This paper proposes the creation of strain powered antennas that radiate electromagnetic energy by mechanically vibrating a piezoelectric or piezomagnetic material. A closed form analytic model of electromagnetic radiation from a strain powered electrically small antenna is derived and analyzed. Fundamental scaling laws and the frequency dependence of strain powered antennas are discussed. The radiation efficiency of strain powered electrically small antennas is contrasted with a conventional electric dipole. Analytical results show that operating at the first mechanical resonance produces the most efficient strain powered radiation relative to electric dipole antennas. A resonant analysis is exploited to determine the material property space that produces efficient strain powered antennas. These results show how a properly designed strain powered antenna can radiate more efficiently than an equally sized electric dipole antenna.

A micromagnetic and elastodynamic finite element model is used to compare the 180° out-of-plane magnetic switching behavior of CoFeB and Terfenol-D nanodots with perpendicular magnetic easy axes. The systems simulated here consist of 50 nm diameter nanodots on top of a 100 nm-thick PZT (Pby[ZrxTi1-x]O3) thin film, which is attached to a Si substrate. This allows voltage pulses to induce strain-mediated magnetic switching in a magnetic field free environment. Coherent and incoherent switching behaviors are observed in both CoFeB and Terfenol nanodots, with incoherent flipping associated with larger or faster applied switching voltages. The energy to flip a Terfenol-D memory element is an ultralow 22 aJ, which is 3–4 orders more efficient than spin-transfer-torque. Consecutive switching is also demonstrated by applying sequential 2.8 V voltage pulses to a CoFeB nanodot system with switching times as low as 0.2 ns.

Failure rates of spinal fusion are high in smokers and diabetics. The authors are investigating the development of a piezoelectric composite biomaterial and interbody device design that could generate clinically relevant levels of electrical stimulation to help improve the rate of fusion for these patients. A lumped parameter model of the piezoelectric composite implant was developed based on a model that has been utilized to successfully predict power generation for piezoceramics. Seven variables (fiber material, matrix material, fiber volume fraction, fiber aspect ratio, implant cross-sectional area, implant thickness, and electrical load resistance) were parametrically analyzed to determine their effects on power generation within reasonable implant constraints. Influences of implant geometry and fiber aspect ratio were independent of material parameters. For a cyclic force of constant magnitude, implant thickness was directly and cross-sectional area inversely proportional to power generation potential. Fiber aspect ratios above 30 yielded maximum power generation potential while volume fractions above 15% showed superior performance. This investigation demonstrates the feasibility of using composite piezoelectric biomaterials in medical implants to generate therapeutic levels of direct current electrical stimulation. The piezoelectric spinal fusion interbody implant shows promise for helping increase success rates of spinal fusion.

Spin-orbit torque (SOT) represents an energy efficient method to control magnetization in magnetic memory devices. However, deterministically switching perpendicular memory bits usually requires the application of an additional bias field for breaking lateral symmetry. Here we present a new approach of field-free deterministic perpendicular switching using a strain-mediated SOT switching method. The strain-induced magnetoelastic anisotropy breaks the lateral symmetry, and the resulting symmetry-breaking is controllable. A finite element model and a macrospin model are used to numerically simulate the strain-mediated SOT switching mechanism. The resultsshow that a relatively small voltage (±0.5 V) along with a modest current (3.5 × 10 7 A/cm 2 ) can produce a 180° perpendicular magnetization reversal. The switching direction ('up' or 'down') is dictated by the voltage polarity (positive or negative) applied to the piezoelectric layer in the magnetoelastic/heavy metal/piezoelectric heterostructure. The switching speed can be as fast as 10 GHz. More importantly, this control mechanism can be potentially implemented in a magnetic random-access memory system with small footprint, high endurance and high tunnel magnetoresistance (TMR) readout ratio.

Spinal fusion surgeries have a high failure rate for difficult-to-fuse patients. A piezoelectric spinal fusion implant was developed to overcome the issues with other adjunct therapies. Stacked generators were used to improve power generation at low electrical load resistances. The effects of the number of layers on average maximum power and the optimal electrical load resistance were characterized. The effects of mechanical preload, load frequency, and amplitude on maximum power and optimal electrical load resistance were also characterized. Increasing the number of layers from one to nine was found to lower the optimal electrical load resistance from 1.00 GΩ to 16.78 MΩ while maintaining maximum power generation. Mechanical preload did not have a significant effect on power output or optimal electrical load resistance. Increases in mechanical loading frequency increased average maximum power, while decreasing the optimal electrical load resistance. Increases in mechanical loading amplitude increased average maximum power output without affecting the optimal electrical load resistance.