Università degli Studi di Roma3
Dipartimento di Ingegneria Elettronica
1. CAPACITIVE MICROFABRICATED ULTRASONIC TRANSDUCERS (CMUT)
G. Caliano, A. Iula, M. Pappalardo
Collaborations: Dip. Ing. dell'Inf. e Ing. Elettrica Universita' di Salerno, CNR IMM Roma, Fondazione Bruno Kessler (FBK) Trento, Maxim IP SpA
2. High power ultrasonic actuators
A. Iula, G. Caliano
Collaborations: Dip. Ing. dell'Inf. e Ing. Elettrica Universita' di Salerno, CNR dAc Roma, CSIC InAc Madrid}
3. Ultrasound Imaging for Biometric Recognition
A. Iula, G. Caliano
Collaborations: Dip. Ing. dell'Inf. e Ing. Elettrica Universita' di Salerno, CNR IdAc Roma, CSIC InAc Madrid}
CAPACITIVE MICROFABRICATED ULTRASONIC TRANSDUCERS (CMUT)
G. Caliano, A. Iula, M. Pappalardo
Medical ultrasonography is a powerful and cost-effective diagnostic technique. To date, high-end medical imaging systems are able to efficiently implement real-time image formation techniques that can dramatically improve the diagnostic capabilities of ultrasound. Highly performing and thermally efficient ultrasound probes are then required to successfully enable the most advanced techniques. In this context, ultrasound transducer technology is the current limiting factor. Capacitive micromachined ultrasonic transducers (CMUTs) are micro-electro-mechanical systems (MEMS) based devices that have been widely recognized as a valuable alternative to piezoelectric transducer technology in a variety of medical imaging applications. Wideband operation, good thermal efficiency, and low fabrication cost, especially for those applications requiring high-volume production of small-area dice, are strength factors that may justify the adoption of this MEMS technology in the medical ultrasound imaging field.
Capacitive ultrasonic transducers, consisting of thin membranes scratched over a conducting backplate, offer many advantages compared to piezoelectric transducers, such as low impedance mismatch, low energy density and low cost. Recent developments in micro fabrication technology have spurred novel design for transducers in the ultrasonic range both for air and water applications; in fact, surface micromachining technology allows size reduction of the membranes up to tens of micron in diameter and 3000 - 5000 Å in thickness in order to enable MHz range operations; further, good sensitivity is easily obtained with an array layout.
The CMUT transducer inherently has a larger bandwidth for immersion application and, because it takes advantage of the well-established microelectronic technology it is, potentially, less expensive and gives much more flexibility in the design of complex 1D and 2D arrays than piezoelectric transducers. In perspective, a further advantage of the CMUT is the possibility to be integrated with the front-end electronics on the same silicon wafer.
We have reported the design, development, fabrication, and characterization of a 12-MHz ultrasound probe for medical imaging, based on a CMUT array. The CMUT array is microfabricated and packed using a novel fabrication concept specifically conceived for imaging transducer arrays. The performance of the developed probe is optimized by including analog front-end reception electronics. Characterization and imaging results are used to assess the performance of CMUTs with respect to conventional piezoelectric transducers.
Publications in 2011
1) G. Caliano, A.S. Savoia, A. Iula, “An Automatic Compact Schlieren Imaging System for Ultrasound Transducers Testing”; in press on IEEE Trans. On Ultrasonic, Ferroelectrics and Frequency Control; December 2011
2) A. Savoia, G. Caliano, B. Mauti, M. Pappalardo, “Performance Optimization of a High Frequency CMUT Probe for Medical Imaging”, 2011 IEEE Ultrasonics Symposium, Orlando (USA), 2011;
3) G. Caliano, N. Lamberti, A. Savoia, A. Iula, “A Track-pad Device Based on a Piezoelectric Bimorph”, 2011 IEEE Ultrasonics Symposium, Orlando (USA), 2011; pp. 1676-1679
4) A. Savoia, G. Caliano, M. Pappalardo: “Ultrasound Probes Fabricated on Silicon for Medical Imaging”; Nanotechitaly 2011 International Conference, 23-25 November, Venice, Italy; p. 349-350
5) P. Bellutti, M. Boscardin, A. Bagolini, A.S. Savoia, G. Caliano: “Capacitive Ultrasonic Transducers for medical applications: technological optimization at FBK”; Nanotechitaly 2011 International Conference, 23-25 November, Venice, Italy; pp.305-306
High power ultrasonic actuators
A. Iula, G. Caliano
Ultrasonic motors are based on the concept of driving a rotor by a mechanical vibration excited on a stator via piezoelectric effect. The rotor is in contact with the stator and the driving force is the frictional force between rotor and stator. To transform the mechanical vibration of the stator in a rotor rotation, a travelling wave can be excited on the stator surface. Several methods to excite a travelling wave have been proposed in literature; in all cases the travelling wave is generated by the combination of two standing waves whose phases differ by 90 degree, both spatially and temporally.
The authors have proposed a high power ultrasonic motor composed of a steel ring stator and two cone shaped rotors which are pressed in contact to the stator by a spring-nut prestress system. A well sustained travelling wave is excited in the stator by two or more pairs of power transducers. The motor weighed 0.67 kg, and had a working frequency of 3.6 kHz, maximum rotational speed of 116 rpm, and static torque of 0.94 Nm.
A similar high power travelling wave generation system is employed to experimentally investigate the interaction between the travelling wave and the fluid.
Publications in 2011
1) A. Iula, N. Lamberti, A. Savoia, G. Caliano, "Fluid film force control in lubricated journal bearings by means of a travelling wave generated with a piezoelectric actuators' system", {\em 2011 International Congress on Ultrasonics, AIP Conf. Proc.}, 1433, pp. 697-700, 2011.
Ultrasound Imaging for Biometric Recognition
A. Iula, G. Caliano
Biometrics refers to methods for uniquely recognizing humans based upon one or more physical or behavioral traits. Although biometrics emerged from its extensive use in law enforcement to identify criminals it is being increasingly used to establish person recognition in a large number of civilian applications.
Ultrasound techniques can be profitably exploited for biometric recognitin of characteristics like fingerprint, hand geometry, palmprint, hand vein pattern. Ultrasounds have some intrinsic advantages with respect to other methods; in fact they are not sensitive to the surface contaminations, such as stain, dirt, oil, ink and, more important, they provide information not only of the skin surface but also of the volume under the investigated skin region. Furthermore, ultrasounds detect life (Doppler mode) and therefore they can immediately detect fakes.
Both finger and hand palm regions were investigated by researchers of this unit by exploiting a commercail ultrasound machine and both piezoelectric and cMUT probes. First results have demonstrated that for the fingerprint the currently available probes are not able to provide a sufficient image resolution yet the technique should be tested again when higher frequency probes will be available (20 MHz and up). On the contrary results obtained analyzing the hand palm region were promising and allowed to define some possible biometric characteristics: internal hand geometry, full 3D palmprint and 3D hand vein.
Publications in 2011
1) A. Iula, A. Savoia, G. Caliano, “Capacitive Microfabricated Ultrasonic Transducers for Biometric Applications”, {\em Microelectronic Engineering}, Vol. 88, Issue 8, 2011, pp. 2278-2280.
2) N. Lamberti, A. Savoia, G. Caliano, A. Iula, “A High Frequency cMUT probe for Ultrasound Imaging of Fingerprints”; {\em Sensors & Actuators} A 172-2, December 2011; pp. 561-569
3) A. Iula, M. De Santis, "Experimental evaluation of an ultrasound technique for the biometric recognition of human hand anatomic elements", {\em Ultrasonics}, vol. 51, no. 6, Pages 683-688, 2011.