M. Tecpoyotl-Torres

Design and fabrication of a MEMS thermal actuator for 3D optical switching applications

This paper presents a novel thermally-actuated vertical micromirror for optical communications. Fabricated in a standard surface micromachining process, this micromirror can achieve low insertion loss (< 1 dB) and is capable of operating at CMOS-compatible voltage levels. It has a measured maximum power consumption of only 50-mW and a switching speed in the order of 16 ms with 5-V drive.

Modeling of MEMS Thermal Actuation with External Heat Source

This paper presents the thermal analysis and design of micro-actuators based on standard MEMS technology irrespective of the input heat source. The typical approach for driving this kind of actuators is by applying an electric current that flows through the device and generates Joule heating. However, this requires relatively large currents and the corresponding power consumption. As an alternative to electrically driven thermal actuators, this work explores the possibility of developing thermal actuators that can be activated with an external heat source and, for example, scavenge heat from the surrounding medium. The mathematical description for heat transfer within the MEMS device is presented along with numerical simulation results. A discussion about the opportunities and limitations of externally heated thermo actuators is also presented.

Superheterodyne amplification of sub-millimeter electromagnetic waves in an n-GaAs film

A superheterodyne amplification of sub-millimeter electromagnetic waves in GaAs due to the negative differential mobility is analyzed. The nonlinearity arises from the modulation of concentration, due to a space charge wave, and from the ponderomotive force, due to electromagnetic waves. The case of resonant interaction of two traveling counter propagating electromagnetic waves and the space charge wave in a thin n-GaAs film placed into a dielectric waveguide is considered. The case of 2D electron gas is also analyzed. The simulation of this nonlinear interaction shows a certain increment of the amplification.

Data fitting on a spherical shell

We present in this paper a data fitting method that analyzes a spherical shell that uses the near orthogonality of the Spherical Harmonics Ylm(Θ,Φ) within a discrete data collected on a spherical shell to obtain the best rms fit. This is obtained through the generation of an orthogonal basis from the spherical harmonics Ylm(Θ,Φ) on a discrete and often irregular data set on a spherical shell.

Polysilicon vertical actuator powered with waste heat

This paper presents a new micro thermal actuator with bi-directional vertical motion. Traditional thermal actuators require an electric current to generate heat by Joule effect and obtain motion via thermal expansion. This work offers a simplified polysilicon thermal actuator designed to operate with an external heat source and, for example, scavenge heat from the surrounding medium. The actuator was fabricated using a standard surface micromachining process (PolyMUMPs). The thermal actuation characteristics, analysis, and experimental results for this novel micro-mechanical device are provided to illustrate performance and potential applications.

Polysilicon thermal micro-actuators for heat scavenging and power conversion

This paper describes the design and experimental characterization of two optimized thermal actuators devised to operate by means of scavenging heat from the environment. Different from the traditional MEMS thermal actuator that relies on electric current to generate heat by Joule effect, the devices herein presented have been optimized to absorb external heat and convert it into mechanical displacement and force. The behavior of vertical and horizontal microactuators fabricated in a standard surface micro-machining process (PolyMUMPs) demonstrates the viability of exploiting heat from the surrounding medium to realize batteryless microsystems. Analytical and finite element models are provided in support of the design. Results show that fairly large and useful displacements can be achieved at commonly available operating temperatures.

A semi-spherical irradiance profiles meter used as a quality control device

The design of a semi-spherical irradiance profile detector (SD) is shown. With this device, we obtain the distribution of illumination due to punctual sources in the visible range. This meter can be also used as quality control device for lamps and bulbs. We are interested in the distribution of the irradiance, instead of the total irradiance over a complete region, which is the information given by spherical meters, such as the Ulbrich spheres. The obtained discrete profiles corresponds to the irradiance, as equivalent to the voltage intensity detected in semispherical detector basic sensor. These voltage values permit us to obtain the corresponding profile to each source and give as the capability to chose the better sources for specifics tasks.

Low Cost Prototype of an Outdoor Dual Patch Antenna Array for the Openly TV Frequency Ranges in Mexico

The interest in this area is because of the fact that the openly TV is one of the most important communication media in our country. From information supplied in 2009 in the National Survey over availability and use of Technologies, it reveals that the 72.8% of the population uses the services of the openly TV (Instituto Nacional de Estadistica, Geografia e Informatica [INEGI], 2009). A TV can be found in almost all homes of the country, but only 13.6% correspond to digital technology, while only a half of homes with a digital TV requires signal payment. The availability of TVs in Mexican homes in 2010 remained without severe changes (INEGI, 2010).

Multimode interference effects in optical fiber for pressure sensing applications

Applications of Multimode Interference (MMI) effects in optical devices have been increased today due their excellent properties and easy fabrication. Incorporation of these effects in optical fiber has been achieved through a single-mode - multimode - single-mode (SMS) fiber structure showing high sensitivity to bending-loss phenomenon. The latter has been efficiently implemented in pressure sensing application such as is presented in this work. Basically, the SMS structure is embedded in a pressure-sensitive membrane to convert pressure in a mechanical displacement resulting in an attenuation of the transmitted intensity proportionally to the applied pressure. Under this configuration, an all-fiber pressure sensor with high sensitivity and repeatability is obtained into a pressure range from -13 psi to +13 psi. The max pressure range can be varied to 140 psi with our configuration when the membrane thickness is changed. Important features of the proposed all-fiber MMI pressure sensor are its easy-fabrication and low-cost since an inexpensive instrumentation is required.

Rectangular prototype to determine the irradiance pattern produced by directive sources

In order to determine the irradiance profile of a directive source on a plane XY, we present an arrangement of geometry similar to conventional scanners. It is formed by two vertical bases of a mobile rail. On this rail, a photodetector is located, making it able to move from right to left, covering a mesh of 14x15 detection points. The XY movements of the setup are determined by servo motors, which determine the resolution, but considering the interest of researchers in this area, and the feasibility to use a table XY for the scanning, we implement its use as a part of this meter. The detector is located at the corner of the mobile section. The height of the light source under test is located at the central part of the described area. The utilization of only one photo-detector was decided with the purpose of a higher homogeneity of the irradiance measurements. The detector must have high stability and low noise. The resolution XY is determined by the movements on the axes of a length determined by the DSPIC programming. The use of this device instead of commercial hardware for data acquisition contributes to the low costs of the prototype. It was realized all the necessary tests for the generation of reliable information, establishing the time needed to achieve the stability of the system, as well as the levels of noise due to the presence of the detector and of the electronic elements. This prototype has a very simple geometry and relatively low cost. It constitutes a good option to determine the irradiance profile of directive sources.