Kaburagi Tokihiko, Honda Masaaki
Department of Acoustic Design, Kyushu Institute of Design, Fukuoka, Japan.
J Acoust Soc Am. 2002 Mar;111(3):1414-21. doi: 10.1121/1.1445785.
Electromagnetic articulograph (EMA) devices are capable of measuring movements of the articulatory organs inside and outside the vocal tract with fine spatial and temporal resolutions, thus providing useful articulatory data for investigating the speech production process. The position of the receiver coil is detected in the EMA device on the basis of a field function representing the spatial pattern of the magnetic field in relation to the relative positions of the transmitter and receiver coils. Therefore, the design and calibration of the field function are quite important and influence the accuracy of position detection. This paper presents a nonparametric method for representing the magnetic field, and also describes a method for determining the receiver position from the strength of the induced signal in the receiver coil. The field pattern in this method is expressed by using a multivariate spline as a function of the position in the device's coordinate system. Because of the piecewise property of the basis functions and the freedom in the selection of the rank and the number of the basis functions, the spline function has a superior ability to flexibly and accurately represent the field pattern, even when it suffers from fluctuations caused by the interference between the transmitting channels. The position of the receiver coil is determined by minimizing the difference between the measured strength of the received signal and the predicted one from the spline representation of the magnetic field. Experimental results show that the error in estimating the receiver position is less than 0.1 mm for a 14 x 14-cm measurement area, and this error can be further reduced by using a spline-smoothing technique.
电磁关节运动描记仪（EMA）设备能够以精细的空间和时间分辨率测量声道内外发音器官的运动，从而为研究语音产生过程提供有用的发音数据。在EMA设备中，基于表示与发射线圈和接收线圈的相对位置相关的磁场空间模式的场函数来检测接收线圈的位置。因此，场函数的设计和校准非常重要，并且会影响位置检测的准确性。本文提出了一种表示磁场的非参数方法，还描述了一种根据接收线圈中感应信号的强度确定接收器位置的方法。该方法中的场模式通过使用多元样条作为设备坐标系中位置的函数来表示。由于基函数的分段特性以及在基函数的秩和数量选择上的自由度，即使样条函数受到发射通道之间干扰引起的波动影响，它也具有灵活且准确地表示场模式的卓越能力。通过最小化接收信号的测量强度与磁场样条表示所预测的强度之间的差异来确定接收线圈的位置。实验结果表明，对于14×14平方厘米的测量区域，估计接收器位置的误差小于0.1毫米，并且通过使用样条平滑技术可以进一步降低该误差。
