This report explains the use of a complementary series, Golay codes, for probing the impulse response of the external ear. The codes are used to measure both the resonance of the human ear canal, using a sealed sound-delivery system, and to measure the transfer function of the pinna, using a free-field source. With two series of 512 binary numbers, the improvement in signal-to-noise ratio over a single impulse approaches the theoretical value of 30.1 dB [10 log(2.512)]. This technique has many of the same properties as maximal-length sequences [M. R. Schroeder, J. Acoust. Soc. Am. 66, 497-500 (1979)], but it has the added advantage that the sequence length is an integer power of two and is, therefore, particularly convenient to use with modern Fourier transform techniques.

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Abstract:To measure various components with nano-scale precision, a new high-precision touch-trigger probe using a single low-cost sensor for a micro-coordinate measuring machine (CMM) is presented in this paper. The sensor is composed of a laser diode, a plane mirror, a focusing lens, and a quadrant photo detector (QPD). The laser beam from the laser diode with an incident angle is reflected by the plane mirror and then projected onto the quadrant photo detector (QPD) via the focusing lens. The plane mirror is adhered to the upper surface of the floating plate supported by an elastic mechanism, which can transfer the displacement of the stylus's ball tip in 3D to the plane mirror's vertical and tilt movement. Both motions of the plane mirror can be detected by respective QPDs. The probe mechanism was analyzed, and its structural parameters that conform to the principle of uniform sensitivity and uniform stiffness were obtained. The simulation result showed that the stiffness was equal in 3D and less than 1 mN/µm. Some experiments were performed to investigate the probe's characteristics. It was found that the probe could detect the trigger point with uniform sensitivity, a resolution of less than 5 nm, and a repeatability of less than 4 nm. It can be used as a touch-trigger probe on a micro/nano-CMM.