This paper experimentally demonstrates the operating principles of a near-field multiferroic antenna. The antenna uses a piezoelectric lead-zirconate-titanate stack to apply a time varying strain to a magnetoelastic iron gallium Fe_80.77Ga_19.23 (FeGa) rod. The voltage induced strain controls the net magnetization of the FeGa rod to generate oscillating magnetic fields in free space surrounding the antenna. Direct experimental measurements of the mechanical force, strain, magnetic field, and magnetic flux inside the FeGa rod were collected and show a strong correlation with the dynamic magnetic field measured in free space. Additionally, an analytical dipole model is used to demonstrate that the free space signal originates from the changing magnetization in the FeGa rod, providing a clear multiferroic antenna proof-of-concept demonstration. Finally, analysis is provided to highlight the importance of device geometry and demagnetization fields when optimizing the antenna response.

An unconditionally stable finite-difference time-domain (FDTD) algorithm is proposed to predict and understand the complex response in strain-mediated multiferroic RF devices such as antennas. A system of three coupled sets of governing equations is solved simultaneously: (1) Maxwell's equations for electromagnetic (EM) wave propagation, (2) the Landau-Lifshitz-Gilbert (LLG) equation for magnetic spin response, and (3) Newton's law for acoustic behavior. The formulation of this algorithm is elaborated on in detail followed by a demonstration of its capability through the simulation of a 1.3 μm thick bulk-acoustic-wave (BAW) based strain-mediated multiferroic antenna. Analysis of the far-field radiation efficiency of this antenna as a function of magnetic DC bias demonstrates the importance of aligning the ferromagnetic resonance (FMR) and the mechanical BAW resonance to enhance EM radiation performance. Results also show that reducing the magnetic loss, or in other words reducing the FMR linewidth, represents the dominating feature to achieve higher radiation efficiencies in these antennas.

This review describes recent experimental developments in the study of nonlinearities for flexural microelectromechanical systems (MEMS) structures. It includes motivation for studying a variety of nonlinear phenomena, highlighting applications where nonlinearities are relevant. Examples are described where nonlinearities are seen as a nuisance, along with techniques used to mitigate the nonlinearities. More recently, efforts to exploit nonlinearities for improved performance have emerged and are also described. After a summary of the theory behind nonlinear mechanisms, the article describes progress in several areas of nonlinearity: engineering nonlinearities to enhance performance, bifurcations and multistability, parametric processes, frequency mixing, nonlinearly coupled resonances, and nonlinear dissipation.

Arbitrary patterning of micro-objects in liquid is crucial to many biomedical applications. Among conventional methodologies, acoustic approaches provide superior biocompatibility but are intrinsically limited to producing periodic patterns at low resolution due to the nature of standing waves and the coupling between fluid and structure vibrations. This work demonstrates a near-field acoustic platform capable of synthesizing high resolution, complex and non-periodic energy potential wells. A thin and viscoelastic membrane is utilized to modulate the acoustic wavefront on a deep, sub-wavelength scale by suppressing the structural vibration selectively on the platform. Using 3 MHz excitation (λ ∼ 500 μm in water), we have experimentally validated such a concept by realizing patterning of microparticles and cells with a line resolution of 50 μm (one tenth of the wavelength). Furthermore, massively parallel patterning across a 3 × 3 mm² area has been achieved. This new acoustic wavefront modulation mechanism is powerful for manufacturing complex biologic products.

Enhancing the magnetoelectric coupling in a strain-mediated multiferroic composite structure plays a vital role in controlling magnetism by electric fields. An enhancement of magnetoelastic coupling between ferroelectric single crystal (011)-cut [Pb(Mg_1/3Nb_2/3)O₃]_(1-x)-[PbTiO₃]_x (PMN-PT, x≈ 0.30) and ferromagnetic polycrystalline Ni thin film through an interposed benzocyclobutene polymer thin film is reported. A nearly twofold increase in sensitivity of remanent magnetization in the Ni thin film to an applied electric field is observed. This observation suggests a viable method of improving the magnetoelectric response in these composite multiferroic systems.

Frequency conversion is an essential tool in modern communication devices. Traditionally, frequency conversion is achieved through parametric coupling via nonlinear inductors or capacitors whose reactance is modulated by a carrier wave. In this study, nonlinear acoustic Lamb wave devices are explored for simultaneous signal filtering and frequency conversion. Three sets of interdigitated transducers are fabricated on a piezoelectric aluminum nitride (AlN) thin film to provide a carrier wave, a low-power signal wave, and to receive a frequency converted mixed wave. Two devices are fabricated and tested to demonstrate frequency upconversion and downconversion by utilizing mechanical nonlinearity of AlN, and the results are compared to a nonlinear circuit model. The nonlinear circuit model is used to link experimentally observed phenomenon to the acoustic material's intrinsic nonlinearity. The nonlinearity of AlN reaches a maximum of 2.8% with a carrier wave power at 28 dBm. An analytical model is used to predict device performance along with physical dimensions. These analytical results show that nonlinear acoustic mixers and filters can approach sub-millimeter sizes, which is orders-of-magnitude smaller than conventional structures using nonlinear inductors and capacitors.