Thermpon Ativanichayaphong

A combined wireless neural stimulating and recording system for study of pain processing

Clinical studies have shown that spinal or cortical neurostimulation could significantly improve pain relief. The currently available stimulators, however, are used only to generate specific electrical signals without the knowledge of physiologically responses caused from the stimulation. We thus propose a new system that can adaptively generate the optimized stimulating signals base on the correlated neuron activities. This new method could significantly improve the efficiency of neurostimulation for pain relief. We have developed an integrated wireless recording and stimulating system to transmit the neuronal signals and to activate the stimulator over the wireless link. A wearable prototype has been developed consisting of amplifiers, wireless modules and a microcontroller remotely controlled by a Labview program in a computer to generate desired stimulating pulses. The components were assembled on a board with a size of 2.5 cm x 5 cm to be carried by a rat. To validate our system, lumbar spinal cord dorsal horn neuron activities of anesthetized rats have been recorded in responses to various types of peripheral graded mechanical stimuli. The stimulation at the periaqueductal gray and anterior cingulate cortex with different combinations of electrical parameters showed a comparable inhibition of spinal cord dorsal horns activities in response to the mechanical stimuli. The Labview program was also used to monitor the neuronal activities and automatically activate the stimulator with designated pulses. Our wireless system has provided an opportunity for further study of pain processing with closed-loop stimulation paradigm in a potential new pain relief method.

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.

An Infant Monitoring System Using CO/sub 2/ Sensors

In this paper, we proposed an infant monitoring system to reduce the potential risks for sudden infant death syndrome (SIDS). This system can be used for infants at home or in a hospital nursery room. The system consists of carbon dioxide (CO2 ) sensors and active radio frequency identification (RFID) technology. A commercial metal-oxide based CO2 sensor was chosen and characterized in sensitivity, selectivity and humidity dependence. A proof-of-concept system, to be used for two infants in the same room, was designed and assembled. The RFID transmission was accomplished with a wireless module at two different operating frequencies. The results are promising. A method for further practical applications in a large nursery room is also discussed in details in this paper.

Development of an Implanted RFID Impedance Sensor for Detecting Gastroesophageal Reflux

A new method to detect gastroesophageal reflux is presented. Based on passive RFID principles, the impedance of the refluxate can be determined. We have designed and fabricated planar coils integrated with electrodes on flexible substrates using standard photolithography processes. The device can be implanted in the esophagus using currently available clinical techniques. In vitro experiments with simulated stomach acid were conducted. An approach to integrate the sensor with RFID systems is proposed. This device can help diagnose gastroesophageal reflux disease effectively.

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 ...

A Simple Wireless Batteryless Sensing Platform for Resistive and Capacitive Sensors

In this paper, a simple wireless platform to transduce data from sensors without the need for a battery in the sensors is introduced. The sensor can be either resistor-or capacitor-based. The sensing systems adapt RFID operation principles including a reader and a transponder. Our platform is fully analog and contains few components making it easy to implement with existing ICs and sensors. The platform for temperature sensing has been demonstrated. The device includes a 1times2.5 cm2 coil antenna and a thermistor. The read range is 4 cm using a 6times6 cm2 reader antenna powered at 970 kHz. A temperature range of 5-90degC is monitored resulting in read frequencies from 6 to 10 kHz.

A wireless sensor for detecting gastroesophageal reflux

In this paper, we propose a new method to detect gastroesophageal reflux wirelessly. Based on passive telemetry using inductive links, impedance of the refluxate can be determined. We have designed and fabricated planar coils integrated with electrodes on flexible substrates using standard photolithography processes. The device can be implanted in the esophagus using currently available clinical techniques. In vitro experiments were conducted by passing different acidic or non-acidic solutions onto the implanted electrodes and measuring the signal amplitudes with an external receiver. Air, drinking water and different concentrations of artificial stomach fluids were used to test the impedance sensor. System configuration, device designs, fabrication processes and measurement results will be presented in this paper.

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.

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.