DESIGN AND APPLICATION OF WIRELESS PASSIVE MAGNETOELASTIC RESONANCE AND MAGNETOHARMONIC FORCE SENSORS

The objective of the work described in this dissertation is the development of new wireless passive force monitoring platforms for applications in the medical field, specifically monitoring lower limb prosthetics. The developed sensors consist of stress sensitive, magnetically soft amorphous metallic glass materials. The first technology is based on magnetoelastic resonance. Specifically, when exposed to an AC excitation field along with a constant DC bias field, the magnetoelastic material mechanically vibrates, and may reaches resonance if the field frequency matches the mechanical resonant frequency of the material. The presented work illustrates that an applied loading pins portions of the strip, effectively decreasing the strip length, which results in an increase in the frequency of the resonance. The developed technology is deployed in a prototype lower limb prosthetic sleeve for monitoring forces experienced by the distal end of the residuum. This work also reports on the development of a magnetoharmonic force sensor comprised of the same material. According to the Villari effect, an applied loading to the material results in a change in the permeability of the magnetic sensor which is visualized as an increase in the higher-order harmonic fields of the material. Specifically, by applying a constant low frequency AC field and sweeping the applied DC biasing field, the higher-order harmonic components of the magnetic response can be visualized. This sensor technology was also instrumented onto a lower limb prosthetic for proof of deployment; however, the magnetoharmonic sensor illustrated complications with sensor positioning and a necessity to tailor the interface mechanics between the sensing material and the surface being monitored. The novelty of these two technologies is in their wireless passive nature which allows for long term monitoring over the life time of a given device. Additionally, the developed technologies are low cost. Recommendations for future works include improving the system for real-time monitoring, useful for data collection outside of a clinical setting

Design, fabrication, and implementation of a wireless, passive implantable pressure sensor based on magnetic higher-order harmonic fields

A passive and wireless sensor was developed for monitoring pressure in vivo. Structurally, the pressure sensor, referred to as the magneto-harmonic pressure sensor, is an airtight chamber sealed with an elastic pressure membrane. A strip of magnetically-soft material is attached to the bottom of the chamber and a permanent magnet strip is embedded inside the membrane. Under the excitation of an externally applied AC magnetic field, the magnetically-soft strip produces a higher-order magnetic signature that can be remotely detected with an external receiving coil. As ambient pressure varies, the pressure membrane deflects, altering the separation distance between the magnetically-soft strip and the permanent magnet. This shifts the higher-order harmonic signal, allowing for detection of pressure change as a function of harmonic shifting. The wireless, passive nature of this sensor technology allows for continuous long-term pressure monitoring, particularly useful for biomedical applications such as monitoring pressure in aneurysm sac and sphincter of Oddi. In addition to demonstrating its pressure sensing capability, an animal model was used to investigate the efficacy and feasibility of the pressure sensor in a biological environment

A wireless, passive sensor for quantifying packaged food quality

This paper describes the fabrication of a wireless, passive sensor based on aninductive-capacitive resonant circuit, and its application for in situ monitoring of thequality of dry, packaged food such as cereals, and fried and baked snacks. The sensor ismade of a planar inductor and capacitor printed on a paper substrate. To monitor foodquality, the sensor is embedded inside the food package by adhering it to the package’sinner wall; its response is remotely detected through a coil connected to a sensor reader. Asfood quality degrades due to increasing humidity inside the package, the paper substrateabsorbs water vapor, changing the capacitor’s capacitance and the sensor’s resonantfrequency. Therefore, the taste quality of the packaged food can be indirectly determined bymeasuring the change in the sensor’s resonant frequency. The novelty of this sensortechnology is its wireless and passive nature, which allows in situ determination of foodquality. In addition, the simple fabrication process and inexpensive sensor material ensure alow sensor cost, thus making this technology economically viable

Implantable biosensors for real-time strain and pressure monitoring

Implantable biosensors were developed for real-time monitoring of pressure and strain in the human body. The sensors, which are wireless and passive, consisted of a soft magnetic material and a permanent magnet. When exposed to a low frequency AC magnetic field, the soft magnetic material generated secondary magnetic fields that also included the higher-order harmonic modes. Parameters of interest were determined by measuring the changes in the pattern of these higher-order harmonic fields, which was achieved by changing the intensity of a DC magnetic field generated by a permanent magnet. The DC magnetic field, or the biasing field, was altered by changing the separation distance between the soft magnetic material and the permanent magnet. For pressure monitoring, the permanent magnet was placed on the membrane of an airtight chamber. Changes in the ambient pressure deflected the membrane, altering the separation distance between the two magnetic elements and thus the higher-order harmonic fields. Similarly, the soft magnetic material and the permanent magnet were separated by a flexible substrate in the stress/strain sensor. Compressive and tensile forces flexed the substrate, changing the separation distance between the two elements and the higher-order harmonic fields. In the current study, both stress/strain and pressure sensors were fabricated and characterized. Good stability, linearity and repeatability of the sensors were demonstrated. This passive and wireless sensor technology may be useful for long term detection of physical quantities within the human body as a part of treatment assessment, disease diagnosis, or detection of biomedical implant failures

A wireless and passive implantable pressure sensor

A wireless and passive implantable sensor was fabricated for monitoring pressures in a liquid-flowing conduit such as blood vessels. The implantable pressure sensor, referred to as the magneto-harmonic sensor, consisted of a pressure chamber, as well as a permanent magnetic film attached to a thin membrane and a magnetically soft film at the bottom of the chamber. When excited by an external AC magnetic field, the magnetically soft film generated magnetic higher-order harmonic fields that were remotely detected with a detection coil. The presence of a permanent magnetic film generated a biasing magnetic field, causing these higher-order harmonic signals to change. An increase in the ambient pressure pushed the membrane closer to the bottom of the chamber, reducing the separation distance between the permanent magnetic film and the magnetically soft film. This increased the biasing field experienced by the magnetically soft film, which increased the change in harmonic fields. This study demonstrated that the magneto-harmonic pressure sensor exhibited good repeatability and stability within the pressure range of interest. In addition, it was shown that the temperature of the surrounding medium only had a minimal effect on the sensor\u27s response. The wireless and passive nature of this sensor is favorable for continuous and long-term in vivo pressure monitoring, thus this sensor will be applicable for chronic patients who suffer from cardiovascular diseases. Copyright © 2009 American Scientific Publishers All rights reserved

A wireless, passive magnetoelastic force-mapping system for biomedical applications

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. © 2014 by ASME

Partially loaded magnetoelastic sensors with customizable sensitivities for large force measurements

© 2014 IEEE. Magnetoelastic sensors are typically made of strips of magnetostrictive materials that efficiently convert magnetic energy into mechanical energy, and vice versa. When exposed to an ac magnetic field, the sensor vibrates, producing a secondary magnetic flux that can be remotely detected. If the frequency of the ac magnetic field matches the sensor\u27s resonant frequency, the magnetic-mechanical energy conversion is optimal, resulting in a large secondary magnetic flux. The magnetoelastic sensor has been used to monitor physical parameters relevant to force, such as mass or stress, since its resonant frequency, indirectly through the ΔE effect, is dependent on the magnitude of an applied force. Typically, the applied force must be significantly less than the weight of the sensor or it completely dampens the sensor\u27s resonance. Presented here is the design and operation of a magnetoelastic sensor capable of monitoring large forces by applying partial loading to strategic points on a sensor. The characterization and analysis of this new magnetoelastic sensor is presented along with numerical modeling to illustrate the proposed sensing mechanism. Additionally, an array of magnetoelastic sensors were deployed to demonstrate monitoring of force loading on the lock-in portion of a lock-in style lower limb prosthetic sleeve

A wireless embedded sensor based on magnetic higher order harmonic fields: Application to liquid pressure monitoring

A wireless sensor based on the magnetoelastic, magnetically soft ferromagnetic alloy was constructed for remote measurement of pressure in flowing fluids. The pressure sensor was a rectangular strip of ferromagnetic alloy Fe40 Ni38 Mo4 B18 adhered on a solid polycarbonate substrate and protected by a thin polycarbonate film. Upon excitation of a time-varying magnetic field through an excitation coil, the magnetically soft sensor magnetized and produced higher order harmonic fields, which were detected through a detection coil. Under varying pressures, the sensor\u27s magnetoelastic property caused a change in its magnetization, altering the amplitudes of the higher order harmonic fields. A theoretical model was developed to describe the effect of pressure on the sensor\u27s higher order harmonic fields. Experimental observations showed the second-order harmonic field generated by the pressure sensor was correlated to the surrounding fluid pressure, consistent with the theoretical results. Furthermore, it was demonstrated that the sensor exhibited good repeatability and stability with minimal drift. Sensors with smaller dimensions were shown to have greater sensitivity but lower pressure range as compared to their larger counterparts. Since the sensor signal was also dependent on the location of the sensor with respect to the excitation/detection coil, a calibration algorithm was developed to eliminate signal variations due to the changing sensor location. Because of its wireless and passive nature, this sensor is useful for continuous and long-term monitoring of pressure at inaccessible areas. For example, sensors with these capabilities are suitable to be used in biomedical applications where permanent implantation and long-term monitoring are needed. © 2006 IEEE