Abstract: A method for active noise cancellation in a volume generates a mathematical model of a noise process to be cancelled. Using the mathematical model, a noise signal in a next sample period is predicted from a measured noise signal. The predicted signal is inverted and applied to the volume. Destructive interference of the noise signal and the inverted signal cancels the noise in the volume.

Abstract: A device and a process for analysis of acoustic reflectance directs acoustic energy for a range of frequencies including resonance frequencies of the object being analyzed. The device detects waves reflected by the object to produce what is called an acoustic reflectance curve. The electronic signal applied to an acoustic transducer at each frequency is gradually increased in amplitude to a desired amplitude. After applying the signal for a period of time at the desired amplitude, the amplitude is gradually decreased. This technique reduces noise that would otherwise occur if a signal of the desired amplitude was applied directly. The signal applied to the acoustic transducer also may be scaled according to a measured response of the device to open air, i.e., without any expected reflectance. Normalizing the signal applied to the acoustic transducer rather than the signal received from a microphone increases the dynamic range of the device.

Abstract: The disclosed system for measuring the periodic content of an input signal includes an autocorrelation function generator for generating a sequence of autocorrelation functions. Each of the autocorrelation functions is representative of an autocorrelation function of a portion of the input signal. The system further includes a temporal filter for filtering the autocorrelation functions and thereby generating a lag histogram.In other forms the system may comprise a fetal heart rate monitor for measuring the heart rate of a fetus in vivo. The monitor generates a lag histogram and uses the lag histogram for stabilizing the determination of the fetal heart rate.

Abstract: An automatic organization of images in computer memory is provided as a doubly-linked (or multiply-linked) list data structure which reflects in its interconnections to relationships between various stages in complex image processing tasks. Data structures, implemented in an appropriate high-level computer language such as C, contain pertinent information about the image as well as pointers (memory addresses) to other data structures and their associated images. These pointers allow the construction and maintenance of the linked list relationships between images. Since the relationships between images in the linked lists are equivalent to the relationships between stages of image processing tasks, the complex tasks of image processing are automatically documented in the linked list data structure without the necessity of maintaining an auxiliary written record.

Abstract: A fluid debubbler 10 for removing bubbles from fluids such as blood. The debubbler utilizes an ultrasonic transducer 22 to produce low power anisotropic sound waves at about the resonant frequencies of the bubbles to be removed. The sound waves impart a force on bubbles in a fluid chamber 20 so that they will be driven towards a rejected fluid drain 18. Debubbled fluid is removed from the debubbler through an outlet port 16.