Patent Application
20080121947
The present invention relates generally to the field of MEMS (micro-electromechanical systems) and more particularly to a MEMS acoustic sensor which is powered with the use of a solar cell and to a system for providing physical security in a geographical area with use thereof.
One possible mechanism for providing physical security in an open geographical area is to distribute a number of acoustic sensors—i.e., microphones—in and around the given area, in order to enable the detection of an intrusion via acoustical wave (i.e., sound) detection. In particular, such unattended acoustic sensors might be advantageously placed on the ground (which are then referred to as “ground sensors”), and may be advantageously placed at locations around the border of the given geographical area. In military applications, for example, it is often desirable to deploy such unattended ground sensors along the border or within an area of conflict in which improvised explosive devices (IEDs) may also be placed.
In both military and commercial applications, these sensors should advantageously be of a very small physical size so that they cannot be seen by intruders. Moreover, these sensors must necessarily have a source of power if they are to be able to receive acoustical waves and transmit acoustic signals. As such, one might naturally employ conventional batteries in order to power such devices.
For example, U.S. Pat. No. 6,967,362, “Flexible MEMS Transducer And Manufacturing Method Thereof, And Flexible MEMS Wireless Microphone,” issued on Nov. 22, 2005 to Yun-woo Nam et al., discloses a “flexible wireless MEMS microphone [which] includes a substrate of a flexible polymeric material, a flexible MEMS transducer structure formed on the substrate by PEVCD, an antenna printed on the substrate for communicating with an outside source, a wire and interface circuit embedded in the substrate to electrically connect the flexible MEMS transducer and the antenna, a flexible battery layer electrically connected to the substrate for supplying power to the MEMS transducer, and a flexible bluetooth module layer electrically connected to the battery layer.” (See U.S. Pat. No. 6,967,362, abstract.) Thus, U.S. Pat. No. 6,967,362 describes a small battery-powered MEMS acoustic sensor. U.S. Pat. No. 6,967,362 is hereby incorporated by reference as if fully set forth herein.
However, in many applications in which unattended acoustic ground sensors are used (especially, for example, in military applications), it may well be impractical to replace the devices or the batteries thereof on a periodic basis, a necessary requirement for any battery-powered device, such as the device disclosed in U.S. Pat. No. 6,967,362. Thus, it would be advantageous to have an unattended acoustic ground sensor which does not need to be periodically replaced or “serviced” (e.g., by replacing the battery thereof).
In accordance with the principles of the present invention, a MEMS microphone is fabricated into an integrated physical device which also comprises a solar cell. The solar cell advantageously provides power to the MEMS microphone, and, in accordance with certain illustrative embodiments of the present invention, does so with use of a capacitor, which is also advantageously incorporated into the device. In embodiments of the present invention which include a capacitor, the capacitor advantageously serves to provide power to the MEMS microphone when the solar cell is unable to do so (e.g., at night).
In accordance with certain illustrative embodiments of the present invention, a wireless transmitter and antenna are also incorporated into the device, in order to transmit acoustic data which has been captured by the MEMS microphone. And, moreover, in accordance with one illustrative embodiment of the present invention, the MEMS microphone comprises a fixed backplate and a diaphragm, and the solar cell is advantageously comprised in the diaphragm thereof.
Note that the use of capacitor 13 advantageously allows the illustrative solar-powered MEMS acoustic sensor to operate at night and during other periods of time where there is insufficient sunlight to stimulate the solar cell to generate power. And in accordance with one illustrative embodiment of the present invention, wireless transmitter 14 is advantageously activated (and thereby transmits the acoustic signal) only when MEMS microphone 12 has actually detected the presence of sound (i.e., when the acoustic signal power is above a minimal threshold), thereby indicating the possible presence of an intruder.
In accordance with the illustrative embodiment of the present invention shown in
As is also shown in
It will be obvious to those skilled in the art that the solar-powered MEMS acoustic sensors described above may be physically implemented in numerous ways, most preferably by fabricating the elements of each such acoustic sensor (i.e., a solar cell and MEMS microphone, as well as, possibly, a capacitor, and also, possibly, a wireless transmitter and antenna) into a single integrated device. For example, these elements may be advantageously integrated into a substrate, which may, for example, comprise a semiconductor substrate, a dielectric substrate, or a crystalline silicon substrate, each of which is fully familiar to those of ordinary skill in the art. The design and fabrication of each of these possible implementations will be fully obvious to those skilled in the art.
It should be noted that all of the preceding discussion merely illustrates the general principles of the invention. For example, it will be obvious to one skilled in the art to design specific physical and electrical implementations of the above-described device in accordance with the principles of the invention in order to create particular devices which embody the inventive concept described herein. It will also be appreciated that those skilled in the art will be able to devise various other arrangements, which, although not explicitly described or shown herein, embody the principles of the invention, and are included within its spirit and scope. In addition, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. It is also intended that such equivalents include both currently known equivalents as well as equivalents developed in the future—i.e., any elements developed that perform the same function, regardless of structure.
