Recent experiments demonstrated emerging alternating insulator and metal phases in Mott insulators actuated by a direct bias voltage, leading to oscillating voltage outputs with characteristic frequencies. Here, we develop a physics-based nonequilibrium model to describe the dynamics of oscillating insulator-metal phase transitions and experimentally validate it using a ${\text{VO}}_{\text{2}}$ device as a prototype. The oscillation frequency is shown to scale monotonically with the bias voltage and series resistance and terminate abruptly at lower and upper device-dependent limits, which are dictated by the nonequilibrium carrier dynamics. We derive an approximate analytical expression for the dependence of the frequency on the device operating parameters, which yields a fundamental limit to the frequency and may be utilized to provide guidance to potential applications of insulator-metal transition materials as building blocks of brain-inspired non-von Neumann computers.

Antennas that operate in the very low frequency (LF) band and below are useful for a number of applications, including long-distance and underwater communication. When constrained in size, the antennas are electrically small and very inefficient. This has motivated the need for novel approaches to LF antenna design. Here, we present concepts for antennas that generate electromagnetic signals from mechanical motion. We first review the generated fields and efficiency of conventional magnetic and electric dipole transmitters. This is then extended to their mechanical counterparts for comparison. Our results show that the motion of magnets or electrets (the electrical analog of a magnet) can efficiently radiate electromagnetic energy when coupled to a low-loss electromechanical suspension. Mechanical antennas, with spatial dimensions on the order of a meter, can theoretically exceed the performance of conventional short dipole and coil transmitters by more than eight orders of magnitude for frequencies of 1 kHz and below. This paper is intended to lay the foundation for future development involving the implementation of efficient, small form-factor, mechanically actuated antennas.

We have designed, built, and tested novel low-power (less than 10 nW) resonant acceleration switches. The switches respond to vibration at specifically designed frequencies between 30 and 1000 Hz by resonating with sufficient displacement to close an electrical contact and consume power only while vibration is occurring. A rotational design avoids switch closings from DC acceleration, and the quality factor, adjustable between 102 and 105 by tuning the vacuum level, sets the resonant detection threshold. The design includes electrostatic combs for self-test and frequency tuning (up to several Hz), compliant contacts to reduce squegging and contact damage, and ruthenium-coated contacts for improved reliability. Fabrication is accomplished with deep reactive ion etching at up to 50:1 aspect ratios, HF vapor release, and XeF2 frequency trimming (up to 30% of the as-fabricated frequency). Testing with vibration recordings played back through a shaker table demonstrates that the switches correctly identify a target without any false alarms.

We present a study of co-sputtered VO2-SiO2 nanocomposite dielectric thin-film media possessing continuous temperature tunability of the dielectric constant. The smooth thermal tunability is a result of the insulator-metal transition in the VO2 inclusions dispersed within an insulating matrix. We present a detailed comparison of the dielectric characteristics of this nanocomposite with those of a VO2 control layer and of VO2/SiO2 laminate multilayers of comparable overall thickness. We demonstrated a nanocomposite capacitor that has a thermal capacitance tunability of ∼60% between 25 °C and 100 °C at 1 MHz, with low leakage current. Such thermally tunable capacitors could find potential use in applications such as sensing, thermal cloaks, and phase-change energy storage devices.

We have designed a novel microelectromechanical systems (MEMS) resonant acoustic wake-up switch which is actuated by ambient sound waves, using zero power while waiting for a signal at its resonant frequency and less than 10 nW when the signal is detected. The system uses a battery to charge a capacitor through MEMS switches activated only by the target signals. The sensor is of rotational design allowing it to be insensitive to linear vibration and static gravity forces. Analysis and experimental results maximizing the Q of these resonators in air are presented. A simple, novel fabrication process is presented which uses silicon-on-insulator bonded wafers and still provides metal-metal electrical contacts. These devices have successfully detected 80-Hz sound as low as 0.005 Pa rms (48-dB SPL // 20 mu Pa) from a generator.

Wireless neural stimulators are being developed to address problems associated with traditional lead-based implants. However, designing wireless stimulators on the sub-millimeter scale (<1 mm3) is challenging. As device size shrinks, it becomes difficult to deliver sufficient wireless power to operate the device. Here, we present a sub-millimeter, inductively powered neural stimulator consisting only of a coil to receive power, a capacitor to tune the resonant frequency of the receiver, and a diode to rectify the radio-frequency signal to produce neural excitation. By replacing any complex receiver circuitry with a simple rectifier, we have reduced the required voltage levels that are needed to operate the device from 0.5 to 1 V (e.g., for CMOS) to ~0.25-0.5 V. This reduced voltage allows the use of smaller receive antennas for power, resulting in a device volume of 0.3-0.5 mm3. The device was encapsulated in epoxy, and successfully passed accelerated lifetime tests in 80°C saline for 2 weeks. We demonstrate a basic proof-of-concept using stimulation with tens of microamps of current delivered to the sciatic nerve in rat to produce a motor response.

In this paper, an alternative approach to beam steering is presented through the use of a novel quadrifilar helix antenna, with a monopole in its center to get a low form factor and high performance. By altering the phase and amplitude of the monopole, the beam can be 'steered' 360 degrees in the phi direction, and 90 degrees in the theta direction. Simulated test data showing antenna performance is compared to current beam steering methodologies. Measured results are compared to simulated test data.

Reports on major events, discussions, and topics of interest that are part of the IMS 2015 Conference.

A frequency and polarization reconfigurable antenna based on electrowetting liquid metal microswitches is presented. The microswitches consist of electrostatically actuated mercury droplets that selectively connect solid metal traces. This mechanism is designed into a single-feed patch antenna configurable between two communication bands and the GPS band with different circular polarizations. The antenna topology is based on a corner truncated square patch with switched sets of extensions to achieve resonant frequency and axial ratio control. Measurements of manually reconfigured prototypes demonstrate frequency and polarization configurability.

A new method is presented for integrating high performance wire-based inductors into thin, planar, chip-scale formats. The method is designed for compatibility with commonly-used rapid prototyping tools, and fabrication can be automated for volume production. The chip-scale inductors are designed for inductances in the 1-10 nH range, self-resonant frequencies above 5 GHz, and quality factors exceeding 75-100. The process can produce a stand-alone chip or can be integrated with existing multi-chip modules and integrated circuits.

IMS Special Issue May 2014 The IEEE Microwave Theory and Techniques Society (MTT-S) has launched major strategic initiatives to connect with and to provide science, technology, engineering, and math (STEM) educational programs to high school and undergraduate college students. The MTT-S and the 2014 International Microwave Symposium (IMS2014) Steering Committee fully recognize that the future of RF and microwave technology depends on stimulating the interest of the best and brightest from our younger generation in these exciting technologies. In support of these MTT-S strategic initiatives, IMS2014 is pleased to launch two unique programs that offer outreach to a new generation of younger students in high school and college. While maintaining a valuable tradition of programs for graduate student participants, IMS2014 will also create a unique professional experience for younger students. These programs serve an important educational mission as well as a long-term goal to attract a diverse pool of highly motivated students to the field of microwave and RF engineering. The two programs are IMS STEM and Project Connect.

The authors discuss an overview of strongly correlated electron systems and metal-insulator transition (MIT) oxide materials. Microwave applications of MIT materials are also introduced. This overview offers a vision for future microwave devices with adaptive capabilities.

The geometry of a MEMS tuning fork resonator was optimized using a bio-inspired binary particle swarm optimization (BPSO) technique in order to reduce energy dissipation from thermoelastic dissipation (TED). The optimization technique combines fundamental physics with bio-inspired algorithms to navigate the complicated design space that arises from multiphysical problems. Fully-coupled thermomechanical simulations were used for optimization of QTED, which is the quality factor (Q) as limited by thermoelastic dissipation (TED). Through this approach, a TED-limited Q of 57,000 was simulated, showing a 40% improvement over previous designs that were generated from the conventional intuitive design approach. This trend of improved Q for BPSO-optimized designs over previous optimization using manual slot placement was also confirmed with experiments.

In micro- and nano-scale resonators, a key performance metric is the quality factor (Q), which is the ratio of stored mechanical energy to the energy dissipated. In well-optimized designs, Q is limited by thermal physics and specific energy loss mechanisms including thermoelastic, Akhieser, and Landau-Rumer damping. The relative importance of each effect depends on the time and length scales dominating the device. Most published analyses focus on special regimes where only one mechanism dominates, though real devices may operate in regimes that are not the limiting case. This paper presents thermal damping across the range of frequency and length scales. Data on acoustic loss is compared with theory.

We experimentally verify the phase-noise model for oscillators operating in a nonlinear regime by testing a micromechanical resonator-based oscillator (MEMS oscillator). Operation of oscillators in the nonlinear regime had been believed to induce instability - a belief we have demonstrated to be mistaken. As a result of this misunderstanding, little study has been devoted to the phase-noise performance of oscillators in the nonlinear regime. In this study, we compare measurements of the phase noise of MEMS oscillators far into the nonlinear regime and compare them with a recent prediction. This paper provides confirmation that low phase-noise performance is possible in the nonlinear regime, and confirms that models can be used to predict and optimize performance.