Abstract: Comb filter having a comb like band pass characteristic curve by using an ultrasonic delay line (9) is improved to reduce its size. An input signal is given through an impedance element 13 to a single terminal 10a of an improved delay line 9, wherein the single terminal serves as the input terminal and at the same time as the output terminal. Signals at both ends of the impedance element 13 are given to a mixing circuit 15 for summing or subtracting thereby. In the improved delay line 9, the ultrasonic wave radiated from the input terminal travels twice the conventional delay line and comes back to the original terminal, and thereby a sufficient propagation distance is obtainable in a small delay line.

Abstract: The invention relates to a piezoelectric relay in which a bimorph is used as a flexible element. First, second and third relay contacts (14), (14') and (14") are disposed coplanar with the third relay contact sandwiched between the first and second relay contacts. First and second flexible members (11) and (11'), each of which is supported as a cantilever, are displaced in directions opposite to each other when an electric field is applied to one. The first flexible member (11) displaces the first and second relay contacts (14) and (14'), and the second flexible member (11') displaces the third relay contact (14"). Thus, the first and third relay contacts (14) and (14") and the second and the third relay contacts (14') and (14") are turned on or off in response to the different polarities of the applied electric field.

Abstract: A piezoelectric transducer is secured to the surface of a glass sheet to translate mechanical vibrations generated in the glass sheet into an electrical signal when a crack is produced. A detection circuit is connected to the transducer to determine whether the frequency of the signal is above or below a predetermined value. If the frequency is higher than the predetermined value, a warning signal is derived to indicate a crack and therefore probably a burglary. Alternatively, the piezoelectric transducer in the transmit mode is excited electrically by an impulse to introduce an elastic wave into the glass sheet. A gate circuit is connected to the transducer to pass signals resulting from reflection of the elastic wave from discontinuities in the glass sheet which result from a crack. The reflected crack indicating signals are passed through the gate to the transducer when it is in the receive mode.

Abstract: A small-sized gas ignition device comprising a self-oscillation circuit, a piezo-electric transformer which steps up the output of the self-oscillation circuit, a capacitor which accumulates the output voltage of the piezo-electric transformer, and a discharging gap which is connected in parallel with the capacitor and is adapted to discharge the accumulated voltage for performing gas ignition. With this device gas ignition is obtained with certainty by single operation requiring only a light touch.

Abstract: An ultrasonic ceramic microphone having a wide operating frequency range, including piezoelectric ceramic plates disposed on upper and lower surfaces of a metal plate, wherein the ultrasonic ceramic microphone is operated near two or three adjacent resonance frequencies and in a frequency band covering those resonance frequencies, of a fundamental wave and respective higher order harmonics of the deflection vibration of a transducer comprising the metal plate and the pair of piezoelectric ceramic plates.

Abstract: A piezoelectric pressure sensor for detecting the amount of oil in an engine oil pan of an automobile, and liquid level or the amount of liquid such as water level in a water bath, makes use of the phenomenon that an impedance of an excited piezoelectric element varies between in a gas and in a liquid. The pressure sensor is insensitive to surrounding temperature, and has high response and is of simple construction.