NASA's Langley Research Center researchers have developed a wireless, connection-free inductor capacitor sensor system that can be placed on or embedded in materials and structures to monitor for and detect damage. The sensors can also be used to detect package tampering and pilfering. This innovation — SansEC (Sans Electrical Connections) — makes sensors more damage-resilient and more environmentally friendly to manufacture and use.
The sensors use a NASA award-winning magnetic field response measurement acquisition device to provide power to the sensors, and to acquire physical property measurements from them. The sensors can be continuously or occasionally monitored to detect cracks, material strain, or impact damage. Damage location can also be readily identified with this system.
The SansEC sensor system consists of multiple pairs of inductor-capacitor sensors, with no electrical connections, that are placed throughout the material being monitored for damage. The sensors are embedded in or placed directly onto the surface of the material. Strains and breaks are detected by changes in resonant frequency read by the accompanying magnetic field data acquisition system. When pulsed by a sequence of magnetic field harmonics from the acquisition system, the sensors become electrically active and emit a wireless response. The magnetic field response attributes of frequency, amplitude, and bandwidth of the inductor correspond to the physical property states measured by the sensor. The received response is correlated to calibration data to determine the physical property measurement. Each sensor pair has its own frequency response, and when damage occurs to that circuit, the frequency response changes. This change identifies the damage location within the material.
A unique feature achieved by eliminating electrical connections is that damage to a single point will not prevent the sensor from being powered or interrogated. If a sensor is broken, two concentric inductively coupled sensors are created, thus identifying tamper or damage location.
Possible applications include package tamper/pilfering detection, puncture detection in hazmat suits or other protective clothing, finding cracks or anomalies in composite vehicle structures, and damage detection of multilayer materials.