Combining photoacoustic and ultrasonic imaging allows both optical and acoustic properties to be displayed simultaneously. In this paper, we describe a dual-band transducer for implementing such a multimodality imaging setup. The transducer exhibits two frequency bands so that it matches the frequency of interest in both imaging methods. An optical fiber is included in the center so that it is inherently coregistered. The transducer was fabricated from lithium niobate and comprises two concentric rings whose center frequencies are 4.9 MHz and 14.8 MHz. Pulse-echo measurements and phantom imaging were performed to demonstrate its performance characteristics.

This paper presents the first monolithic multidirection-looking ultrasonic imager for minimally invasive medical diagnosis. In contrast to the traditional planar ultrasonic imagers that can only view in one direction, this 3-D array is able to view in multiple directions by using seven planar imagers integrated on a hexagonal silicon prism. Each facet on the prism is integrated with a planar 1-or 2-D capacitive-micromachined ultrasonic-transducer imager array for viewing in a specific direction. Each facet is connected by a flexible dielectric membrane, which is monolithically fabricated with the transducers. The dielectric membranes also support the thin-film electrical interconnects between the arrays on different facets. The substrate is folded into a hexagonal prism after completion of the transducer microfabrication process. With this architecture, a one flip-chip bonded or monolithically integrated front-end electronic circuit will be able to manage all the imagers on the 3-D array. The number of bonding wires for a connection to external electronics can therefore be reduced. Imager prisms, which are ranging from 1 to 4 mm in diameter and 2 to 4 mm in length, and positioned to view in seven directions, have been prototyped. Preliminary testing shows that the imager transducers behaved consistently before and after the assembly process. Applications of this 3-D imager array include capsule ultrasound endoscope, intravascular ultrasound, and other internal imaging needs.[ 2006-0269]Index Terms-Acoustic transducers. I. INTRODUCTIONE VOLVED from sonar technology, ultrasound imaging[1]-[3] has been widely used for medical diagnosis since the early 1970s. In this imaging process, high-frequency acoustic waves interact with biological tissue, so that the images of anatomical structures inside the body can be revealed in real time from the reflected ultrasonic pulses. Compared with other medical imaging techniques (X-ray, MRI, CT, etc.) [4], [5], the advantages of ultrasonic imaging include nonradioactivity, real-time acquisition, affordable equipment cost, and feasibility for the miniaturization in minimally invasive applications. In Manuscript

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The purpose of this study is to propose and implement a new type of high-frequency single-element annular transducer (SEAT) with increased bandwidth. Such a broadband transducer can be used to improve the axial resolution and/or to perform contrast and tissue harmonic imaging. Compared with the conventional single element uniform thickness (SEUT), the SEAT has an annular geometry with the thickness of the piezoelectric material increasing from the center to the outside. The SEAT consisted of six subelements, whose thickness ranged from 60 μ m to 110 μ m. Note that each side of annular pattern is electrically connected by a single electrode. For comparisons, both SEAT and SEUT transducers were designed and fabricated. The mean center frequencies of the SEUT and SEAT were 41.3 MHz and 42.4 MHz, respectively. The -6 dB fractional bandwidths were 69% for the SEUT and 82% for the SEAT. The two-way insertion losses of the SEUT and SEAT were 16.4 dB and 19.5 dB, respectively. The measured -6 dB lateral beam widths were 92 μ m for the SEUT and 108 μ m for the SEAT. The depth of field of SEAT was increased by 33.5 % as compared with the SEUT. Fabrication methods for such transducers were successfully developed and implemented. The SEAT enhanced the overall bandwidth and with a tradeoff of slight degradation in sensitivity. Finally, this type of transducers can also be used for multiple band imaging.

A capacitive micromachined ultrasonic transducer (CMUT) array for minimally invasive medical diagnosis has been developed. Unlike traditional ultrasonic transducers, which generally use a bulky piece of substrate, this transducer array was integrated on a 40-µm-thick micromachined silicon substrate into a probe shape with a typical shank width of 50-80 µm and a shank length of 4-8 mm. For 1-D arrays, 24-96 CMUT devices were integrated on one such silicon probe and formed an accurately configured phase array. In addition to miniaturization, reduction of the substrate thickness also decreases the intertransducer crosstalk due to substrate Lamb waves. Due to its miniature size, this array can be placed or implanted close to the target tissue/organ and can perform high-resolution high-precision diagnosis and stimulation using high-frequency ultrasounds. The issue of conflict between resolution and penetration depth of ultrasonic diagnosis can therefore be resolved. A two-layer polysilicon surface micromachining process was used to fabricate this device. Suspended polysilicon membranes of diameters ranging from 20 to 90 µms and thicknesses from 1.0 to 2.5 µm were used to generate and detect ultrasounds of frequencies ranging from 1 to 10 MHz. B-mode imaging using this transducer array has been demonstrated.[ 2007-0125]Index Terms-Acoustic devices, acoustic transducers, actuators. I. INTRODUCTIONU LTRASOUND has been widely used for medical diagnosis [1] and stimulation [2] for more than 40 years. In an ultrasonic diagnostic process, low-power acoustic waves are used to interact with tissue or organs, and the reflected and transiting ultrasounds can reveal information about anatomical structures, tissue characteristics, blood flow velocity, and muscle movement/contraction in real time. For example, by measuring the propagation speed of ultrasounds in tissue, the tissue temperature can be determined [3]. Piezoelectric thin films [4], [5] have been the most widely used materials for fabricating medical ultrasound transducers. Piezoelectric ultrasonic transducers have been arranged in 1-or 2-D arrays [4], [5], and they are used in different areas of medical diagnosis and stimulation, including destroying cancerous tumors. As a mature technology Manuscript