Lun Chen Hsu

An implantable batteryless wireless impedance sensor for gastroesophageal reflux diagnosis

A new method for long term monitoring of gastroesophageal reflux is presented. The impedance of the reflux in the esophagus can be determined remotely without the need of a battery in the sensor implant. The implant includes an energy harvesting circuit, sensing electrodes, an antenna and an impedance to frequency converter. An external reader provides power to the implant and measures the impedance values simultaneously. A prototype with an overall size of 0.5×1×3.1cm3 was made with a printed circuit board and discrete components, and packaged in polydimethylsiloxane. In vivo experiments were conducted in pig cadavers. The results show good correlation between impedance and pH values of the acid solutions flushed into the esophagus, and good signal-to-noise ratios with the transducer inside the body. The impedance sensor can detect nonacid materials due to the frequency shift differences between air and solutions. The batteryless wireless impedance sensor is able to detect every reflux episode, either acid or non-acid, which provides more accurate diagnosis for the gastroesophageal reflux disease.

Evaluation of commercial metal‐oxide based NO2 sensors

Purpose – Selection of a gas sensor requires consideration of environmental effects that can significantly affect performance and cause false alarms. Metal‐oxide sensors have high sensitivity due to the specific interactions of gas molecules with thin metal‐oxide films, however, the films can also be sensitive to variations in temperature and humidity and some oxidizing and deoxidizing gases. The purpose of this paper is to evaluate the environmental effect on metal‐oxide nitrogen dioxide (NO2) sensors quantitatively.Design/methodology/approach – Three commercial metal‐oxide NO2 sensors and one electrochemical sensor were tested simultaneously under controlled gas concentrations and various environmental conditions. For this test, a customized sensor testing setup was prepared including a gas mixer, heating module, gas chamber, electronics, and data acquisition units.Findings – Based on the test results for NO2 gas concentrations ranging from 0 to 10 ppm, the metal‐oxide sensors showed significant signal ...

Remote detection of gastroesophageal reflux using an impedance and pH sensing transponder

In this work, we developed a dual-sensor system to monitor the symptoms in gastroesophageal reflux disease (GERD). The system consists of an implantable transponder and an external reader. The passive telemetry for signal transduction is based on an inductive link between two coil antennas. The reader supplies radio frequency power, obtains and stores the backscattered sensory data. The dual-sensor transponder detects both impedance and pH changes associated with the gastroesophageal reflux episodes and sends load-modulated signals back. Bench-top experiments were conducted to examine the robustness of the wireless transponding system. Preliminary in vivo experiments were conducted with a live pig. Our dual-sensor transponder system has successfully demonstrated its capability for effective GERD symptom monitoring.

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.

Design and modeling of a high accuracy three degrees of freedom MEMS manipulator

A new design for a high accuracy, 3-degree of freedom (DOF) MEMS manipulator is proposed. The 3-DOF robotic manipulator is to be used for biomedical applications such as cell probing, tissue sampling, neuron signal reading and drug delivery, in which high accuracy and repeatability of positioning is required. While sensing or imaging elements are not available in the integration with the manipulator to provide feedback for positioning, we investigated a calibration approach to minimize the positioning errors. In-plane and vertical MEMS thermal actuators are chosen to perform the required tasks. The modeling of the thermal actuators was first studied and the results match with experimental results. A calibration algorithm is implemented to allow the minimization of accumulated motion errors. The algorithm was successfully applied to the manipulator and results were obtained. A MATLAB script was written to simplify the calibration procedure. Problems faced in the design and potential solutions will be also discussed.

A polymer-based Fabry-Perot filter integrated with 3-D MEMS structures

Polymers have been considered as one of the most versatile materials in making optical devices for communication and sensor applications. They provide good optical transparency to form filters, lenses and many optical components with ease of fabrication. They are scalable and compatible in dimensions with requirements in optics and can be fabricated on inorganic substrates, such as silicon and quartz. Recent polymer synthesis also made great progresses on conductive and nonlinear polymers, opening opportunities for new applications. In this paper, we discussed hybrid-material integration of polymers on silicon-based microelectromechanical system (MEMS) devices. The motivation is to combine the advantages of demonstrated silicon-based MEMS actuators and excellent optical performance of polymers. We demonstrated the idea with a polymer-based out-of-plane Fabry-Perot filter that can be self-assembled by scratch drive actuators. We utilized a fabrication foundry service, MUMPS (Multi-User MEMS Process), to demonstrate the feasibility and flexibility of integration. The polysilicon, used as the structural material for construction of 3-D framework and actuators, has high absorption in the visible and near infrared ranges. Therefore, previous efforts using a polysilicon layer as optical interfaces suffer from high losses. We applied the organic compound materials on the silicon-based framework within the optical signal propagation path to form the optical interfaces. In this paper, we have shown low losses in the optical signal processing and feasibility of building a thin-film Fabry-Perot filter. We discussed the optical filter designs, mechanical design, actuation mechanism, fabrication issues, optical measurements, and results.

Nanofabricated Sensing Electrodes in a Batteryless Endoluminal Sensing Telemeter for Diagnosis of Gastroesophageal Reflux Disease (GERD)

Gastroesophageal reflux disease (GERD) is recognized the primary risk factor associated with esophageal cancers. Therefore, monitoring GERD symptoms accurately is important for early diagnosis of such cancers. In this work, interdigitated impedance sensing electrodes and nanofabricated IrOx-based pH sensing electrodes were made on the flexible substrates that can be easily embedded into an implantable device. The dual sensor electrodes were integrated into a batteryless wireless capsule packaged with biocompatible material for implant applications. The proposed sensing system has been tested with stimulated solutions of different pH values recording modulated sensor data in terms of frequency shifts to verify its performance. The experimental results showed that the impedance electrodes responded to ion content variations and the pH electrodes identified the pH values of various pH solutions. Our sensing system has demonstrated the ability to detect gastroesophageal reflux activities more accurately, which could help doctors to provide precise treatment methods, consequentially lowering the risks of esophageal cancer development.Copyright

A wireless batteryless piezoresistive pressure sensing system

A wireless batteryless piezoresistive pressure sensing system was presented. The sensing system adapts RFID operation principles including a transponder and a reader. The transponder device includes an energy harvesting circuit, force sensing resistors, a resistance-to-frequency converter, and an antenna. The reader provides radio frequency power to the device remotely and measures the sensor values in terms of frequency shift simultaneously. The performance of the system was characterized form 0 to 10 psi while the corresponding modulated frequency shift by the reader was between 7.35 kHz and 8.55 kHz. A pressure sensor array was arranged to identify high pressure points dynamically for long-term usage.

Performance evaluation of a chemical fume extractor for indoor working environment improvement

The purpose of this study is to systematically evaluate the performance of a portable chemical fume extractor used for cleaning chemical fume in small work places. Four chemical liquids, a closed chamber, and a metal-oxide sensor were used to evaluate its performance. The experimental results show that the unit under test is able to extract high concentrations of the tested chemical vapors and the cleaning processes take 5 minutes in average to clean out a strong-smelling fume concentration of 29 ppm. The performance is evaluated in terms of the cleaning efficiency (η) and clean air delivery rate (CADR).

An Active Interconnecting Mechanism for Free-Space Optic Applications

In this paper, a new method for interconnecting free-space micro-optoelectromechanical system (MOEMS) devices is developed. The heterogeneous design and assembly concept is demonstrated by a pair of V-shape actuators and related assembly mechanism, fabricated on a silicon-on-insulator (SOI) wafer. A two-channel free-space DWDM filter has been assembled and characterized. The results show low insertion losses. The device architecture allows hybrid optical system integration on a single platform. The assembled optical devices can be made of different materials, on different substrates and/or with incompatible fabrication techniques. The integration platform provides potentials for realizing a micro optical bench with equivalent optical performance that currently require bulk optics setups.