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Fe-rich Fe-Co-B magnetostrictive alloys have been considered as good high-frequency sensor materials. In this paper, Fe-rich Fe-Co-B thin films with the composition of Fe57Co29B14, Fe55Co28B17, Fe53Co27B20, Fe51Co26B23 and Fe49Co25B26 were fabricated. The structure, morphology, magnetic property and resonant behavior of the films were studied. Among the different compositions, Fe55Co28B17 has the highest Q value and relatively high amplitude, which is beneficial for sensor application. Au/Fe55Co28B17/Au magnetostrictive particles (MSPs) were prepared by electrodeposition and microfabrication. The 500 μm×100 μm×6 μm MSP shows a resonant frequency of 3.320 MHz and Q value of 127. Fe-Co-B thin film sensors with good performance can be potentially utilized for high-frequency application and food safety detection.

High performance biosensors for the detection of bacterial in various media have been developed using magnetostrictive/magnetoelastic resonators (MSRs). An MSR is a strip of magnetostrictive alloy coated with biological molecular recognition unit, such as antibody and phage. The sensor is based on the change in its resonant frequency. Therefore, it is critical to determine the resonant frequency of an MSR. The MSR biosensors have been developed for the detection of various pathogenic bacteria in liquid food and on the surface of fresh produce in real-time and in-situ manner. However, the instruments used to determine the resonant frequency of these sensors are bulky and expensive. Here an inexpensive circuit is developed to characterize the resonant frequency of the MRS sensors. The unique circuit design makes it is possible to have a real handheld device for the interrogation of MRS sensors. Additionally, a new methodology to enhance the signal is also introduced.

In this paper, we present the distribution functions of magnetic field intensity and eddy current intensity within a rectangular magnetostrictive material plate. Firstly, on the basis of Maxwell's theory, the mathematical model for the magnetic field within the plate is established. Then, the governing equation for determining the magnetic field is solved by Fourier transform; an error in Stoll's book (1983) is corrected. Furthermore, the function of eddy current intensity is deduced. Next, the expressions of the magnetic field and eddy current are given in the case of the external magnetic field and the plate makes an angle of θ. Lastly, taking rectangular giant magnetostrictive plate is parallel to external magnetic field as example, the influencing factors of the inner magnetic field and eddy current are unveiled: the skin effect is enhanced with the increase of the exciting frequency, the relative permeability or conductivity; the higher the relative permeability or conductivity, the more significant the eddy current density increases.

Two types of magnetostrictive resonators – magnetostrictive microcantilever (MSMC) and magnetostrictive particle (MSP) – have been introduced as sensor platforms. Their principles and advantages as sensor platforms are discussed along with the materials selection. A detailed and complete comparison between the MSMC and MSP is given. It is concluded that for the resonators with the same size, an MSP exhibits a higher sensitivity and has a much higher resonant frequency. For the resonators with the same resonant frequency, MSMCs exhibit a much higher sensitivity and have a much smaller size than MSPs. Using antibody as the sensing element, MSP biosensors for in situ detection of Escherichia coli and Listeria monocytogenes are developed and characterized. These biosensors exhibit a high performance. For example, the MSP-antibody biosensors of 1 mm × 0.3 mm × 15 μm exhibit a detection limit less than 100 cfu/ml for in situ detection of bacterial cell in water. A new type actuator is introduced using MSPs. The MSP actuator is operated using AC magnetic field with a frequency close to, but different than, its resonant frequency. The MSP actuator exhibits an unlimited displacement, and its moving direction is controlled by the operating frequency used.

Magnetostrictive microcantilever (MSMC), as a high-performance biosensor platform, was introduced recently. By using physical absorption, an antibody against Escherichia coli is immobilized onto the surface of the MSMC to form a biosensor. The real-time and in situ detection of E. coli in water using the biosensor is reported. The responses of the biosensor in E. coli suspension with different concentrations were studied, which were used to determine the detection limit of the biosensor. It is confirmed by using SEM observation and a control sensor approach, respectively, that the experimentally observed response of the biosensor is due to the binding of E. coli on the surface of the biosensor. It is found that the detection limit is improved by reducing the size of the MSMC, which is consistent with the theoretical calculation. For an MSMC with the size of 1.5 mm × 0.8 mm × 35 μm, the detection limit is 105 cfu/ml.

The magnetostrictive microcantilever (MSMC) as a high-performance transducer was introduced for the development of biosensors. The principle and characterization of MSMC are presented. The MSMC is wireless and can be easily actuated and sensed using magnetic field/signal. More importantly, the MSMC exhibits a high Q value and works well in liquid. The resonance behavior of MSMC is characterized in air at different pressures and in different liquids, respectively. It is found that the Q value of the MSMC in water reaches about 40. Although the density and viscosity of the surrounding media affect the resonance frequency and the Q value of MSMC, the density has a stronger influence on the resonance frequency and the viscosity has a stronger influence on the Q value, which result in that, for MSMC in air at pressure of less than 100 Pa, the resonance frequency of MSMC is almost independent of the pressure, while the Q value increases with decreasing pressure. MSMC array was developed and characterized. It is experimentally demonstrated that the characterization of an MSMC array is as simple as the characterization of a single MSMC. A filamentous phage against Salmonella typhimurium was utilized as bio-recognition unit to develop an MSMC based biosensor. The detection of S. typhimurium in water demonstrated that the MSMC works well in liquid.

In this paper, we presented a theoretical method for studying the behavior of magnetic field intensity and eddy current inside a magnetostriction based bi-layered composite. Firstly, the mathematical model for the electromagnetic field in the composite was established. Then, the governing equation for determining the magnetic field intensity and eddy current was solved. Furthermore, the effect of the composite’s conductivity on the magnetic field intensity and eddy current were discussed. Lastly, by comparing with the well known R.L. Stoll’s equation, the magnetic field intensity calculated based on our equation showed a less than 0.5% error.

In this work, we propose a novel wireless actuator which is composed of magnetostrictive material/copper bi-layer film. The actuator can be controlled to move like a snake bi-directionally along a pipe by tuning the frequency of external magnetic field near its first order resonant frequency. The governing equation for the actuator is established and the vibration mode shape function is derived. Theoretical analysis shows that motion of the actuator is achieved by asymmetric vibration mode shape, specific vibration bending deformation, and effective net total impacting force. The simulation and experimental results well confirm the theoretical analysis. This work provides contribution to the development of wireless micro robots and autonomous magnetostrictive sensors.

Utilizing magnetostrictive effect, the metallic glass is used to form mechanical resonators with different configurations. The resonance behaviors of these resonators are studied under different conditions, including different dc magnetic bias fields and different ac magnetic driving field. It is found that the resonators made of metallic glass exhibit a higher quality merit factor. Based on the results, it is also found that the acoustic wave velocity of the metallic glass decreases with increasing frequency. The application of these resonators as sensor platform is investigated. It is found that both odd and even vibration modes can be detected. Therefore, it provides a unique device that is capable to detect the target species on the sensor surface without “blind point(s)”, which is a challenge for all sensors based on other types of resonators. For the biosensors based on these resonators, a high sensitivity was observed. The advantages of these sensors over the current devices are demonstrated by the detection of Salmonella typhimurium (S. typhimurium) in water.

High performance biosensors are urgently needed from medical diagnosis, to food safety/security, to the war on bio-terrorist. Recently, magnetostrictive microcantilever (MSMC) and magnetostrictive particle (MSP) have been developed as high performance biosensor platform. Both MSMC and MSP are wireless sensors and exhibit advantages over current acoustic wave biosensor platforms. Theoretical analysis and experimental results indicate that micro/nano scale MSMC and MSP have ultra-high sensitivities. However, in real detection, there is a challenge faces all micro/nano scale sensors because of their small size. That is, a long time is required for the tiny sensors to react with the target species. Due to the magnetic and wireless nature, MSP provides a unique way to bring the nanosensors to target species. The fabrication of bar-like MSPs in nanoscale is reported. Amorphous Fe-B alloy was selected as target magnetostrictive materials for fabrication. The properties of these nanobars were determined. The morphology and magnetic properties of the nanobars were characterized. The results ware analyzed and the size effect on the microstructure and properties is discussed.

Microcantilevers (MCs) as state-of-art sensor platforms have been widely investigated. We recently introduced a new type of MC, magnetostrictive microcantilever (MSMC), as high performance sensor platform. The MSMC is a remote/wireless sensor platform and exhibits a high quality merit factor in liquid. In this paper, a MSMC-based biosensor is developed for detecting B. anthracis spores in liquid, a potential biothreaten agent. The results demonstrated the advantages of MSMCs as a sensor platform. MSMCs with different sizes were fabricated and utilized in the experiments. The MSMCs were coated with the filamentous phage as a bio-recognition element to capture the B. anthracis spores. The phage-coated MSMCs as biosensors were exposed to cultures containing target spores with concentrations ranging from 5 * 10 4 spores/mL to 5 * 10 8 spores/mL. The resonance frequency of the MSMC sensors in cultures was monitored in a real-time manner. The results showed that for MSMCs of 2.8 mm * 1.0 mm * 35 mm and with 1.4 mm * 0.8 mm * 35 mm have a detection limit of 10 5 and 10 4 spores/mL, respectively.

Recently, the magnetostrictive microcantilever (MSMC) as a high performance biosensor platform was introduced. The MSMC is a wireless acoustic wave (AW) sensor and exhibits a high Q value. More importantly, the MSMC works well in liquid. In this paper, the detection of Bacillus anthracis spores using MSMCs with filamentous phage as the bioprobe is reported. The phased-coated MSMC biosensors were exposed to cultures containing target spores with increasing concentrations ranging from 5 × 104 to 5 × 108 spores/mL. By monitoring the shift in the resonance frequency of the MSMCs, the spores were detected in a real-time manner and a detection limit of 105 spores/mL was obtained for the MSMCs used in this research. Higher sensitivity is expected for the MSMCs with smaller size.

The existence of “blind point” lowers the mass sensitivity and reliability of magnetostrictive particle (MSP) based biosensors. In addition, asymmetric distribution of mass loading (e.g. bacteria) will cause the shift of “blind point” and change of mass sensitivity of an MSP based biosensor. In this work, a modal analysis method was introduced and conducted to derive the governing vibration equation for an MSP biosensor with asymmetric mass loading. The effects of asymmetric mass loading on the “blind point” shift and mass sensitivity were unveiled by solving the governing vibration equation. It was found that the plot of “blind point” shift showed an “M” shape with the valley located at a/l ∼ 0.5 and two peaks located at a/l ∼ 0.25 and a/l ∼ 0.75. In addition, the theoretical results showed that the resonance frequency shift (Δf) depends on the value of a/l (i.e. both the attached mass and mass distribution) and their relationship is nonlinear. Based on the definition of mass sensitivity (Sm), the values of Sm were derived for the selected values of a/l. The results showed that Sm decreased initially with increasing a/l, reaching the minimum, and then increased until a/l = 1. That is, the maximum mass sensitivity is obtained when a/l equals to a critical value Xc (0 < Xc < l). Based on the result, an optimal mass loading distribution design criterion for developing a more sensitive MSP based biosensor was proposed.