T. D. Clark

Electric potential probes - new directions in the remote sensing of the human body

In this paper we describe a new approach to the detection of human body electrical activity which has been made possible by recent advances in ultra-low-noise, ultra-high-input-impedance probes. As we demonstrate, these probes, which do not require a real current conducting path in order to operate, can be used non-invasively both on and off body. We present remarkable new data showing the application of these probes to the remote, off-body, sensing of the electrical activity of the heart at distances of up to 1 m from the body and to high-resolution electrocardiograms. We suggest that in the future such probes may form the basis of a radically new technology for measuring the dynamics of the human body as well as in non-contact, imaging systems for pre-emptive and diagnostic medicine.

An ultra-low-noise electrical-potential probe for human-body scanning

In this paper we describe a new very-low-noise, high-input-impedance probe developed to make non-contact measurements of electrical potentials generated by currents flowing in the human body. With a noise level of 2 µV Hz-1/2 at 1 Hz, down to 0.1 µV Hz-1/2 at 1 kHz, and an operational bandwidth from 0.01 Hz to 100 KHz, this probe would seem well suited to the detection of a wide range of electrical activity in the body.

Feasibility of hybrid Josephson field effect transistors

We consider the feasibility of fabricating planar superconductor‐semiconductor‐superconductor Josephson junctions in which the junction supercurrent is controlled by a gate electrode isolated from the junction by either a dielectric film (MOS‐JOFET) or a Schottky barrier (MES‐JOFET). We find that device critical currents between ∼1 and 100 μA and critical temperatures approximately a few K appear possible. We discuss the circuit applications of such devices.

Remote Detection of Human Electroencephalograms using Ultrahigh Input Impedance Electric Potential Sensors

In this letter, we demonstrate the use of very high performance, ultrahigh impedance, electric potential probes in the detection of electrical activity in the brain. We show that these sensors, requiring no electrical or physical contact with the body, can be used to monitor the human electroencephalogram (EEG) revealing, as examples, the α and β rhythms and the α blocking phenomenon. We suggest that the advantages offered by these sensors compared with the currently used contact (Ag/AgCl) electrodes may act to stimulate new developments in multichannel EEG monitoring and in real-time electrical imaging of the brain.

High resolution ambulatory electrocardiographic monitoring using wrist-mounted electric potential sensors

In this paper we describe the application of an electric potential sensor to the ambulatory monitoring of the human electrocardiogram (ECG). We show that a high resolution ECG can be acquired using two of these sensors mounted wristwatch style, one on each wrist. These sensors, which do not require a real current conducting path in order to operate, are used non-invasively without making electrical contact to the subject. Furthermore, their sensitivity and low noise floor have made it possible to detect a peak which corresponds, in timing, to the His bundle depolarization?a feature not normally seen in conventional surface ECGs. We predict that these new devices will rapidly find application in the areas of clinical medicine and ambulatory monitoring.

Ultrahigh impedance capacitively coupled heart imaging array

We describe a prototype electrocardiographic (ECG) array system comprising 25 ultrahigh impedance sensors, which does not require ohmic electrical contact with the body.

Non-contact VLSI imaging using a scanning electric potential microscope

We describe the design and use of a novel scanning microscope which detects changes in electric potential above a surface. We demonstrate that this can be employed to image integrated circuits of considerable complexity in various modes of operation and at a spatial resolution of m. We discuss the advantages of applying this imaging technique to the non-invasive evaluation of very large scale integrated circuits and consider possible limits to its resolution and sensitivity in this role.

Noninvasive imaging using an array of electric potential sensors

We present a design for a linear array of eight electric potential sensors arranged with 1 mm spacing and configured to measure spatially varying potential at the microscopic scale. The array successfully detects a 50 µm wide feature associated with one of the samples tested. In a single sensor arrangement we have demonstrated <1 µm resolution, but the data acquisition times can become prohibitive. The sensors operate noninvasively by capacitively coupling to the sample. The issues associated with using an array of sensors in close proximity are addressed. Cross coupling and strategies for matching the response of the sensors are described in detail. Results are presented for a range of samples including a resistive potential divider, a ceramic microwave circuit board, and a section taken from an oil drill pipe containing a known fault. The data acquisition times are compared with those of a single sensor system, with improvements of 4.5 times in speed reported. In one case real-time simultaneous data acquisition is demonstrated using all eight sensors. Since these sensors operate via the displacement current they may also be applied to the characterization of material properties, including, for example, insulators, dielectrics, and poorly conducting composite materials. It is concluded that we see significant improvements in the data acquisition times for the linear array over a single sensor as expected and are able to overcome the difficulties associated with operating an array of sensors in close proximity.

Compact room-temperature induction magnetometer with superconducting quantum interference device level field sensitivity

In this article, we describe significant developments in the design and construction of robust and compact room-temperature induction magnetometers with magnetic field sensitivities comparable to those usually associated only with superconducting quantum interference device (SQUID) magnetometers operating at cryogenic temperatures. In this system, we make use of both temperature independent amorphous magnetic core materials and ultralow noise signal processing electronics to achieve a spot noise figure of 14?fT/ at 300 Hz measured in a specially constructed, very low field environment. We present results over an operating bandwidth of 30 mHz to 3 kHz and show that linearity is preserved over almost six decades in an applied magnetic field amplitude. We compare the spectral noise of our systems with recently published data on SQUID magnetometers.

Ultra low noise induction magnetometer for variable temperature operation

Abstract In recent publications, the authors have reported on the performance of compact broadband induction magnetometer systems with an operating bandwidth from 100 μHz to 1 MHz. The best room temperature noise performance achieved was ∼500 fT/√Hz from 10 kHz to 1 MHz. In this paper, we describe improvements to the coil design and signal processing electronics, which result in a further reduction of the noise (∼50 fT/√Hz, in the range 1–30 kHz). In addition, we have chosen a magnetic material with a very small temperature dependence allowing us to investigate whether a reduction in noise may be achieved by operating the system at a reduced temperature (77 K).