Abstract: Passive wireless sensors include an antenna. The antenna receives a combined signal. The combined signal includes a low frequency modulating signal modulated on a high frequency carrier wave. A demodulator receives the combined signal and extracts the modulating signal. A sensor receives the extracted modulating signal and produces an output signal with a time delay indicative of a property to be sensed. A modulator receives the output signal and the high frequency carrier wave and modulates the output signal onto the high frequency carrier wave to create a combined output signal broadcast by the antenna.

Abstract: Passive wireless sensors include an antenna. The antenna receives a combined signal. The combined signal includes a low frequency modulating signal modulated on a high frequency carrier wave. A demodulator receives the combined signal and extracts the modulating signal. A sensor receives the extracted modulating signal and produces an output signal with a time delay indicative of a property to be sensed. A modulator receives the output signal and the high frequency carrier wave and modulates the output signal onto the high frequency carrier wave to create a combined output signal broadcast by the antenna.

Abstract: Passive wireless sensors include an antenna. The antenna receives a combined signal. The combined signal includes a low frequency modulating signal modulated on a high frequency carrier wave. A demodulator receives the combined signal and extracts the modulating signal. A sensor receives the extracted modulating signal and produces an output signal with a time delay indicative of a property to be sensed. A modulator receives the output signal and the high frequency carrier wave and modulates the output signal onto the high frequency carrier wave to create a combined output signal broadcast by the antenna.

Abstract: Passive wireless sensors include an antenna. The antenna receives a combined signal. The combined signal includes a low frequency modulating signal modulated on a high frequency carrier wave. A demodulator receives the combined signal and extracts the modulating signal. A sensor receives the extracted modulating signal and produces an output signal with a time delay indicative of a property to be sensed. A modulator receives the output signal and the high frequency carrier wave and modulates the output signal onto the high frequency carrier wave to create a combined output signal broadcast by the antenna.

Abstract: A low profile transducer (11, 12) is provided for use in flow meter for pipes of small diameter. The transducer (11, 12) has a transducer (18) or other form of transducer which transmits and receives electrical signals of three volts and 1 MHz and converts between these electrical signals and acoustic waves. In one embodiment, the transducer (18) produces surface acoustic waves (SAW), while in another embodiment the transducer (32) produces plate waves known as Lamb waves. These waves are converted to bulk acoustic waves (BAW) transmitted between the pair of transducers (11, 12).

Abstract: A method and apparatus for measuring the thickness of sludge being deposited on the sidewall of a rotating turbine can in a centrifuge by measuring the electrical admittance (capacitance or conductance) between the sidewall of the turbine can and the base, shaft, or body of the centrifuge which is electrically isolated from the turbine can. An electrical circuit is coupled to the sidewall of the turbine can to measure a change in the thickness of the sludge being deposited on the inner surface of the sidewall by measuring a change in voltage, admittance, capacitance, or conductance between the turbine can and the base, shaft or body of the centrifuge which are all at ground potential. The apparatus of the invention includes a typical centrifuge which is modified by adding a pair of insulating rings to the structure of the centrifuge to electrically isolate the turbine can from the rest of the centrifuge structure.

Abstract: A new type of acoustic wave which is nearly polarized in the shear horizontal direction, and which can propagate in thin elastic plates if the ratio h/.lambda. is less than about 3 where h is the plate thickness and .lambda. is the acoustic wavelength. Attractive properties of this quasi-SH wave include: (i) nearly nondispersive propagation, (ii) very large value of K.sup.2, the electromechanical coupling coefficient, and (iii) ability to propagate in contact with a liquid medium without suffering excessive attenuation. The nondispersive propagation and large value of K.sup.2 makes the wave attractive for use in signal processing and sensing devices. Further, the fact that the wave can propagate in contact with a liquid medium allows the wave to be used in sensors that have to operate in contact with a liquid medium.

Abstract: The use of a surface acoustic wave (SAW) device to measure rate of fluid flow. A SAW oscillator heated to a suitable temperature above ambient is placed in the path of the flowing fluid. Convective cooling caused by fluid flow results in a change in the oscillator frequency. A 73 MHz oscillator fabricated on 128.degree. rotated Y-cut lithium niobate substrate and heated to 55.degree. C. above ambient shows a frequency variation greater than 142 kHz for flow rate variation from 0 to 1000 cm.sup.3 /min.

Abstract: A variable delay line for surface acoustic waves includes spaced input and output transducers affixed on the wave-propagating surface of a piezoelectric substrate for sending and receiving acoustic waves. An AC or DC voltage is applied to the substrate through a pair of electrodes as a strain inducing signal. The applied voltage changes the time delay of the wave by physically altering the length of the propagation path, and/or by altering the effective properties of the substrate to vary the propagation velocity of the wave. The time delay will vary proportionately in response to the applied voltage.