Duplex ultrasonic muscle activity sensor

For ultrasonic muscle activity sensor (UMS), a signal processing method was proposed. The proposed method improved correlation coefficient between estimated joint torque and actual torque from 0.987 to 0.999 in an experiment. UMS is a brand-new noninvasive sensor for muscle activity. In this sensor, ultrasound is emitted and detected by transducers, though electrical change is detected in electromyogram (EMG) which is a common sensing method for muscle activity. In previous study, we measured only one ultrasound from transmitter on opposite side. In this study, we made a transmitter switching circuit and measured ultrasound coming from another transducer. Knee joint torque was estimated with neural networks in experiment. Correlation coefficient between actual torque and estimated torque was calculated as the index of the accuracy. New method (duplex UMS) showed higher correlation than existing method. The proposed method is effective to improve the accuracy of the torque estimation