Wei Tan

Single- and Triaxis Piezoelectric-Bimorph Accelerometers

This paper describes the novel single- and triaxis piezoelectric-bimorph accelerometers that are built on parylene beams with ZnO films. The unamplified sensitivity and the minimum detectable signal of the fabricated single-axis accelerometer are measured to be 7.0 mV/g and 0.01 g, respectively, over a frequency range from 60 Hz to subhertz. The linearity of the sensitivity as a function of acceleration is measured to be 0.9% in the full scale. A highly symmetric quad-beam bimorph structure with a single proof mass is used for triaxis acceleration sensing and is demonstrated to produce high sensitivity, low cross-axial sensitivity, and good linearity, all in a compact size. The unamplified sensitivities of the X-, Y-, and Z-axis electrodes (of the triaxis accelerometer) in response to the accelerations in X-, Y-, and Z-axes are 0.93, 1.13, and 0.88 mV/g, respectively. The worst-case minimum detectable signal of the triaxis accelerometer is measured to be 0.04 g over a bandwidth ranging from subhertz to 100 Hz. The cross-axial sensitivity among the X-, Y-, and Z-axis electrodes is less than 15% in the triaxis accelerometer. The theoretical analyses of the charge sensitivities and resonant frequencies along with the effects of residual stress on the charge sensitivities are presented for both the single- and triaxis accelerometers.

RF-powered BIONs/spl trade/ for stimulation and sensing

Virtually all bodily functions are controlled by electrical signals in nerves and muscles. Electrical stimulation can restore missing signals but this has been difficult to achieve practically because of limitations in the bioelectric interfaces. Wireless, injectable microdevices are versatile, robust and relatively inexpensive to implant in a variety of sites and applications. Several variants are now in clinical use or under development to perform stimulation and/or sensing functions and to operate autonomously or with continuous coordination and feedback control.

Feasibility of Prosthetic Posture Sensing Via Injectable Electronic Modules

A bionic neuron (BION) is an inductively powered, miniature implant developed for functional electric stimulation (FES) to reanimate paralyzed limbs. This paper investigates the possibility of reusing the BION antenna coil as a magnetic sensor to provide meaningful posture information for feedback control of FES. A variety of techniques have been developed to model and cancel nonideal effects caused by the shapes of the internal and external coils, ferrite material, and electronic connections. Field warping has been employed to both amplitude and direction to achieve more accurate description of the dipole magnetic field generated by external coils suitable for generating a reference magnetic frame in the environment of a wheelchair. Models of the transmitting coil and the receiving BION coil were validated against experimental data, providing a solid foundation for implementing a sensor system. Based on the established model, a magnetic sensing system combined with customized microelectromechanical systems (MEMS) accelerometer has been designed and tested as a prototype on the bench. The sensor output can be employed to compute 6-D position and orientation. A two-step algorithm integrated with multiple error-cancelling techniques demonstrated sufficient accuracy in bench tests to appear promising for control of reach-and-grasp tasks. A sensor fusion step is proposed to estimate the position and orientation of a limb segment using data from multiple implants in muscles, where they will also function as neuromuscular stimulators to produce the movements to be controlled.

Sensing human arm posture with implantable sensors

In order to achieve functionally useful movement, sensory information is required for control of neuromuscular activation. This paper describes implantable sensor modalities to replace normal proprioceptors in feedback control. They can be packaged into miniature, wireless neural stimulators called BIONs/spl trade/. Sensing techniques and strategies for analyzing and combining various sensor signals are presented. These sensors include a DC accelerometer and RF magnetic sensor. Several sensor system configurations are proposed to accommodate different clinical requirements and real-time measurement of the position and orientation of human arms.

Implantable biaxial piezoresistive accelerometer for sensorimotor control

This paper describes the design, fabrication and test results of a novel biaxial piezoresistive accelerometer and its incorporation into a miniature neuromuscular stimulator called a BION/spl trade/. Because of its highly symmetric twin mass structure, the X and Z axis acceleration can be measured at the same time and the cross axis sensitivity can be minimized by proper piezoresistor design. The X and Z axis sensitivities of the biaxial accelerometer are 0.10 mV/g/V and 1.40 mV/g/V, respectively, which are further increased to 0.65 mV/g/V and 2.40 mV/g/V, respectively, with extra silicon mass added to the proof mass. The cross-axis sensitivity is less than 3.3% among X, Y and Z-axis. An orientation tracking method for human segments by measuring every joint angle is also discussed in this paper. Joint angles can be obtained by processing the outputs of a pair of biaxial accelerometers (placed very close to the joint axis on the adjacent limb links), without having to integrate acceleration or velocity signals, thereby avoiding errors due to offsets and drift.

Biomimetic Posture Sensing and Feedback for Proprioception

Kinesthesia is a sense of body posture and motion that arises from the interactions among the musculoskeletal system, a rich set of biological proprioceptors and the sensorimotor nervous system that mediates between them. This paper describes implantable sensor modalities to replace normal proprioceptors in feedback control. They can be packaged into miniature, wireless neural stimulators called BIONstrade. Their digitized signals can be transmitted efficiently to the external control system, which must then mediate between the sensing and stimulation functions in the available set of implants. This interaction will be perceived by the user of the prosthesis through residual sensory modalities such as proprioceptors in muscles and joints still under voluntary control and direct vision, as well as by a sense of effort in issuing commands to the prosthesis. These rich sources of information may be expected to induce a sense of kinesthesia similar that associated with manipulation of mechanically active tools and prosthetic limbs, perhaps obviating the need for more direct presentations of sensory data to the central nervous system

Highly symmetric tri-axis piezoelectric bimorph accelerometer

This paper describes the design, fabrication and test results of a novel bimorph tri-axis piezoelectric accelerometer (built on symmetric quad Parylene beams with ZnO film). Because of its highly symmetric quad-beam bimorph structure and single proof mass, this tri-axis piezoelectric accelerometer has high sensitivity, low cross-axial sensitivity, good linearity and compact size. The un-amplified sensitivities of the X, Y and Z-axis electrodes in response to accelerations in X, Y and Z-axis are 0.93 mV/g, 1.13 mV/g and 0.88 mV/g, respectively. The minimum detectable signal is measured to be 0.04 g over a subHz /spl sim/100 Hz bandwidth. The cross-axial sensitivity among the X, Y and Z-axis electrodes is less than 15%.

Implantable bimorph piezoelectric accelerometer for feedback control of functional neuromuscular stimulation

This paper describes the design, fabrication and testing results of a novel bimorph piezoelectric accelerometer (built on a parylene beam with ZnO film) and its application in an injectable neuromuscular stimulator (BION/spl trade/). In order to control limb motion using such stimulation, it is necessary to sense the acceleration of the body or its inclination with respect to the gravitational field. This paper describes a MEMS piezoelectric accelerometer that meets the requirements of this application, which include small size, extremely low power consumption, simple detection circuit and high sensitivity. The unamplified sensitivity of the bimorph piezoelectric accelerometer is around 7.0 mV/g and the minimum detectable signal level is around 0.01 g. The working frequency range is from 60 Hz down to sub Hz with high linearity of the sensitivity.

Multimodal injectable sensors for neural prosthetic proprioception

A BION/sup TM/ is a miniature implant developed for Functional Electric Stimulation (FES). This paper describes a new posture sensing system designed for these implants. The new system contains three sensing modalities: 1) artificial muscle spindles; 2) a DC accelerometer; and 3) a magnetic reference frame. Because of limiting factors such as sensor size and power consumption, each sensing modality used alone provides inaccurate or incomplete information on the posture. However, signals from the individual sensors can be integrated for more accurate and complete results. First, signals from each sensor are processed separately to extract basic information. Then sensor fusion algorithms (including extended Kalman filtering) combine all the sensor signals and generate 6-D posture data. Finally the data can be used in real-time to provide command and feedback signals for the FES controller.