Hangue Park

A Power-Efficient Wireless System With Adaptive Supply Control for Deep Brain Stimulation

A power-efficient wireless stimulating system for a head-mounted deep brain stimulator (DBS) is presented. A new adaptive rectifier generates a variable DC supply voltage from a constant AC power carrier utilizing phase control feedback, while achieving high AC-DC power conversion efficiency (PCE) through active synchronous switching. A current-controlled stimulator adopts closed-loop supply control to automatically adjust the stimulation compliance voltage by detecting stimulation site potentials through a voltage readout channel, and improve the stimulation efficiency. The stimulator also utilizes closed-loop active charge balancing to maintain the residual charge at each site within a safe limit, while receiving the stimulation parameters wirelessly from the amplitude-shift-keyed power carrier. A 4-ch wireless stimulating system prototype was fabricated in a 0.5-μm 3M2P standard CMOS process, occupying 2.25 mm2. With 5 V peak AC input at 2 MHz, the adaptive rectifier provides an adjustable DC output between 2.5 V and 4.6 V at 2.8 mA loading, resulting in measured PCE of 72 ~ 87%. The adaptive supply control increases the stimulation efficiency up to 30% higher than a fixed supply voltage to 58 ~ 68%. The prototype wireless stimulating system was verified in vitro.

The Tongue Enables Computer and Wheelchair Control for People with Spinal Cord Injury

Individuals with severe spinal cord injury control a computer and powered wheelchair by using a wireless tongue-operated assistive technology called the Tongue Drive System. Tying the Tongue to Motor Control Voluntary tongue motion may help people with limited upper limb mobility, such as those with high-level spinal cord injury, to access computers and to drive wheelchairs. The Tongue Drive System (TDS) is a wireless and wearable assistive technology that allows individuals with severe motor impairments to access their environments using voluntary tongue motion. Kim et al. report on a new study of TDS efficacy in patients with severe spinal cord injury. Two groups of able-bodied participants and a group of patients with spinal cord injury received a magnetic tongue barbell. Participants used the TDS during five to six testing sessions. Comparisons between the TDS and the keypad for the able-bodied groups and a sip-and-puff device (a traditional assistive technology) for those with tetraplegia were based on widely accepted measures of speed and accuracy. A combination of TDS flexibility and inherent human tongue abilities enabled individuals with severe motor impairments to access computers and drive wheelchairs more quickly but just as accurately as when using traditional assistive technologies. The Tongue Drive System (TDS) is a wireless and wearable assistive technology, designed to allow individuals with severe motor impairments such as tetraplegia to access their environment using voluntary tongue motion. Previous TDS trials used a magnetic tracer temporarily attached to the top surface of the tongue with tissue adhesive. We investigated TDS efficacy for controlling a computer and driving a powered wheelchair in two groups of able-bodied subjects and a group of volunteers with spinal cord injury (SCI) at C6 or above. All participants received a magnetic tongue barbell and used the TDS for five to six consecutive sessions. The performance of the group was compared for TDS versus keypad and TDS versus a sip-and-puff device (SnP) using accepted measures of speed and accuracy. All performance measures improved over the course of the trial. The gap between keypad and TDS performance narrowed for able-bodied subjects. Despite participants with SCI already having familiarity with the SnP, their performance measures were up to three times better with the TDS than with the SnP and continued to improve. TDS flexibility and the inherent characteristics of the human tongue enabled individuals with high-level motor impairments to access computers and drive wheelchairs at speeds that were faster than traditional assistive technologies but with comparable accuracy.

New ergonomic headset for tongue-drive system with wireless smartphone interface

Tongue Drive System (TDS) is a wireless tongue-operated assistive technology (AT), developed for people with severe physical disabilities to control their environment using their tongue motion. We have developed a new ergonomic headset for the TDS with a user-friendly smartphone interface, through which users will be able to wirelessly control various devices, access computers, and drive wheelchairs. This headset design is expected to act as a flexible and multifunctional communication interface for the TDS and improve its usability, accessibility, aesthetics, and convenience for the end users.

Wireless Communication of Intraoral Devices and Its Optimal Frequency Selection

This paper explores communication methods and frequencies for wireless intraoral electronic devices, by using an intraoral tongue drive system (iTDS) as a practical example. Because intraoral devices do not meet the operating conditions of the body channel communication, we chose radio frequency communication. We evaluated and compared three frequencies in industrial, scientific, and medical bands (27 MHz, 433.9 MHz, and 2.48 GHz ) in terms of their data link performance based on path loss and radiation patterns over horizontal and vertical planes. To do so, we dynamically minimize the impedance mismatch caused by the varying oral environment by applying the adaptive impedance matching technique to 433.9 MHz and 2.48 GHz bands. Experimental results showed that 27 MHz has the smallest path loss in the near-field up to 39 cm separation between transmitter and receiver antennas. However, 433.9 MHz shows the best performance beyond 39 cm and offers a maximum operating distance of 123 cm with 0 dBm transmitter output power. These distances were obtained by a bit error rate test and verified by a link budget analysis and full functionality test of the iTDS with computer access.

Development and preliminary evaluation of an intraoral tongue drive system

Tongue Drive System (TDS) is a wireless tongue-operated assistive technology (AT), developed for people with severe physical impediments to control their environments using their tongue motion. We have developed a new intraoral TDS (iTDS) in a form of a dental retainer, which can tightly clasp onto the upper teeth, completely hidden inside the mouth, using commercial off-the-shelf components (COTS). The iTDS retainer was tested by two healthy subjects and their performance was compared with that of an external TDS (eTDS) implemented in the form of a headset. The iTDS retainer showed comparable performance with the eTDS headset. The iTDS is expected to improve the stability and robustness of the TDS, while giving users a certain degree of privacy.

Tongue-operated assistive technology with access to common smartphone applications via Bluetooth link

Tongue Drive System (TDS) is a wireless and wearable assistive technology (AT) that enables people with severe disabilities to control their computers, wheelchairs, and electronic gadgets using their tongue motion. We developed the TDS to control smartphones (iPhone/iPod Touch) built-in and downloadable apps with a customized Bluetooth mouse module by emulating finger taps on the touchscreen. The TDS-iPhone Bluetooth mouse interface was evaluated by four able-bodied subjects to complete a scenario consisting of seven tasks, which were randomly ordered by using touch on the iPhone screen with index finger, a computer mouse on iPhone, and TDS-iPhone Bluetooth mouse interface with tongue motion. Preliminary results show that the average completion times of a scenario with touch, mouse, and TDS are 165.6 ± 14.50 s, 186.1 ± 15.37 s, and 651.6 ± 113.4 s, respectively, showing that the TDS is 84.37% and 81.16% slower than touch and mouse for speed of typing with negligible errors. Overall, considering the limited number of commands and unfamiliarity of the subjects with the TDS, we achieved acceptable results for hands-free functionality.

A real-time closed-loop control system for modulating gait characteristics via electrical stimulation of peripheral nerves

We have developed a real-time closed-loop control system for modulating gait characteristics via electrical stimulation of peripheral nerves in the cat. The system monitors gait metrics and applies appropriate electrical stimulus to peripheral sensory nerves to change the gait metrics in the desired direction. Stimulation parameters are determined by the stimulation controller in real-time based on the measured gait metric, the target gait metric, and the relationship between the stimulus parameters and gait metric found in experiments in the walking cat. As a proof of concept, we controlled the spatial step symmetry as a gait metric by modulating stimulation amplitude during cat walking on a split-belt treadmill. The results demonstrated that the developed system could reliably maintain the spatial step symmetry of the cat in the vicinity of a set target value in real-time.

A Prototype of a Neural, Powered, Transtibial Prosthesis for the Cat: Benchtop Characterization

We developed a prototype of a neural, powered, transtibial prosthesis for the use in a feline model of prosthetic gait. The prosthesis was designed for attachment to a percutaneous porous titanium implant integrated with bone, skin, and residual nerves and muscles. In the benchtop testing, the prosthesis was fixed in a testing rig and subjected to rhythmic vertical displacements and interactions with the ground at a cadence corresponding to cat walking. Several prosthesis functions were evaluated. They included sensing ground contact, control of transitions between the finite states of prosthesis loading, and a closed-loop modulation of the linear actuator gain in each loading cycle. The prosthetic design parameters (prosthesis length = 55 mm, mass = 63 g, peak extension moment = 1 Nm) corresponded closely to those of the cat foot-ankle with distal shank and the peak ankle extension moment during level walking. The linear actuator operated the prosthetic ankle joint using inputs emulating myoelectric activity of residual muscles. The linear actuator gain was modulated in each cycle to minimize the difference between the peak of ground reaction forces (GRF) recorded by a ground force sensor and a target force value. The benchtop test results demonstrated a close agreement between the GRF peaks and patterns produced by the prosthesis and by cats during level walking.