Passive wireless strain sensors
Miniature magnetoelastic strain gauges that do not require an external power source can be used to measure bone deformation in medical and dental implants, and to attach to bridges or large buildings to monitor potential structural deformation. When such a device is stretched, structural rearrangements occur within the material and changes its elasticity and electrical or magnetic conductivity as a function of the stretch distance (also known as strain). These sensors can also be incorporated into orthopedic surgeries, after which the doctors can obtain real-time diagnostic information about the implant without resorting to invasive procedures. A number of strain sensors based on magnetoelastic coupling have been previously demonstrated, but the signal output is either dependent on orientation of read-out coils with respect to the sensor, or the sensor dynamic range is limited by material properties.
Improving the dynamic range of wireless magnetoelastic sensors
Gianchandani and his team has managed to overcome dynamic range limitations on wireless magnetoelastic sensors by incorporating a strain-limiting spring structure into a prototype. They report an unstrained resonance signal peak is at 227.4 kHz, and a frequency response of 350 Hz/mstrain. The total dynamic range is 8 mstrain, which is the largest reported for a magnetoelastic sensor. Linear operation in the tensile and compressive regimes can be achieved by pre-stressing the sensor and by biasing at a higher DC magnetic field prior to use. Such devices can be used in orthopedic and dental implants, which is one of the largest medical device markets in the United States.
- Orthopedic and dental implants
- Structural integrity monitors
- Tire pressure monitors
- Large dynamic strain range