A new detection method for capacitive micromachined ultrasonic transducers

Cataloged from PDF version of article.Capacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They consist of many small circular membranes that are connected in parallel. In this work, we report; a new detection method for cMUTs. We model the membranes as capacitors and the interconnections between the membranes as inductors. This kind of LC net-work is called an artificial transmission line. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the frequency of the signal through it. By measuring the electrical length of the artificial line at a high RF frequency (in the gigahertz range), the vibrations of the membranes can be detected in a very sensitive manner. Far the devices we measured, we calculated the minimum detectable displacement to be in the order of 10(-5) Angstrom/root Hz with a possible improvement to 10(-7) Angstrom/root Hz

Analytic Expressions for the Ultimate Intrinsic Signal-to-Noise Ratio and Ultimate Intrinsic Specific Absorption Rate in MRI

Cataloged from PDF version of article.The ultimate intrinsic signal-to-noise ratio is the highest possible signal-to-noise ratio, and the ultimate intrinsic specific absorption rate provides the lowest limit of the specific absorption rate for a given flip angle distribution. Analytic expressions for ultimate intrinsic signal-to-noise ratio and ultimate intrinsic specific absorption rate are obtained for arbitrary sample geometries. These expressions are valid when the distance between the point of interest and the sample surface is smaller than the wavelength, and the sample is homogeneous. The dependence on the sample permittivity, conductivity, temperature, size, and the static magnetic field strength is given in analytic form, which enables the easy evaluation of the change in signal-to-noise ratio and specific absorption rate when the sample is scaled in size or when any of its geometrical or electrical parameters is altered. Furthermore, it is shown that signal-tonoise ratio and specific absorption rate are independent of the permeability of the sample. As a practical case and a solution example, a uniform, circular cylindrically shaped sample is studied. Magn Reson Med 66:846–858, 2011. © 2011 Wiley-Liss, In

Theory and analysis of electrode size optimization for capacitive microfabricated ultrasonic transducers

Cataloged from PDF version of article.Theoretical analysis and computer simulations of capacitive microfabricated ultrasonic transducers indicate that device performance can be optimized through judicious patterning of electrodes. The conceptual basis of the analysis is that electrostatic force should be applied only where it is most effective, such as at the center of a circular membrane. If breakdown mechanisms are ignored, an infinitesimally small electrode with an infinite bias voltage results in the optimal transducer, A more realistic design example compares the 3-dB bandwidths of a fully metalized transducer and a partially metalized transducer, each tuned with a lossless Butterworth network. It is found that the bandwidth of the optimally metalized device is twice that of the fully metalized device

Micromachinable ultrasonic leaky wave air transducers

Cataloged from PDF version of article.Ultrasonic air transducers using leaky waves on thin membranes are analyzed using perturbation and normal mode approaches. The transducers utilize the efficient coupling of ultrasonic energy to air through radiation of these leaky wave modes when their phase velocity is close to the sound speed in air. Theoretical results on optimum transducer dimensions and bandwidth estimation show that a minimum conversion loss of 8.7 dB with a 78% fractional bandwidth is possible. Common micromachining materials are shown to be suitable transducer materials and result in feasible devices. This is demonstrated by fabricating a 580 kHz transducer using a silicon membrane bonded to a ring of PZT-5H. With this configuration the transducer is self line focusing. Results of through transmission experiments on silicon and transmission images on paper are reported. © 1998 American Institute of Physic

Micromachined two-dimensional array piezoelectrically actuated transducers

Cataloged from PDF version of article.This letter presents micromachined two-dimensional array flextensional transducers that can be used to generate sound in air or water. Individual array elements consist of a thin piezoelectric ring and a thin, fully supported, circular membrane. We report on an optimum design for an individual array element based on finite element modeling. We manufacture the transducer in two-dimensional arrays using planar silicon micromachining and demonstrate ultrasound transmission in air at 2.85 MHz. Such an array could be combined with on-board driving and an addressing circuitry for different applications. © 1998 American Institute of Physic

A sensitive detection method for capacitive ultrasonic transducers

Cataloged from PDF version of article.We report a sensitive detection method for capacitive ultrasonic transducers. Detection experiments at 1.6 MHz reveal a minimum detectable displacement around 2.5 x 10(-4) Angstrom/root Hz. The devices are fabricated on silicon using surface micromachining techniques. We made use of microwave circuit considerations to obtain a good displacement sensitivity. Our method also eliminates the dependence of the sensitivity on the ultrasound frequency, allowing the method to be used at low audio frequency and static displacement sensing applications. (C) 1998 American Institute of Physics

Peptide functionalized superparamagnetic iron oxide nanoparticles as MRI contrast agents

Cataloged from PDF version of article.Magnetic resonance imaging (MRI) attracts great attention in cellular and molecular imaging due to its non-invasive and multidimensional tomographic capabilities. Development of new contrast agents is necessary to enhance the MRI signal in tissues of interest. Superparamagnetic iron oxide nanoparticles (SPIONs) are used as contrast agents for signal enhancement as they have revealed extraordinary magnetic properties at the nanometre size and their toxicity level is very low compared to other commercial contrast agents. In this study, we developed a new method to functionalize the surface of SPIONs. Peptide amphiphile molecules are used to coat SPIONs non-covalently to provide water solubility and to enhance biocompatibility. Superparamagnetic properties of the peptide-SPION complexes and their ability as contrast agents are demonstrated. In vitro cell culture experiments reveal that the peptide-SPION complexes are biocompatible and are localized around the cells due to their peptide coating

Surface micromachined capacitive ultrasonic transducers

Cataloged from PDF version of article.The current state of a novel technology, surface microfabricated ultrasonic transducers, is reported. Experiments demonstrating both air and water transmission are presented. Air-coupled longitudinal wave transmission through aluminum is demonstrated, implying a 110 dB dynamic range for transducers at 2.3 MHz in air. Water transmission experiments from 1 to 20 MHz are performed, with a measured 60 dB SNR at 3 MHz. A theoretical model is proposed that agrees well with observed transducer behavior. Most significantly, the model is used to demonstrate that microfabricated ultrasonic transducers constitute an attractive alternative to piezoelectric transducers in many applications

Design of a Gd-DOTA-Phthalocyanine Conjugate Combining MRI Contrast Imaging and Photosensitization Properties as a Potential Molecular Theranostic

Cataloged from PDF version of article.The design and synthesis of a phthalocyanine - Gd-DOTA conjugate is presented to open the way to novel molecular theranostics, combining the properties of MRI contrast imaging with photodynamic therapy. The rational design of the conjugate integrates isomeric purity of the phthalocyanine core substitution, suitable biocompatibility with the use of polyoxo water-solubilizing substituents, and a convergent synthetic strategy ended by the use of click chemistry to graft the Gd-DOTA moiety to the phthalocyanine. Photophysical and photochemical properties, contrast imaging experiments and preliminary in vitro investigations proved that such a combination is relevant and lead to a new type of potential theranostic agent

The rare cancer network: ongoing studies and future strategy.

The Rare Cancer Network (RCN) was formed in the early 1990's to create a global network that could pool knowledge and resources in the studies of rare malignancies whose infrequency prevented both their study with prospective clinical trials. To date, the RCN has initiated 74 studies resulting in 46 peer reviewed publications. The First International Symposium of the Rare Cancer Network took place in Nice in March of 2014. Status updates and proposals for new studies were heard for fifteen topics. Ongoing studies continue for cardiac sarcomas, thyroid cancers, glomus tumors, and adult medulloblastomas. New proposals were presented at the symposium for primary hepatic lymphoma, solitary fibrous tumors, Rosai-Dorfman disease, tumors of the ampulla of Vater, salivary gland tumors, anorectal melanoma, midline nuclear protein in testes carcinoma, pulmonary lymphoepithelioma-like carcinoma, adenoid cystic carcinoma of the trachea, osteosarcomas of the mandible, and extra-cranial hemangiopericytoma. This manuscript presents the abstracts of those proposals and updates on ongoing studies, as well a brief summary of the vision and future of the RCN