This paper presents development of a new MEMS-based tactile microsensor to replicate the delicate sense of touch in robotic surgery. Using an epoxy-based photoresist, SU-8, as substrate, the piezoresistive type sensor is flexible, robust, and easy to fabricate in mass. Sensor characteristic tests indicate adequate sensitivity and linearity, and the multiple sensor elements can match full range of surgical tissue stiffness. Such characteristic nearly match the most delicate sense of touch at the human fingertip. It is expected such a sensor is essential for delicate surgeries, such as handling delicate tissues and microsurgery.
Passive millimeter-wave (PMMW) imagers using a single radiometer, called single pixel imagers, employ raster scanning to produce images. A serious drawback of such a single pixel imaging system is the long acquisition time needed to produce a high-fidelity image, arising from two factors: (a) the time to scan the whole scene pixel by pixel and (b) the integration time for each pixel to achieve adequate signal to noise ratio. Recently, compressive sensing (CS) has been developed for single-pixel optical cameras to significantly reduce the imaging time and at the same time produce high-fidelity images by exploiting the sparsity of the data in some transform domain. While the efficacy of CS has been established for single-pixel optical systems, its application to PMMW imaging is not straightforward due to its (a) longer wavelength by three to four orders of magnitude that suffers high diffraction losses at finite size spatial waveform modulators and (b) weaker radiation intensity, for example, by eight orders of magnitude less than that of infrared. We present the development and implementation of a CS technique for PMMW imagers and shows a factor-of-ten increase in imaging speed.
Passive millimeter wave (PMMW) imaging has shown distinct advantages for detection of terrestrial targets under
optically obscuring conditions such as cloud, haze, snow, and light rain. The purpose of this paper is to evaluate the
performance of a PMMW imager for terrestrial target recognition with respect to range of detection and climatic
variables such as cloud, light rain, and snow. We used a dual polarization MMW radiometer in the frequency range of
70-100 GHz for the evaluation. We present experimental results and analyze the effect of weather conditions on the
image quality and its polarization contrast. These results will be useful for quantitative prediction of PMMW system
performance for long-range terrestrial imaging.
We present a Hadamard transform based imaging technique and have implemented it on a single-pixel passive
millimeter-wave imager in the 146-154 GHz range. The imaging arrangement uses a set of Hadamard transform masks
of size p x q at the image plane of a lens and the transformed image signals are focused and collected by a horn antenna
of the imager. The cyclic nature of Hadamard matrix allows the use of a single extended 2-D Hadamard mask of size
(2p-1) x (2q-1) to expose a p x q submask for each acquisition by raster scanning the large mask one pixel at a time. A
total of N = pq acquisitions can be made with a complete scan. The original p x q image may be reconstructed by a
simple matrix operation. Instead of full N acquisitions, we can use a subset of the masks for compressive sensing. In
this regard, we have developed a relaxation technique that recovers the full Hadamard measurement space from sub-sampled
Hadamard acquisitions. We have reconstructed high fidelity images with 1/9 of the full Hadamard acquisitions,
thus reducing the image acquisition time by a factor of 9.
We have built a passive millimeter wave imaging and spectroscopy system with a 15-channel filter bank in the 146-154
GHz band for terrestrial remote sensing. We had built the spectroscopy system first and have now retrofitted an imaging
element to it as a single pixel imager. The imaging element consisted of a 15-cm-diameter imaging lens fed to a
corrugated scalar horn. Image acquisition is carried out by scanning the lens with a 2-axis translation stage. A
LabVIEW-based software program integrates the imaging and spectroscopy systems with online display of spectroscopic
information while the system scans each pixel position. The software also allows for integrating the image intensity of
all 15 channels to increase the signal-to-noise ratio by a factor of ~4 relative to single channel image. The integrated
imaging and spectroscopy system produces essentially 4-D data in which spatial data are along 2 dimensions, spectral
data are in the 3<sup>rd</sup> dimension, and time is the 4<sup>th</sup> dimension. The system performance was tested by collecting imaging
and spectral data with a 7.5-cm-diameter and 1m long gas cell in which test chemicals were introduced against a liquid
Passive millimeter-wave (mmW) systems have been used in the past to remotely map solid targets and to measure low-pressure spectral lines of stratospheric and interstellar gases; however, its application to pressure-broadened spectral detection of terrestrial gases is new. A radiative transfer model was developed to determine the detection feasibility and system requirements for passive mmW spectral detection. A Dicke-switched multispectral radiometer that operates at 146-154 GHz was designed and built for remote detection of stack gases. The radiometer was tested in the laboratory using a gas cell; the spectra of acetonitrile were detected passively against a cold background, which mimicked typical remote detection scenarios in the field. With Dicke-switched integration of radiometric signals, on-line calibration, and novel signal processing to minimize atmospheric fluctuation, spectral line detection of polar molecules is possible from chemical plumes a few kilometers away.
Development of a passive millimeter-wave (mm-wave) system is described for remotely mapping thermal and chemical signatures of process effluents with application to arms control and nonproliferation. Because a large amount of heat is usually dissipated in the air or waterway as a by-product of most weapons of mass destruction facilities, remote thermal mapping may be used to detect concealed or open facilities of weapons of mass destruction. We have developed a focal-plane mm-wave imaging system to investigate the potential of thermal mapping. Results of mm-wave images obtained with a 160-GHz radiometer system are presented for different target scenes simulated in the laboratory. Chemical and nuclear facilities may be identified by remotely measuring molecular signatures of airborne molecules emitted from these facilities. We have developed a filterbank radiometer to investigate the potential of passive spectral measurements. Proof of principle is presented by measuring the HDO spectral line at 80.6 GHz with a 4-channel 77 - 83 GHz radiometer.
This paper discusses the development and field testing of a remote chemical detection system that is based on millimeter- wave (mm-wave) spectroscopy. The mm-wave system is a monostatic swept-frequency radar that consists of a mm-wave sweeper, a hot-electron-bolometer detector, and a trihedral reflector. The chemical plume to be detected is situated between the transmitter/detector and the reflector. Millimeter-wave absorption spectra of chemicals in the plume are determined by measuring the swept-frequency radar return signals with and without the plume in the beam path. The problem of pressure broadening, which hampered open-path spectroscopy in the past, has been mitigated in this work by designing a fast sweeping source over a broad frequency range. The heart of the system is a Russian backward-wave oscillator (BWO) tube that can be tuned over 225 - 315 GHz. A mm-wave sweeper that includes the BWO tube was built to sweep the entire frequency range within 10 ms. The radar system was field-tested at the DOE Nevada Test Site at a standoff distance of 60 m. Methyl chloride was released from a wind tunnel that produced a 2-m diameter plume at is exit point. The mm-wave system detected methyl chloride plumes down to a concentration of 12 ppm. The measurement results agree well with model-fitted data.
This paper discusses the development of an open-path millimeter-wave spectroscopy system in the 225-315 GHz atmospheric window. The new system is primarily a monostatic swept-frequency radar consisting of a mm-wave sweeper, hot- electron-bolometer or Schottky detector, and trihedral reflector. The heart of the system is a Russian backward- wave oscillator (BWO) tube that is tunable over 225-350 GHz. A mm-wave sweeper has been built with the BWO tube to sweep the entire frequency range within 1 s. The chemical plume to be detected is situated between the transmitter/receiver and the reflector. Millimeter-wave absorption spectra of chemicals in the plume are determined by measuring swept- frequency radar signals with and without the plume in the beam path. Because of power supply noise and thermal instabilities within the BWO structure over time, the BWO frequencies fluctuate between sweeps and thus cause errors in baseline subtraction. To reduce this frequency-jitter problem, a quasi-optical Fabry-Perot cavity is used in conjunction with the radar for on-line calibration of sweep traces, allowing excellent baseline subtraction and signal averaging. Initial results of the new system are given for open-path detection of chemicals.
A millimeter-wave (mm-wave) sensor in the frequency range of 225-315 GHz is being developed for continuous emission monitoring for airborne effluents from industrial sites with applicability to environmental compliance monitoring and process control. Detection of chemical species is based on measuring the molecular rotational energy transitions at mm- wave frequencies. The mm-wave technique offers better transmission properties than do optics in harsh industrial environemnts such as those with smoke, dust, aerosols, and steam, as well as in adverse atmospheric conditions. Laboratory million-meter with this technology. Proof of principle of the open-path system has been tested by releasing and detecting innocuous chemicals in the open air. The system uses a monostatic radar configuration with transmitter and receiver on one side of the plume to be measured an a corner cube on the other side. A wide-band swept-frequency mm-wave signal is transmitted through the plume, and the return signal from the corner cube is detected by a hot-electron-bolometer. Aborption spectra of the plume gases are measured by comparing the return signal processing technique based on deconvolution, we have shown a high specificity of detection for resolving individual chemicals from a mixture. This technology is applicable for real-time measurement of a suite of airborne gases and vapors emitted from vents and stacks of process industries. A prototype sensor is being developed for wide-area monitoring of industrial sites and in-place monitoring of stack gases.
Preliminary results are presented for a millimeter-wavelength free-space imaging system used to detect and characterize defects in layered dielectric composite slabs. Such systems throughout the microwave spectrum have shown great potential as alternative nondestructive evaluation tools for on-line, in-situ examination of low-loss dielectric materials such as plastics, ceramics, and various dielectric composites. Results of a fixed-frequency W-band imaging system operating in either through-transmission or reflection mode are presented here. Incorporation of focused-beam antennas allows high-resolution measurement of small variations within the sample under test. The results are based on measurement of the relative amplitude and phase of the reflected or transmitted wave in monostatic or bistatic configurations, respectively. With proper calibration, the measured parameters can be used to estimate dielectric property variations within the material media. A theoretical simulation for plane wave propagation in a multilayered media is used to interpret the measurement results.