Mu Chiao

A Passive Radio-Frequency pH-Sensing Tag for Wireless Food-Quality Monitoring

We present a new method, suitable for food quality management by wirelessly monitoring pH level changes in food with a flexible pH sensor embedded in a batteryless radio-frequency (RF) transponder. The wireless sensor tag includes a flexible pH sensor based on miniature iridium oxide (IrOx) and silver chloride (AgCl) sensing electrodes integrated on a deformable substrate, and batteryless wireless communication circuitry. The sensor tag and reader system is designed to achieve convenient, long-term, and on-demand wireless in situ monitoring of food quality, especially for large-quantity applications and continuous monitoring from place of production to retail stores. Low-cost IrOx sol-gel fabrication process was applied on polymeric substrates to form the flexible sensing films, and a sensitivity of -49.7 mV/pH was achieved. Inducting coupling provides electromagnetic energy from the reader to drive the transponder circuits that retransmit the sensor-data modulated signals back to the reader. The electrochemical potential created by the IrOx/AgCl sensing electrodes is converted to a modulated frequency and the system achieves a sensitivity of 633 Hz/pH. The wireless pH sensing system was tested for in situ monitoring of the spoilage processes in fish meats continuously for over 18 h. The feasibility of wirelessly monitoring pH values in fish meats that could be used to identify spoilage remotely has been demonstrated.

Sol-Gel Iridium Oxide-Based pH Sensor Array on Flexible Polyimide Substrate

Iridium oxide pH sensing film is demonstrated with wide pH-sensing ranges, high durability, and small drifts in potentials. Using sol-gel process, a lower fabrication cost and less labor-intensive method, to deposit iridium oxide thin films for pH sensing is reported previously by our group with expected advantages. In this paper, we fabricate and test pH sensing characteristics of 4 × 4 anhydrous iridium oxide thin-film electrode arrays on flexible substrates. The sensors in arrays exhibit Nernstian potential responses in the range of 57.0-63.4 mV/pH. Stability, repeatability, and hysteresis effects of the pH sensor arrays are examined. A multichannel recording system is built to demonstrate the functionality of the pH sensor arrays in monitoring spatial and temporal pH changes across a surface.

Fabrication techniques and RF performances of transmission lines on polymer substrates

The advantages of polymers have made them popular choices in many micro device applications. The benefits of low material and fabrication costs have been demonstrated in many micro-fluidic devices. The low conductivities and low dielectric constants of polymers provide potentials for high quality-factor RF MEMS applications. Nevertheless, the extension of using polymers for electronic components has not been well explored. In this work, we investigated the fabrication processes and RF performances of coplanar waveguide (CPW) transmission lines, with which many RF MEMS phase shifters, tuners, switches and interconnects are built, on polymer dielectric layers. In order to achieve optimum results, the CPW transmission lines were fabricated on benzocyclobutene (BCB), kapton and polyimide polymers. Our experimental results indicated very low insertion losses of CPW transmission lines with BCB as a dielectric layer and with kapton as substrate, and a moderate insertion loss with polyimide as a dielectric layer.

Investigation of repeatability of sol-gel iridium oxide pH sensor on flexible substrate

In this paper, we presented the fabrication process of miniature pH sensor arrays on flexible polymer substrates. The repeatability of the sensors based on sol-gel fabrication processes was investigated. The sensor repeatability was characterized with linearity, decay time, environmental parameter control and potential stability. Similar linear responses were found in different batches of sensor arrays. Near super- Nernstian responses were measured on each sensor with slope ranges from -71.6 to -110 mV/pH within a pH range between 2 and 12. The response times were compared in different batches. Six to twenty five seconds of average decay time were shown in each sample repeatedly. Three sensors showed the close potential response in different volumes of pH buffer solution. The sensor showed good stability in each step of the titration process between pH values of 1.8 and 11.9. The peak and saturated potential values presented high correlation with pH values with minor noises. The results showed good sensitivity, stability and repeatability using the sol-gel processes for iridium-oxide pH sensors on flexible substrates.

A cantilever-type electrostatic zipping actuator

This paper discussed modeling, design, fabrication and characterization of a new cantilever-type electrostatic zipping actuator. The actuator was designed to achieve high displacements and fabricated using multi-layer polysilicon foundry fabrication process PolyMUMPS. The high out-of-plane displacement is to satisfy the requirements in specific optical applications. In this paper we presented the design considerations in displacement, electrostatic forces and electrostatic stability. The electrostatic force between the curved cantilever and the bottom electrode on the substrate pulls the cantilever down. With a warped cantilever, the force closes the gap from the anchor end and gradually the zipping effect actuates the entire cantilever without increasing the biasing voltages. Previous electrostatic zipper actuators require a thin layer of dielectric material on top of the bottom electrode to prevent electrical shorting. They may have an issue with electrical breakdown of the thin dielectric layer due to the film quality. We designed a new mechanical structure to avoid the electrical shorting problem without a layer of dielectric material. Our analysis and experimental results demonstrated that the proposed design can withstand high voltages without shorting and is capable of high deflection. The vertical displacements of different device configurations were found ranging from 30.4μm to 450μm while the actuation voltages varied in the range from 12V to 45.3V for complete actuation. The pull-in voltages for various configurations were analyzed and presented.

Dual-Axes Confocal Microlens for Raman Spectroscopy

This paper presents a novel dual-axes scanning microlens for in vivo near infrared (NIR) Raman spectroscopy. In vivo Raman spectra of fibrosarcoma tumor skin and normal mouse skin measured from the microlens are reported. Out-of-plane (Z-axis) and transverse (X-axis) actuations are demonstrated using electrostatic and electromagnetic forces, respectively. The microlens achieves 120 ¿m scan in Z-axis at 286 Hz, and 163 ¿m scan in X-axis at 480 Hz.

An Optical Scanner Based on Cantilever-type Electrostatic Zipping Actuators

This paper discusses modeling, design, fabrication and characterization of an optical scanner based on cantilever-type electrostatic zipping actuators. The electrostatic actuator has been designed to achieve high displacements for large optical scanning angles at lower actuation voltages. The zipping actuators are fabricated using multi-layer polysilicon foundry fabrication processes. The electrostatic force between the cantilever and the bottom electrode on the substrate pulls the cantilever down. With a warped cantilever, the force closes the gap from the anchored end and gradually the zipping effect actuates the entire cantilever. In our design, mechanical structures are arranged to avoid electrical shortcircuit. With various annealing temperatures, the warped angles are controllable. The cantilever serves as a reflective surface and the high out-of-plane displacement is used to steer a reflected laser beam for imaging and scanning applications. In this paper we present the design considerations in electrostatic zipping actuator displacement and control as well as the arrangement for optical scanning.

Development of an IrOx micro pH sensor array on flexible polymer substrate

pH sensor is an essential component used in many chemical, food, and bio-material industries. Conventional glass electrodes have been used to construct pH sensors, however, have some disadvantages in specific applications. It is difficult to use glass electrodes for in vivo biomedical or food monitoring applications due to size limitation and no deformability. In this paper, we present design and fabrication processes of a miniature iridium oxide thin film pH sensor array on flexible polymer substrates. The amorphous iridium oxide thin film was used as the sensing material. A sol-gel dip-coating process of iridium oxide film was demonstrated in this paper. A super-Nernstian response has been measured on individual sensors of the array with a slope of -71.6±3 mV/pH at 25°C within the pH range between 2.83 and 11.04.

An electromagnetically actuated fiber optic switch using magnetized ferromagnetic materials

This paper presents the design, fabrication and testing of a fiber optic switch actuated electromagnetically. The ferromagnetic gel coated optical fiber is actuated using external electromagnetic fields. The ferromagnetic gel consists of ferromagnetic powders dispersed in epoxy. The fabrication utilizes a simple cost-effective coating setup. A direct fiberto-fiber alignment eliminates the need for complementary optical parts and the displacement of fiber switches the laser coupling. The magnetic characteristics of magnetized ferromagnetic materials are performed using alternating gradient magnetometer and the magnetic hysteresis curves are measured for different ferromagnetic materials including iron, cobalt, and nickel. Optical fiber switches with various fiber lengths are actuated and their static and dynamic responses for the same volume of ferromagnetic gel are summarized. The highest displacement is 1.345 mm with an input current of 260mA. In this paper, the performance of fiber switches with various coating materials is presented.

Design considerations of reconfigurable antennas using MEMS switches

In this paper, reconfigurable antenna design consideration is discussed. The antenna design constrains are base on the use of radio frequency microelectromechanical system (RF MEMS) switches. The design consideration includes practical issues in using the switches to either change the antenna feeding networks or change the antenna topologies. In the first design, a coplanar waveguide (CPW)-to-microstripline transition technique is used to integrate the small switches onto the antenna feeding networks to achieve beam steering. In the second design, the switches are used to change the antenna ground plane topology to achieve frequency switching. Both antennas are modeled using our Finite-Difference Time-Domain (FDTD) simulator. The beam steering antenna will be capable of more than 60° scanning angles and the frequency switching antenna can operate at 2.4GHz and 5.8 GHz for WLAN applications.