Bruce C. Towe

A magneto-acoustic method for the noninvasive measurement of bioelectric currents

A method for the noninvasive measurement of low-level ionically conducted electric currents flowing in electrolytes and tissue is investigated. Experiments show that the application of oscillating magnetic fields to current-carrying media will cause focal Lorentz forces which generate detectable vibrations. These vibrations can be sensitively and noninvasively detected by surface contact detectors and can be used to determine the magnitude of internal current flows. Microampere-level currents introduced in hamsters to simulate natural bioelectric currents have been sensitively detected by this approach.<<ETX>>

A miniature shape memory alloy pinch valve

Abstract A normally closed miniature pinch valve employing a Nitinol shape memory alloy actuator to control flow in silicone microbore tubing has been designed, fabricated, and tested. The valve can withstand long term exposure to fluids because only the tubing interior is contacted by the regulated fluid. The valve has application to microflow chemistry and has the advantage of compact and simple construction. At a differential pressure of 3 psi the valve permits a maximum flow rate of about 0.28 ml/s and has a 398 mW power dissipation. The maximum differential pressure the valve can withstand is greater than 30 psi.

X-Ray Backscatter Imaging

This paper describes a new type of X-ray Compton scatter imaging technique which has potential application to medical diagnostic radiography. This system detects the Compton interacted radiation which is scattered back toward the X-ray source and uses the information to generate an interior view of an object from a frontal backprojection imaging perspective. X-ray scatter radiographs can provide a three-dimensional imaging ability that is different from computerized axial tomography and may provide additional medical diagnostic information which is difficult or expensive to derive from conventional techniques.

Miniature ultrasonically powered wireless nerve cuff stimulator

We present a wireless neural stimulator composed of only three discrete components. The capsule was 8 mm long and was designed to be clasped directly upon a peripheral nerve. Power was supplied by low-intensity 1 MHz ultrasound transmitted into the body. The prototype was capable of generating currents in excess of 1 mA. For in vivo testing the device was implanted in a rat hind limb on the sciatic nerve, and when insonated with pulse intensities of 10-150 mW/cm2 the stimulator excited motor axons inducing predictable contractions of the lower leg muscles.

Passive Biotelemetry by Frequency Keying

A novel method for passive biotelemetry is presented which has the advantages of greater range and the ability to telemeter bioelectric data compared to conventional passive telemetry approaches.

A Fully Passive Wireless Microsystem for Recording of Neuropotentials Using RF Backscattering Methods

The ability to safely monitor neuropotentials is essential in establishing methods to study the brain. Current research focuses on the wireless telemetry aspect of implantable sensors in order to make these devices ubiquitous and safe. Chronic implants necessitate superior reliability and durability of the integrated electronics. The power consumption of implanted electronics must also be limited to within several milliwatts to microwatts to minimize heat trauma in the human body. In order to address these severe requirements, we developed an entirely passive and wireless microsystem for recording neuropotentials. An external interrogator supplies a fundamental microwave carrier to the microsystem. The microsystem comprises varactors that perform nonlinear mixing of neuropotential and fundamental carrier signals. The varactors generate third-order mixing products that are wirelessly backscattered to the external interrogator where the original neuropotential signals are recovered. Performance of the neurorecording microsystem was demonstrated by wireless recording of emulated and in vivo neuropotentials. The obtained results were wireless recovery of neuropotentials as low as approximately 500 microvolts peak-to-peak (μVpp) with a bandwidth of 10 Hz to 3 kHz (for emulated signals) and with 128 epoch signal averaging of repetitive signals (for in vivo signals).

Optical pH, oxygen and carbon dioxide monitoring using a microdialysis approach

Abstract Microdialysis coupled with optical absorbance or fluorescence measurement has been used to monitor pH, pCO2, and pO2 in blood and buffer solutions. The system employs micro-flow streams of reagents, a simple optical system and a method of achieving steady microliter per minute flow rates. When integrated in a recirculating flow loop, the sensor has an excellent resolution in the physiologic range in buffer of ±0.003 pH units, ±0.5 mm Hg pCO2, and ±1.5 mm Hg pO2 with response times in heparinized bovine blood of 4.8 min, 1.8 min, and 2.1 min for pH, pCO2, and pO2, respectively.

Thermoelectric enzyme sensor for measuring blood glucose

A new calorimetric sensor has been developed which employs a thin-film thermopile in association with an immobilized enzyme. The thermopile detects the minute temperature rise that occurs when a specific chemical substrate is catalyzed by the enzyme. A prototype sensor is described which generates an equivalent proportional voltage response to glucose concentrations present in either buffer solution or blood. These sensors have remained useful for up to 18 days when operated intermittently for measuring glucose in buffer solutions, or for up to 4 days when operated continuously. When implanted inside cardiovascular shunts on anesthetized dogs, the sensors responded appropriately to changes in the blood glucose concentration.

Applications and stability of a thermoelectric enzyme sensor

Abstract Remarkable room-temperature sensitivity and stability have been achieved with thermoelectric enzyme sensors that detect the heat generated by various substrates reacting selectively on their enzyme-immobilized surfaces. Thin-film thermopiles together with cross-linked membranes of glucose oxidase and catalase have been employed to measure a linear voltage response to glucose [30 nV/ (mg/dl)] for concentrations ranging from 16 to 280 mg/dl in oxygen-saturated solutions. 90% response time values are typically less than six seconds. One sensor stored at room temperature and operated intermittently did not significantly change its response to glucose over the course of five days, and ultimately failed after nine days. Another sensor stored at 37°C exhibited a daily decrease in sensitivity and failed after five days. Four sensors operated continuously at room temperature showed an average normalized decline in response to glucose of 0.0087 ± 0.0005 h−1 and operating times ranging between 30 and 78 h. Through the use of alternative enzymes, other sensors have been made that respond to either hydrogen peroxide or urea. The use of an alternative sensing mode in which the rate of voltage change is measured following a step change in concentration appears to extend the upper range of linear response to glucose.

Passive Backscatter Biotelemetry for Neural Interfacing

Wireless telemetry of low level biopotentials from bioelectrodes can be accomplished over decimeter-order distances by using the biopotential to directly modulate the characteristics of a simple passive resonant circuit consisting of two varactor diodes and an inductor. Backscattered radio frequency energy at or near the circuit resonance in the 300 MHz region is amplitude modulated by the biopotential and detected by a remote receiver. The varactor circuit exhibits a high input impedance suited to bioelectrodes and a sensitivity to submillivolt levels. The circuit is miniaturizable to several cubic millimeters and can be realized with conventional commercially available surface mount components.