Design of Micro robotic Detector Inspiration from the fly’s eye

This paper describes the design and testing method of a micro robotic detector. The detector was implemented with capacitors. The chip employs the concept of an ultrasonic rangefinder. The fly can detect and locate objects in all directions easily. The micro robot needs to have this capability. In order to implement this, detectors was built to resemble a “soccer ball”. A robust fabrication process is required for the ultrasonic transducer. Since its resonant frequency will shift as function proportional to the membrane thickness. The fabrication process described in this paper also allows the integration of electronics into the capacitive-micromachined ultrasonic transducers [1]. The method of testing is also presented. INTRODUCTION Detection is an important issue in the design of micro robot in MEMS (micro-electro-mechanical systems) technology. Different from the detection issue in our daily life, the detection for micro robot requires a short-range, high resolution and low power consumption implementation. Inspired by the structure of fly’s eye and radar technology, we are going to implement the ultrasonic micro robot detector. Ultrasonic rangefinder is composed of a capacitor with one fixed plate and one moveable plate. A high frequency voltage is applied across the two plates of the capacitor. An ultrasonic wave is sent out from the transmitter to an object (if there is any). By calculating the time difference t, of transmitted and received signal, the distance D, of the object is located. Distance=Velocity * Time/2 (1) We choose capacitive ultrasonic transducers over piezoelectric transducers because the performance of piezoelectric transducers is limited by its strict geometric tolerances, array configurations and electrical characteristics. Micro capacitive detector has an advantage in size reduction and potential electronic integration. The successful design of capacitive acoustic transducers composed of a suspended silicon nitride membrane was reported within the past decade [8]. Instead of using a nitride membrane with a layer of aluminum as the top electrode, our design of a capacitive ultrasonic rangefinder consists of an aluminum layer, which acts as the top electrode that is suspended above a silicon bulk, which acts as the bottom electrode. The supporting structure is composed of Silicon nitride, which is a nonconducting layer. By closing the air gap between the two plates, we are able to change the output voltage. The parameters involved in the calculations are the thickness of the movable top plate, air-gap thickness and sidewall spacing. We apply a dc voltage between the two electrodes; the law of charge force predicts that the plates will attract each other, closing the air gap. However the two plates will also repel each other due to their residual stress. Ultrasound is generated by applying an ac voltage to the structure. In this paper, we report on the theory and calculations behind our design decisions and the fabrication process used to build the structure. We will also include the test structure so as to verify the performance of our design. 5 by 5 arrays of micro detectors are shown in Figure 0 as to