Sensors and Systems for the Detection of Explosive Devices - An Overview: The paper presents analyses of current research projects connected with explosive material sensors. Sensors are described assigned to X and γ radiation, optical radiation sensors, as well as detectors applied in gas chromatography, electrochemical and chemical sensors. Furthermore, neutron techniques and magnetic resonance devices were analyzed. Special attention was drawn to optoelectronic sensors of explosive devices.

A design of an overtone oscillator a with surface-acoustic-wave (SAW) resonator is described in this paper. The circuit works stably on the frequency 4.710 GHz (29th harmonic of loaded resonator) at about the -2 dBm level. In the construction, distributed-constant circuits have been applied. Commercially available SAW sensors usually work within the range of frequency from a few dozen to a few hundred megahertz. On the other hand, it is a well-known fact that the mass sensitivity of such devices is directly proportional to the square of its operating frequency, and SAW sensors for organic vapors, for instance, are usually mass sensitive. For this reason, an increase in the SAW sensors' operating frequency seems to be useful. The circuit described in this paper shows the possibility of a dramatic rise in SAW operating frequency by exerting its operation through a specific high overtone (harmonic frequency) of the SAW resonator. The overtone frequency in such a solution then plays the role of basic mode. The oscillator proposed in this paper seems to be a good tool for chemisensitive-SAW-coating investigation

The relative humidity sensor based on the high-frequency surface acoustic wave (SAW) resonator has been presented in this paper. In the device, a two-port SAW resonator with Nafion coating was used. To increase the sensitivity of the sensor, the higher resonator harmonics have been employed. The sensor exhibits a very high sensitivity and linearity as well as relatively short response time. Due to the Nafion properties, it is extremely resistant to chemical compound interactions, e.g., it can operate in the atmosphere with sulfur dioxide, acidic and alkaline vapors, strong oxidizing agents, and dust.