'Search balls': Sensor units for searching inside rubble

'Search balls' for searching inside rubble are proposed. A search ball is a small sensor unit which contains some sensors for searching for disaster victims, such as cameras and microphones, and a radio transceiver; it does not have actuators. Many balls are thrown into rubble and fall down while repeatedly colliding; they are scattered inside the rubble. The sensor information from the balls is transmitted by radio from the rubble and monitored at a safe area. In this way, rescuers can search a wide area inside the rubble rapidly. In the present paper, an impact-resistant ball structure is proposed: sensors, an electronic circuit, a radio transceiver and a battery are wrapped up in cushion material and packed into an impact-resistant outer shell. As a method of distributing balls inside rubble, the effect of the ball shape is discussed. The influence of ball shape and size on the distribution of balls inside rubble is experimentally evaluated using miniature rubble. One-to-one communication between balls and external computers for identifying the balls and acquiring the sensor information from them is discussed. Then a sphere-type search ball is developed: it contains three wireless cameras, IR LEDs, a radio receiver and a battery. The impact resistance of this ball is evaluated by experiments. Using a realistic model of rubble, it is experimentally verified that the external computer can send commands to the ball inside this rubble and the video signal from the ball can be transmitted out.