2023-10-13 16:30:00
Sensor technology Making hand prostheses more sensitive with ultrasonic sensors
October 13, 2023 | Source: Fraunhofer IBMT | Reading time: 3 min
Scientists involved in the EU research project “SOMA” are working towards improving the control of prosthetic hands, specifically down to individual fingers, with the use of ultrasonic sensors. The aim is to implement commands with greater precision and also research sensory feedback from the prosthesis to the brain.
As part of their research, the scientists at Fraunhofer Institute for Biomedical Engineering IBMT have developed a demonstrator using an ultrasonic sensor bracelet to measure hand movements in test subjects. These sensors are capable of detecting various movements such as bending, stretching, and rotating.
A functional prosthetic hand provides a significant relief in the everyday lives of individuals who have lost their hand. The control of the prosthetic hand can be greatly enhanced by using ultrasonic sensors, according to researchers from Fraunhofer IBMT and their project partners from five different countries. This improvement allows for more precise movements of individual fingers, surpassing the capabilities of previous myoelectric prosthetics. Myoelectric prosthetics utilize electrodes on the skin to record electrical signals from muscle contractions and transmit them to an electronic module, which then controls the prosthesis.
Sound waves enable detailed recording of muscle contractions
The scientists at Fraunhofer IBMT use ultrasonic sensors that continuously emit sound pulses into the muscle tissue of the forearm. Unlike electrical impulses, sound waves are reflected by tissue. By analyzing the transit times of these reflected signals, the researchers can gather information about the spatial depth of the muscle strand that reflects each sound wave. This detailed observation allows for the recognition of specific hand or finger movements based on the contractions in the muscle tissue triggered by nerve stimuli in the brain. The ultimate goal of the project is to develop compact AI-controlled software that can detect these muscle contractions in real-time. The software would then translate the detected signals into commands for the actuators in the prosthetic hand, enabling precise movement of the fingers.
The technology in detail
The piezoelectric sound transducers developed by Fraunhofer IBMT emit pulses into the muscle tissue at a frequency ranging from one to four megahertz dozens of times per second. The AI-powered software analyzes the collected data by sorting it based on the location and depth of the signals. It then identifies the activation patterns and converts them into control commands that are sent to the corresponding finger on the prosthesis. The amplitude and time course of the electrical voltages provided by each sensor module are evaluated by the AI.
To integrate the sensors seamlessly, they will be incorporated into a bracelet that will sit in the shaft of the hand prosthesis. Patients will undergo a short training session to establish the link between muscle signals and desired finger movements. The activity patterns generated during the training will serve as a reference for the system.
Sensory feedback from the hand prosthesis on the horizon
The consortium is also working towards making the system bidirectional, allowing the prosthetic hand to provide feedback to the wearer. Potentially, the wearer could experience sensory stimuli transmitted by the prosthesis through implanted electrodes made from biologically compatible materials. These electrodes would stimulate nerves to convey signals from the prosthesis to the brain, enabling the wearer to perceive feedback from the artificial hand and respond accordingly. According to Fraunhofer IBMT, the electrodes would be implanted in or on nerves, and the wearer would not be able to physically feel them.
This groundbreaking research is expected to greatly enhance the control and functionality of hand prostheses, providing improved quality of life for individuals who have lost their hand.
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