Previously, larger mechanical sensors were employed to detect washer load unbalance or severe out-of-control speed conditions which would turn off the machine. Piezoelectric film sensors are also commonly used as alternatives to traditional piezoelectric sensors in washing machines which measure out-of-balance vibration during the spin cycle. Because the piezoelectric film generates its own voltage no external power is required. It sends a signal to an in-vehicle automotive alarm system when a bump, motion, or physical break-in effort is detected. Here, the piezoelectric film acts like an accelerometer. This data preservation is especially important within mobile or portable applications, such as laptops, personal digital assistants (PDAs), and airborne or in-vehicle drives.Īnother practical application of piezoelectric film is as a wake-up switch for automotive burglar alarms. In this application, the piezoelectric film sensor commands a controller to immediately stop writing data so that no adjacent track data is destroyed. In these applications, mechanical shocks such as those caused by a laptop dropping onto the floor, can send computer disk drive read/write heads off track, potentially overwriting good adjacent track data and causing memory loss or file destruction. The use of piezoelectric film as a low-cost, shock, and vibration sensor is used in computer hard disk and CD-ROM drives where space is at a premium and mass loading may be a concern. When buried, the piezoelectric cable becomes a microphone for detecting footsteps or vehicle activity. Any attempts to cut or climb a fence are easily detected. In the second approach, the cable is buried a few centimeters underground along a security fence or wall. In this manner, the piezo cable becomes a microphone from which security personnel can monitor activities along the fence. The cable becomes sensitive to acoustic noises that may occur on the fence. In the first approach, the cable is strung or woven along a chain link fence. Measurement Specialties’ piezoelectric cable is used for perimeter security in two ways. This is a major design advantage within battery-device environments where power consumption is important. Since the film generates its own signals, it has no external power requirements. Mylar material will generate several hundred volts when a cantilever beam is flexed by just one inch. Piezoelectric film of just 0.001-in thickness laminated onto a 2-in. As the beam flexes in response to a mechanical stimulus, large surface strains are coupled into the piezoelectric film resulting in large voltage signals. Since piezoelectric film provides its highest output per unit strain when elongated, laminating film to a flexible cantilever beam provides a simple, reliable vibration and motion sensor in these devices. Measurement Specialties’ tamper sensor technology is used in a variety of electronic module applications and helps meet stringent US government-imposed security requirements (FIPS 140-2) as well as those by banks and credit card companies through Payment Card Industry (PCI) standards.įor instance, piezoelectric film is often designed into cantilever beams in computer disk drives, home appliances, and in-vehicle security systems. These attributes make piezoelectric film an alternative to traditional sensing products for a number of dynamic applications such as described in the following 12 examples. Because it is lightweight and flexible, it can also serve as a low-cost and reliable accelerometer or dynamic switch element in applications where space is at a premium. Even a small bit of piezoelectric film can generate thousands of volts and its signals can be used to effectively monitor vibration, strain, and pressure. When compressive or tensile mechanical stress is applied to the elements the crystal generates a proportional voltage - the property of an ideal dynamic strain gauge. Piezoelectric film is made of multiple, tiny, interlocking crystal domains that have positive and negative charges.
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