In this paper is addressed the development of an ultrasonic sensor for the material identification. This sensor had to be appropriate, in terms of computational cost, in order to be implemented in small robots. This implementation was achieved by a novel signal processing method called Peniel. The associated electronic circuit and the algorithm of this method have as main strengths their circuital simplicity and the low computational cost, respectively. These two characteristics let the sensor to be implemented in two robots of the low cost robotic kit TEAC2H- RI, which was constructed as part of the master thesis of one the authors. The developed system was proved with acrylic, aluminium and glass samples. In the performed experiments those materials were identified with 100% accuracy in all often trials. According to the literature review, it is the first time which is achieved the implementation of the ultrasonic material identification in a robotic system.