Abstract: The present invention relates to a wireless sensor network, and more particularly, to a head node selection method for clustering in a wireless sensor network and a wireless sensor network. The wireless sensor network for determining a head node that includes: a first node; and a second node wirelessly being in communication with the first node, wherein the first node broadcasts a final head node message which is a message indicating that the first node itself is a final head node to the second node if the residual energy of the first node is larger than the residual energy of the neighboring nodes. It is therefore possible to minimize clustering process time.

Abstract: The invention discloses an in-line polarization-state converter. In the polarization converter, a laser beam is radiated onto the side of a photosensitive optical fiber. The laser beam causes the refractive index of an optical fiber core to asymmetrically vary. Birefringence is induced in a core mode of the optical fiber by the variation in the asymmetrical refractive index. An optical fiber segment having the birefringence is generally disposed on a waveguide path of the optical fiber to change the polarization state of an optical signal passing through the optical fiber segment. That is, the phase of the optical signal passing through the optical fiber is changed by radiation of laser beams, which results in a variation in polarization state. The polarization converter disposed on the waveguide path is covered with a metal tube in order to prevent the polarization converter from being bent or broken.

Abstract: An optical DPSK signal demodulator includes a signal separator that separates an optical signal into an input optical signal and an output optical signal in a signal optical path. First and second reflectors are provided at a predetermined interval and reflect the optical signals with a predetermined time delay to have substantially the same intensity. A phase shifter is provided between the first and second reflectors and configured to allow the optical signals reflected from the first and second reflectors to have a phase difference.

Abstract: The invention relates to a sensor for measuring bladder volume that includes an RFID chip (particularly, a passive RFID chip) to generate driving power using an electric wave generated by a reader, and to transmit information on the measured bladder volume to the reader using an elastic wave or an electromagnetic wave, and to a system and method of managing a bladder using the same. A sensor for measuring bladder volume according to an embodiment of the invention includes an antenna that receives an electric wave, a transducer generates a predetermined wave and measures the bladder volume indicating the size of a bladder using the predetermined wave, and an RFID chip that generates and supplies power using the electric wave received by the antenna, generates information on the bladder volume from the measured bladder volume, and transmits the generated information to the outside through the antenna. The sensor for measuring bladder volume is attached to the skin in an abdominal region of a user.