Abstract: A temperature compensation system that adjusts the temperature of an acoustic lens fluid in a prescribed manner to maintain the index of refraction of the fluid constant relative to the surrounding water thereby maintaining the focal length of the lens constant over its operating temperature range. The system comprises two temperature sensors, a programmed lens fluid temperature prescriber and an error amplifier all cooperating to direct a servomechanism system to adjust a temperature control system to either heat or cool the lens fluid to the prescribed temperature so that its index or refraction and focal length are held constant.

Abstract: A driving apparatus for electrically driving a vibrator constituting an acoustic apparatus, wherein the output impedance of the driving apparatus is negative at least one frequency associated with the output sound pressure of the acoustic apparatus among resonance frequencies when the acoustic apparatus is viewed from a terminal for driving the vibrator, and the ratio of the output impedance to the internal impedance inherent in the vibrator never becomes constant over all the acoustic reproduction range of the acoustic apparatus. Then, it is possible to eliminate mutual dependency between resonance systems having the resonance frequencies, design of the resonance systems become easy, and improved performance of sound radiation can be expected.

Abstract: A tactile hearing aid has electro-mechanical transducers which emit vibrations to the sense of touch of the skin surface for the transmission of signals. The transducers are small and lightweight and have low power consumption. The vibratory member is composed of piezoelectric, high-polymer material and has the form of a film which is provided with electically conductive coatings at both sides between which the signals to be transmitted can be applied. The film may be bent to form a ring and may be arranged in a folded stack of a number of plies to the outside surface of a carrier ring which is approximately 90.degree. open. The transducer can thus be worn on the fingers of a hand. The transducer unit is employable with particular advantage in devices for the transmission of messages via the sense of touch such as in hearing prothesis for persons extremely hard of hearing or for deaf persons.

Abstract: The sonic or ultrasonic distance measuring device used for example to measure the filling level in a container comprises an electroacoustic transducer which operates alternately as transmission transducer for the transmission of sonic or ultrasonic pulses and as reception transducer for the reception of the reflected echo pulses. Connected to the transducer is a signal processing circuit which includes an amplifier with controllable gain and a threshold value discriminator. A gain control circuit controls the gain of the amplifier during a predetermined period after the start of each transmission pulse in accordance with a stored function which is fixed in accordance with the dying-down behaviour of the transducer so that the electrical signals originating from the dying-down of the transducer after amplification are smaller than the threshold value of the threshold value discriminator but are as close as possible to said threshold value.