Surface Acoustic Wave Sensor for Battery-Free Muscle Torque Estimation
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Solution Overview
Problem
Existing muscle torque measurement technologies, such as electromechanical dynamometry, sEMG, EIM, and IMUs, face challenges like high costs, injury risks, skin contact requirements, motion artifacts, and limited mobility, while FMG systems with wired power and battery constraints hinder real-time, continuous monitoring.
Innovation Solution
A surface acoustic wave (SAW) sensor integrated into a wearable armband for FMG, providing wireless, battery-free operation, that measures muscle movement by converting electric signals into surface acoustic waves, reflecting strain-induced delays to estimate torque using a 2D polynomial model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electromechanical dynamometry is used for precise torque measurement, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the complex electromechanical dynamometer system with a simplified surface acoustic wave sensor that measures muscle torque through acoustic wave propagation. The SAW sensor converts mechanical strain from muscle contraction into measurable acoustic signals, eliminating the need for complex mechanical loading systems while maintaining measurement capability.
Solution Approach 2:
The patent uses surface acoustic waves as a proxy measurement method. Instead of directly measuring torque through mechanical means, the SAW sensor measures the acoustic wave propagation characteristics that are influenced by muscle strain, creating an indirect but accurate representation of torque through the relationship between acoustic wave speed and material density.
2Duration of action of moving object
If wired FMG systems with batteries are used for continuous monitoring, then duration of action is improved, but device complexity and weight increase
Solution Approach 1:
The patent removes the battery and wired power components from the FMG system, extracting only the essential sensing function. The SAW sensor is designed to operate without an onboard power source, eliminating the need for battery management, charging circuits, and associated complexity while enabling continuous monitoring through passive or externally-powered operation.
Solution Approach 2:
The SAW sensor system is designed to be self-sufficient without requiring active battery power management. The sensor can operate in a passive mode where the measurement process itself does not require continuous power input, or it can be interrogated by external equipment, allowing the sensor to serve itself without complex power management circuitry.
3Ease of operation
If surface electromyography is used for muscle force estimation, then ease of operation is improved, but measurement precision deteriorates due to motion artifacts
Solution Approach 1:
The patent replaces the electrical measurement approach of sEMG with an acoustic wave-based measurement system. The SAW sensor measures mechanical strain through acoustic wave propagation through the tissue, which is less susceptible to motion artifacts and electrical interference compared to electrical potential measurements, while maintaining ease of wearable application.
4Adaptability or versatility
If traditional FMG sensors are used for torque estimation, then adaptability is improved, but measurement precision deteriorates
Solution Approach 1:
The patent utilizes the ability to change the propagation characteristics of surface acoustic waves by adjusting frequency, wavelength, and sensor geometry to optimize measurements for different muscle groups and anatomical locations. This allows the same basic SAW sensor technology to be adapted to various muscles while maintaining measurement precision through parameter optimization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The SAW sensor offers accurate torque estimation at isometric and isokinetic conditions, overcoming the limitations of traditional methods with enhanced flexibility, stability, and real-time monitoring capabilities, suitable for continuous wear and diverse anatomical regions.
Implementation Method 1
Each IDT utilizes an inverse piezoelectric output to convert electric signals into surface acoustical waves on the piezoelectric substrate
Implementation Method 2
surface acoustic wave (SAW) sensor device to determine muscle movement
Implementation Method 3
strain applied to the substrate by the muscle of the user delays receipt of the reflected waves at the first interdigital transducer corresponding to the torque applied by the muscle
Data Source
AI summary
A force myographic system utilizes a surface acoustic wave sensor to gather information about muscle activity to provide an estimate of torque provided by a muscle. The force myographic system includes the surface acoustic wave sensor, a conducting mounting bar and an adjustable band on which the sensor is mounted for application to a user's body to provide information indicative of torque provided by a muscle in the user's body.