Nanocrystalline porous silicon ultrasonic transmitter with patterned emission area

We propose a nanocrystalline porous silicon (nc-PS) ultrasonic transmitter with a variable directional pattern. The directional pattern is realized by using an interference effect. An ultrasonic wave is emitted from electrodes on the nc-PS layer according to the applied electrical current. The emission areas of the transmitter were patterned in order to use the interference between the emitted ultrasonic waves. To observe the interference effect, our device was designed to have two emission areas. The directional pattern induced by the interference effect depends on the distance between the emission areas, and the frequency and the phase difference of the currents applied to the emission areas. We confirmed that the sharpness and the lobe number of the directional pattern can be changed by the phase difference between two emission areas. We also confirmed that the direction of the main lobe can be changed by the phase difference. With the characteristics of the designable and controllable directional pattern, the proposed device is suitable for distance sensors, especially for proximity sensors.