Microwave Photonic Distributed Radar System for Target Positioning Based on Joint Polarization and Sideband Multiplexing

Refrigerant natural circulation (RNC) system is a closed loop recycling system which is composed of evaporator, condenser, gas pipe and the liquid pipe. The difference in indoor and outdoor temperatures will lead to the refrigerant phase-change, and the gravity difference caused by different heights of condenser and evaporator will make the low boiling point refrigerants carry on natural circulation to realize the indoor heating or cooling. In order to analyze the effect of changes in the RNC system upon the working conditions of the indoor and outdoor units as well as the function of the indoor unit, this paper describes the incidence relations among the various components of the RNC system, and establishes gas–liquid two-phase fluid network mathematical model by using the method of fluid network; besides utilizing the model, it also conducts simulator investigation of coupling characteristics of the RNC system's refrigeration condition, and makes an analysis of indoor temperature, indoor unit's air volume, the number of indoor units and the indoor unit capacity and other factors' changes on the coupling characteristics of the RNC system. The results show that under refrigeration conditions, the increase in the air volume of a single indoor unit or room temperature will result in an increase in the cooling capacity of its own indoor units, a decrease in the cooling capacity of other indoor units and a reduction in the total cooling capacity of indoor units of the RNC system; however, the decrease in the outdoor units' inlet temperature will lead to a drop in the evaporation temperature of the system and increase in the cooling capacity.

In distributed microwave photonic (MWP) radar systems, the detection performance is highly sensitive to the quality of optical signals transmitted over the long fibers connecting the indoor and outdoor units. In this Letter, we propose an MWP radar system that, in addition to its standard range measurement capability, integrates optical frequency domain reflectometry (OFDR) for distributed vibration sensing along the optical fibers. A carrier-suppressed double-sideband (CS-DSB) optical signal is generated in the indoor unit, which serves as a light source and the local reference for the OFDR, as well as a transmitted signal for the radar transmitter. For radar detection, an echo received from an antenna is sent back to the indoor unit, where it is mixed with the local reference to perform de-chirping. For OFDR, a beat signal is produced by the coherent interference of the backscattered Rayleigh signal with the local reference, which realizes distributed optical fiber sensing. The dual functions of the system are evaluated by an experiment. For range measurement, a resolution of 4.8 cm at a transmitted bandwidth of 4 GHz is obtained. For distributed sensing, a reflection point detection with a resolution of 6.7 cm and a vibration measurement with a spatial resolution of 6 m at a vibration frequency of 4 kHz are demonstrated. The experiment also verified that utilizing OFDR to determine the vibration frequency, its impact on radar detection performance can be mitigated through digital signal processing.

Single type air conditioners (STAC) consist of one outdoor unit and one indoor unit. Multi-type air conditioner (MTAC) consist of one compressor in outdoor unit and some indoor units. In this paper, we use the free joint MTAC which can joint six indoor units to one outdoor unit. In the control of the refrigerant distribution, there are three procedures: to measure the pipe pressure of indoor unit; to calculate the amount of the refrigerant for each indoor units accurately, and to analyze the relation between the room temperature and outdoor temperature of the system. In the conventional refrigerant distribution control, the cooling load are estimated by using a experimental relation between evaporating coil target temperature and present temperature. In this paper, we apply the fuzzy logic control method to the linear valve control for the stable refrigerant distribution in the presence of operating condition change.

Split-type air conditioning systems, or heat pump systems with multiple indoor and outdoor units, are becoming very popular for room cooling and heating of small or middle-sized non-residential buildings in Japan. However, their running performance is yet to become known due to the difficulty of measuring the actual amount of heat transferred by the system. Mixed irregular flow of vapor and liquid refrigerant prevents building engineers from obtaining accurate heat flow data between indoor and outdoor units. This study introduces an alternative method to calculate heat transferred by the system from air volume and enthalpy measured with simple sensors attached to the indoor units. Experimental results on a national university campus in suburban Tokyo showed unexpectedly low COP values both in summer and winter mainly due to the prevailing low partial load factors under 20-30% of the system capacity.

Sporadic COVID-19 cases will be predicted to occur in coming few years ahead as observed in previously known influenza virus related pandemics. Herd immunity due to natural infection and hybrid immunity after COVID-19 vaccination has played crucial role in waning of this pandemic. COVID-19 pneumonia has a very ‘typical’ radiological presentations, observed globally; classified as GGO and consolidations involving peripheral parts of lung, bilateral disease, predominantly pleural based areas initially and involves central portions as disease process advances. Such radiological presentations are never documented in history before this pandemic, which has helped in suspecting COVID-19 illness in cases with negative microbiological results initially and such illness were classified as SARI (severe acute respiratory illness). Cases with typical radiological features for COVID-19 with RT PCR positive results were defined as case of COVID-19 illness. Both the clinical scenarios were managed with similar protocol during hospitalization. COVID-19 case burden has significantly decreased in last one year since declaration of end of pandemic by WHO and now we are in post pandemic phase. Since beginnings of pandemic, many corona virus variants were emerged with variable infectivity, virulence, pathogenesis, mortality and morbidity. As pandemic is over, cases are rarely observed with lung involvement, COVID RT PCR testing, HRCT reporting’s in line with pandemic protocol and requirement of resources to treat these cases are less required and utilized today. In present case report, 32-year male, presented in outdoor unit with history of acute febrile respiratory illness with dry cough, high grade fever and chest tightness and chest discomfort of acute onset. HRCT thorax documented Pleural based, peripheral, unifocal or solitary opacity with predominant GGOs in right lower lobe with normal left lung. He is treated in indoor unit in line with community acquired pneumonia protocol and observed clinical worsening with four-fold raised in inflammatory markers. Oxygenation is worsened and raised IL-6, CRP and LDH has given clue to think towards COVID-19 etiology. Thorat swab for COVID-19 RT PCR is positive and managed according to protocol for COVID-19 illness. This is the only observed COVID-19 pneumonia case in last six months, in which; clinical-radiological patters were typical of pandemic illness of second wave of COVID-19 illness due to delta variant. Our case is the sporadic case reported with all clinical features of pandemic illness. We have suspected COVID-19 etiology in spite of ‘atypical unilateral lung involvement’ due to worsened clinical features and abnormally raised inflammatory markers with poor response to standard treatment protocol for community acquired pneumonia. High index of suspicion is must, and; timely interventions with use of rational treatment including remdesivir, heparin & steroids combination during hospitalization has documented successful outcome. We recommend COVID-19 RT PCR testing in all community acquired cases nonresponding to standard guidelines to have timely diagnosis and treatment. Sporadic cases rare to occur, and they do occur for few years ahead of this end of pandemic due to virus variant, and we must quote ‘rare things are not rare to happen’.

Dynamic pricing refers to a system in which a tariff varies, according to a level of charging and applied time depending on time change. The power billing system used in the Korean Electric Power Corporation (KEPCO) is based on time of use (TOU) pricing, which is one of the dynamic pricing systems. This paper aimed to determine the operational results of a variable refrigerant flow system, to which a new control algorithm was applied, in order to respond to dynamic pricing, in summer and the utility of the new control. To do this, real measured data was acquired from a VRF system installed in a building for educational purposes, where dynamic pricing was applied for about 100 days during summer time. At the maximum load operation time period in TOU, the new control minimized operation within the indoor comfort range, an increase in refrigerant evaporation temperature in the indoor unit and the number of revolutions in a compressor in the outdoor unit was limited. As a result, power usage was decreased by 11%, and the operational cost by 14.6%. Furthermore, measurement results using the Predicted Mean Vote (PMV) model, that represented satisfaction of thermal environment, showed that 82.8% to 90.4% of the occupants of the building were satisfied during operation when the new control was applied.

This study developed a program for detecting charged refrigerant amount in system air-conditioner. System air-conditioner is an air-conditioning system with multiple indoor units. Due to the complexity of the system, it is more difficult to detect the refrigerant amount charged in system air-conditioner than in a general single air-conditioner. Experiments were performed for 6 HP outdoor units with 3 indoor units in a psychrometric calorimeter. The experimental amount of charged refrigerant was ranged from 60% to 140% with 10% increase. Fuzzy algorithm was employed for detecting the charged refrigerant amount in a system air-conditioner. The experimental data were used for curve fitting for general ranges for indoor and outdoor temperature conditions. Membership function were determined for whole ranges of experimentally measured data and rule-base were defined for each amount of refrigerant charge. Developed program successfully predicted the measured data within 10% resolution range.

In this study, the performance of the VRF systems applying a bypass cycle and injection cycle using a sub-cooler is compared by numerical method. In the simulation for a multi-split variable refrigerant flow (VRF) system, it is important to predict the input power and mass flow rate of a scroll compressor with considering the refrigerant injection process in a compression chamber, and pressure drop and heat transfer in pipe lines between an outdoor unit and indoor units. Therefore, the simulation for a multi-split VRF system was developed with considering those, and validated with experimental data. The bypass and refrigerant injection have improvement potential to increase the cooling capacity due to increasing enthalpy difference in an evaporator. The refrigerant injection cycle has more improvement potential of performance than bypass cycle. Sub-cooling degree at inlet of EEV is above 10°C degree in two cycles, which can avoid flash gas generation.

Photonics-assisted simultaneous detection of distances and directions for multi-targets based on polarization multiplexing and spectrum symmetry

Nonlinear frequency modulated excitation signal and modified compressing filter for improved range resolution and side lobe level of ultrasound echoes

Frequency diversity in linear frequency modulated (LFM) waveforms can introduce unintended range shifts among receive radars in a distributed environment. This can make it difficult to predict where interference will occur in those receive radars, particularly when multipath is considered. This paper introduces the concept of interference region in range-frequency space to characterize the interference levels at a receive radar caused by waveforms transmitted from different radars in a distributed architecture. Linear frequency modulated (LFM) stretch-processed waveforms provide wide bandwidth and high range resolution while imposing only modest demands on the digital processing capabilities of a radar system. For this reason they are the waveform family of choice for many current wideband radar systems, including synthetic aperture radar (SAR) systems. However, LFM waveforms do not easily lend themselves to applications that require orthogonality, such as distributed radar architectures. The widespread use of these waveforms and the processing advantages they provide make it worthwhile to examine schemes for their use in a distributed environment. The paper uses interference region analysis to assess the effectiveness of frequency diversity, upchirp-downchirp diversity and chirp slope mismatch using LFM stretch-processed waveforms in a distributed environment.

A novel direction of arrival (DOA) estimation method is proposed when uncorrelated and coherent wideband linear frequency modulated (LFM) signals coexist in multipath environment. By using the concentration property of signals, the wideband LFM signals are first transformed into fractional Fourier (FRF) domain to construct the array model, in which the time-variant steering vector is changed into time-invariant one. Afterwards, the DOAs of uncorrelated wideband LFM signals are estimated by the total least square estimation of signal parameters via rotation invariance technique (TLS-ESPRIT). Then, a spatial difference matrix is constructed to eliminate uncorrelated wideband LFM signals, and the coherent wideband LFM signals are resolved by performing a forward spatial smoothing technique. The proposed method can resolve more accute DOAs of uncorrelated and coherent wideband LFM signals in multipath environment with no a priori knowledge of the initial frequency and chirp rate of wideband LFM signals simultaneously. Simulation results demonstrate the effectiveness of the proposed method.

Radar system uses Pulse compression techniques to provide the benefits of larger range detection and high range resolution. The transmitted signal undergoes modulation to obtain this and after that matching is carried out with the echo signal (received signal) and transmitted signal. In the past several pulse compression techniques are used, out of which the well known method is linear frequency modulation (LFM). This paper deals with the design to develop and simulate pulse compression and matched filter algorithm in MATLAB to study the LFM pulse compression technique. Matched filter is used as the pulse compression filter which provides high SNR at the output. Matched Filter is mathematically equivalent to convolving the received signal with a conjugated time-reversed version of the reference signal. The main application of pulse compression Radars includes tracking of launch vehicles, abdicable components in space, Missile guidance etc. Here, in this paper we are discussing the pulse compression application in tracking the launch vehicle so as to check whether it had followed the predetermined path or not.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Recently, optical phase modulation has been widely used in microwave photonics (MWP) systems, such as radio over fiber systems, photonic microwave filters, optical microwave and millimeter-wave signal generators, and optical subcarrier frequency up-converters. An optical phase-modulated signal can be converted to an intensity-modulated signal in a dispersive optical fiber. Due to the intrinsic nonlinearity of optical phase modulation, for linear applications such as microwave signal distribution and filtering, the modulation index should be kept small to minimize the unwanted modulation nonlinearity. However, for nonlinear applications such as microwave frequency multiplication and subcarrier frequency upconversion, the modulation index should be large to maximize the frequency multiplication and upconversion efficiency. In this paper, for the first time to our knowledge, we develop a thorough theoretical framework for the characterization of phase-modulation-based MWP systems, in which the phase modulation to intensity modulation conversion is realized using a dispersive fiber. Analytical models for the distributions of single-tone and two-tone microwave signals and for microwave frequency multiplication and subcarrier frequency upconversion are developed, which are verified by numerical simulations. The analytical models for single-tone and two-tone transmissions are further confirmed by experiments. The developed analytical models provide an accurate mathematical tool in designing phase-modulation-based MWP systems. </para>

Through investigation and theoretical analysis, the author designed a condensed water system of Household Air-conditioner. Focus on how to solve droplets flow of condensed water of outdoor unit of household air conditioner. For the hot summer and cold winter areas, the winter season or the transition season need for heating, the outdoor unit does not have a set of condensation of water pipes and drip everywhere. The article from the recycling of condensed water of outdoor unit of household air conditioner, the condensed water from heating and cooling conditions will unified recycling or discharge by producing an additional set of catch plate, catch trough and other devices. After the theoretical study the author proposed that in the cooling conditions the low-temperature condensed water of indoor unit on the evaporator drainage to the outdoor unit on the condenser fins, thereby reducing the condensing temperature to improve the cooling of the condenser, and enhance the air-conditioning refrigeration coefficient , that is, to achieve the purpose of air conditioning energy efficiency.