Micromachined magnetic ultrasound transducer in post-processed CMOS
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Micromachined magnetic ultrasound transducer in post-processed CMOS Rohit Viswanathan*, Nicholas Jankowski*, Whye-Kei Lye*, Gregory Petit Dufrenoy*, Michael J. Harrison*, John A. Hossack†, Travis N. Blalock*, and Michael L. Reed*† *Department of Electrical and Computer Engineering, †Department of Biomedical Engineering University of Virginia, Charlottesville, VA
ABSTRACT This paper presents a novel MEMS Ultrasound Electro-Magnetic transducer. With advances in CMOS MEMS fabrication processes [2] we can explore and build miniature devices which could only be designed till a few years back. As our understanding in MEMS evolved ,we explored the use of Electro-Magnetism as an effective way to produce ultrasound waves. Thus we can use a highly efficient and inexpensive fabrication technique to fabricate transducers with a fairly good capability to produce and detect ultrasound waves. The transducer consists of 2 concentric spiral coils, one carrying an AC current (which is tethered to the substrate at one end and free to vibrate at the other ,also called the “Flapper”) and other coil carrying DC current (enveloping the inner coil, fixed and called “Stator”). The force arising from the interaction of the coupled magnetic fields induces a mechanical vibration of the flapper structure. The transducer serves as an actuator or a sensor (where we simply apply a pressure force on the flapper and note the frequency response of the flapper). The current mode helps to associate the transducer with front-end electronics, which is one of the most critical components of ultrasound imaging systems Advantages of this approach as compared to traditional PZT ceramics and capacitative micromachined devices are explored. Different dimensions of the transducer to accommodate the limitations in the processes are explored and a comparison of the parameters is presented. Potential uses and future challenges are discussed.
INTRODUCTION Ultrasound has two main characteristics that make it well suited for therapeutic and imaging purposes. The first is a good beam penetration at frequencies where the wavelengths are on the order of millimeters that allows for focusing deep into the tissue with sharp margins and good control over the power deposition pattern .The second feature is the technical feasibility of constructing ultrasound sources of almost any size and shape.[4] Piezoelectric materials such as lead zirconate titanate (PZT) are often the choice for fabricating imaging ultrasound transducers. However with demand for a variety of ultrasound applications increasing at a tremendous pace and desire to keep fabrication process repeatable and cheap, it has become increasing difficult to integrate these materials as device dimensions shrink .Often,
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in low voltage circuits , piezoel
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