EM sensor measurement of glottal structure versus time
John F. Holzricher, Lawrence C. Ng, Gerald J. Burke, James B. Kobler, John J. Rosowski · The Journal of the Acoustical Society of America · 2002
EM wave sensors are being used to measure human vocal tract movements during voiced speech. However, when used in the glottal region there remains uncertainty regarding the contributions to the sensor signal from the vocal fold opening and closing versus those from pressure induced trachea–wall movements. Several signal source hypotheses were tested on a subject who had undergone tracheostomy 4 years ago as a consequence of laryngeal paresis. Measurements of vocal fold and tracheal wall motions were made using an EM sensor, a laser-Doppler velocimeter, and an electroglottograph. Simultaneous acoustic data came from a subglottal pressure sensor and a microphone at the lips. Extensive 3-D numerical simulations of EM wave propagation into the neck were performed in order to estimate the amplitude and phase of the reflected EM waves from the 2 different sources. The simulations and experiments show that these sensors measure, depending upon location, both the opening and closing of the vocal folds and the movement of the tracheal walls. When placed over the larynx, the vocal folds are the dominant source. The understanding of the signal sources is important for many potential applications under consideration.