Daesil Kang

A micro-machined source transducer for a parametric array in air.

Parametric array applications in air, such as highly directional parametric loudspeaker systems, usually rely on large radiators to generate the high-intensity primary beams required for nonlinear interactions. However, a conventional transducer, as a primary wave projector, requires a great deal of electrical power because its electroacoustic efficiency is very low due to the large characteristic mechanical impedance in air. The feasibility of a micro-machined ultrasonic transducer as an efficient finite-amplitude wave projector was studied. A piezoelectric micro-machined ultrasonic transducer array consisting of lead zirconate titanate uni-morph elements was designed and fabricated for this purpose. Theoretical and experimental evaluations showed that a micro-machined ultrasonic transducer array can be used as an efficient source transducer for a parametric array in air. The beam patterns and propagation curves of the difference frequency wave and the primary wave generated by the micro-machined ultrasonic transducer array were measured. Although the theoretical results were based on ideal parametric array models, the theoretical data explained the experimental results reasonably well. These experiments demonstrated the potential of micro-machined primary wave projector.

Design and Fabrication of the High Directional Ultrasonic Ranging Sensor to Enhance the Spatial Resolution

A new ultrasonic ranging transducer with high directionality is developed to enhance the spatial resolution in the pulse-echo measurement in air. The concept of the parametric transmitting array is applied to the design. A high-performance piezoelectric micro-machined ultrasonic transducer (pMUT) array is designed and fabricated in this study. The indirectly generated pulse has a beam-width of around 5deg and a sound pressure level (SPL) of over 85 dB at the peak. For a practical application, the higher sound pressure level should be achieved.

Microelectromechanical-systems-based parametric transmitting array in air - Application to the ultrasonic ranging transducer with high directionality

A new ultrasonic ranging transducer with high directionality is proposed because ultrasonic transducers generally need to be designed for high directionality to enhance the spatial resolution in the pulse-echo measurement in air. Parametric transmitting array as a generation method of the high directional ultrasonic wave is used in the transducer design. Reduction of the transducer size decreases the efficiency of the secondary wave generation in the parametric transmitting array. To overcome this problem, MEMS-based transducer radiating high intensity sound is required in the parametric array. A high-performance PZT MEMS ultrasonic transducer composed of many small membrane-type radiator units is designed and fabricated by bulk micro-machining, and the secondary wave generated by the transducer is observed. The 40-kHz difference tone, the measuring signal, is generated using 100- and 140-kHz primary tones by the PZT MEMS ultrasonic transducer. The difference tone has a half-power beam width of around 5 deg and a sound pressure level of over 85 dB at the peak. For the real application, higher sound pressure level should be achieved, and this will be included in the future work

Micro-Machined Capacitive Linear Encoder with a Mechanical Guide

Contact-type Linear Encoder-like Capacitive Displacement Sensor (CLECDiS) is a novel displacement sensor which has wide measurable range with high resolution. The sensor, however, is very sensitive to relative rotational alignment between stator and mover of the sensor as well as its displacement. In addition to, there can be some disturbances in the relative rotational alignment, so some noises occur in the sensor`s output signal by the disturbances. This negative effect of the high sensitivity may become larger as increasing sensitivity. Therefore, this negative effect of the high sensitivity has to be compensated and reduced to achieve nanometer resolution of the sensor. In this study, a new type capacitive linear encoder with a mechanical guide is presented to reduce the relative rotational alignment problem. The presented method is not only to reduce the alignment problem, but also to assemble the sensor to the stage conveniently. The method is based on a new type CLECDiS that has mechanical guide autonomously. In the presented sensor, when the device is fabricated by micro-machining, the guide-rail is also fabricated on the surface of the sensor. By the direct fabrication of the guide-rail with high precision micro-machining, errors of the guide-rail can be reduced significantly. In addition, a manual yaw alignment is not required to obtain large magnitude of the output signal after the assembly of the sensor and the stage. The sensor movement is going to follow the guide-rail automatically. The prototype sensor was fabricated using the presented method, and we verify the feasibility experimentally.

Drift compensation technique of an area-varying capacitive displacement sensor for nanometer resolution

Since a widely-used gap variation type capacitive displacement sensor has small measurable range, an area-variation type capacitive displacement sensor was proposed for a larger measurable range. The area-variation type sensors, however, may show considerably large drifts in its out signals. The drift is thought to be caused by such parameters as stage alignment errors, thermal effects, external electric waves, etc. In this study, the drift is successfully reduced without loss in SNR (signal to noise ratio) by adopting two sets of electrodes.

Optimization of a capacitive sensor for high dynamic range

The capacitive sensor has a simple structure, compact size and low cost, but a small dynamic range. The small range is caused by use of gap variation. If the sensor takes area variation type with one plate moving horizontally, it can have a large measurable range. While the area variation has relatively low sensitivity, some studies have found methods to improve the sensitivity. Even though the methods are effective, parameters of the results are limited and 2 dimensional. This study provides more practical and 3 dimensional analysis and suggests relations between parameters. Using the results, the optimized design parameters of a high dynamic range capacitive sensor can be found.