A Miniaturized RF Acceleration Measuring System
SNL (Sandia National Laboratories (SNL), Albuquerque, NM, and Livermore, CA (United States)), Donald L. Trapp, US Atomic Energy Commission (AEC) · 1966
This :paper will describe the design and development of a miniaturized high-shock :package utilizing an FM modulated 19.8 me transmitter and a :piezoresistive accelerometer.This :program was initiated in October 1965 for the :purpose of measuring ~deceleration :profiles generated by small diameter (1-1/4 inch) vehicles that :penetrate targets of known composition with input velocities u:p to 1500 feet :per second.Shock levels were anticipated to be in the 0 -10,000 g range, with rise times varying as a function of :projectile ogives and anticipated to be as fast as 100 ~sec.The system was designed to an existing volume described by a right circular cylinder, 1 inch in diameter by 6 inches in length, and an allowable volume of 3/4-inch diameter by 4-inches long was allocated for the 19.8 me transmitting antenna.The first operational usage of this system •was in late January 1966.Introduction.-A complicating factor in the design of the system was the necessity for the RF -transmission through targets which offered relatively high mitigation of RF carrier frequencies.Loss in efficiencies of up to 60 db were anticipated.This :problem, in addition to high shock, led us to the development of the relatively low frequency (19.8 me) transmitter.All other system components had to be designed or modified due to the unusual packaging and shock conditions.In addition to the above, the new system was to be compatible with existing horizontal and vertical sled track facilities and likewise was to have the capability for use in gun environments.Standard FM trailer .mountedground stations were to be utilized.Method of Approach.-The basic system was laid out as shown in Figure 1.From previous experience in high-g, fast-risetime shock environments, a decision was made to use a low-source impedance :piezoresistive bridge type acceierometer.The signal conditioning circuit was designed to amplify the 0 -500 mv signal from the transducer and condition it for the 0 -5 volt input to a wide-band 70 kc voltage-controlled oscillator.The VCO would then deviate the 19.8 me, 100 mw transmitter approximately 6o kc.An autotransformed loopstick-ty:pe antenna was designed to radiate the RF signal.Power to the system was supplied by a specially designed and :packaged water activated silver chloride battery, which :provided 24 volts at 100 ma for approximately 30 minutes.As is shown in Figure 1, the transducer was mounted in the signal conditioning module along with the 70 kc VCO and this module acted as a wrench for screwing the transducer to the mounting stud.Elco connectors mounted on this module and on the battery module allowed for easy interconnection.A guide :pin insured proper connector aligruil.ent.A loading ring forcing against the transmitter :placed the entlre package in high com:pre~sion.A second loading r;i.ng affixed the antenna to the rest of the package.Component Design and Development.-Thedesign parameters of the individual components will be described along with their size and :performance g