Capacitive Micromachined Ultrasonic Transducers for Therapeutic Ultrasound Applications

Therapeutic ultrasound guided by MRI is a noninvasive treatment that potentially reduces mortality, lowers medical costs, and widens accessibility of treatments for patients. Recent developments in the design and fabrication of capacitive micromachined ultrasonic transducers (CMUTs) have made them competitive with piezoelectric transducers for use in therapeutic ultrasound applications. In this paper, we present the first designs and prototypes of an eight-element, concentric-ring, CMUT array to treat upper abdominal cancers. This array was simulated and designed to focus 30–50 mm into tissue, and ablate a 2- to 3-cm-diameter tumor within 1 h. Assuming a surface acoustic output pressure of 1 MPa peak-to-peak (8.5 W/cm$^2$) at 2.5 MHz, we simulated an array that produced a focal intensity of 680 W/cm$^2$ when focusing to 35 mm. CMUT cells were then designed to meet these frequency and surface acoustic intensity specifications. These cell designs were fabricated as 2.5 mm $times$ 2.5 mm test transducers and used to verify our models. The test transducers were shown to operate at 2.5 MHz with an output pressure of 1.4 MPa peak-to-peak (16.3 W/cm$^2$). With this CMUT cell design, we fabricated a full eight-element array. Due to yield issues, we only developed electronics to focus the four center elements of the array. The beam profile of the measured array deviated from the simulated one because of the crosstalk effects; the beamwidth matched within 10% and sidelobes increased by two times, which caused the measured gain to be 16.6 compared to 27.4.      

Milestones on the road to higher resolution, quantitative, and functional ultrasonic imaging

Ultrasonography is evolving rapidly with important recent advances in high-density transducer arrays, one-and-one-half-dimensional transducers, broad-band transducers, increased scanner bandwidth, and more sophisticated image-formation routines. Technical advances have clearly improved accuracy of image readings, heightened contrast and resolution, reduced noise, and reduced image slice thickness. It is within this fertile environment that very high-frequency ultrasound, harmonic imaging, and ultrasound contrast agents have emerged. Clinical applications of ultrasonography have also been extended to new fields, such as skeletal status assessment, which have long been considered beyond ultrasound's reach, and over the past 15 years, quantitative ultrasound bone densitometry has become an important part of the armamentarium for osteoporosis diagnosis. The state of these innovations, their contributions to diagnostic and monitoring capabilities, as well as the new applications they bring into reach will be discussed. We will explore several applications currently under development including ultrasound biomicroscopy (eye, skin, small animals), quantitative perfusion assessment, and pathology evaluation. Thus, ongoing research has not only significantly added to diagnostic ultrasound's existing capabilities, but also promises to further broaden the range of its clinical and biological applications.     

基于薄板理论的密排结构CMUT发射声场研究

由微机电系统(MEMS)工艺制作的电容式微机械超声换能器(CMUT),其具有宽频带,易与电子电路集成制作等优势,在医学成像领域具有广阔的应用前景。为了研究一种密排结构CMUT超声换能器的发射声场特征,该文提出了一种简单的物理域相互作用分析方法。基于薄板的振动理论,由CMUT单元的声学辐射原理及特性计算得到CMUT阵元辐射声场的解析解。通过振膜振动分布实验验证了采用薄板振动理论一阶振型方程的正确性。通过仿真和实验研究了CMUT发射单元在不同排布方式和条件下的声场分布、声轴声压和指向性,为CMUT的设计和性能分析提供了理论依据。     

Silicon Geiger mode avalanche photodiodes

In this letter we present the results regarding the electrical and optical characterization of Geiger mode silicon avalanche photodiodes(GMAP) fabricated by silicon standard planar technology. Low dark count rates,negligible afterpulsing effects,good timing resolution and high quantum detection efficiency in all the visible range have been measured. The very good electro-optical performances of our photodiodes make them attractive for the fabrication of arrays with a large number of GMAP to be used both in the commercial and the scientific fields,as telecommunications and nuclear medical imaging.     

Facile Fabrication of Ordered Crystalline‐Semiconductor Microstructures on Compliant Substrates

Buckling and wrinkling of thin films on a compliant material has proved to be a resource in several applications, such as flexible electronics, thin‐film metrology and fabrication of tunable optical components. A versatile approach for the fabrication of two‐dimensional and linear arrays of buckled structures is demonstrated here using a stiff material, in the form of a nanomembrane, on a compliant substrate. The novelty of the fabrication process is that the substrates are strained by isotropic volume expansion in solvents. This work illustrates in detail the potential of our technology to fabricate ordered arrays of 3D structures on large‐area compliant substrates, with important implications for a large number of fields. Furthermore, this paper discusses the interesting interface chemistry and mechanics leading to controllable and reproducible fabrication of our 3D structures.     

Integrated reconfigurable high-voltage transmitting circuit for CMUTs

In this paper a high-voltage transmitting circuit aimed for capacitive micromachined ultrasonic transducers (CMUTs) used in scanners for medical applications is designed and implemented in a 0.35 \(\upmu\)m high-voltage CMOS process. The transmitting circuit is reconfigurable externally making it able to drive a wide variety of CMUTs. The transmitting circuit can generate several pulse shapes with voltages up to 100 V, maximum pulse range of 50 V, frequencies up to 5 MHz and different driving slew rates. Measurements are performed on the circuit in order to assess its functionality and power consumption performance. The design occupies an on-chip area of 0.938 mm\(^{2}\) and the power consumption of a 128-element transmitting circuit array that would be used in an portable ultrasound scanner is found to be a maximum of 181 mW.     

Inverter-based 1 V analog front-end amplifiers in 90 nm CMOS for medical ultrasound imaging

In this paper, we present the design and experimental evaluation of 1 V analog front-end amplifiers designed in 90 nm CMOS technology for capacitive micro-machined ultrasound transducers (CMUTs) for medical ultrasound imaging systems. We propose two front-end amplifier topologies based on an inverter-based cascode amplifier; the first is a continuous time amplifier and the second is a charge sampling amplifier (CSA). The proposed front-end amplifiers are designed to amplify the signals from CMUTs in the frequency bandwidth from 15 to 45 MHz with a centre frequency of 30 MHz. From the measurements, the continuous time single-ended transimpedance amplifier achieves a voltage gain of 19 dB, an output noise power spectral density of 0.042 (μV)/SQRT(Hz) at a centre-frequency of 30 MHz, and a total harmonic distortion of −23 dB at 450 mV p–p output voltage at 30 MHz input signal frequency. It draws only 598 μA per amplifier from a 1 V power supply. Its area measured only about 32 μm × 32 μm per amplifier. On the other hand, a sampling based front-end amplifier [CSA] achieves a transfer gain of 17.4 dB at an input signal frequency of 30 MHz and an upper 3 dB cut-off frequency of 46 MHz at a sampling clock frequency of 100 MHz. It consumes 586 μA per amplifier from a 1 V power supply and achieves a signal-to-noise (SNR) ratio of 45.7 dB with a peak-to-peak output signal amplitude of 500 mV at a sampling frequency of 100 MHz. It occupies an area of 1470.2 μm² (which is equivalent to 38 μm × 38 μm), which also includes the area of the switches for the CSA that will be used for the single CMUT element.     

基于环形相控阵的超声CT成像系统的设计

为了更好地实现乳腺癌的早期精确诊断,设计了一种基于聚焦环阵的新型超声CT成像系统。256个电容式微加工超声换能器(CMUT)环形分布于乳腺四周,采用64个换能器发射,对面64个换能器接收的方式进行,在COMSOL中依次进行256次仿真来实现环形扫描。根据超声相控阵原理进行发射聚焦后,采用滤波反投影算法进行图像重建。聚焦到乳腺外部时,重建偏差值小于0.05%,聚焦到4号肿瘤时,该区域重建偏差值仅为0.002%。实验结果表明,该系统可以用于乳腺癌的早期精确诊断,且能提高内部肿瘤的检测质量。     

Amorphous silicon arrays develop a medical image

Several X-ray imaging techniques are reviewed, and the use of amorphous silicon detector arrays for X-ray imaging is discussed. An important aspect of the amorphous silicon technology is the large size of the image sensor array, which is particularly significant for radiation imaging because it is not presently possible to focus X-rays over large fields of view. Current techniques allow an array size of about 10 in×10 in. Several medical applications for imaging arrays, including radiation therapy, real-time fluoroscopy, diagnostic radiographic imaging, and nuclear medicine techniques are also discussed     

Deep tissue photoacoustic imaging using a miniaturized 2-D capacitive micromachined ultrasonic transducer array

In this paper, we demonstrate 3-D photoacoustic imaging (PAI) of light absorbing objects embedded as deep as 5 cm inside strong optically scattering phantoms using a miniaturized (4 mm × 4 mm × 500 μm), 2-D capacitive micromachined ultrasonic transducer (CMUT) array of 16 × 16 elements with a center frequency of 5.5 MHz. Two-dimensional tomographic images and 3-D volumetric images of the objects placed at different depths are presented. In addition, we studied the sensitivity of CMUT-based PAI to the concentration of indocyanine green dye at 5 cm depth inside the phantom. Under optimized experimental conditions, the objects at 5 cm depth can be imaged with SNR of about 35 dB and a spatial resolution of approximately 500 μm. Results demonstrate that CMUTs with integrated front-end amplifier circuits are an attractive choice for achieving relatively high depth sensitivity for PAI.     

Integrated silicon-PVF2acoustic transducer arrays

A new type of transducer array has been designed which employs a piezoelectric polymer, polyvinylidene fluoride (PVF2), as the sensing material. Acoustic properties possessed by this piezoelectric polymer provide a reasonable match to those of the human body making it very attractive for medical ultrasonic imaging systems. Using planar integrated-circuit (IC) technology, an array of MOSFET input amplifiers is fabricated on a silicon wafer. A single sheet of PVF2is bonded to the surface of the wafer. Spatially varying acoustic signals detected by the PVF2are converted to corresponding charge distributions on the underlying array of amplifiers. A linear 34-element receiving transducer array has been built and evaulated. Array transverse dimensions are 14.7 × 9 mm, so that the silicon die area is approximately 1.32 cm². Individual transducers are 0.42 × 9 mm corresponding to the requirements of a particular system. Associated with each of the 34 transducers is a DMOS-bipolar cascode amplifier. Experimentally measured transducer impulse response decays 20 dB in two cycles. Using silicon technology, arrays of almost arbitrary size and complexity appear feasible.     

非致冷测辐射热计红外焦平面阵列

非致冷测辐射热计以其高性能和低价格 ,成为红外热成像技术新的研究热点。焦平面设计为桥式结构 ,器件制作采用微机械加工技术。文章介绍了该器件的设计、制作、性能和应用。     

Microlens lithography: A new approach for large display fabrication

Microlens lithography is a new lithographic method, that uses microlens arrays to image a lithographic mask onto a substrate layer. Microlens lithography provides photolithography at a moderate resolution for an almost unlimited area. The imaging system consists of stacked microlens arrays forming an array of micro-objectives. Each micro-objective images a small part of the mask pattern, the images overlap in the image plane. Potential applications for microlens lithography are the fabrication of large area flat panel displays (FPD), color filters, and micromechanics.     

微柱透镜阵列的全息-光刻胶热熔制作技术

为改善微柱透镜阵列的制作技术、消除光刻工艺对光刻掩模版的依赖,研究了利用全息-热熔技术制作微柱透镜阵列的新方法,即首先采用了全息技术进行曝光,然后利用光刻胶热熔技术在K9玻璃基底上制作出了面形良好的微柱透镜阵列。实验结果表明,进行全息曝光并显影后,能够在光刻胶表面产生良好的正弦阵列表面结构,之后采用光刻胶热熔技术可将光刻胶的正弦阵列结构转变为微柱透镜阵列,且实验结果良好。     

Fabrication of a Macroporous Microwell Array for Surface‐Enhanced Raman Scattering

Here, a colloidal templating procedure for generating high‐density arrays of gold macroporous microwells, which act as discrete sites for surface‐enhanced Raman scattering (SERS), is reported. Development of such a novel array with discrete macroporous sites requires multiple fabrication steps. First, selective wet‐chemical etching of the distal face of a coherent optical fiber bundle produces a microwell array. The microwells are then selectively filled with a macroporous structure by electroless template synthesis using self‐assembled nanospheres. The fabricated arrays are structured at both the micrometer and nanometer scale on etched imaging bundles. Confocal Raman microscopy is used to detect a benzenethiol monolayer adsorbed on the macroporous gold and to map the spatial distribution of the SERS signal. The Raman enhancement factor of the modified wells is investigated and an average enhancement factor of 4 × 10⁴ is measured. This demonstrates that such nanostructured wells can enhance the local electromagnetic field and lead to a platform of ordered SERS‐active micrometer‐sized spots defined by the initial shape of the etched optical fibers. Since the fabrication steps keep the initial architecture of the optical fiber bundle, such ordered SERS‐active platforms fabricated onto an imaging waveguide open new applications in remote SERS imaging, plasmonic devices, and integrated electro‐optical sensor arrays.     

Micromachining for improvement of integrated ultrasonic transducersensitivity

A micromachined diaphragm structure for integrated ultrasonic transducers is discussed. The micromachining significantly reduces a large parasitic capacitance, resulting in improved sensitivity compared with identical transducers on solid substrates. For the particular geometry tested, sensitivity improved 8.9 dB; this result matches a prediction of 10.9 dB, based on a simple model, reasonably well. This level of improvement is considered significant for the applications under consideration (medical imaging and nondestructive evaluation)     

An in-probe receiver amplifier with 3 dB noise figure and 50 dB dynamic range for medical ultrasound imaging using CMUTs

This paper presents the design and measurements of an in-probe receiver amplifier for ultrasound imaging applications using a capacitive micromachined ultrasonic transducer (CMUT). In such applications, the noise and the dynamic range play very important roles, as the former dictates the minimum input signal level and the latter defines the maximum input signal level that can be applied to a system. This work concentrates on both of these specifications. The amplifier consists of a transimpedance amplifier followed by a voltage gain stage implemented using a current feedback amplifier. It is designed and fabricated using a 180 nm CMOS process. A noise figure of 3 dB is measured for a CMUT model with 10–30 MHz frequency range. The amplifier shows a dynamic range of 50 dB with 0.8 % total harmonic distortion for the full scale input current of 7 µA peak-to-peak.     

太赫兹单像素计算成像原理及其应用(特邀)

太赫兹成像技术具有透视性、安全性以及光谱分辨能力等独特优点,有着广泛的应用前景。由于太赫兹面阵探测器的技术成熟度低、价格昂贵,太赫兹成像技术在较长时间内以单点扫描方案为主,存在系统复杂、成像耗时长等问题。近年来,基于计算成像算法的太赫兹单像素成像技术发展迅速,成为了获取太赫兹图像的重要途径之一。文章综述了太赫兹单像素计算成像技术的基本原理、技术实现手段和应用前景,总结了现存的一些关键问题,并展望了一些今后可能的发展方向。     

New considerations in the design of microstrip antennas

Printed microstrip antennas and arrays are known to have limitations in terms of bandwidth and efficiency, all imposed by the very presence of the dielectric substrate. Microstrip arrays printed on a very thin film and separated from the ground-plane by foam were successfully designed; however, the fabrication difficulties associated with the use of foam considerably increases the fabrication cost. In this paper, a new concept is presented. Rather than using a superstrata geometry, the “printed circuit” is etched out of metal and supported at “strategic points” by (metallic or nonmetallic) posts. The main motivation for this work was to obtain large microstrip arrays, which exhibit a higher efficiency than conventional ones, and can be fabricated using inexpensive large quantity production techniques. However, this technology was also used to develop many new types of microstrip antennas. Microstrip elements and arrays based on this technology were designed and fabricated for the L, S, and C bands     

改性PbTiO3陶瓷的发展及应用

在以往几年内,已经研制出了一些具有大的各向异性压电特性的改性PbTiO_8陶瓷。它们在水声和超声技术的应用上是一些很有前途的材料。本文简要地叙述了PbTiO_8陶瓷的改性,着重介绍了这些改性后的材料在水声和超声换能器上的应用。