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No description available.

No description available.

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Free vibration of composite piezoelectric transducers is analyzed by a modified two-dimensional axisymmetric finite element in this study. The modified finite element is formulated based on assumed displacement fields and electric potential, and is capable for three-dimensional analyses of vibration of axisymmetric composite piezoelectric structures. Different arrangements and radius of piezoelectric disk and metal ring, with various thicknesses will be considered and first radial vibration frequencies are derived and their mode shapes are demonstrated, which might be helpful for the design of radial composite transducers. Also, the results of the present study will be compared with those by other methods.

This work presents the fabrication, modeling, and characterization of two first-generation acoustic in-plane pressure gradient sensors. The first is a micromachined piezoelectric microphone. The microphone structure consists of a semi-rigid beam structure that rotates about torsional pivots in response to in-plane pressure gradients across the length of the beam. The rotation of the beam structure is transduced by piezoelectric cantilevers, which deflect when the beam structure rotates. Sensors with both 10 and 20-μm-thick beam structures are presented. An analytical model and multi-mode, multi-port network model utilizing finite-element analysis for parameter extraction are presented and compared to acoustic sensitivity measurements. Directivity measurements are interpreted in terms of the multi-mode model. A noise model for the sensor and readout electronics is presented and compared to measurements. The second sensor is a capacitive sensor which is comprised of two vacuum-sealed, pistons coupled to each other by a pivoting beam. The use of a pivoting beam can, in principle, enable high rotational compliance to in-plane small-signal acoustic pressure gradients, while resisting piston collapse against large background atmospheric pressure. A design path towards vacuum-sealed, surface micromachined broadband microphones is a motivation to explore the sensor concept. Fabrication of surface micromachined prototypes is presented, followed by finite element modeling and experimental confirmation of successful vacuum-sealing. Dynamic frequency response measurements are obtained using broadband electrostatic actuation and confirm a first fundamental rocking mode near 250 kHz. Successful reception of airborne ultrasound in air at 130 kHz is also demonstrated, and followed by a discussion of design paths toward improve signal-to-noise ratio beyond that of the initial prototypes presented. A method of localizing sound sources is demonstrated using the piezoelectric sensor. The localization method utilizes the multiple-port nature of the sensor to simultaneously extract the pressure gradient and pressure magnitude components of the incoming acoustic signal. An algorithm for calculating the sound source location from the pressure gradient and pressure magnitude measurement is developed. The method is verified by acoustic measurements performed at 2 kHz. / text

The origin of this project was the problem of foot ulceration in the diabetic patient. Whilst the principal cause of the susceptibility to foot ulceration in patients with this pathology, and others such as leprosy, is abnormal physiology, there is no doubt the mechanical forces that are applied to the foot surface are a major factor. Currently several devices are available to measure the perpendicular forces at the foot-shoe interface (ie. the "pressure" distribution). However the full assessment of tri-axial forces at this interface has largely eluded quantification despite the fact that it has been demonstrated that shear forces may be of equal significance to those of direct pressure. The purpose of this study was to develop a transducer for the assessment of the three dimensional forces experienced, over a very localised area, at the foot-shoe interface during normal functional locomotor activity. The application of such a device in the clinical setting will provide valuable information for the medical and orthotic professions and thereby assist them in the treatment of many patients who are at risk of foot ulceration. The principle for a transducer to be embedded in an insole and utilising electromagnetic induction between air-cored coils was proposed. Coil winding techniques were developed to enable manufacture of coils within constrained sizes. Examination of the inductive coupling possible between the coils and its variation with displacement in space was carried out using a purpose built testing rig. Transducer electronics were designed and manufactured and a data logging system implemented. Various approaches to the derivation of 3D interpretation from the system were implemented in software. An examination of the accuracy of the approach was made. A prototype design and manufacturing method was suggested utilising a specific grade of silicone rubber. The results indicated that the design proposed could be implemented effectively in a size suited to in-shoe application. The design offers a relatively low cost method which could be adapted for use in many applications requiring three dimensional displacement or force measurements.

No description available.

No description available.