In this paper, implementing a guard-ring electrode in a capacitive Transducer system is described.The performance of the Transducers with and without a guard-ring in terms of output linearity and dynamic range is investigated and deviations from the expected theoretical results are reported.The two-terminal capacitors perform well only for a small gap distance in the range of 2-3 mm while the three-terminal sensor (50 mm diameter) demonstrates a very good performance for a wide range of 0.5-5 mm. For a gap distance of 3 mm. the slope deviation for the sensors without a guard-ring is in the range of 15%-29%. Whereas for the system with a guard-ring is only 6%, which clearly shows the range effectiveness of the third electrode for such Transducer systems.

In this paper, application of a capacitive sensor system in recording small displacements is discussed. Through using a simple Transducer and a monitoring circuit, change in capacitance has been detected as a function of the capacitor air-gap distance. There is a linear relation between gap distance and output of a sensor for a wide gap range of 0.5 to 5 mm. The reported system provides means for measuring displacements up to 5 mm with a resolution better than 250 nm. By decreasing the dynamic range of the Transducer to 250 mm, a small displacement of the order of 100nm is detectable. With the present system, a minimum displacement of about 200 nm (200 ppm) for the gap distance of 1 mm is obtained. However, through changing the sensor design, the measuring circuit becomes capable of recording smaller distances of the order of 10 nm at this operating range.

Transducers as a heart of ultrasonic heads are one of the most important parts of systems. Among them, sandwiching, adhesive and screw Transducers are more applicable, so the applications of ultrasonic waves will widely improve if they are designed correctly. The calculations of dimensions, especially the lengths of pieces, are very important in Transducer designing because even a very small miscalculation causes differences in vibration conditions, and afterwards, decreasing or appliance malfunctions will result. The differential equation of the longitudinal vibration mode with its boundary conditions is solved to determine the length of the Transducer. After that, the Transducer is modeled with the finite element method to evaluate the theoretical calculations, and their resonance frequency is also determined by modal analysis. Finally a prototype Transducer is manufactured and tested. The results of theoretical, finite element modeling and experimental tests are very close to each other, so this method was found to be a suitable base for Transducer designing.

This paper has been devoted to such approach for designed and fabricated the dual frequency piezoelectric ultrasonic Transducer having longitudinal vibrations for high power application. By using analytical analysis, the resonance frequency equations of the Transducer in the half-wave and the all-wave vibrational modes were determined for the assumed first resonance frequency of 25kHz. According to the resonance frequency equation, four Transducers with two different constructions (Type A and B) were designed and made. The finite element method provided by commercial ANSYS was employed for FEM modeling and analysis of the Transducer to observe its vibration behavior. It was shown that there is a good agreement between the experimental and FEM results. The designed and fabricated Transducer can be excited to vibrate at two resonance frequencies, which correspond to the half-wave and the all-wave vibrational modes of the Transducer, and use of Type B Transducer greatly increased the mechanical quality factor (Q) of piezoelectric Transducers.