A-Metrics has developed an innovative linear measurement device that operates as a basic transducer for sensors. The device can be used in a wide range of applications including seismic infra wave detection, minute barometric pressure changes, sonar, and medical imaging technologies. The A-Metrics transducer converts the linear displacement of a measurement surface into discrete pulses that are counted and analyzed.

Transducers built using the A-metrics patented technology track linear displacements of a surface that is influenced by the external environment. This technology is ideal for monitoring and detecting low level, high amplitude, and low frequency signals. A key advantage of the A-Metrics technology is the unique method of counting the digital, discrete steps of a tracking pin that follows the movement of the measurement surface as it reacts to the external environment (seismic waves, minute pressure changes, acoustic vibrations, etc). 

The digital nature of the device distinguishes it from existing devices that produce an analogue voltage output. Analog devices are inherently limited by the inverse relationship between sensitivity and range.  A-Metrics transducers combine a long range of measurement with sub-angstrom sensitivity. When coupled with real-time signal processing algorithms, the
device will reveal the frequency signatures that are embedded in a higher amplitude signals. 

Figure 1: Operation of the A-Metrics Device. The tracking pin follows the movement of the measurement surface in discrete steps in order to maintain a current value between the pre set trigger levels. This happens very fast and depends on the pin material and size. As the actuator pulses the pin to move in accord with the measurement surface, a count is recorded.  Analysis of the counts with time yields frequency characteristics of the detected signals. Further signal processing removes background and other noise signatures revealing the frequencies of interest.

Technology

The A-Metrics transducer is a compact integrated unit containing a measurement surface, a tracking pin, and an actuator that moves the pin (Figure 1). The pin and the inside of the measurement surface are made of highly conductive metals that form an electrical circuit when a bias voltage is applied. Initially, the pin is positioned very close to, but not in physical contact with the surface. Due to the small separation, the resulting current is a non classical tunneling current, termed Field Electronic Emission (FEE). 

The value of the FEE current is monitored and is proportional to the distance between the pin and surface. The pin rests between two preset FEE current values (the upper and lower trigger levels). As the surface moves away from the pin, the separation distance grows and the monitored FEE current drops. When the current falls below the lower trigger level value, the actuator is energized pushing the pin toward the surface.  When the upper trigger level value is reached, the actuator switches off resulting in the registration of a single pulse or count.

On the opposite side of the measurement surface is an identical pin/actuator configuration. When the surface moves in the opposite direction, the second pin follows the movement of the measurement surface in the same manner.

Continued Research

Currently, A-Metrics is working on a design that will move a single pin in both directions.  In this configuration, the tracking pin can be pushed and pulled by the same actuator.  As the measurement surface approaches the pin, the actuator will pull the pin away in discrete steps.   By counting the steps over a measured time frame, a reconstruction of the wave is achieved.  A Fourier transform of the digital counts with time will reveal the frequencies of vibration of the surface.  Further signal processing will eliminate any background noise, revealing only the desired signals.

Verification of Sub Angstrom Sensitivity

A prototype device was built for A-Metrics at the National Physical Laboratory (NPL) in the UK. In this device the plunger arm (long metal rod extending from the front of the transducer was made to contact the reference mirror of a Jamin laser interferometer.  The tests, which were completed in November of 2006, verified that sub angstrom level sensitivity had been
achieved.

Conclusion

The versatile A-Metrics platform technology can be applied to many different sensing applications including hydrophones for sonar and sonobuoys, geophones for vibration monitoring, oil and gas exploration, and for medical imaging technologies.  For example, high amplitude measurements that require a long travel distance of the tracking pin may require one particular transducer design, while shorter amplitude, higher frequency movements of the pin will dictate a different design.

Measurement characteristics such as sensitivity, speed of actuation, range of motion and measurement type are application-specific parameters built into the transducers during manufacture. The actuators can be electro-magnetic coils, piezoelectric drives or other high speed systems, but it is the patented method of using a tracking pin that follows a moving surface in discrete steps that differentiates the A-Metrics technology. Applications are further expanded due to the low operational energy consumption that allows for battery operated, field deployable devices. 

High sensitivity, low energy consumption, digital registration, and low manufacturing costs make the A-Metrics transducer attractive for a wide range of applications.