A sophisticated THz system with 3D imaging and narrow band spectroscopy capability is presented in the paper. The key system components are the THz source, THz detector/mixer array, scanning optics, and the signal processing unit. The system is all electronic and is portable. A battery operation option allows several hours of autonomy. The most important parameters of the THz source are output power, illumination beam size and directivity, frequency modulation range, and maximal modulation frequency. The low phase noise is also a very important parameter. Optimization of these parameters is discussed in the paper. The THz source is all solid state, composed of a phase-locked oscillator, an amplifier, and frequency multipliers. The most important element of the THz system is its sensor, which performs both signal detection and at the same time mixing of the LO signal and received signal from the target. The sensor is antenna coupled nanobolometer fabricated in a linear array of eight pixels. The sensors are suspended in the vacuum to achieve an excellent signal-to-noise ratio. The quadratic characteristic of the nano-bolometer extends over six decades allowing a large dynamic range and very high LO signal levels. The scanning mirror integrated into the system allows imaging of 1024 to 8162 pixels in the x and y dimensions that are expanded to the third dimension with a resolution of few micrometers.
The objective of this paper is the development of a compact low cost imaging THz system, usable for observation of the
objects near to the system and also for stand-off detection. The performance of the system remains at the high standard
of more expensive and bulkiest system on the market. It is easy to operate as it is not dependent on any fine mechanical
adjustments. As it is compact and it consumes low power, also a portable system was developed for stand-off detection
of concealed objects under textile or inside packages. These requirements rule out all optical systems like Time Domain
Spectroscopy systems which need fine optical component positioning and requires a large amount of time to perform a
scan and the image capture pixel-by-pixel. They are also almost not suitable for stand-off detection due to low output
In the paper the antenna - bolometer sensor microstructure is presented and the THz system described. Analysis and
design guidelines for the bolometer itself are discussed. The measurement results for both near and stand-off THz
imaging are also presented.
Resonant THz antenna-coupled micro-bolometers are considered as a potential candidates for room temperature THz
imaging, as well as spectroscopic applications. Micromachining technology is found to be well-suitable to fabricate a
micro-meter bolometer sensor suitable for MEMS implementation. The sensitivity of the sensor is determined to be up to
1000V/W and the noise equivalent power (NEP) – is down to 5pW /√Hz. The sensor parameters are designed to be easily
implemented with a low cost standard preamplifier array which increases the pixel sensitivity to 106V/W without
compromising the noise equivalent power.
The precise position of objects in the industrial process, assembly lines, conveyers, or processing bins is essential for fast and high quality production. In many robotized setups the material type and its properties are crucial. When several types of materials or parts are used, material recognition is required. Advanced robotics systems depend on various sensors to recognize material properties, and high resolution cameras with expensive laser measuring systems are used to determine the precise object position. The purpose of this paper is to present how the THz sensor and THz waves can be applicable for such precise object position sensing and its material properties in real time. One of the additional features of such a THz sensor array is also the ability to see behind barriers that are transparent for THz waves. This allows the system to obtain precise dimensions, position, and material properties of the object, which are invisible for visible light or anyhow obscured to other vision systems. Furthermore, a 3D THz image of the object can also be obtained and, in cases when a visual picture is available, its fusion with a THz image is possible. In the paper a THz sensor array, operating at a 300GHz central frequency and at room conditions is presented, together with the proposed vision system description. The target is illuminated with a frequency modulated, solid state THz source, and provides output power around 1mW. By mixing of the illuminating and reflected signals, the resulting difference frequency signal is obtained. Its amplitude and phase carry all relevant information of the target. Some measurement results are also shown and discussed.
Numerous applications require fast and accurate range measurement of concealed objects. As THz waves penetrate
almost all materials except metals, they are a candidate to perform this task. In this paper a system consisting of an
illumination THz source and a THz detector array is presented.
A solid state 300GHz THz source signal is frequency modulated and guided to a detector array using a beam splitter. The
detector array consists of ultra-sensitive bolometers with 1000V/W sensitivity and NEP of 5pW/√Hz. Their square law
sensitivity characteristic allows mixing of the reflected wave with the illumination wave, resulting in a mixed product
with a difference frequency of few kHz proportional to the target distance, the frequency modulation span, and its rate.
Parallel signal processing of all 16 signals results in fast range detection of the target. All 16 detectors provide four
readings per second for all X and Y positions of the image. A compact and portable system with 40GHz frequency
modulated source provides Δf/Δt = 160GHz/sec. This corresponds to a 1kHz difference frequency per one meter distance
of the target. A resolution accuracy in the micrometer range has been achieved using advanced signal processing.
In the paper the processing algorithms and the obtained results are presented and discussed. The complete hardware
structure of the system is described together with the required signal processing procedures. The advantage of the
presented system is that it operates at room temperature and is therefore cost effective and very robust.
We present results on the comparison of different THz technologies for the detection and identification of a variety of
explosives from our laboratory tests that were carried out in the framework of NATO SET-193 “THz technology for
stand-off detection of explosives: from laboratory spectroscopy to detection in the field” under the same controlled
conditions. Several laser-pumped pulsed broadband THz time-domain spectroscopy (TDS) systems as well as one
electronic frequency-modulated continuous wave (FMCW) device recorded THz spectra in transmission and/or
In the paper a frequency modulated THz system is presented. The system is constructed with a solid state THz source and is modulated approx. ±10% of central frequency of 0.3THz. The detector is room temperature sensor array with a square low characteristic allowing a mixer operation between a portion of transmitted signal from the beam splitter and the received signal. Due to this heterodyne approach a very good signal to noise ratio has been achieved, allowing accurate and repeatable signal analysis. The phase of the received signal is very stable and can be used for fine position measurements with the resolution well below 1μm. In this paper the focus is on measurements of thin foil thickness. Various experiments set-ups and measured results are presented.
A near real-time THz-vision system is presented in the paper. The most important part of it is the THz sensors focal
plane array operating at the room temperature, featuring low NEP (5pW/√Hz) and high sensitivity (1e6 V/W). Its
architecture allows direct digital processing of the output signal. The system performance is upgraded with large parallel
processing of up to 64 channels. The second important building block is the FM THz source used for illumination. A
wide FM range, of up to ±10% of the central frequency allows using the system for various applications. The THz source
is a solid-state source using a GHz range frequency synthesizer followed by frequency multipliers and microwave
amplifiers. Such a compact THz source can cover the lower region of the THz spectrum, i.e. below 1THz using different
frequency bands. The band selection depends on the application.
Three different areas of applications are discussed in the paper: 3D imaging of hidden objects as one of the most
attractive features of the presented system, an accurate range finder with the resolution within a fraction of the wave
length and a narrow band CW spectrometer operating in the FM range of the source.
The objective of this work was to create a low cost sensor array that operates at room temperature for millimeter wave
applications and could be used for FM radars and various heterodyne receivers. The selected technology was silicon
wafer micromachining allowing the creation of microstructures on silicon membranes using different metal layers. The
technology used allowed submicron dimensions for a photolithography pattern and thin membranes down to a few
micrometers. One of the most critical requirements for the sensor was to achieve a high signal-to-noise ratio and a high
bandwidth for a mixed frequency. The sensor is a titanium-based micro-bolometer connected to the micro-antenna which
is integrated with the bolometer. The results are very promising. The measured NEP is below 5pW/√Hz and the
sensitivity is close to 1000 V/W. In the paper the antenna - bolometer sensor microstructure is analyzed. Theoretical analysis and design guidelines for the bolometer itself are discussed. Simulation results of the bolometer and antenna show very close matching to the measured results. Characterization measurements were performed, and thermal behavior of microbolometer structure was simulated and measured. The measurement results are presented for THz FM radar different targets, and a technology demonstrator is also described.