Special Note: Utilizing a Standing UJave

It is possible to produce a standing wave at the face of the transducer TD1 and improve the system sensi­tivity. Point the device at a steady, low-intensity source of high-frequency energy and carefully adjust

Special Note: Utilizing a Standing UJave

Note shielded cable is 18" and is routed through a small hole in the raar cap CAP3 and in PARA12 reflector

TD1 is fitted into bushing BU1 Assembly is then inserted into the 5.5” x 1.625” diameter enclosure TUBE and is spaced by Ihe O-RING. This scheme shock mounts the Ira nsducer and secures it in place

Transducer is wired as shown in set Fig 26-5

Figure 26-6 Final view showing a reflector

the distance of the 1 X 1" metal flat plate relative to the transducer face, noting an increase in the signal. This effect will occur at half-wave multiples with the most pronounced being closest to the face. Use your own ingenuity in retrofitting this simple step.

Circuit Description

An ultrasonic transducer mike (TD1) picks up high – frequency sounds and converts them to electrical sig­nals via the piezoelectric effect (see Figure 26-2). Inductor LI tunes the inherent capacity of the trans­ducer to a window frequency centering around 25 kHz. This parallel, equivalent resonant circuit pro­duces a high-impedance signal source that is coupled to field-effect transistor (FET) Q1 amplifier through capacitor C2. Resistor R1 and capacitor Cl decouple the bias voltage to the drain. Layout and input lead shielding is important, as this section is prone to noise, feedback, and extraneous signal sensitivity.

The output of Ql is taken across the drain resistor R2 and is capacitance coupled to amplifier II A. Gain is set to X50 by the ratio of resistors (R6/R4).

The output of 11A is AC coupled to the combina­tion mixer/amplifier 11B through capacitor C4.The output of oscillator 11C is coupled into the circuit by a “gimmick” capacitor, CM. This is a short lead from pin 8 of IC1 and is twisted with a similar lead from pin 2 of 11B. (It is suggested to check performance without this gimmick.) The oscillator now generates a frequency that is mixed with the picked-up signals. The resultant is two signals, one being the sum and the other the difference.

Capacitor C7 and resistor RI7 form a filter net­work attenuating the higher-frequency component of the mixed frequencies while allowing the lower fre­quency to pass by a factor of 20 decibels (db).The lower-frequency results are the difference between the oscillator frequency and the actual signal fre­quency. This is similar to a superheterodyne effect. The high frequency is obviously bypassed by filter C7 and R17. The filtered signal, being the composite dif-

Circuit Description

"Gimmick"- See text as may

Proper routing of input power leads will improve noise figure.

Leads to J1 must be short and direcl as possible

Leads lo power must be routed direct to underside of mounting plate.

Rd is chosen to dampen transducer response Suggested value is around 3SK.

Twist all lead pairs wherever possible

Figure 26-2 Ultrasonic microphone schematic

;,0

Circuit Description

ference, is rectified by diode Dl and integrated with capacitor CB. This signal is in the audio frequency range and is what you actually hear. It is tuned by control pot R12 in the oscillator section and enables the selective tuning of certain target frequencies within an acceptance window of the transducer TD1. These resulting audio frequencies are coupled to vol­ume control R19 through DC blocking capacitor CIO. Capacitor Cl2 bypasses any higher frequencies that may leak through. The arm of R14 teeds the audio signal into headphone amplifier 12. The output is H ohms and is capacitance-coupled to the headset jack J1. You may use a small speaker in a quiet loca­tion for group listening. Network R21 /С4 further attenuates any further higher frequencies.

Power to 12 is decoupled through resistor R20 and capacitor С15. This provides circuit stability, prevent­ing feedback oscillations and other undesirable effects.

The operating points of 11 A, 11B. and 11С are set at the supply voltage midpoint selected by divider resistors R7 and R11. Resistors R5, RIO, and R15 compensate for offset currents.

Construction Steps

To begin constructing the device, follow these steps:

1. Identify all the parts and pieces and verify them with the bill of materials.

2. Insert the components, starling from one end of the perforated circuit board, and follow the locations shown in Figure 26-3, using the indi­vidual holes as guides. The board is cut 2.25 x 2.25 X.1. A printed circuit board (PCB) is also available from www. amazingl. com.

Use the leads of the actual components as the connection runs, which are indicated by the dashed lines. It is a good idea to trial-fit the larger parts before actually starting to solder.

Always avoid bare wire bridges, messy solder joints, and potential solder shorts. Also check for cold or loose solder joints.

Pay attention to the polarity of the capacitors wilh polarity signs and to all the semiconduc­tors. The positioning of the control pots must

Circuit Description

allow physical alignment with the mounting holes in RPl.

3. Cut, strip, and tin the wire leads tor connect­ing to J1 and solder them. These leads should be 2 inches long and twisted.

4. Fabricate the CHASl chassis, the RPl front panel section, the EN1 enclosure, and the HAND1 handle, as shown in Figure 26-4.

5. Prepare the SHI shielded cable at both ends as follows. If the optional reflector is used, you will need a length of 18 inches; if not, you will need 6 inches. This is shown in Figure 26-5.

a. Carefully remove 3A of an inch of the outer insulation, being careful not to nick the shielded braid.

b. Shred the shielding braid using a pointed object, such as a pin, and twist it into a lead. Carefully tin only the ends to hold the wires together.

c. Carefully strip 4a of an inch of the insul­ation from the center conducior and tin.

d. Check the finished cable for shorts or leakage with a high-resistance meter.

6. Solder the inductor LI and the damping resis­tor Rd, as shown in Figure 26-5. Solder one end of the SHI cable, being careful not to overheat the transducer pins or the insulation of the center conductor. Overheating these pins will ruin this part. If in doubt, you must perform a simple test of measuring a short cir­cuit to the metal case of the part to the shorter pin. If this resistance is above 1 ohm, you have trashed this part and need a replace­ment. The inset in Figure 26-5 suggests using mechanical connections such as crimpling, wire nuts, and so on.

7. Assemble as shown. Figure 26-6 shows an assembly using the parabolic reflector, whereas Figure 26-7 shows one without.

Note that hole in ENt for handle is best cut with a 1 g" circle saw. Fit must be tight to properly secure handle in place. The handle serves as the housing for the single 9-volt orS AA cells

From Figure 26-3

Cut out center of 3.5” plastic cap by placing on the enclosure tube and cutting out the center section with an x-acto knife, using the inner wall as a guide

Front Panel Fab

Dashed lines indicate t/2" mounting lip. Note clearance holes for SW1 mating to holes in RPt rear panel

section.

HAND1

RP1 PANEL

Circuit Description

Panel is cut from a3|x 3|’ piece of 045 aluminum or 03 gal. Cut corners to approach a circular shape.

Circuit Description

W.375 V^375

OFF/ON/VOL TUNING

Note that holes must be accuralely positioned for proper alignment to R12, R19, and J1 on the assembly or printed circuit board.

Figure 26-4 Final blowup and fabrication

Electrical Pretest

To run a test on the system, follow these steps:

1. Turn the controls to “off,” plug in the HS30 headset, and insert a 9-volt battery. Connect a meter set to read 100 milliamperes across the switch pins of R19 and quickly read a current of around 20 milliamperes. Remove the meter and turn control pot R19 to the midway point.

Note a smooth, rushing sound in the headsets. Then turn on a computer or TV monitor, and adjust the R12 control until you hear a clear tone. Turn off the sound source and gently rub two fingers together, noting a distinct sound. Check the range of the controls for unwanted feedback or spurious signals.

The unit is now ready for final assembly. Note the test points and wave shapes shown in Fig­ure 26-2.

її cannot be stressed the importance of proper heat sinking of the pins 10 the transducer TD1 before attempting soldering. If you are in doubt, use a vwre nut or "slip on" pin connections Note the shorter pin is internally connected to the transducer case and connects to the ground side of the circuit You should measure a short circuii from this pm to the aluminum shell or ihe transducer is no good!

CHAS1

Circuit Description

You may use a 9-volt battery or 12 volts using an 8 AA pack that will fit into the HA1 handle. The 12 volts allow a small 8-ohm speaker to be used as it produces more volume.

RP1

Short pin is connected to shield e note in Fig. 26-4 before connecting to ihe pins on TD1.

Circuit Description

Figure 26-5 Chassis assembly with board connections

Circuit Description

R12 Tuning

Circuit Description

R19/S1 Volume

Power Note that J1 is wired for mono operation

2. Complete the final assembly, adding parabolic reflector PARA 12 for a greatly enhanced, per­formance, as shown in Figure 26-6.

Note that your unit may pick up strong magnetic fields, as it is not shielded for such. Performing the Doppler shift test, as noted earlier in these plans, eas­ily differentiates these fields.

Ultrasonic Microphone

This interesting electronic project enables you to clearly hear a world of sounds beyond that of human ability. The possible applications of the ultrasonic microphone you will create (see Figure 26-1) range from the detection of leaking gases, liquids, the mechanical wear of bearings, rotational and recipro­cating devices, and electrical leakage on power-line insulators. A whole world of sounds coming from liv­ing creatures is also audible. Simple events like a cat walking across wet grass, the rattling of key chains, and even a collapsing plastic bag all are clearly heard. On a warm summer night, the sounds that can be heard are remarkable, as bats to small insects all perform a cacophony of nature’s own orchestra at its best.

Ultrasonic Microphone

Figure 26-1 Ultrasonic microphone with parabolic reflector

This handheld and directional microphone easily dclecls and locates these high-frequency sounds. The addition of a parabolic reflector further enhances the performance of this project. Expect to spend $30 lo $50 for this rewarding effort.

This project enables you to listen to a world of sound that few people even know exists. The unit is built in a gun configuration with the barrel housing the elec­tronics. A rear panel contains the on/off volume, the tuning control pot. and the headphone jack. The front of the unit contains the directional receiving trans­ducer. The handle houses the batteries.

The addition of an optional parabolic reflector greatly enhances the device’s performance, providing super-high gain and directivity.

Rpplications

One of the most interesting sources of high-fre – quency sound is the many species of insects emitting their mating and warning calls. On a typical summer night, one can spend hours listening to bats and other strange insect noises. A whole new world of natural sound awaits the user. Many man-made sounds also generate high-frequency sounds easily detected by the devicc. Several examples are as follows, yet these only represent a small fraction of the potential sources of high-frcquency sounds:

• Leaking gases and rushing air.

■ Water from sprinklers or leaks.

• Corona leakage, sparking devices, or lightning.

■ Fires and chemical reactions.

■ Animals walking in wet grass or in the brush can be heard over a considerable distance. This is an excellent aid for hunters or trackers, or for iust finding pets ai night.

■ Computer monitors. TV sets, high-frequency oscillators, mechanical wear bearings, rattle detection often developing in automobiles, plastic bags, and rattling change.

An excellent demonstration of this ultrasonic microphonc would involve Doppler shifts where motion toward the source produces a rise in fre­quency and motion away from it does the opposite.

Doppler shift is when an observer moving toward a source of sound experiences an increasing fre­quency. This is easy to visualize when one realizes that sound propagates as a longitudinal wave at a rel­atively constant velocity. As the observer moves toward the direction of the sound source, he inter­cepts more waves in a shorter period of time, thus hearing a sound that seems to be shorter in wave­length or higher in frequency.

A fun game both for children and adults is to hide a small test oscillator and attempt to have your oppo­nent locate it in a minimal amount of time.

Exploding ULIire Disruption Suuitch (High-Pouuer, High – Frequency Pulse)

This is where the stored energy in the circuit induc­tance is released as an explosion of electromagnetic energy at broadband proportions. The released energy is a function of LI2 where I is the current rise in the spark gap switch at the moment the wire explodes and L is the inductance. The actual power lost in the spark switch is but a fraction of that emit­ted in the explosion of the wire.

Selection of the wire size must take into considera­tion the elcctrical circuit parameters for the proper timing of the optimum release of energy. We experi­mented with a .I-millimeter (.004 inch) to.3-miIlime – ter (.012 inch) diameter of brass and aluminum wire about 50 centimeters in length. The wire is attached by a sandwiching action between two flat brass wash­ers as shown. Note that a longer wire will tend to pro­duce more of a magnetic pulse, whereas a shorter will produce more of an electric pulse.

Charger

The charger for the system can be any current – limited source with an open-circuit voltage in excess of 50 Kv. The charging current rate will determine the amount of time necessary to reach a firing level and need not be that fast for this experimental system. A single charging cycle produces approximately 500 joules per shot and requires reloading of the wire for an exploding disrupter switch. A 2-milIiampere cur­rent source will charge the.5 mfd capacitor to 50 Kv in approximately 5 seconds. This is shown mathemati­cally by t = cv/i(.5)(10e — 6)(5 X 10,000/.002). This rate is more than ample and there is no advantage to a higher-current system unless you are planning to do a multiple discharge system using a spark gap-driven radiator or wire-dispensing scheme.

The ion supply described in Chapter 1 can supply an open-circuit voltage of 50 Kv by easily adding four more capacitors and high-voltage diodes to the multi­plier section. Everything else can remain the same.

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Rssembly

RFC1 Radio Frequency Choke

This component is necessary to keep the fast current pulse rise isolated from the charger multiplier diodes that could be avalanched by the rapid dv/dt. The sug­gested value is around.2 mh with.3 Uh tertiary coils. The assembly can be a single-layer close wound winding of 150 turns for the.2 mh section. Wind three turns spaced over 1 inch for the.3 Uh section. Use #28 magnet wire on a 1 Ч2- X 12-inch PVC plastic tube.

R1 Resistor

Intended as a safety precaution, this resistor provides a high impedance should a short occur in the output stage of the current driver. Use approximately 50 to 100K with at least 100 watts.

Our lab pulser is shown constructed using materials and parts available from any hardware store. The structure uses a combination of 3/<j-inch schedule 40 PVC tubing for the pillars and flat-faced end caps for the retainers (see Figure 25-4). Partitions are made from nonconductive material of structural integrity for the application. We used 3/s-inch, clear, acrylic plate stock. Figure 25-3 shows the scheme we used to attach these sections to the flat-faced end caps. The sections are secured by drilling clearance holes and plastic tie wraps keep them together. PVC cement is obviously stronger but prevents disassembly unless you destroy the support structure.

The pillar and cap assemblies are attached to the partition plates using 1-inch X */4-20 bolts and nuts. A cradle assembly fabricated from wood or plastic secures the capacitor Cl to the bottom partition. This scheme stabilizes the bottom of the capacitor.

The metal plate sections extend the terminal con­nections of the capacitor. These attach to the termi­nals connecting to the exploding wire cavity section

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Figure 25-4 Side view of EMP pulser

via brass-threaded rods sleeved into pieces of -’/4-inch made adjustable by adjusting the bottom nut on the

PVC pillar tubing. The bottom spark gap electrode is extended rod.

You will note the four longer pillars are positioned at the corners of the bottom and middle partition plates. The shorter pillars, however, are positioned at the midsections of the middle and top partition plates. This layout is shown in figure 25-5. Figure 25-6 illustrates the final view of the pulser and Figure 25-7 shows the spark switch setup for coupling to the antenna.

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Figure 25-5 Top view of middle partition plate, showing the x-ray view of capacitor placement and mounting holes

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Event action occurs along the wire that explodes. The foci point of the dish is not exact for all points of the explosion event Expenment for best results

Our low-cost open-air spark switch is shown Serious experimenters may want to consider our triggered enclosed devices as on cover sheet

Charging

resistor

Figure 25-6 Final view of pulser, showing conic antenna

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Rpplication

This system is intended for research into the suscepti­bility of sensitive electronic equipment to an EMP The system can be scaled down for portable field use and operate on rechargeable batteries. It can be

scaled up to produce kilojoule pulses at the user’s own risk. No attempt to construct or use this device should be considered unless thoroughly experienced in the use of high-pulse energy systems.

The electromagnetic energy pulse can be focused or made parallel by use of a parabolic reflector. Experimental targets can be any sensitive electronic

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Form coil from 3 turns o! J" ID coppertube 3” diameter Adjust to 3 to 6" length to obtain required inductance

}■’ threaded rod is sleeved into ID of copper tubing and soldered with a propane torch Rod is retained in position by shaft collars

Exploding ULIire Disruption Suuitch (High-Pouuer, High - Frequency Pulse)

Figure 25-7 Spark switch setup and layout for low-frequency coupling to antenna

equipment or even a gas-discharge lamp. Hie acousti­cal spark energy can produce a sonic shockwave of high sound pressure at the focal length of the para­bolic antenna.

Sources

High-voltage chargers, transformers, capacitors, gas – filled and isotope doped spark switches, MARX impulse generators up to 2 megavolts, and EMP gen­erators are all available at www. amazingl. com.

Spark Sujitch

The spark gap switches the energy from the capacitor into the inductor where a resonant tank is momentar­ily set up (see Figure 25-2). The current rise time occurs over the period pi/2 X (LC) ‘.The gap separa­tion distance is set to fire at the desired breakdown voltage. The impedance of the spark switch is deter­mined by the equation ZSP = (к X l)/Q, where к equals.8 X 10 I equals the spark gap distance in centimeters, and Q equals ihe amps per second (coulombs) of discharge. The gap is self-firing and requires no external triggering. The gap assembly is an integral part of the discharge path and must be constructed to minimize inductance and resistance.

Spark Sujitch

before V reaches 50,000 volts. Once fired, a peak current rise cf di/dt=V/L occurs. The period of circuit response is functional of 16 x (LC)S The capacitor now discharges into ihe circuit inductance in 1/4t with the peak current now causing Ihe wire to explode and imerrupting lhis current just before it peaks. The inductive energy (LI2) is released in an explosive burst of broadband electromagnetic radiation. The peak power is derived via the following and rs m excess of many megawatts!’!!!

1. Charging Cycle – dv=ldt/C (Expresses the voitage charging on Ihe capecitor as a f(t) with I constant current)

2. Storage energy in С as a f(v): E=.5Cv2 (Expresses energy in joules as the voltage increases)

3 Response time 1/4 cycle current peak: 1 57(LC) fi (Expresses the time for the first resonant current peaking when ihe spark switch fires)

4. Peak current in 1/4 cycle. V(C/L)S (Expresses the peak current)

5. Initial response as a (1)1. Ldi/dt+iR+1 /С+1 /Cint idt = 0 [Expresses voltages as a f(t)l 6 Energy joules in inductor E= ,5Li2

7. Response when circuit is disrupted at max current through L:

Ld2 i/dt2 + Rdi/dt + it/C = dv/dt. One now sees the explosive effects of the first term of this simpte equation as the energy in the inductor must go somewhere in a very short time, resulting in an explosive E X В field energy release.

An appreciable pulse of many megawatts in the upper RF energy spectrum can be obtained by destabilizing the LCR circuit as shown above. The only limiting factor is the intrinsic real resistance that is always present in several forms, such as leads, skin effect, dielectric and switching losses, etc. These losses must be minimized for optimum resuits. The RF output can be coupled to a parabolic microwave dish or tuned hom. The Q of the output will depend to an extent on the geometry of the wire switch. Longer lengths will produce more "B" field characteristics while short more "E" field. These perameters will enter into the coupling equations regarding the radiation efficiency of the antenna. Experimenting is the besi approach using your math skills only for approximating key parameters Damage to circuitry usuallly is the result of very high di/dt (B field) pulse properties. This is a point of discussion!!

Figure 25-2 EMPpitlser schematic

a threaded rod and locking jam nut scheme. The top ball also uses a threaded rod that fits into the 74-inch PVC tubing used for the structural support of the wire disruption scheme.

The fabrication of our lab test unit is shown and you may deviate with your own ideas, but the objective must be minimal circuit impedance.

You will note that the bottom ball of the spark gap switch is at a high potential and is made adjustable by

Foci вгва ot parabolic алмпла

COMMOWGRD

Retaining blocks to keep bottom of С1 secured

Figure 25-3 Front view of pulser showing spark switch

Low-induclanee extension pieces are used to lengthen the capacitor terminals and are fabricated from ‘/4-inch brass plates with mating holes to the existing block terminals of the capacitor. The edges are rounded and smoothed to prevent corona.

Dimension of spark switch and output section will depend on the maximum value of the charging voltage used

Tungsten/cerium electrodes are recommended The brass spheres provide a frictional press fit as well as some cooling.

Spark Sujitch

Partition plate—’ Nut & bolt

The method we used to attach pillars to partition plates using fist-faced end caps attached with 1/4-20 nuts and bolts Drill holes through cap and pillar for tie wraps to secure together Note there are 24 of these attachment points!

I he open-air, self-triggering spark switch is intended as a low-cost approach to this very strategic part. A system of this type requires the fastest switch­ing times possible. Gas-filled, triggered gaps will switch faster ihan open air. and isotope doped elec­trodes will further enhance performance.