interest to measure the value of these parameters. Traditional methods including tensile test, flexure test, and others are destructive methods often cause damages to specimen and have low accuracy. In recent years, the impulse excitation technique (IET), a non-destructive technique to determine Young’s modulus and internal friction of the material has attracted great attention. The detection system used for IET is normally microphone, accelerometer and so on. Selfmixing interferometry (SMI), an emerging sensing technique, which is non-destructive, non-contact, compact structure, and low-cost has been developed for high accuracy sensing applications, such as displacement, velocity and distance measurement and so on is suitable for the material related parameters measurement. A normal SMI system consists of a laser diode (LD) and a target to form the external cavity of the LD. When a portion of the light is reflected or backscattered to the laser cavity, leading to a modulated laser power of LD. This modulated laser power is referred as SMI signal, which carries the information of vibration of the target. In this thesis, a measurement method combining IET with SMI for material related parameters measurement is proposed. By applying wavelet transform onto the SMI signal, both resonant frequency and damping factor of the specimen vibration can be retrieved at the same time. Therefore, both Young’s modulus and internal friction of the specimen can be calculated simultaneously. The optical fibre is introduced to the system. With the installation of the optical fibre, the flexibility of the measurement is greatly improved. The measurement results show the feasibility for simultaneous measurement of material related parameters. A graphical user interface is designed to improve the user experience for the measurement

Phase-changing Nanodroplets as Nanotheranostic Platform for Combination Cancer Therapy

Cancer is a cluster of diseases, and 1.8 million Americans are newly diagnosed each year. Treatment issues such as drug instability, the occurrence of severe side effects, as well as resistance make the need for solutions to improve conventional methods, like chemotherapy, apparent. Nano-sized drug-delivery platforms, particles loaded with therapeutic molecules that escape the immune system clearance and accumulate at the tumor site, were proposed as one of these solutions. Despite the expansion of the field, several aspects still need to be addressed: inconsistent delivery of the drugs, inability of measuring the effective dose being delivered to the tumor, lack of predictability of a response. Hence, the field of nanotheranostics was born, that combines drug-delivery nanoparticulate systems with imaging capabilities. By enabling a noninvasive visualization of delivered therapeutic molecules, nanotheranostics offer the opportunity of rapid optimization of drug delivery systems during in vivo testing. This insight into the kinetics and the fate of nanoparticle-encapsulated therapeutics can aid validate basic properties without needing to wait a long time for a pathological outcome. In the clinic, this feature would allow for a fast response in modifying a treatment course. This work describes a versatile nanotheranostic platform capable of triggered release of therapeutic molecules and strong ultrasound imaging contrast simultaneously. The activatable release is designed to minimize off-target effects, while the ultrasound contrast can enable visualization of the delivered dose to a region of interest. The particles described herein consist of a shell-core structure, with a perfluorocarbon iii core that can be externally vaporized by acoustical or optical stimuli. The activation generates highly echogenic microbubbles, together with the release of the loaded compounds. Notably, the release of the payload is correlated to the ultrasound magnitude after activation, enabling the basis for ultrasound dose-monitoring. The design, synthesis and characterization of perfluorocarbon nanodroplets aimed at several applications are described. These include co-delivery of hydrophobic and hydrophilic chemotherapeutics, delivery of a-PD-L1 immunecheckpoint inhibitors together with chemotherapeutics, as well as multimodal imaging capabilities. Overall, this work contributes towards expanding the utility of perfluorocarbon nanodroplets towards combinatorial therapies, and proposes necessary improvements for increased translatability of the technology

Stepper microactuators driven by ultrasonic power transfer

Advances in miniature devices for biomedical applications are creating ever-increasing requirements for their continuous, long lasting, and reliable energy supply, particularly for implanted devices. As an alternative to bulky and cost inefficient batteries that require occasional recharging and replacement, energy harvesting and wireless power delivery are receiving increased attention. While the former is generally only suited for low-power diagnostic microdevices, the latter has greater potential to extend the functionality to include more energy demanding therapeutic actuation such as drug release, implant mechanical adjustment or microsurgery. This thesis presents a novel approach to delivering wireless power to remote medical microdevices with the aim of satisfying higher energy budgets required for therapeutic functions. The method is based on ultrasonic power delivery, the novelty being that actuation is powered by ultrasound directly rather than via piezoelectric conversion. The thesis describes a coupled mechanical system remotely excited by ultrasound and providing conversion of acoustic energy into motion of a MEMS mechanism using a receiving membrane coupled to a discrete oscillator. This motion is then converted into useful stepwise actuation through oblique mechanical impact. The problem of acoustic and mechanical impedance mismatch is addressed. Several analytical and numerical models of ultrasonic power delivery into the human body are developed. Major design challenges that have to be solved in order to obtain acceptable performance under specified operating conditions and with minimum wave reflections are discussed. A novel microfabrication process is described, and the resulting proof-of-concept devices are successfully characterized.Open Acces

Design and Analysis of Capacitive Parametric Ultrasound Transducers for Wireless Power Transfer

For wireless ultrasonic power delivery to implantable medical devices, a capacitive parametric ultrasound transducer system is analyzed and improved upon. While 1D modeling had sufficed for proof of concept and power transfer with low efficiency has been demonstrated, a more detailed model gives insight to behavior that were previously overlooked. Simulations of large capacitive membrane arrays show higher power transfer efficiencies in some cases when the array is operating at a higher order mode. Analysis also shows that in tissue, fluid damping dominates the mechanics of the membrane array, allowing the array frequency to be tuned by adjusting the membrane thickness through analytical or finite element methods. To complete the power delivery chain, a modified power rectification circuit is simulated, demonstrated experimentally, and compared to a traditional rectification circuit highlighting improvements in power transfer efficiency. Finally, a capacitive membrane design optimized for 1MHz operation in fluid is fabricated in a cleanroom environment and used to demonstrate viable passive ultrasonic wireless power transfer, from hydrophone to load application.M.S