Development of acoustic input and output devices far MRI scanners and nuclear plants

导波光学麦克风甚至可以在危险环境中工作，例如高磁场（如MRI），高RFI场以及其他需要EMI/RFI抗扰度的环境。光学传声器由一个矩形膜片和膜片上的直波导组成。传声器的灵敏度和振膜的共振频率取决于振膜的尺寸。在本研究中，相灵敏度目标值为2.5 mrad/Pa，共振频率目标值为3.4 kHz。通过设计考虑，膜片尺寸确定为20 mm×20 mm×0.15 mm。测得的灵敏度为L3 mrad/Pa，几乎是目标值的一半。制作的麦克风检测到1 kHz和2 Pa的声波，对应于100 dB-SPL（声压级）。此外，通过测量膜片为20 mm×20 mm×0.15 mm的三种自制传声器的频率特性，谐振频率分别为2.7、3.3和3.7 kHz，与理论谐振频率相似。顺便提一下，硅是一个有吸引力的衬底，因为它具有优异的力学性能，这为光学传声器提供了小型化的可行性。在过去的两年中，硅基导光传声器也得到了发展，并成功地检测到0.2 Pa （80 dB-SPL）和1 kHz的声波。此外，从频率特性上，实验确定的共振频率为5.3 kHz，与理论的5.6 kHz非常接近。

The guided-wave optical microphone can work even in a hazardous environment, such as a high magnetic field like the MRI, high RFI fields, and other environments that require EMI/RFI immunity.The optical microphone consists of a rectangular diaphragm and a straight waveguide on the diaphragm. The sensitivity of the microphone and the resonance frequency of the diaphragm are dependent on the diaphragm dimensions. In this study, the target values for phase sensitivity and resonance frequency were set at 2.5 mrad/Pa and 3.4 kHz, respectively. By design considerations, the diaphragm dimensions were determined to be 20 mm×20 mm×0.15 mm. Measured sensitivity of the fabricated microphone was L3 mrad/Pa, almost a half of the target value. The fabricated microphone detected a sound wave of 1 kHz and 2 Pa, corresponding to 100 dB-SPL (sound pressure level). Moreover from measured frequency characteristics of three fabricated microphones with a 20 mm×20 mm×0.15 mm diaphragm, resonance frequencies were 2.7, 3.3 and 3.7 kHz, similar to the theoretical one.Incidentally, silicon is an attractive substrate because of its excellent mechanical properties, which provide the optical microphone with minituarization feasibility. In the last two years, the silicon-based guided-optic microphone has also been developed, and the fabricated optical microphone with a 10 mm×10 mm×40μm diaphragm successfully detected a sound wave of 0.2 Pa (80 dB-SPL) and 1 kHz. Moreover from the frequency characteristic, resonance frequency was experimentally determined to be 5.3 kHz, quite similar to the theoretical one of 5.6 kHz.