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We report on the magnetic properties of passivated and unpassivated ferromagnetic Fe/sub 3/C nanoparticles made by laser pyrolysis. The particles have a Curie temperature well above that measured for the bulk material, and a room temperature coercive force of approximately 600 Oe. The nanoparticles offer the possibility of high temperature magnets, sensors, or materials for temperature dependent EMI shielding.

A new type of sensor is presented that allows for remote, in-situ, continuous, long term monitoring of given chemical stimuli. The sensor is comprised of a thin polymeric layer made so that it swells in the presence of certain stimuli, bounded on each side by a magnetically soft thin film. The magnetic switching characteristics of the sensor are dependent upon the thickness of the intervening polymeric spacer layer. Placed within a sinusoidal magnetic field the sensor generates a series of voltage spikes in suitably located detecting coils. The magnitude of the voltage spikes are dependent upon how much the spacer layer has swollen in response to the given stimuli. The polymeric chemistry is very flexible, and can be made to selectively swell in response to, for example, moisture, pH, ion concentration, or atmospheric CO/sub 2/. The sensor principle has been demonstrated using lightly crosslinked poly (dimethylamino)-ethylmethacrylate to detect pH.

It is commonly accepted that efficient, electrically small antennas cannot be built; the general acceptance of this premise comes from analytic work based upon use of the complex Poynting thereom (CPT). In contrast to CPT based results, earlier analytic work has shown that the input reactance of a pair of identical, perpendicularly oriented electrically small electric (TM) or magnetic (TE) dipoles can be canceled if the antennas support circular polarization; these analytic results have been confirmed via finite difference time domain numerical modeling in combination with the time dependent Poynting theorem. We have built and characterized such antennas, using both wire and microstrip dipole elements. In agreement with earlier analytic and numerical work, we find that the input reactance of the antenna can be controlled as a function of the relative phase difference between the two dipoles comprising the antenna. In contrast to the frequency domain predictions, the experimental results confirm the validity of the time domain description of standing energy, or local power. Canceled by controlling the relative phasing between elements, the results show that efficient, electrically small antennas can be built with operating characteristics superior to what has long been thought possible.