Yub Je

Design of an ultrasonic sensor for measuring distance and detecting obstacles.

This paper introduces a novel method for designing the transducer of a highly directional ultrasonic range sensor for detecting obstacles in mobile robot applications. The transducer consists of wave generation, amplification, and radiation sections, and a countermass. The operating principle of this design is based on the parametric array method where the frequency difference between two ultrasonic waves is used to generate a highly directional low-frequency wave with a small aperture. The aim of this study was to design an optimal transducer to generate the two simultaneous longitudinal modes efficiently. We first derived an appropriate mathematical model by combining the continuum model of a bar and countermass with the compatibility condition between a piezoelectric actuator and a linear horn. Then we determined the optimal length of the aluminum horn and the piezoelectric actuator using a finite element method. The proposed sensor exhibited a half-power bandwidth of less than+/-1.3 degrees at 44.8 kHz, a much higher directivity than existing conventional ultrasonic range sensors.

A stepped-plate bi-frequency source for generating a difference frequency sound with a parametric arraya)

An ultrasonic radiator is developed to generate a difference frequency sound from two frequencies of ultrasound in air with a parametric array. A design method is proposed for an ultrasonic radiator capable of generating highly directive, high-amplitude ultrasonic sound beams at two different frequencies in air based on a modification of the stepped-plate ultrasonic radiator. The stepped-plate ultrasonic radiator was introduced by Gallego-Juarez et al. [Ultrasonics 16, 267-271 (1978)] in their previous study and can effectively generate highly directive, large-amplitude ultrasonic sounds in air, but only at a single frequency. Because parametric array sources must be able to generate sounds at more than one frequency, a design modification is crucial to the application of a stepped-plate ultrasonic radiator as a parametric array source in air. The aforementioned method was employed to design a parametric radiator for use in air. A prototype of this design was constructed and tested to determine whether it could successfully generate a difference frequency sound with a parametric array. The results confirmed that the proposed single small-area transducer was suitable as a parametric radiator in air.

The impact of micromachined ultrasonic radiators on the efficiency of transducers in air

The use of micromachined thin-film ultrasonic radiators to improve the efficiency of conventional in-air acoustic transducers is investigated. We conduct a theoretical investigation of the parameters that determine the efficiency of thin-film transducers, using a lumped parameter model, and show that the efficiency can be improved by choosing a radiating plate thickness that can be realized by micromachining. We also identified the problems that should be overcome to design and fabricate a micromachined ultrasonic transducer with the theoretically predicted efficiency. Based on the lumped parameter model, we showed that the problems can be resolved via an appropriate design scheme. A piezoelectric micromachined ultrasonic transducer is designed and fabricated to demonstrate the impact of the proposed design method. Test results for the fabricated radiator indicated that it provided an electroacoustic efficiency of 58.4%, up to 300% greater than either the unit previously fabricated by the authors or conventional unimorph ultrasonic transducers. An array of the proposed transducers was also designed, fabricated, and tested as a source transducer for a parametric array, since transducer efficiency is important for practical applications of a parametric array. The test results for the proposed transducer demonstrate its potential for improving the practicality of parametric array sources, such as parametric loudspeakers and directional ultrasonic ranging sensors.

Resonant frequency variations in a piezoelectric microcantilever sensor under varying operational conditions

The dependence of the resonant frequency of a piezoelectric microcantilever sensor (PEMS) on electrostatic discharge (ESD), oscillating voltage, dc bias and time was measured from its electrical response. Linear and nonlinear characteristics of the PEMS were analyzed using a lumped parameter model. In particular, the Duffing model?a nonlinear phenomenological model?was adopted to analyze the effects of varying oscillating voltage. The results showed that the ESD can produce a variation in resonant frequency, but can be prevented by earth grounding. In addition, an increase in the oscillating voltage led to a decrease in the resonant frequency owing to the nonlinear spring effect. The resonant frequency exhibited hysteretic behavior with varying dc bias and increased with time. The resonant frequency changed by approximately 18.5?kHz when the oscillating voltage was increased from 0.05?V to 1?V, approximately 9?kHz when the dc bias voltage was increased from 0?V to 20?V and approximately 3.062?kHz over 12?h owing to time drift. The time drift over a period of 30?min remarkably reduced from approximately 0.09% to 0.0049% after a stabilizing time period of approximately 6?h.

A micromachined efficient parametric array loudspeaker with a wide radiation frequency banda)

Parametric array (PA) loudspeakers generate directional audible sound via the PA effect, which can make private listening possible. The practical applications of PA loudspeakers include information technology devices that require large power efficiency transducers with a wide frequency bandwidth. Piezoelectric micromachined ultrasonic transducers (PMUTs) are compact and efficient units for PA sources [Je, Lee, and Moon, Ultrasonics 53, 1124-1134 (2013)]. This study investigated the use of an array of PMUTs to make a PA loudspeaker with high power efficiency and wide bandwidth. The achievable maximum radiation bandwidth of the driver was calculated, and an array of PMUTs with two distinct resonance frequencies (f1 = 100 kHz, f2 = 110 kHz) was designed. Out-of-phase driving was used with the dual-resonance transducer array to increase the bandwidth. The fabricated PMUT array exhibited an efficiency of up to 71%, together with a ±3-dB bandwidth of 17 kHz for directly radiated primary waves, and 19.5 kHz (500 Hz to 20 kHz) for the difference frequency waves (with equalization).

An advanced equivalent circuit for a piezoelectric micromachined ultrasonic transducer and its lumped parameter measurement

In this work, we developed an advanced equivalent circuit model for a piezoelectric micromachined ultrasonic transducer. The mechanical lumped parameters and the radiation impedance were obtained by considering the double-layer plate of a unimorph circular plate. Through the equivalent circuit model, the effect of a piezoelectric layer on the mechanical lumped parameters was considered. The model-produced admittance curves were compared with the measured admittance curves of the pMUT unit to verify the equivalent circuit model. A pMUT unit with a circular silicon radiating plate (radius 600 μm, thickness 15 μm) was used for measurements.

Design and Development Research of a Parametric Array Transducer for High Directional Underwater Communication

A parametric array is a nonlinear phenomenon that generates a narrow beam of low-frequency sound using the nonlinearity of the medium. The low-frequency sound so generated has a low sound pressure compared with that of sound generated directly. Consequently, a transducer that can generate a primary wave with high directivity and level is required. This study designed, fabricated, and evaluated a multi-resonance transducer as a parametric array source. The designs of the unit transducers and array transducer were based on an analysis model. The design process was repeated to fabricate the optimum transducer. The fabricated transducer array can generate a 189 dB, 190 dB primary wave level at 6.3 m and a 134 dB difference frequency wave using the parametric array phenomenon. The difference frequency wave has a frequency of 15 kHz and high directivity with an half power beam width in a water tank.

An experimental and computational study of beam-steering of parametric array

A parametric array is a nonlinear conversion process that can generate a highly directional sound beam with a small aperture. It is expected that electrical beam steering of directional sound beams generated by the parametric array may be useful in many applications such as ultrasonic raging sensors or directional loudspeakers in air. One of the major issues of beam steering of the parametric array is to precisely predict the steered difference frequency wave field in the medium. In this study, beam steering of the parametric array is computed by using a time-domain numerical code that solves the Khokhlov-Zabolotskaya-Kuznetsov equation. Since it is impossible to compute the exact difference wave field due to a complex primary source distribution in the medium, a simplified numerical model is proposed. The computed result is compared with the experimental result. For experimental study, 16-channel piezoelectric micromachined ultrasonic transducer array, which consists of two resonant type unit drivers to ...

Development of a multi-resonance transducer for highly directional underwater communication

The parametric array is a nonlinear conversion process that generates a narrow beam of low-frequency sound using small aperture. It can be applied to underwater communication between two nodes with known locations, since the highly directional sound beam may provide such benefits as privacy, no interference due to the multi-path. The difference frequency wave (DFW) from the parametric array shows small side lobes and extraordinary directivity. The shortcoming of the DFW generated by the parametric array may be its low sound pressure level relative to that of the directly generated sound beams. In this study, we designed and fabricated a multi-resonance transducer as a parametric array source and evaluated its feasibility as a transmitter. For that purpose, we determined the proper design parameters for midrange communication. We selected 10 kHz as the communication frequency and then determined the primary frequencies as 100 and 110 kHz. We composed the source transducer using the two kinds of unit transducers. The fabricated transducer array and the developed operating techniques enabled us to successfully transmit letters, words, and drawings inside the water tank. By testing the characteristics, we confirmed that the developed operating scheme and transducer can be used for underwater communication. [Work supported by ADD (UD130007DD).]

The performance enhancement of a micro-machined microphone based on field-effect-transistor and electrets

Most microphones use a capacitive type transduction. However, this form of transduction faces problems with microminiaturization. The most prominent issue is a decrease in sensitivity at low frequency. Although several works suggested a microphone based on the field-effect-transistor (FET) to solve this problem, other issues, such as low signal to noise ratio and a need for high bias voltage due to metal electrode, remained. To overcome this limit, a micro-machined microphone based on the FET and electret was proposed, and its feasibility was shown in 2012. Its principle is that the electric field arising from the electret controls the channel of the FET embedded on the membrane. Although its feasibility as an acoustic-sensitive device was shown, several problems still exist in terms of stability, sensitivity, and noise. To realize stable and highly sensitive modulation, parametric analysis for the transduction was done to enhance performance. In particular, the surface potential of the electret was incre...