An amplifier circuit converts a charge signal into a voltage signal. The charge signal indicates a detection result outputted from a piezoelectric device that detects a detection object as a change in an amount of a charge. The charge signal includes a displacement signal in a predetermined frequency band. The amplifier circuit includes an operational amplifier including an inverting input terminal receiving the charge signal and an output terminal for outputting the voltage signal, a resistor electrically connected between the inverting input terminal and the output terminal, and a capacitor connected in parallel with the resistor. A resistance value of the resistor and a capacitance value of the capacitor are set such that, in the frequency band of the displacement signal, an absolute value of an impedance of the resistor is lower than an absolute value of an impedance of the capacitor.

An accelerometer including: a housing having an internal cavity; a piezoelectric material disposed in the internal cavity; a mass movable disposed in the internal cavity; and a spring disposed between the piezoelectric material and a portion of the housing, the spring being compressively preloaded against the piezoelectric material; wherein the mass is movable when the housing experiences an acceleration such that the mass acts upon the spring and the spring acts against the piezoelectric material, the piezoelectric material outputting a signal corresponding to a magnitude of the acceleration.

A substrate for a sensor includes: a base section; a movable section connected to the base section; an arm portion as a support portion extending along the movable section from the base section; a first gap portion having a protrusion portion in which one of the movable section and the arm portion protrudes toward the other of the movable section and the arm portion, and having a predetermined gap between the protrusion portion on one side and the other of the movable section and the support portion; and a second gap portion which is located further toward the base section side than the first gap portion has a gap wider than the predetermined gap, in which in the first gap portion, one of the movable section and the arm portion has a ridge portion on the side facing the first gap portion.

An acceleration measuring device includes a piezoelectric system, a seismic mass, and a base plate. The seismic mass exerts onto the piezoelectric system, a force that is proportional to the acceleration. The piezoelectric system responds to the force by generating piezoelectric charges that are electrically transmitted as acceleration signals. The seismic mass includes a first mass element responsible for generating positive piezoelectric charges. The seismic mass includes a second mass element responsible for generating negative piezoelectric charges.

An acceleration measuring device includes a piezoelectric system, a seismic mass, and a base plate. During acceleration of the device, the seismic mass exerts onto the piezoelectric system a force that is proportional to the acceleration of the device. The force causes the piezoelectric system to generate piezoelectric charges that can be electrically processed as acceleration signals. The piezoelectric system includes two system elements, and the seismic mass correspondingly includes two mass elements. The device includes a preloading assembly that mechanically preloads the system elements against the mass elements.

A substrate for a sensor includes: a base section; a movable section connected to the base section; an arm portion as a support portion extending along the movable section from the base section; a first gap portion having a protrusion portion in which one of the movable section and the arm portion protrudes toward the other of the movable section and the arm portion, and having a predetermined gap between the protrusion portion on one side and the other of the movable section and the support portion; and a second gap portion which is located further toward the base section side than the first gap portion has a gap wider than the predetermined gap, in which in the first gap portion, one of the movable section and the arm portion has a ridge portion on the side facing the first gap portion.

A MEMS sensor comprising preloaded suspension springs and a method for mechanically preloading suspension springs of a MEMS sensor are described. The MEMS sensor comprises a MEMS support structure; a plurality of suspension springs connected to said support structure; and, a proof mass flexibly suspended by said suspension springs; wherein at least one of said suspension springs is mechanically preloaded with a compressive force for reducing the natural frequency of said proof mass.

A surface mountable piezoelectric sensor includes a pair of oppositely polarized, spaced, parallel piezoelectric members separated by an isolator. A first electrode is associated with the piezoelectric members bridging the isolator resulting in a series circuit when the pair of piezoelectric members are mounted to a printed circuit board. A second electrode is associated with one piezoelectric member and electrically isolated from a third electrode associated with the other piezoelectric member for surface mounting to the printed circuit board.