Dimitris Kouzoudis

The 500 MHz to 5.50 GHz complex permittivity spectra of single-wall carbon nanotube-loaded polymer composites

Abstract The 500 MHz to 5.50 GHz complex permittivity spectra of a thick-film polymer loaded with 0–23 wt% single-wall carbon nanotubes is measured. At 500 MHz, as the weight percentage loading of the carbon nanotubes increases from 0 to 23% the real permittivity is found to increase by a factor of ∼35, and the imaginary permittivity by a factor of 1200. The spectral magnitudes decrease rapidly from the 500 MHz value over the measured frequency range. Experimental data are in qualitative agreement with values predicted using an effective medium theory for materials comprised of elongated cylindrical conductors [A.N. Lagarkov, A.K. Sarychev, Phy. Rev. B 53 (1996) 6318].

Magnetoelastic sensors for remote query environmental monitoring

Magnetoelastic thin film sensors can be considered the magnetic analog of surface acoustic wave sensors, with the characteristic resonant frequency of the magnetoelastic sensor changing in response to different environmental parameters. We report on the application of magnetoelastic sensors for remote query measurement of pressure, temperature, liquid viscosity and, in combination with a glucose-responding mass-changing polymer, glucose concentrations. The advantage of using magnetoelastic sensors is that no direct physical connections, such as wires or cables, are required to obtain sensor information allowing the sensor to be monitored from inside sealed containers. Furthermore since it is the frequency response of the sensor that is monitored, rather than the amplitude, the relative orientation of the sensor with respect to the query field is unimportant.

Remote query measurement of pressure, fluid-flow velocity, and humidity using magnetoelastic thick-film sensors

Free-standing magnetoelastic thick-film sensors have a characteristic resonant frequency that can be determined by monitoring the magnetic flux emitted from the sensor in response to a time varying magnetic field. This property allows the sensors to be monitored remotely without the use of direct physical connections, such as wires, enabling measurement of environmental parameters from within sealed, opaque containers. In this work, we report on application of magnetoelastic sensors to measurement of atmospheric pressure, fluid-flow velocity, temperature, and mass load. Mass loading effects are demonstrated by fabrication of a remote query humidity sensor, made by coating the magnetoelastic thick film with a thin layer of solgel deposited Al2O3 that reversibly changes mass in response to humidity.

Monitoring blood coagulation with magnetoelastic sensors

The determination of blood coagulation time is an essential part of monitoring therapeutic anticoagulants. Standard methodologies for the measurement of blood clotting time require dedicated personnel and involve blood sampling procedures. A new method based on magnetoelastic sensors has been employed for the monitoring of blood coagulation. The ribbon-like magnetoelastic sensor oscillates at a fundamental frequency, which shifts linearly in response to applied mass loads or a fixed mass load of changing elasticity. The magnetoelastic sensors emit magnetic flux, which can be detected by a remotely located pick-up coil, so that no direct physical connections are required. During blood coagulation, the viscosity of blood changes due to the formation of a soft fibrin clot. In turn, this change in viscosity shifts the characteristic resonance frequency of the magnetoelastic sensor enabling real-time continuous monitoring of this biological event. By monitoring the signal output as a function of time, a distinct blood clotting profile can be seen. The relatively low cost of the magnetoelastic ribbons enables their use as disposable sensors. This, along with the reduced volume of blood required, make the magnetoelastic sensors well suited for at-home and point-of-care testing devices.

The frequency response of magnetoelastic sensors to stress and atmospheric pressure

Earlier work demonstrated that the characteristic resonant frequency of magnetoelastic thick-film sensors shifts linearly downwards in response to increasing atmospheric pressure. In this paper, the response mechanism is detailed and shown to be a function of both pressure and the way that the sensor is mechanically stressed. Stressing the sensor, in either the elastic or plastic regime, induces out-of-plane vibrations that act as a pressure-dependent damping force to the longitudinal sensor oscillations excited by the interrogation field. This damping force, in turn, acts to shift the resonant frequency of the magnetoelastic sensor lower in response to increasing pressure.

Simultaneous measurement of liquid density and viscosity using remote query magnetoelastic sensors

Earlier work [C. A. Grimes et al., Smart Mater. Struct. 8, 639, (1999)] has shown that upon immersion in liquid the resonant frequency of a magnetoelasticsensor shifts linearly in response to the square root of the liquid density and viscosity product. It is shown that comparison between a pair of magnetoelasticsensors with different degrees of surface roughness can be used to simultaneously determine the liquid density and viscosity.

Magnetoelastic sensors in combination with nanometer-scale honeycombed thin film ceramic TiO2 for remote query measurement of humidity

Ribbonlike magnetoelastic sensors can be considered the magnetic analog of an acoustic bell; in response to an externally applied magnetic field impulse the sensors emit magnetic flux with a characteristic resonant frequency. The magnetic flux can be detected external to the test area using a pick-up coil, enabling query remote monitoring of the sensor. The characteristic resonant frequency of a magnetoelastic sensor changes in response to mass loads. [L.D. Landau and E. M. Lifshitz, Theory of Elasticity, 3rd ed. (Pergamon, New York, 1986). p. 100].Therefore, remote query chemical sensors can be fabricated by combining the magnetoelastic sensors with a mass changing, chemically responsive layer. In this work magnetoelastic sensors are coated with humidity-sensitive thin films of ceramic, nanodimensionally porous TiO2 to make remote query humidity sensors.

Remote query fluid-flow velocity measurement using magnetoelastic thick-film sensors (invited)

The characteristic resonant frequency of a thick-film ribbon-shaped magnetoelastic sensor is dependent upon its length, density, Poisson’s ratio, and modulus of elasticity [J. M. Barandiaran and J. Guitierrez, Sens. Actuators A 59, 38 (1997)]. In a manner analogous to surface acoustic wave (SAW) sensors, this characteristic resonant frequency also changes with effective mass load or with friction force applied to the surface of the magnetoelastic sensor [L. D. Landau and E. M. Lifshitz, Theory of Elasticity, 3rd ed. (Pergamon, New York, 1986), Chap. II]. The time varying magnetic flux emitted from magnetoelastic sensors can be monitored remotely using pickup coils. Hence, in contrast with SAW devices, no direct physical connections are required to obtain magnetoelastic sensor information, allowing them to be monitored from within sealed, opaque containers. Reported here is application of magnetoelastic sensors to the measurement of fluid flow from within sealed pipes. Within the laminar fluid flow regime ...

Remote query pressure measurement using magnetoelastic sensors

Two magnetostriction-based methods for measuring atmospheric pressure are presented. Each technique correlates changes in pressure with the characteristic resonant frequency of a magnetoelastic magnetostrictive thick-film sensor. In each case the sensor is monitored remotely, using an adjacently located pickup coil, without the use of physical connections to the sensor.

Thin-Film Magnetoelastic Microsensors for Remote Query Biomedical Monitoring

Magnetoelastic thin-film sensors can be considered the magnetic analog of an acoustic bell: in response to an externally applied magnetic field impulse the sensors ring like a bell, emitting magnetic flux with a characteristic resonant frequency. The magnetic flux can be detected remotely, external to the test area, using a pick-up coil. By monitoring changes in the characteristic resonant frequency of the sensor multiple environmental parameters can be measured. In this work we report on application of magnetoelastic sensors for remote query measurement of temperature, pressure, viscosity and, in combination with a glucose-responding mass-changing polymer, in situ measurement of biological-level glucose concentrations. The advantage of using magnetoelastic sensors is that they are monitored remotely, without the need for direct physical connections such as wires or cables, nor line-of-sight alignment as needed with optical detection methods. The remote query capability allows the magnetoelastic sensors to be monitored from inside sealed, opaque containers. Depending upon the application magnetoelastic sensors can be sized from micrometer to millimeter dimensional scales, and have a material cost of approximately