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Research Papers

A Wireless, Passive Magnetoelastic Force–Mapping System for Biomedical Applications

[+] Author and Article Information
Brandon D. Pereles

e-mail: bdperele@mtu.edu

Andrew J. DeRouin

e-mail: ajderoui@mtu.edu

Keat Ghee Ong

e-mail: kgong@mtu.edu
Department of Biomedical Engineering,
Michigan Technological University,
1400 Townsend Drive,
Houghton, MI 49931

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received May 23, 2013; final manuscript received October 17, 2013; accepted manuscript posted October 31, 2013; published online December 4, 2013. Assoc. Editor: Jeffrey Ruberti.

J Biomech Eng 136(1), 011010 (Dec 04, 2013) (7 pages) Paper No: BIO-13-1238; doi: 10.1115/1.4025880 History: Received May 23, 2013; Revised October 17, 2013; Accepted October 31, 2013

A wireless, passive force–mapping system based on changes in magnetic permeability of soft, amorphous Metglas 2826MB strips is presented for long-term force/stress monitoring on biomedical devices. The presented technology is demonstrated for use in lower-limb prosthetics to ensure proper postoperative fitting by providing real-time monitoring of the force distribution at the body-prosthesis interface. The sensor system consisted of a force-sensitive magnetoelastic sensing strip array that monitored applied loading as an observed change in the peak amplitude of the measured magnetic higher-order harmonic signal of each array element. The change in higher-order harmonic signal is caused by the change in the magnetic permeability of the sensing strips that corresponds to an increase in strip magnetization. After loading, the measured higher-order harmonic signals were fed into an algorithm to determine the applied forces, allowing for determination of the real-time loading profile at the body prosthesis interface.

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References

Figures

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Fig. 1

The sensor deployed on an Otto Bock lower limb prosthetic

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Fig. 2

Illustration of the sensor strip placement and the location of the regions and monitoring positions where “region” refers to the location of force application and “position” refers to the location of the detection coil

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Fig. 3

(a) The experimental setup consisting of ac/dc excitation coils, function generator, ac amplifier, power supply, spectrum network analyzer, and control box. (b) The dimensions (mm) and locations of the sensors and coils.

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Fig. 4

Plot illustrating the loading procedure in which a changing load is applied to R1 while a constant load, changed between load cycles, is held on R2

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Fig. 5

An increasing sensor response was observed while monitoring from (a) coil 1 and (b) coil 3 with a changing load applied to R1 and R3 and constant loading applied to R2 and R4

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Fig. 6

A decreasing sensor response was observed while monitoring from (a) coil 2 and (b) coil 4 with a changing load applied to R1 and R3 and constant loading applied to R2 and R4

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Fig. 7

The raw sensor data was recalculated using the developed algorithm for testing, where a changing load was applied to R1 and R3 and a constant load was held on R2 and R4 when monitoring from (a) coil 1, (b) coil 3, (c) coil 2, and (d) coil 4

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Fig. 8

The applied loading was recalculated using the developed algorithm for testing, where a changing load was applied to R1 and R3 and a constant load was held on R2 and R4 when monitoring from (a) coil 1, (b) coil 3, (c) coil 2, and (d) coil 4

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Fig. 9

Cyclic loading of the sensor was performed from 0.044 kN to 0.133 kN over the course of ten loading cycles with results illustrating low drift in sensor response

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Fig. 10

Stability testing of the sensor while applying a changing load from 0.044 kN to 0.133 kN at (a) R1 and (b) R3 with constant loads, changed at 0.022 kN intervals between load cycles, held on R2 and R4. The sensor responses were monitored from coil 1 and coil 3 and illustrated stepped pyramid responses with low hysteresis and drift.

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Fig. 11

Illustration of the implementation of the stress/force-monitoring system. To wirelessly monitor responses of the sensors, the system will feature attached electronics, including a power supply, excitation circuitry, and transceiver for wireless data transmission. The excitation/detection coils will be attached to the prosthetic, with the sensing strips sandwiched in between the coupler that connects the shank to the socket.

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