Passive Wireless Resonant Galfenol Sensor for Osteosynthesis Plate Bending Measurement

• Published in: IEEE sensors journal 2012-05, Vol.12 (5), p.1226-1233
• Main Authors: Sauer, S., Marschner, U., Adolphi, B., Clasbrummel, B., Fischer, W.
• Format: Article
• Language: English
• Subjects: Coils; Frequency domain measurement; Frequency measurement; Galfenol ( {\hbox {Fe}}_{83}{\hbox {Ga}}_{17} ); inductance change; inductive coupling; Magnetic resonance; Magnetic sensors; Magnetostriction; magnetostrictive bending sensor; rectangular planar coil; resonance frequency; time domain measurement; wireless resonant bending sensor
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2011.2167747

The healing process of bone fractures can be monitored by a measurement of the osteosynthesis plate bending. For this purpose a wireless magnetostrictive bending sensor is proposed. A planar rectangular coil on top of a magnetostrictive Galfenol ( alloy) layer forms an electrical resonant circuit. The sensor is manufactured in thin film technology. Coil turns were electrodeposited by pattern plating. Sensors with overall dimensions of (13 2 0.5) mm were manufactured with varied turn numbers showing self-resonance frequencies from 5 to 50 MHz. Examined sensors possess linear frequency-force characteristic up to 6 N with frequency shifts of 6 kHz . In order to obtain the sensor resonance frequency wirelessly, several measurement techniques were employed using inductively coupled coils. Frequency domain measurements have been carried out by employing a network analyzer with a single detection coil and a lock-in amplifier with separate coils for excitation and detection. In time domain measurements, two coils for transmission and reception are used. In the transmit case a short sine pulse excites the sensor and afterwards its decaying response signal is received. To determine the resonance frequency, a frequency counting, Fourier or wavelet technique can be used. By integrating additional cores of high permeability into sensor and detection coil, measurement ranges can be increased.