Curtis C. Johnson

Hydrogen, Calcium, and Potassium Ion-Sensitive FET Transducers: A Preliminary Report

The application of integrated circuit technology to the field of physiological data acquisition may produce a significant impact on patient monitoring, diagnosis and therapeutic medical decisions. Biomedical sensors based on IC technology have several potential advantages not available in present biomedical sensors. These include small size, reliability, rapid time response, multi-sensor chip, and onchip signal processing to achieve high to low impedance transformation, temperature compensation, signal multiplexing, etc.

Optical temperature probe

A temperature probe measures temperature changes of biological tissue whilehe tissue is being irradiated with microwaves. The temperature probe is completely nonmetallic to minimize perturbation of the microwave field, and the structure of the probe includes a plurality of optic fibers which carry light to and from a reflective liquid crystal film. The liquid crystal is enclosed in a housing at the tip of the probe which is in contact with the biological tissue, and the liquid crystal undergoes changes in absolute reflectance proportional to the temperature changes of the tissue. The optic fibers are gathered in a bundle with a first portion of the bundle transmitting light from a light generation device to the liquid crystal and the remainder of the bundle transmitting reflected light from the crystal back to a photo transistor. The reflected light received by the photo transistor is converted into an electrical signal and displayed as a representation of temperature.

Ion-selective field effect transistors with polymeric membranes

The construction and operation of ion-selective field effect transistors (ISFET) with polymeric membranes are described, and their electrical and chemical performance are discussed. The H+, K+, and Ca2+ ISFETs all show responses similar to those of the corresponding ion-selective electrodes, with t95% response times of approximately 40 ms and accurate ion activity measurements for periods up to one month.

An Empirical Formula for Broad-Band SAR Calculations of Prolate Spheroidal Models of Humans and Animals

An empirical relation for calculating approximate values of the average specific absorption rate (SAR) over a broad-frequency range for any prolate spheroidal model is derived for E-polarized incident plane waves. This formula provides a simple and inexpensive method for calculating the SAR for human and animal models, which otherwise requires complicated and expensive methods of calculation. The formula satisfies the f/sup 2/ SAR behavior at lower frequencies, the resonance characteristic at intermediate frequencies, the 1/f behavior past resonance, and the dependence on the dielectric constant at the geometrical optics limits. An expression for the resonance. frequency f/sub 0/ in terms of the dimensions of the model is also derived. The unknowm expansion coefficients were determined by curve-fitting all the data available in the second edition of the Radiofrequency Radiation Dosimetry Handbook. Numerical results obtained from the empirical relations are generally in good agreement with those calculated by other methods. Limitations of the formula and suggestions for its improvement are also discussed.

Microwave Reflection and Transmission Measurements for Pulmonary Diagnosis and Monitoring

The potential of using low intensity penetrating microwave energy in diagnosis and monitoring of pulmonary diseases such as edema and emphysema has been investigated theoretically and in selected animal models. These diseases are characterized by changes in total lung water which modify the permittivity and conductivity of the lung tissue, and consequently affect the microwave reflection from or transmission through the lung. Both reflection and transmission measurement techniques have been examined. Animal experiments have indicated changes in microwave reflection with lung water changes. The diagnostic capabilities of transmission measurements have been evaluated experimentally on a phantom model, and theoretically on a planelayered tissue model.

A Nonperturbing Temperature Sensor for Measurements in Electromagnetic Fields

ABSTRACTAn electro-optical temperature measuring device which neither perturbs electromagnetic fields nor causes hot spots has been developed for use in monitoring temperature in biological systems during microwave irradiation.

An Investigation of the Use of Microwave Radiation for Pulmonary Diagnostics

This communication describes a new technique in which penetrating microwave radiation is used for the diagnosis and monitoring of pathological cardiopulmonary conditions, such as pulmonary edema. Edema causes changes in the electromagnetic characteristics of the lung tissue, which in turn produces a change in the reflected and transmitted microwave radiation. Both the amplitude and phase changes of the microwave signals are measured.

Instrumentation for Measuring Continuous Oxygen Consumption of Surgical Patients

A system has been developed for continuously monitoring the oxygen consumption (V02) of surgical patients. A replenishment technique is used whereby the oxygen removed by the patient from a closed rebreathing circuit is replaced. This is accomplished using a feedback-controlled pump to add oxygen at a rate necessary to maintain a constant inspired oxygen percent. A second feedback loop adds nitrous oxide to the circuit at a rate equal to the patients nitrous oxide uptake rate, thus maintaining a constant circuit volume. These two feedback loops constitute a system to monitor oxygen and nitrous oxide uptake during nitrous oxide anesthesia. The instrument responds to a step change in V02 in 4 min. System accuracy has been shown to be ±6% in an in vivo comparison, the major error resulting from oxygen sensor or electronics dnift, leaks in the system, or changes in residual volume. The record of a surgical patients VO2 while under balanced anesthesia shows a practical application of the system.

Theory of Fast‐Wave Parametric Amplification

A new type of low‐noise beam‐type parametric amplifier has recently been introduced by Adler, Hrbek, and Wade. This device is characterized by its use of the fast‐cyclotron wave for amplification purposes instead of the conventionally used slow space‐charge wave. The fast‐cyclotron wave is selected because it can be made relatively noiseless by appropriate coupling processes. Since the input beam noise is the principal source of noise in beam‐type tubes, a very great reduction in noise figure is obtained. Amplification of the fast‐cyclotron wave is achieved by use of the parametric principle.An analytical description of the device is presented which includes a discussion of parametric amplification of the fast‐cyclotron wave. A method of coupling to cyclotron waves is investigated, and design procedures for establishing optimum low‐noise characteristics are outlined.

Research Needs for Establishing a Radio Frequency Electromagnetic Radiation Safety Standard

ABSTRACTThe rapidly expanding use of radar, television, industrial and medical heating units, communication systems, and many other related devices has raised a question concerning radio frequency electromagnetic radiation effects on man. The presence of radio frequency electromagnetic radiation in the environment was negligible prior to World War II. Now, for the first time in evolutionary history, man is being subjected to appreciable levels of this form of radiation. In 1966 the American National Standards Institute (ANSI) published a document entitled, “Safety Level of Electromagnetic Radiation with Respect to Personnel” (see Appendix), establishing an incident power density safety level of 10 mW/cm2from 10 MHz to 100 GHz for periods greater than 0.1 hour. This standard was formulated primarily from research results on tissue heating considerations. The safety level in the USSR and East European countries is 10 µW cm2 based on their research relating to central nervous system (CNS) and behaviorial eff...