Pseudo-Random Codes for Single-Mode and Simultaneous Multi-Mode Operation in Ultrasonic Imaging Systems

Conventional pulse-echo imaging systems used in ultrasonics can become limited in average transmit power by transmitter, transducer, and medium peak-power limitations. In addition, imaging systems which use multi-element arrays are limited in speed by the necessity to transmit sequentially when scanning in more than one direction in order to avoid interfering echoes. A new system is studied which can overcome both the speed and power limitations by using correlation receivers and pseudo-random transmit codes. First, the performance of several single-mode correlation systems are compared to conventional pulse-echo systems in the presence of clutter and moving targets. The system which uses special pseudo-random codes called Golay codes is shown to provide the best overall performance. A multi-mode correlation system is then studied which images in many different modes (e.g. scan directions) simultaneously. This multi-mode system is studied under the effects of moving targets, clutter and background receiver noise. A comparison with the operation of Conventional sequentially-scanned phased array systems is made under a variety of signal-to-noise ratio (SNR) conditions and operating speeds to determine the optimal type of imaging system. Results indicate that under many conditions, a simultaneous multi-mode system can provide improved SNR and/or speed over conventional sequential multi-mode systems. The multi-mode system which uses Golay codes is shown to provide the best overall performanc

Investigation of methods for data communication and power delivery through metals

PhD ThesisThe retrieval of data from a sensor, enclosed by a metallic structure, such as a naval vessel, pipeline or nuclear flask is often very challenging. To maintain structural integrity it is not desirable to penetrate the wall of the structure, preventing any hard-wired solution. Furthermore, the conductive nature of the structure prevents the use of radio communications. Applications involving sealed containers also have a requirement for power delivery, as the periodic changing of batteries is not possible. Ultrasound has previously been identified as an attractive approach but there are two key challenges: efficient/reliable ultrasonic transduction and a method of overcoming the inherent multipath distortion resulting from boundary reflections. Previous studies have utilised piezoelectric contact transducers, however, they are impractical due to their reliance on coupling, i.e. the bond between the transducer and the metal surface, which leads to concerns over long term reliability. A non-contact transducer overcomes this key drawback, thus highlighting the electromagnetic acoustic transducer (EMAT) as a favourable alternative. This thesis presents the design and testing of an EMAT with appropriate characteristics for through-metal data communications. A low cost, low power data transmission scheme is presented for overcoming acoustic multipath based on pulse position modulation (PPM). Due to the necessary guard time, the data rate is limited to 50kbps. A second solution is presented employing continuous wave, Quadrature phase shift keying (QPSK) modulation, allowing data rates in excess of 1Mbps to be achieved. Equalisation is required to avoid intersymbol interference (ISI) and a decision feedback equaliser (DFE) is shown to be adept at mitigating this effect. The relatively low efficiency of an EMAT makes it unsuitable for power delivery, consequently, an alternative non-contact approach, utilising inductive coupling, is explored. Power transfer efficiency of ≈ 4% is shown to be achievable through 20mm thick stainless steel.ICS department of BAE Systems Submarine Solutions, EPSR

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 Measurement of Thin Condensing Fluid Films

The condensation of vapor onto a cooled surface is a phenomenon which can be difficult to quantify spatially and as a function of time; this thesis describes an ultrasonic system to measure this phenomenon. The theoretical basis for obtaining condensate film thickness measurements, which can be used to calculate growth rates and film surface features, from ultrasonic echoes will be discussed and the hardware and software will be described. The ultrasonic system utilizes a 5MHz planar piston transducer operated in pulse-echo mode to measure the thickness of a fluid film on a cooled copper block over the fluid thickness range of 50 microns to several centimeters; the signal processing algorithms and software developed to carry out this task are described in detail. The results of several experiments involving the measurement of both non-condensing and condensing films are given. In addition, numerical modeling of specific condensate film geometries was performed to support the experimental system; the results of modeling nonuniform fluid layers are discussed in the context of the effect of such layers on the measurement system

High bit-rate digital communication through metal channels

The need to transmit digital information across metallic barriers arises frequently in industrial control applications. In some applications, the barrier can be penetrated with wiring, while in others this may not be possible. For example, metal bulkheads, pressure vessels, or pipelines may require a level of mechanical integrity that prohibits mechanical penetration. This study investigates the use of ultrasonic signaling for data transmission across metallic barriers, discusses the associated challenges, and analyzes several alternative communication system implementations.Several recent e orts have been made to develop through-metal ultrasonic communication systems, with approaches ranging widely in bitrate, complexity, and power requirements. The transceiver designs presented here are intended to cover a range of target applications. In systems having low data rate requirements, simple transceivers with low hardware/software complexity can be used. At high data rates, however, severe echoing in the ultrasonic channel leads to intersymbol interference. Reliable high speed communication therefore requires the use of channel equalizers, and results in a transceiver with higher hardware/software complexity.In this thesis, issues related to the design of reliable through-metal ultrasonic communication systems are discussed. These include (1) the development of mathematical models used to characterize the channel, (2) application of equalization techniques needed to achieve high-speed communication, and (3) analysis of hardware/software complexity for alternative transceiver designs.Several groups have developed through-metal ultrasonic communication systems in the recent past, though none has produced a mathematical model that accurately describes the phenomena found within the channel. The channel model developed in this thesis can be used at several stages of the transceiver design process, from transducer selection through channel equalizer design and ultimately system performance simulation.Using this channel model, we go on to develop and test several ultrasonic throughmetal transceiver designs. Ultrasonic through-metal communication systems are finding use in a wide variety of applications. Some require high throughput, while others require low power consumption. The motivation for developing several designs { ranging from low complexity, low power to high complexity, high throughput { is so that the best design can be matched to each application.After these transceiver designs are developed, we present an analysis of their computational requirements so that the most appropriate transceiver can be chosen for a given application.Ph.D., Electrical Engineering -- Drexel University, 201

Real-time digital signal processing system for normal probe diffraction technique

Ultrasonic systems are widely used in many fields of non-destructive testing. The increasing requirement for high quality steel product stirs the improvement of both ultrasonic instruments and testing methods. The thesis indicates the basics of ultrasonic testing and Digital Signal Processing (DSP) technology for the development of an ultrasonic system. The aim of this project was to apply a new ultrasonic testing method - the Normal Probe Diffraction method to course grained steel in real-time and investigate whether the potential of probability of detection (POD) has been improved. The theories and corresponding experiment set-up of pulse-echo method, TOFD and NPD method are explained and demonstrated separately. A comparison of these methods shows different contributions made by these methods using different types of algorithms and signals. Non-real-time experiments were carried out on a VI calibration block using an USPC 3100 ultrasonic testing card to implement pulse-echo and NPD method respectively. The experiments and algorithm were simulated and demonstrated in Matlab. A low frequency Single-transmitter-multi-receiver ultrasonic system was designed and built with a digital development board and an analogue daughter card to transmit or receive signals asynchronously. A high frequency high voltage amplifier was designed to drive the ultrasonic probes. A Matlab simulation system built with Simulink indicates that the Signal to Noise Ratio (SNR) can be improved with an increment of up to 3dB theoretically based on the simulation results using DSP techniques. The DSP system hardware and software was investigated and a real-time DSP hardware system was supposed to be built to implement the high frequency system using a rapid code generated system based on Matlab Simulink model and the method was presented. However, extra effort needs to be taken to program the hardware using a low-level computer language to make the system work stably and efficiently

Study of the viscoelastic properties of liquids at microwave frequencies

Imperial Users onl

Integrated Electronics for Wireless Imaging Microsystems with CMUT Arrays

Integration of transducer arrays with interface electronics in the form of single-chip CMUT-on-CMOS has emerged into the field of medical ultrasound imaging and is transforming this field. It has already been used in several commercial products such as handheld full-body imagers and it is being implemented by commercial and academic groups for Intravascular Ultrasound and Intracardiac Echocardiography. However, large attenuation of ultrasonic waves transmitted through the skull has prevented ultrasound imaging of the brain. This research is a prime step toward implantable wireless microsystems that use ultrasound to image the brain by bypassing the skull. These microsystems offer autonomous scanning (beam steering and focusing) of the brain and transferring data out of the brain for further processing and image reconstruction. The objective of the presented research is to develop building blocks of an integrated electronics architecture for CMUT based wireless ultrasound imaging systems while providing a fundamental study on interfacing CMUT arrays with their associated integrated electronics in terms of electrical power transfer and acoustic reflection which would potentially lead to more efficient and high-performance systems. A fully wireless architecture for ultrasound imaging is demonstrated for the first time. An on-chip programmable transmit (TX) beamformer enables phased array focusing and steering of ultrasound waves in the transmit mode while its on-chip bandpass noise shaping digitizer followed by an ultra-wideband (UWB) uplink transmitter minimizes the effect of path loss on the transmitted image data out of the brain. A single-chip application-specific integrated circuit (ASIC) is de- signed to realize the wireless architecture and interface with array elements, each of which includes a transceiver (TRX) front-end with a high-voltage (HV) pulser, a high-voltage T/R switch, and a low-noise amplifier (LNA). Novel design techniques are implemented in the system to enhance the performance of its building blocks. Apart from imaging capability, the implantable wireless microsystems can include a pressure sensing readout to measure intracranial pressure. To do so, a power-efficient readout for pressure sensing is presented. It uses pseudo-pseudo differential readout topology to cut down the static power consumption of the sensor for further power savings in wireless microsystems. In addition, the effect of matching and electrical termination on CMUT array elements is explored leading to new interface structures to improve bandwidth and sensitivity of CMUT arrays in different operation regions. Comprehensive analysis, modeling, and simulation methodologies are presented for further investigation.Ph.D