Design of a 2x8 Microstrip Conformal Antenna with Radome on a Cylindrical Surface

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Development of a Piezoelectric Micro-machined Ultrasonic Transducer for Photoacoustic Imaging that Accounts for the Added Mass Effect of the Acoustic Medium

Typically, photoacoustic images are obtained in water or gelatin because the impedance of these mediums is similar to that of the human body. However, these acoustic mediums can have an additional mass effect that changes the resonance frequency of the transducer. The acoustic radiation impedance in air is negligible because it is very small compared to that of the transducer. However, the high acoustic impedance of mediums such as the human body and water is quite large compared to that of air, making it difficult to ignore. Specifically, in a case where the equivalent mass is very small, such as with a micro-machined ultrasound transducer, the additional mass effects of the acoustic medium should be considered for an accurate resonance frequency design. In this study, a piezoelectric micro-machined ultrasonic transducer (pMUT) was designed to have a resonance frequency of 10 MHz in the acoustic medium of water, which has similar impedance as thehuman body. At that time, the resonance frequency of the pMUT in air was calculated at 15.2 MHz. When measuring the center displacement of the manufactured pMUT using a laser vibrometer, the resonance frequencies were measured as 14.3–15.1 MHz, which is consistent with the finite element method (FEM) simulation results. Finally, photoacoustic images of human hair samples were successfully obtained using the fabricated pMUT.22Nkc

다공진을 이용한 압전 기반 광대역 초음파 트랜스듀서의 제작 기술

DoctorWideband transducers have advantages in various applications such as underwater communication, medical probes, and general loudspeakers. In the underwater communication field, wideband transducers can simultaneously transfer more information owing to the wide bandwidth. In medical probes, higher frequency ultrasonic transducers can acquire higher resolution images, whereas lower frequency ultrasonic transducers can acquire deeper images. In general loudspeakers, it requires a bandwidth of at least 10 kHz, because the audible frequency band is 20 Hz–20 kHz. One of the methods to achieve a wide frequency bandwidth in a single device is by modeling the transducer to a multi-resonance system. However, in one structure or one transducer, it is very difficult to implement the multi-resonances of the desired mode at the required frequency bandwidth. It is because the resonance of the primary mode, which is mainly used in acoustic transducers, is determined by the thickness or diameter of the transducers for simple structure using the thickness or thin film mode. Therefore, it is difficult to implement the additional structures that have another resonance on one transducer. Especially for MEMS-based transducers manufactured by micromachining processes, the structural limitations make them even more difficult. Due to this limitation, the previous pMUT arrays achieved wideband by arranging two pMUTs with different resonances and driving them with out-of-phase, not by multi-resonances. Previous pMUT arrays could reportedly generate wideband ultrasounds of approximately 17 kHz with an electro-acoustic efficiency of 70% direct sounds. Although it achieved a high efficiency, it had a dividing the sound output power at a given resonance, as two pMUTs with different resonance were used. This required additional circuits and complex electrode implementation for different driving of two pMUTs. Furthermore, previous pMUTs had various limitations, such as uniformity issues and mechanically vulnerable thin membrane is exposed to air directly, and has the disadvantage of using a structurally and electrically vulnerable air-bridge structure. In this study, a new pMUT array is designed and fabricated by multi-resonance system. The new pMUT is based on silicon dioxide (SiO2) membrane. It designed using one membrane part and additional two acoustic structures (waveguide part, back chamber part) to achieve wideband. All acoustical structures were designed considering the micro-machining process, and new fabrication concepts were introduced to implement the precise multi-resonance systems, which included a SiO2 footing barrier, PZT sputtering method, cap wafer, TSV, etc. The SiO2 footing barrier essentially prevented the footing effect, thus improving the performance of the array transducer. By using the PZT sputtering method, structurally and electrically vulnerable air-bridge structure could be avoided. Using cap wafer and TSV process, it was able to protect structurally vulnerable thin membrane and improve the ASIC compatibility. The fabricated single pMUT unit demonstrated electro-mechanical efficiency, mechano-acoustic efficiency and electro-acoustic efficiency of 95.6%, 93.3% and 89.1 %, which has developed 5.8%, 18.5% and 21.9% compared to previous pMUTs. And it demonstrated a maximum sound pressure level of 64.6dB at 1st peak of 105 kHz and 62.4 dB at 2nd peak of 126 kHz. And a wideband of 101 – 130 kHz (-7.7 dB). However, -3 dB bandwidth of the wideband was 102.5 – 109 kHz and 124 – 126.3 kHz, and there is deep null between two peaks, the reason of which was considered by the fabrication process issues. And, the pMUT array were not implemented by fabrication issues. In this study, these fabrication process issues was analyzed and a method was proposed to solve these process issues. The potential of performance improvement of pMUT was also discussed

Design of piezoelectric micro-machined ultrasonic transducer for wideband ultasonic radiation in air

본 논문에서는 공기 중 광대역 초음파 방사용 압전 박막 기반 초소형 초음파 트랜스듀서(piezoelectric Micro-machined Ultrasonic Transducer, pMUT)의 설계 연구가 진행되었다. 하나의 트랜스듀서로 광대역을 달성하 는 방법 중 하나는 다공진 시스템으로 설계하는 것이다. 새로운 pMUT은 박막 구조의 앞면과 뒷면에 적절한 음향 구조 를 추가하여 다공진 시스템을 구현하도록 설계되었다. 박막 앞쪽은 도파관 구조로 모델링된 방사 파트로, 박막 뒷쪽은 음향 공동으로 모델링된 패키징 파트로 이루어져있다. 박막 파트, 방사 파트, 패키징 파트로 구성된 새로운 pMUT은 집중 변수 모델로 설계되었으며, 최종적으로 유한요소해석으로 검증되었다. 최종 설계된 pMUT은 102 kHz ~ 132 kHz (-3 dB)의 주파수 대역을 달성하였다.11Nscopuskc

Design and Fabrication of a Piezoelectric Micromachined Ultrasound Array Transducer for Photoacoustic Imaging Applications

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Piezoelectric Micromachined Ultrasound Array Transducer with 31 Channels for Photoacoustic Imaging

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압전 박막형 초소형 초음파 트랜스듀서의 설계 연구

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

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수중 물체 탐지 시스템 설계 시뮬레이션을 위한 트랜스듀서 모델 개발

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Transducer models for simulating detection processes for underwater mining

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