Kyounghun Been

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.

A new lumped parameter model for the design of the free-flooded ring transducer

The free-flooded ring (FFR) transducer is the well-known low-frequency sound sources in underwater because its operating frequency bandwidth is broad and relatively small size. Previous researches were preformed to predict the characteristics of FFR transducers using ECM which is a type of LPM because ECM is widely used to understand its characteristics in transducer design process. However, it is hardly to predict the characteristics of an FFR transducer because the acoustic field is generated from its top and bottom openings, connected by the inner fluid, as well as the cylindrical ring surface. Here, the authors investigated an ECM of an FFR transducer consisting of three parts: the piezoelectric ring, the cylindrical cavity, and the radiation load. In addition, an LPM which can consider mutual radiation loads was proposed to improve the accuracy of the model. The proposed models were verified using commercial finite element method (COMSOL Multiphysics). It was confirmed that LPM could predict characte...

A lumped parameter model of the single free-flooded ring transducer

A free-flooded ring (FFR) transducer can generate low-frequency sound in a small device and has a wide operating frequency bandwidth. Many studies have been performed that can predict the characteristics of an FFR transducer using analytical techniques and an equivalent circuit model (ECM), and methods to predict properties using numerical simulations have recently been developed. However, an ECM, a type of lumped parameter model (LPM), is still widely used to interpret the properties of such transducers in the design process. In this study, the authors investigated an ECM of an FFR transducer. The ECM consists of three parts: the piezoelectric ring, the cylindrical cavity, and the radiation load. Moreover, it can be included readily in a circuit to drive an FFR transducer. Additionally, an LPM was proposed, considering the mutual radiation loads, to improve the accuracy of the model. Each model was tested in comparisons with the finite element method; it was confirmed that an LPM could predict the properties of an FFR transducer with much better accuracy than an ECM. The LPM developed can save much time in designing FFR transducers.

Feasibility study on a highly-directional parametric array loudspeaker applicable to mobile devices

A conventional parametric array (PA) loudspeaker has a relatively small aperture and produces a highly directional audible sound beam. Due to limitations arising from their size and power consumption, standard PA loudspeakers are not used in mobile devices. PA loudspeakers are typically larger than 25 cm and require more than 60 W. We show that piezoelectric micro-machined ultrasonic transducer (pMUT) arrays can emit highly directional ultrasonic sounds with a power efficiency of up to 80% [Je and Moon, Ultrasonics 53, 1124-1134 (2014)]. Highly directional sound beams with a frequency bandwidth of 13 kHz can be generated efficiently by pMUT arrays with two resonant frequencies [Je and Moon, JASA 173(4), 1732-1743 (2015)]. We used a signal processor, power amplifier, and pMUT array to build a loudspeaker system that is smaller than, and requires less power than, a conventional PA loudspeaker system. In our loudspeaker system, the maximum sound pressure level (SPL) is 75 dB, ± 3 dB frequency bandwidth is 12...

Design and fabrication of a piezoelectric micromachined ultrasound array transducer for photoacoustic imaging applications

Piezoelectric micromachined ultrasonic transducers (pMUTs) have been developed for various applications [1], and the design may vary according to the intended use. In particular, membrane type transducers have been widely used for ultrasonic applications in air [2], and are frequently using in transducer arrays for medical ultrasonic imaging systems for robotic surgery as well as for conventional surgical procedures [1]. Ultrasonic transducers for imaging systems generally operate around the resonant frequency to obtain high sensitivity. Here, we report apMUT array with a resonant frequency of 10 MHz for photoacoustic imaging (PAI) applications. The array was fabricated using a bulk micromaching process. The characteristics and performance of the pMUT array were evaluated, and the device was found to be an effective transducer for a PAI system.

Piezoelectric micromachined ultrasound array transducer with 31 channels for photoacoustic imaging

Photoacoustic imaging (PAI) is a non-invasive medical imaging technique that has been studied by many research groups. It surpasses the penetration-depth limits of optical imaging and is able to provide functional imaging for tumor-vascular interactions and hemoglobin oxygenation mapping. The imaging quality is dominated by the transducer performance; thus, the transducer plays an important role. In this study, we examined a piezoelectric micromachined ultrasound transducer (pMUT) array with 10 MHz resonant frequency for PAI systems. pMUTs can be used with array or endoscopic probes due to their small size by bulk micromachining process. Additionally, their receiving sensitivity and power efficiency are higher than those of general thickness-mode piezoelectric transducers.

Transducer models for simulating detection processes for underwater mining

Numerical simulations on propagating and scattering processes of sound waves in water and sediment may be useful for designing a detection system for underwater mining. Here a transducer model is developed for the numerical simulation to implement radiating and receiving processes of transducers into numerical calculations. Since the Rayleigh integral approach is adopted for acoustic radiation, the accurate velocity profiles over the radiating surfaces of a transducer array should be estimated considering the mechano-acoustic interactions including the dynamics of unit drivers and the acoustic radiation loadings on the radiation surfaces. We adopted the approach that the surface velocity is calculated using the transducer model with the acoustic loading while the loading effects are estimated via calculating the radiation impedance of transducer array using Rayleigh integrals. The estimated velocity profile of the transducer surface is used for calculating the accurate sound fields generated by the transd...

A modeling and simulation suite for design of buried object scanning sonars

In this talk we highlight a work in progress, concerning the development of a comprehensive modeling and simulation (M&S) suite for design of buried object scanning sonars. The M&S suite is expected to cover almost all aspects of physical and engineering acoustics involved in the design process, ranging from transducers, sound propagation, sediment acoustics, backscattering by buried objects, to sonar image processing. The overview of the M&S suite is given along with a preliminary demonstration in the context of a cylindrical object buried in sandy sediment. [This work was conducted in the Unmanned Technology Research Center (UTRC) sponsored by the Defense Acquisition Program Administration (DAPA) and the Agency for Defense Development (ADD) in the Republic of Korea.] In this talk we highlight a work in progress, concerning the development of a comprehensive modeling and simulation (M&S) suite for design of buried object scanning sonars. The M&S suite is expected to cover almost all aspects of physical and engineering acoustics involved in the design process, ranging from transducers, sound propagation, sediment acoustics, backscattering by buried objects, to sonar image processing. The overview of the M&S suite is given along with a preliminary demonstration in the context of a cylindrical object buried in sandy sediment. [This work was conducted in the Unmanned Technology Research Center (UTRC) sponsored by the Defense Acquisition Program Administration (DAPA) and the Agency for Defense Development (ADD) in the Republic of Korea.]