Smitha Rao

Field Distribution Models of Spiral Coil for Misalignment Analysis in Wireless Power Transfer Systems

This paper presents design and optimization methods for spiral coils utilized for wireless power transfer in wireless medical implant applications. A theoretical model was examined for near-field distributions of spiral-type transmitter antennas in both orthogonal components. Finite-element simulations were performed to verify the theoretical radiation patterns. Receiver antenna voltages were measured at planes of interest as a means to map field distributions. Theoretical, simulation, and experimental results were conducted in free space and they agreed well. Understanding the orthogonal field components and their distributions in various distances between the worn transmitter coil outside the body and the receiver coil of implant that has a much smaller size provides a means to find the optimal location and angle to harvest maximum energy. The analysis method for near-field wireless power transmission can be utilized to determine design strategies of the transmitter spiral coil with considerations also in the amplifier circuit and physical constraints in practical scenarios to obtain maximum power and link efficiency for the implant devices. The method can be extended to investigate field distributions affected by human tissues, which construct a much more complex environment, and will be conducted in future works.

An Implantable, Batteryless, and Wireless Capsule With Integrated Impedance and pH Sensors for Gastroesophageal Reflux Monitoring

In this study, a device for gastroesophageal reflux disease (GERD) monitoring has been prototyped. The system consists of an implantable, batteryless and wireless transponder with integrated impedance and pH sensors; and a wearable, external reader that wirelessly powers up the transponder and interprets the transponded radio-frequency signals. The transponder implant with the total size of 0.4 cm ×0.8 cm ×3.8 cm harvests radio frequency energy to operate dual-sensor and load-modulation circuitry. The external reader can store the data in a memory card and/or send it to a base station wirelessly, which is optional in the case of multiple-patient monitoring in a hospital or conducting large-scale freely behaving animal experiments. Tests were carried out to verify the signal transduction reliability in different situations for antenna locations and orientation. In vitro, experiments were conducted in a mannequin model by positioning the sensor capsule inside the wall of a tube mimicking the esophagus. Different liquids with known pH values were flushed through the tube creating reflux episodes and wireless signals were recorded. Live pigs under anesthesia were used for the animal models with the transponder implant attached on the esophageal wall. The reflux episodes were created while the sensor data were recorded wirelessly. The data were compared with those recorded independently by a clinically used wireless pH sensor capsule placed next to our implant transponder. The results showed that our transponder detected every episode in both acid and non-acid nature, while the commercial pH sensor missed events that had similar, repeated pH values, and failed to detect pH values higher than 10. Our batteryless transponder does not require a battery thus allowing longer diagnosis and prognosis periods to monitor drug efficacy, as well as providing accurate assessment of GERD symptoms.

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.

Body Electric: Wireless Power Transfer for Implant Applications

The electrical properties of biological cells, tissues, and organs studied in electrophysiology not only provide information about the normal/abnormal activities of human bodies but also provide a means to directly restore, repair, replace, or recreate physiological functions in humans to improve quality of life. For example, cardiac pacemakers, implanted in millions of patients, deliver electrical pulses into the right atrium and/or the right/both ventricles to control abnormal heart rhythms. Electrical activities of neurons such as action potentials (specific waveforms of voltage fired by neurons) have been studied for neurodisorders. Recordings of electric signals spatially and temporally around the brain and central nervous system, such as electroencephalography [(EEG) electrical activities along the scalp from the brain] and evoked potential responses (measurement of the time and waveform changes for nerves in other parts of the body in response to electrical stimulation of the brain), help to understand brain functions and diagnose diseases such as multiple sclerosis (nerve cells in the brain and spinal cord gradually degrade causing problems in muscle control and cognition). As activation to targeted tissues, neurostimulation triggers neurons with electrical voltages or currents to excite signal propagation in the nervous system to restore functions. Sensations such as hearing and vision can be restored by cochlear or retinal implants. Tremors can be controlled with deep brain stimulation in the subthalamic nucleus and the globus pallidus interna areas to manage Parkinson?s Disease and dystonia (both with symptoms of involuntary muscle contractions and tremors). Chronic pain can be inhibited by electrically stimulating the periaqueductal gray and periventricular gray areas in the brain for nociceptive pain, and the ventral posterolateral/posteromedial nucleus for neuropathic pain. Brain?computer interfaces have been developed for motor neuroprosthetics, such as robotic hands, arms, or legs that can be controlled by thoughts with decoded action potentials or EEG signals from the brain for patients with paralysis. Recently, experiments on electrical stimulation in the uperolateral branch of the medial forebrain bundle have found a significant antidepressant effect for major depression, especially treatment-resistant depression.

An endoscopic wireless gastrostimulator (with video)

BACKGROUND Gastric electric stimulation (GES) at a high-frequency, low-energy setting is an option for treating refractory gastroparesis. The currently available commercial stimulator, the Enterra neurostimulator (Medtronic Inc, Minneapolis, MN), however, requires surgical implantation and is powered by a nonrechargeable battery. OBJECTIVE To develop and test a miniature wireless GES device for endoscopic implantation in an experimental model. DESIGN In-vivo gastric signals were recorded and measured in a nonsurvival swine model (n = 2; 110-lb animals). INTERVENTION An endoscopically placed, wireless GES device was inserted into the stomach through an overtube; the two GES electrodes were endoscopically attached to the gastric mucosa and secured with endoclips to permit stimulation. MAIN OUTCOME MEASUREMENTS Stable electrogastrogram measures were observed during GES stimulation. RESULTS Electrogastrogram recordings demonstrated that gastric slow waves became more regular and of constant amplitudes when stomach tissues were stimulated, in comparison with no stimulation. The frequency-to-amplitude ratio also changed significantly with stimulation. LIMITATION Nonsurvival pig studies. CONCLUSION Gastric electric stimulation is feasible by our endoscopically implanted, wireless GES device.

Investigation of wireless power transfer in through-wall applications

In this work, we proposed a through-wall wireless power transfer system and investigated effects of various wall materials. The power transfer system was based on inductive coupling of metal coils at 1.3-MHz resonance. Softwood lumber, concrete brick and drywall with insulation filling were tested at two different thicknesses. Two sets of coils, each set consisting of two coils with identical dimensions, having radii of 5 and 15 cm were utilized. Each experiment was conducted with sequential tuning in receiver circuit, operating frequency and in transmitter circuit to reach maximum output power or maximum power transfer efficiency. The output power and transfer efficiency as well as their changes were obtained before and after tuning for different media and thicknesses. It is concluded that the power attenuation with spacing distance dominates the output power and transfer efficiency, while tuning could counteract the parasitic effects in the material and recover the power lost in deviation from resonance. The power attenuation with distance requires design considerations in coil dimensions. With larger coils, more power can be collected through thicker walls and the system tolerates more variation in wall thickness. Tests on randomly chosen walls in our laboratory building were conducted to validate the system performance.

A miniature bidirectional telemetry system for in vivo gastric slow wave recordings

Stomach contractions are initiated and coordinated by an underlying electrical activity (slow waves), and electrical dysrhythmias accompany motility diseases. Electrical recordings taken directly from the stomach provide the most valuable data, but face technical constraints. Serosal or mucosal electrodes have cables that traverse the abdominal wall, or a natural orifice, causing discomfort and possible infection, and restricting mobility. These problems motivated the development of a wireless system. The bidirectional telemetric system constitutes a front-end transponder, a back-end receiver and a graphical userinter face. The front-end module conditions the analogue signals, then digitizes and loads the data into a radio for transmission. Data receipt at the backend is acknowledged via a transceiver function. The system was validated in a bench-top study, then validated in vivo using serosal electrodes connected simultaneously to a commercial wired system. The front-end module was 35 × 35 × 27 mm3 and weighed 20 g. Bench-top tests demonstrated reliable communication within a distance range of 30 m, power consumption of 13.5 mW, and 124 h operation when utilizing a 560 mAh, 3 V battery. In vivo,slow wave frequencies were recorded identically with the wireless and wired reference systems (2.4 cycles min−1), automated activation time detection was modestly better for the wireless system (5% versus 14% FP rate), and signal amplitudes were modestly higher via the wireless system (462 versus 3 86μV; p<0.001). This telemetric system for slow wave acquisition is reliable,power efficient, readily portable and potentially implantable. The device will enable chronic monitoring and evaluation of slow wave patterns in animals and patients.0967-3334/

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.

Wireless power transfer by inductive coupling for implantable batteryless stimulators

This study investigated wireless power transfer with inductive coupling at a distance addressing the power requirement for chronic gastrostimulator implants. The energy harvesting system was designed to collect 3 to 20 mW power to operate an implantable stimulator to deliver 1 to 6 mA electric current into stomach tissues. The power transfer system efficiencies were investigated with different dimensions and turn numbers in coil antennas, distances between the two antennas, and variable loads. Clinical practicality and patient comforts were considered for implanting in the stomach through endoscopic procedures. Thus, the antenna size of the transmitter was configured to be between 4 and 6 cm in diameter, to increase portability while the implant coil was fixed at 10×35 mm2. The distance between the two antennas varied from 4 to 10 cm in air. The system efficiency measured as the ratio of output power to input power included tuning a class-E amplifier in the transmitter at 1.3 MHz carrier frequency. A maximum efficiency was achieved at 9.59%. At all distances measured, the delivered power to the implant was more than 3 mW which was the minimal requirement for the operation of the implant.

Multiple-Inputs and Multiple-Outputs Wireless Power Combining and Delivering Systems

In this paper, we investigated the effect of power combining and delivering in multiinput and multioutput wireless energy transmission systems, which consist of more than one transmitter antennas as sources and more than one receiver antennas as loads and repeaters. Theoretical expressions were developed to model the system operation that can be in a large-scale wireless energy network architecture. System characteristics, such as power transfer between antennas, power losses induced in each antenna, wireless efficiency, coil misalignment, and power fluctuation due to the loss of frequency synchronization were examined by theory and verified with experiments. Measurement results matched well with the theory demonstrating the feasibility of combining and delivering power with high efficiencies in large-scale wireless energy transmission systems.