Kyo D. Song

Microwave power for smart material actuators

The concept of microwave-driven smart material actuators was envisioned and developed as the best option to alleviate the complexity and weight associated with a hard-wire-networked power and control system for smart actuator arrays. The patch rectenna array was initially designed for high current output, but has undergone further development for high voltage output devices used in shape control applications. Test results show that more than 200 V of output were obtained from a 6 × 6 array at a far-field exposure (1.8 m away) with an X-band input power of 18 W. The 6 × 6 array patch rectenna was designed to theoretically generate voltages up to 540 V, but practically it has generated voltages in the range between 200 and 300 V. Testing was also performed with a thin layer composite unimorph ferroelectric driver and sensor and electro-active paper as smart actuators attached to the 6 × 6 array. Flexible dipole rectenna arrays built on thin-film-based flexible membranes are most applicable for NASAs various missions, such as microwave-driven shape controls for aircraft morphing and large, ultra-lightweight space structures. An array of dipole rectennas was designed for high voltage output by densely populating Schottky barrier diodes to drive piezoelectric or electrostrictive actuators. The dipole rectenna array will eventually be integrated with a power allocation and distribution logic circuit and microbatteries for storage of excessive power. The roadmap for the development of wireless power drivers based on the rectenna array for shape control requires the development of new membrane materials with proper dielectric constants that are suitable for dipole rectenna arrays.

Transpiration Cooling Experiment for Scramjet Engine Combustion Chamber by High Heat Fluxes

A transpiration cooling experiment using an optical heating method that provided a heat flux as high as 234 W/cm 2 on the surface of specimen for a scramjet engine was performed. In this experiment, 19-mm-diam sintered, powdered, stainless-steel tubes and a 25-mm square cross-sectional tube of perforated Inconel tube were used to investigate transpiration cooling effectiveness. The cooling effectiveness by transpiration for each specimen was measured and analyzed. As a result, the transpiration cooling mechanism appeared to be a promising approach to remove a large amount of heat from the engine wall. A preliminary analysis of the transpiration cooling mechanism and a scaling conversion study that translates the results from helium tests into the case when a hydrogen medium is used are included.

Microwave power transmission using a flexible rectenna for microwave-powered aerial vehicles

In exploiting the unique capabilities of smart actuators for applications in vehicle systems, even in unmanned or micro aerial vehicles, the power issues for smart actuators and devices have not been well addressed. This is due to the fact that the driving power for smart materials has not reached the level of the power specifications for conventional devices and systems. To answer the power issue, we have developed a wireless power transmission technology using a flexible rectenna system and implemented it for a microwave-powered aerial vehicle (MPAV) system. For this application, two flexible dipole rectennas were designed, manufactured and characterized over a frequency range of 9–12 GHz. These flexible dipole rectennas were attached and tested on the complex structure of small MPAVs. The maximum converted power output of a flexible dipole rectenna array was about 300 mA at 80 VDC. The power output from this rectenna was sufficient to run the propellers of the MPAV. Each electrically driven propeller requires approximately 2 W for operation.

Miniaturization of a Fresnel spectrometer

The core optical parts of an ultra-small spectrometer with less than 1 mm diameter were constructed using Fresnel diffraction. The fabricated spectrometer grating has a diameter of 750 µm and a focal length of 2.4 mm at 533 nm wavelength. The micro-spectrometer was built with a simple negative zone plate that has an opaque center with an ecliptic shadow to remove the zero-order direct beam to the aperture slit. Unlike conventional approaches, detailed optical calculation indicates that the ideal spectral resolution and resolving power in the Fresnel regime do not depend on the miniaturized sizes but only on the total number of rings. We calculated the 2D and 3D photon distributions around the aperture slit and confirmed that improved micro-spectrometers below 1 mm in diameter can be built with Fresnel diffraction. The comparison between mathematical simulation and measured data demonstrates the theoretical resolution, measured performance, misalignment effect, and improvement for the ultra-small Fresnel spectrometer. We suggest the utilization of an array of Fresnel spectrometers for tunable multi-spectral imaging in the ultra-violet range.

Wireless power transmission for medical applications

We studied the wireless power transmission capabilities of microwave through human skin-tissue. Microwave transmission through simulated human skins was tested with rectenna array as a power receiver located under the simulated human skin tissue. Most of transplanted medical devices and sensors require power to operate autonomously but currently by imbedded battery. Wireless power transmission alleviates the needs of imbedded power source and hard-wire power network. We used human skin-like materials, such as various polyurethanes and pork skin, under X-band microwave exposure. Transmission rate through various polyurethanes under the threshold limit value (TLV) and dielectric constant was measured in this experiment. It is also critical to measure specific absorption rates (SAR) of polyurethanes and transmission rates through polyurethanes as well as pork skin. This paper presents power transmission rates under varying thickness of polyurethanes, and effectiveness and efficiency of rectennas under the TLV of microwave power. In addition, we will discuss milimeter wave thermograph and hazards the absorption characteristics of human skin under 8-13 GHz using the results of polyurethanes and pork skin.

Perspective in Nanoneural Electronic Implants With Wireless Power-Feed and Sensory Control

New medical device technology is essential for diagnosing, monitoring, and curing wide spectrum of diseases, anomalies, and inflictions. For neural applications, currently available devices are generally limited to either a curing or a probing function. In this paper, we review the technology requirements for a new neural probe and cure device technology currently under development. The concept of the probe-pin device that integrates the probes for neurochemistry, neuroelectricity, temperature, and pressure into a single embodiment with a wireless power transmission was designed for the purpose of deep brain feedback stimulation (DBFS) with in situ neural monitoring. The probe considered for monitoring neurochemistry is a microspectrometer. The feature and size of the microspectrometer are defined for the DBFS device. Two types of wireless power transmission technology were studied for the DBFS device operation. The test results of pig skin showed that both power transmission technologies demonstrated the feasibility of power feed through human tissue.

Rectenna performance under a 200-W amplifier microwave

The concept of microwave driven smart material actuators is envisioned as the best option to alleviate the complexity associated with hard wired control circuitry for applications such as membrane actuators, insect-like flying objects, or micro-aero-vehicles. Accordingly, rectenna technology was adopted to convert power from microwave to DC and run actuator devices. Previous experimental results showed that 230 VDC output was obtained from a 6 x 6 rectenna array at a far-field exposure (1.8 meters away) with an x-band input power of 20 watts. This result showed the feasibility of using microwaves to power feed and control smart actuators. We have tested a 6 x 6 JPL array patch rectenna which was designed to generate theoretical voltages up to 540 volts. The test result indicated that the performance degradation of Shottky barrier diodes on the rectenna array caused the output voltage to drop. Thus, an estimation of output voltage was made to show the performance beyond the previous measurement by extrapolating and correlating the measured data with a 200 W TWT amplifier in a reverse process. The estimated peak output voltage was 515 volts. In this experiment, due to the degradation of the rectenna performance, we had to measure the output performance based on comparison of the previous result of the rectenna output of a 20W amplifier with the output from the 200 W amplifier. For the real applications, the degradation of Schottky diodes will be a critical issue to be resolved in the fabrication process.

Flexible Patch Rectennas for Wireless Actuation of Cellulose Electro-active Paper Actuator

This paper reports a flexible patch rectenna for wireless actuation of cellulose electro-active paper actuator (EAPap). The patch rectenna consists of rectifying circuit layer and ground layer, which converts microwave to dc power so as to wirelessly supply the power to the actuator. Patch rectennas are designed with different slot length at the ground layer. The fabricated devices are characterized depending on different substrates and polarization angles. The EAPap integrated with the patch rectenna is actuated by the microwave power. Detailed fabrication, characterization and demonstration of the integrated rectenna-EAPap actuator are explained.

Extending PAD (Power Allocation and Distribution)

Microwave-driven smart material actuators were first envisioned and developed as the best option to simplify the complexity and weight of hard wired networked power and control for smart actuator arrays. A power allocation and distribution scheme (PAD) was originally devised to simplify the wiring of thousands of control cables. The original design was limited to 20 volts, the maximum drain-source voltage of a dual-gate MOSFET used in the circuit. The present research sought to extend the usable voltage range to 200 volts.

Microwave-Driven Multifunctional Capability of Membrane Structures

A large, ultra lightweight space structure, such as solar sails and Gossamer spacecrafts, requires a distributed power source to alleviate wire networks, unlike the localized on-board power infrastructures typically found in most small spacecrafts. The concept of microwave-driven multifunctional capability for membrane structures is envisioned as the best option to alleviate the complexity associated with hard-wired control circuitry and on-board power infrastructures. A rectenna array based on a patch configuration for high voltage output was developed to drive membrane actuators, sensors, probes, or other devices. Networked patch rectenna array receives and converts microwave power into a DC power for an array of smart actuators. To use microwave power effectively, the concept of a power allocation and distribution (PAD) circuit is adopted for networking a rectenna/actuator patch array. The use of patch rectennas adds a significant amount of rigidity to membrane flexibility and they are relatively heavy. A dipole rectenna array (DRA) appears to be ideal for thin-film membrane structures, since DRA is flexible and light. Preliminary design and fabrication of PAD circuitry that consists of a few nodal elements were made for laboratory testing. The networked actuators were tested to correlate the network coupling effect, power allocation and distribution, and response time.